[Federal Register Volume 78, Number 80 (Thursday, April 25, 2013)]
[Proposed Rules]
[Pages 24471-24514]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2013-09600]
[[Page 24471]]
Vol. 78
Thursday,
No. 80
April 25, 2013
Part II
Department of the Interior
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Fish and Wildlife Service
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50 CFR Part 17
Endangered and Threatened Wildlife and Plants; Endangered Status for
the Sierra Nevada Yellow-Legged Frog and the Northern Distinct
Population Segment of the Mountain Yellow-Legged Frog, and Threatened
Status for the Yosemite Toad; Proposed Rule
Federal Register / Vol. 78 , No. 80 / Thursday, April 25, 2013 /
Proposed Rules
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[Docket No. FWS-R8-ES-2012-0100; 4500030113]
RIN 1018-AZ21
Endangered and Threatened Wildlife and Plants; Endangered Status
for the Sierra Nevada Yellow-Legged Frog and the Northern Distinct
Population Segment of the Mountain Yellow-Legged Frog, and Threatened
Status for the Yosemite Toad
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Proposed rule.
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SUMMARY: We, the U.S. Fish and Wildlife Service, propose to list the
Sierra Nevada yellow-legged frog and the northern distinct population
segment (DPS) (populations that occur north of the Tehachapi Mountains)
of the mountain yellow-legged frog as endangered species, and the
Yosemite toad as a threatened species under the Endangered Species Act
of 1973, as amended (Act). The effect of this regulation would be to
add the species to the List of Endangered and Threatened Wildlife under
the Act.
DATES: We will accept comments received or postmarked on or before June
24, 2013. Comments submitted electronically using the Federal
eRulemaking Portal (see ADDRESSES below) must be received by 11:59 p.m.
Eastern Time on the closing date. We must receive requests for public
hearings, in writing, at the address shown in the FOR FURTHER
INFORMATION CONTACT section by June 10, 2013.
ADDRESSES: You may submit comments by one of the following methods:
(1) Electronically: Go to the Federal eRulemaking Portal: http://www.regulations.gov. In the Search box, enter Docket No. FWS-R8-ES-
2012-0100, which is the docket number for this rulemaking. Then, in the
Search panel on the left side of the screen, under the Document Type
heading, click on the Proposed Rules link to locate this document. You
may submit a comment by clicking on ``Comment Now!''
(2) By hard copy: Submit by U.S. mail or hand-delivery to: Public
Comments Processing, Attn: FWS-R8-ES-2012-0100; Division of Policy and
Directives Management; U.S. Fish and Wildlife Service; 4401 N. Fairfax
Drive, MS 2042-PDM; Arlington, VA 22203.
We request that you send comments only by the methods described
above. We will post all comments on http://www.regulations.gov. This
generally means that we will post any personal information you provide
us (see Information Requested below for more information).
FOR FURTHER INFORMATION CONTACT: Jan Knight, Acting Field Supervisor,
U.S. Fish and Wildlife Service, Sacramento Fish and Wildlife Office,
2800 Cottage Way Room W-2605, Sacramento CA 95825; by telephone 916-
414-6600; or by facsimile 916-414-6712. Persons who use a
telecommunications device for the deaf (TDD) may call the Federal
Information Relay Service (FIRS) at 800-877-8339.
SUPPLEMENTARY INFORMATION:
This document consists of: a proposed rule to list the Sierra
Nevada yellow-legged frog and the northern DPS of the mountain yellow-
legged frog as endangered, and to list the Yosemite toad as threatened.
Executive Summary
Why we need to publish a rule. Under the Act, if a species is
determined to be an endangered or threatened species throughout all or
a significant portion of its range, we are required to promptly publish
a proposal in the Federal Register and make a determination on our
proposal within one year. Listing a species as an endangered or
threatened species can only be completed by issuing a rule.
This rule proposes the listing of the Sierra Nevada yellow-legged
frog and the northern DPS of the mountain yellow-legged frog as
endangered, and to list the Yosemite toad as threatened.
We are proposing to list the Sierra Nevada yellow-legged
frog as endangered under the Endangered Species Act.
We are proposing to list the northern DPS of the mountain
yellow-legged frog as endangered under the Endangered Species Act.
We are proposing to list the Yosemite toad as threatened
under the Endangered Species Act.
The basis for our action. Under the Act, we can determine that a
species is an endangered or threatened species based on any of five
factors: (A) The present or threatened destruction, modification, or
curtailment of its habitat or range; (B) overutilization for
commercial, recreational, scientific, or educational purposes; (C)
disease or predation; (D) the inadequacy of existing regulatory
mechanisms; or (E) other natural or manmade factors affecting its
continued existence. We reviewed all available scientific and
commercial information pertaining to the five threat factors in our
evaluation of each species.
We have made the following findings related to these criteria:
Sierra Nevada Yellow-Legged Frog (Rana Sierrae)
The Sierra Nevada yellow-legged frog is presently in danger of
extinction throughout its entire range, based on the immediacy,
severity, and scope of the threats to its continued existence. These
include habitat degradation and fragmentation, predation and disease,
climate change, inadequate regulatory protections, and the interaction
of these various stressors impacting small remnant populations. There
has been a rangewide reduction in abundance and geographic extent of
surviving populations of frogs following decades of fish stocking,
habitat fragmentation, and most recently a disease epidemic. Surviving
populations are smaller and more isolated, and recruitment in disease-
infested populations is much reduced relative to historic norms. This
combination of population stressors makes persistence of the species
precarious throughout the currently occupied range in the Sierra
Nevada.
Northern Distinct Population Segment of the Mountain Yellow-Legged Frog
(Rana Muscosa)
Populations within the southern DPS of the mountain yellow-legged
frog inhabiting the Transverse Ranges of Southern California are
currently listed as an endangered species. The northern DPS of the
mountain yellow-legged frog is presently in danger of extinction
throughout its range within the Sierra Nevada, based on the immediacy,
severity, and scope of the threats to its continued existence. These
include habitat degradation and fragmentation, predation and disease,
climate change, inadequate regulatory protections, and the interaction
of these various stressors impacting small remnant populations. There
has been a rangewide reduction in abundance and geographic extent of
surviving populations of frogs following decades of fish stocking,
habitat fragmentation, and most recently a disease epidemic. Surviving
populations are smaller and more isolated, and recruitment in disease-
infested populations is much reduced relative to historic norms. This
combination of population stressors makes persistence of the species
precarious throughout the Sierra Nevada range of the mountain yellow-
legged frog.
The northern DPS of the mountain yellow-legged frog has different
habitat, requires different management, and has
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different primary constituent elements than the already listed southern
DPS . For these reasons, we have proposed a separate DPS for the
northern population in this rule. However, if we finalize this rule,
the entire range of the mountain yellow-legged frog may be listed as
endangered. We request public input on whether we should retain the
northern and southern DPS's or combine the two into one listed species
in the final rule. Thus, we are giving notice that we may combine the
two DPS's into one listed species if we finalize this proposed rule.
Yosemite Toad (Anaxyrus Canorus)
The Yosemite toad is likely to become endangered throughout its
range within the foreseeable future, based on the immediacy, severity,
and scope of the threats to its continued existence. These include
habitat loss associated with degradation of meadow hydrology following
stream incision consequent to the cumulative effects of historic land
management activities, notably livestock grazing, and also the
anticipated hydrologic effects upon habitat from climate change. We
also find that the Yosemite toad is likely to become endangered through
the direct effects of climate change impacting small remnant
populations, likely compounded with the cumulative effect of other
threat factors (such as disease).
We will seek peer review. We are seeking comments from
knowledgeable individuals with scientific expertise to review our
analysis of the best available science and application of that science
and to provide any additional scientific information to improve this
proposed rule. Because we will consider all comments and information
received during the comment period, our final determination may differ
from this proposal.
Information Requested
We intend that any final action resulting from this proposed rule
will be based on the best scientific and commercial data available and
be as accurate and as effective as possible. Therefore, we request
comments or information from other concerned governmental agencies,
Native American tribes, the scientific community, industry, or any
other interested parties concerning this proposed rule. We particularly
seek comments concerning:
(1) Biological, commercial trade, or other relevant data concerning
any threats (or lack thereof) to these species, and regulations that
may be addressing those threats.
(2) Additional information concerning the historical and current
status, range, distribution, and population size of these species,
including the locations of any additional populations of these species.
(3) Any information on the biological or ecological requirements of
these species, and ongoing conservation measures for these species and
their habitats.
(4) The factors that are the basis for making a listing
determination for a species under section 4(a) of the Act 16 U.S.C.
1531 et seq.), which are:
(a) The present or threatened destruction, modification, or
curtailment of its habitat or range;
(b) Overutilization for commercial, recreational, scientific, or
educational purposes;
(c) Disease or predation;
(d) The inadequacy of existing regulatory mechanisms; or
(e) Other natural or manmade factors affecting its continued
existence.
(5) Land use designations and current or planned activities in the
areas occupied by the species, and possible impacts of these activities
on these species.
(6) Information on the projected and reasonably likely impacts of
climate change on the Sierra Nevada yellow-legged frog, the northern
DPS of the mountain yellow-legged frog, and the Yosemite toad.
(7) Input on whether we should retain the northern and southern
DPS's of the mountain yellow-legged frog in the final rule or should we
combine the two DPS's into one listed entity for the species.
Please include sufficient information with your submission (such as
scientific journal articles or other publications) to allow us to
verify any scientific or commercial information you include.
Please note that submissions merely stating support for or
opposition to the action under consideration without providing
supporting information, although noted, will not be considered in
making a determination, as section 4(b)(1)(A) of the Act directs that
determinations as to whether any species is an endangered or threatened
species must be made ``solely on the basis of the best scientific and
commercial data available.''
You may submit your comments and materials concerning this proposed
rule by one of the methods listed in the ADDRESSES section. We request
that you send comments only by the methods described in the ADDRESSES
section.
If you submit information via http://www.regulations.gov, your
entire submission--including any personal identifying information--will
be posted on the Web site. If your submission is made via a hardcopy
that includes personal identifying information, you may request at the
top of your document that we withhold this information from public
review. However, we cannot guarantee that we will be able to do so. We
will post all hardcopy submissions on http://www.regulations.gov.
Please include sufficient information with your comments to allow us to
verify any scientific or commercial information you include.
Comments and materials we receive, as well as supporting
documentation we used in preparing this proposed rule, will be
available for public inspection on http://www.regulations.gov, or by
appointment, during normal business hours, at the U.S. Fish and
Wildlife Service, Sacramento Fish and Wildlife Office (see FOR FURTHER
INFORMATION CONTACT).
Previous Federal Actions
Mountain Yellow-Legged Frog
In February 2000, we received a petition from the Center for
Biological Diversity and Pacific Rivers Council to list the Sierra
Nevada population of the mountain yellow-legged frog (Rana muscosa).
The petition stated that this population met the criteria in our DPS
Policy and that it should be listed as endangered. On October 12, 2000,
we published a 90-day finding on that petition in the Federal Register
(65 FR 60603), concluding that the petition presented substantial
scientific or commercial information to indicate that the listing of
the Sierra Nevada population of the mountain yellow-legged frog may be
warranted, and we concurrently requested information and data regarding
the species. On January 16, 2003, we published a 12-month petition
finding in the Federal Register that listing was warranted but
precluded (68 FR 2283). This finding was in accordance with a court
order requiring us to complete a finding by January 10, 2003 (Center
for Biological Diversity v. Norton, No. 01-2106 (N. D. Cal. Dec. 12,
2001)). Upon publication of the finding, we added the Sierra Nevada DPS
of the mountain yellow-legged frog to our list of species that are
candidates for listing.
The Center for Biological Diversity and Pacific Rivers Council
challenged our finding that listing was warranted but precluded, and
sought to compel the Service to proceed with listing. On June 21, 2004,
the U.S. District Court for the Eastern District of California granted
summary judgment in favor of the United States (Center for Biological
Diversity v. Norton, No. 03-01758 (E.D.
[[Page 24474]]
Cal. June 21, 2004)). In response to an appeal of the District Court
decision, on October 18, 2006, the 9th Circuit Court of Appeals
reversed and remanded the lower Court's judgment, concluding that the
12-month finding we published on January 16, 2003, did not meet the
requirements of section 4(b)(3)(B) of the Act.
We addressed the 9th Circuit Court's remand by amending our January
16, 2003, warranted-but-precluded finding to include a description of
our underlying rationale and an evaluation of the data demonstrating
why listing the Sierra Nevada DPS of the mountain yellow-legged frog
was precluded from listing. We further described the expeditious
progress we had made toward adding qualified species to the Federal
Lists of Endangered and Threatened Wildlife and Plants at the time. The
revised 12-month finding was published on June 25, 2007 (72 FR 34657),
reiterating a warranted-but-precluded finding, and maintaining the
Sierra Nevada DPS of the mountain yellow-legged frog as a candidate for
listing under the Act. In the intervening time, this entity has been
taxonomically split (See Background section in Endangered Status For
Sierra Nevada Yellow-legged Frog and the Northern DPS of the Mountain
Yellow-legged Frog).
Candidate assessments for the Sierra Nevada DPS of the mountain
yellow-legged frog have been prepared annually since the 2007 12-month
finding (2008, 73 FR 75176; 2009, 74 FR 57804, corrected 75 FR 8293;
2010, 75 FR 69222; 2011, 76 FR 66370). The taxonomic split was
officially recognized in the 2011 Candidate Assessment (76 FR 66370),
where we noted that we would include the change in the upcoming
proposed rule. Accordingly, in this proposed rule, we address two
separate species within the mountain yellow-legged frog ``species
complex'': Rana muscosa and Rana sierrae.
Yosemite Toad
In April 2000, we received a petition from the Center for
Biological Diversity and Pacific Rivers Council to list the Yosemite
toad as endangered under the Act, and to designate critical habitat
concurrent with listing. On October 12, 2000, the Service published a
90-day finding (65 FR 60607) concluding that the petition presented
substantial scientific or commercial information to indicate that the
listing of the Yosemite toad may be warranted, and we concurrently
requested information and data regarding the species. On December 10,
2002, we published a 12-month finding (67 FR 75834), concluding that
the Yosemite toad warranted protection under the Act; however,
budgetary constraints precluded the Service from listing the Yosemite
toad as endangered or threatened at the time. This finding was in
accordance with a court order requiring us to complete a finding by
November 30, 2002 (Center for Biological Diversity v. Norton, No. 01-
2106 (N. D. Cal. Dec. 12, 2001)).
Candidate assessments for the Yosemite toad have been prepared
annually since the 2002 12-month finding (2004, 69 FR 24876; 2005, 70
FR 24870; 2006, 71 FR 53756; 2007, 72 FR 69034; 2008, 73 FR 75176;
2009, 74 FR 57804; 2010, 75 FR 69222; 2011, 76 FR 66370).
Status for Sierra Nevada Yellow-Legged Frog and the Northern DPS of the
Mountain Yellow-Legged Frog
Background
In this section of the proposed rule, it is our intent to discuss
only those topics directly relevant to the proposed listing of the
Sierra Nevada yellow-legged frog as endangered and the proposed listing
of the northern DPS of the mountain yellow-legged frog as endangered.
Taxonomy
Mountain yellow-legged frogs were once thought to be a subspecies
of the foothill yellow-legged frog, Rana boylii (Camp 1917, pp. 118-
123), and were therefore designated as R. b. sierrae in the Sierra
Nevada and R. b. muscosa in southern California. At that time, it was
presumed that yellow-legged frog populations from southern California
through northern California were a single species. Additional
morphological data supported the classification of the two subspecies
separate from R. boylii as the species R. muscosa (Zweifel 1955, pp.
210-240). Macey et al. (2001, p. 141) conducted a phylogenetic analysis
of mitochondrial deoxyribonucleic acid (DNA) sequences of the mountain
yellow-legged frog and concluded that there were two major genetic
lineages (and four groups), with populations in the Sierra Nevada
falling into three distinct groups, the fourth being the southern
California population.
Based on mitochondrial DNA, morphological information, and acoustic
studies, Vredenburg et al. (2007, p. 371) recently recognized two
distinct species of mountain yellow-legged frog in the Sierra Nevada,
Rana muscosa and R. sierrae. This taxonomic distinction was
subsequently adopted by the American Society of Ichthyologists and
Herpetologists, the Herpetologists' League, and the Society for the
Study of Amphibians and Reptiles (Crother et al. 2008, p. 11). The
Vredenburg study determined that R. sierrae occurs in the Sierra Nevada
north of the Kern River watershed and over the eastern crest of the
Sierra Nevada into Inyo County at its most southern extent, and that R.
muscosa occurs in the southern portion of the Sierra Nevada within the
Kern River watershed to the west of the Sierra Nevada crest (along with
those populations inhabiting southern California) (Vredenburg et al.
2007, p. 361).
Macey et al. (2001, p. 140) suggested that the initial divergence
between the Sierra Nevada yellow-legged frog and the mountain yellow-
legged frog occurred 2.2 million years before present (mybp). The
biogeographic pattern of genetic divergence as detected in the mountain
yellow-legged frog complex of the Sierra Nevada has also been observed
in four other reptiles and amphibians in this area, suggesting that a
common event fragmented their ranges (Macey et al. 2001, p. 140).
We identify Rana sierrae in this proposed rule as the Sierra Nevada
yellow-legged frog, and refer to the Sierra Nevada populations of R.
muscosa as the northern range of the mountain yellow-legged frog.
Together, these species may be termed the ``mountain yellow-legged frog
complex.'' Figure 1 shows the newly recognized species split within
their historical ranges as determined by Knapp (unpubl. data).
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For purposes of this proposed rule, we recognize the species
designation as presented in Vredenburg et al. (2007, p. 371) and
adopted by the official societies mentioned above (Crother et al. 2008,
p. 11). Specifically, Sierra Nevada yellow-legged frogs occupy the
western Sierra Nevada north of the Monarch Divide (in Fresno County)
and the eastern Sierra Nevada (east of the crest) in Inyo and Mono
Counties. The southern DPS of the mountain yellow-legged frog occupies
the canyons of the Transverse Ranges in southern California, and is
already listed as an endangered species (67 FR 44382, July 2, 2002).
The northern portion of the range of mountain yellow-legged frog
(extending in the western Sierra Nevada from south of the Monarch
Divide in Fresno County through portions of the Kern River drainage) is
referred to in this proposed rule as the northern DPS of the mountain
yellow-legged frog.
Many studies cited in this document include articles and reports
that were published prior to the official species reclassification,
where the researchers may reference either one or both species. Where
possible and appropriate, information will be referenced specifically
(either as Sierra Nevada yellow-legged frog or the northern DPS of the
mountain yellow-legged frog) to reflect the split of the species. Where
information applies to both species, the two species will be referred
to collectively as mountain yellow-legged frogs (or frog complex),
consistent with the designation in each particular source document.
Species Description
The body length (snout to vent) of the mountain yellow-legged frog
ranges from 40 to 80 millimeters (mm) (1.5 to 3.25 inches (in))
(Jennings and Hayes 1994, p. 74). Females average slightly larger than
males, and males have a swollen, darkened thumb base (Wright and Wright
1949, pp. 424-430; Stebbins
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1951, pp. 330-335; Zweifel 1955, p. 235; Zweifel 1968, p. 65.1). Dorsal
(upper) coloration in adults is variable, exhibiting a mix of brown and
yellow, but also can be grey, red, or green-brown, and is usually
patterned with dark spots (Jennings and Hayes 1994, p. 74; Stebbins
2003, p. 233). These spots may be large (6 mm (0.25 in)) and few,
smaller and more numerous, or a mixture of both (Zweifel 1955, p. 230).
Irregular lichen- or moss-like patches (to which the name muscosa
refers) may also be present on the dorsal surface (Zweifel 1955, pp.
230, 235; Stebbins 2003, p. 233).
The belly and undersurfaces of the hind limbs are yellow or orange,
and this pigmentation may extend forward from the abdomen to the
forelimbs (Wright and Wright 1949, pp. 424-429; Stebbins 2003, p. 233).
Mountain yellow-legged frogs may produce a distinctive mink or garlic-
like odor when disturbed (Wright and Wright 1949, p. 432; Stebbins
2003, p. 233). Although these species lack vocal sacs, they can
vocalize in or out of water, producing what has been described as a
flat clicking sound (Zweifel 1955, p. 234; Ziesmer 1997, pp. 46-47;
Stebbins 2003, p. 233). Mountain yellow-legged frogs have smoother
skin, generally with heavier spotting and mottling dorsally, darker toe
tips (Zweifel 1955, p. 234), and more opaque ventral coloration
(Stebbins 2003, pp. 233) than the foothill yellow-legged frog.
The Sierra Nevada yellow-legged frog and the northern DPS of the
mountain yellow-legged frog are similar morphologically and
behaviorally (hence their shared taxonomic designation until recently).
However, these two species can be distinguished from each other
physically by the ratio of the lower leg (fibulotibia) length to snout
vent length. The northern DPS of the mountain yellow-legged frog has
longer limbs (Vredenburg et al. 2007, p. 368). Typically, this ratio is
greater than or equal to 0.55 in the northern DPS of the mountain
yellow-legged frog and less than 0.55 in the Sierra Nevada yellow-
legged frog.
Mountain yellow-legged frogs deposit their eggs in globular clumps,
which are often somewhat flattened and roughly 2.5 to 5 centimeters
(cm) (1 to 2 in) in diameter (Stebbins 2003, p. 444). When eggs are
close to hatching, egg mass volume averages 198 cubic cm (78 cubic in)
(Pope 1999a, p. 30). Eggs have three firm, jelly-like, transparent
envelopes surrounding a grey-tan or black vitelline (egg yolk) capsule
(Wright and Wright 1949, pp. 431-433). Clutch size varies from 15 to
350 eggs per egg mass (Livezey and Wright 1945, p. 703; Vredenburg et
al. 2005, p. 565). Egg development is temperature dependent. In
laboratory breeding experiments, egg hatching time ranged from 18 to 21
days at temperatures of 5 to 13.5 degrees Celsius ([deg]C) (41 to 56
degrees Fahrenheit ([deg]F)) (Zweifel 1955, pp. 262-264). Field
observations show similar results (Pope 1999a, p. 31).
The tadpoles of mountain yellow-legged frogs generally are mottled
brown on the dorsal side with a faintly yellow venter (underside)
(Zweifel 1955, p. 231; Stebbins 2003, p. 460). Total tadpole length
reaches 72 mm (2.8 in), the body is flattened, and the tail musculature
is wide (about 2.5 cm (1 in) or more) before tapering into a rounded
tip (Wright and Wright 1949, p. 431). The mouth has a maximum of eight
labial (lip) tooth rows (two to four upper and four lower) (Stebbins
2003, p. 460). Tadpoles may take more than 1 year (Wright and Wright
1949, p. 431), and often require 2 to 4 years, to reach metamorphosis
(transformation from tadpoles to frogs) (Cory 1962b, p. 515; Bradford
1983, pp. 1171, 1182; Bradford et al. 1993, p. 883; Knapp and Matthews
2000, p. 435), depending on local climate conditions and site-specific
variables.
The time required to reach reproductive maturity in mountain
yellow-legged frogs is thought to vary between 3 and 4 years post
metamorphosis (Zweifel 1955, p. 254). This information, in combination
with the extended amount of time as a tadpole before metamorphosis,
means that it may take 5 to 8 years for mountain yellow-legged frogs to
begin reproducing. Longevity of adults is unknown, but under normal
circumstances, adult survivorship from year to year is very high, so
mountain yellow-legged frogs are presumed to be long-lived amphibians
(Pope 1999a, p. 46).
Habitat and Life History
Mountain yellow-legged frogs currently exist in montane regions of
the Sierra Nevada of California. Throughout their range, these species
historically inhabited lakes, ponds, marshes, meadows, and streams at
elevations ranging from 1,370 to 3,660 meters (m) (4,500 to 12,000 feet
(ft)) (California Department of Fish and Game (CDFG) 2011b, pp. A-1-A-
5). Mountain yellow-legged frogs are highly aquatic; they are generally
not found more than 1 m (3.3 ft) from water (Stebbins 1951, p. 340;
Mullally and Cunningham 1956a, p. 191; Bradford et al. 1993, p. 886).
Adults typically are found sitting on rocks along the shoreline,
usually where there is little or no vegetation (Mullally and Cunningham
1956a, p. 191). Although mountain yellow-legged frogs may use a variety
of shoreline habitats, both tadpoles and adults are less common at
shorelines that drop abruptly to a depth of 60 cm (2 ft) than at open
shorelines that gently slope up to shallow waters of only 5 to 8 cm (2
to 3 in) in depth (Mullally and Cunningham 1956a, p. 191; Jennings and
Hayes 1994, p. 77).
At lower elevations within their historical range, these species
are known to be associated with rocky streambeds and wet meadows
surrounded by coniferous forest (Zweifel 1955, p. 237; Zeiner et al.
1988, p. 88). Streams utilized by adults vary from streams having high
gradients and numerous pools, rapids, and small waterfalls, to streams
with low gradients and slow flows, marshy edges, and sod banks (Zweifel
1955, p. 237). Aquatic substrates vary from bedrock to fine sand,
rubble (rock fragments), and boulders (Zweifel 1955, p. 237). Mountain
yellow-legged frogs appear absent from the smallest creeks, probably
because these creeks have insufficient depth for adequate refuge and
overwintering habitat (Jennings and Hayes 1994, p. 77). Sierra Nevada
yellow-legged frogs do use stream habitats, especially the remnant
populations in the northern part of their range.
At higher elevations, these species occupy lakes, ponds, tarns
(small steep-banked mountain lake or pool), and streams (Zweifel 1955,
p. 237; Mullally and Cunningham 1956a, p. 191). Mountain yellow-legged
frogs in the Sierra Nevada are most abundant in high-elevation lakes
and slow-moving portions of streams (Zweifel 1955, p. 237; Mullally and
Cunningham 1956a, p. 191). The borders of alpine (above the tree line)
lakes and mountain meadow streams used by mountain yellow-legged frogs
are frequently grassy or muddy. This differs from the sandy or rocky
shores inhabited by mountain yellow-legged frogs in lower elevation
streams (Zweifel 1955, pp. 237-238).
Adult mountain yellow-legged frogs breed in the shallows of ponds
or in inlet streams (Vredenburg et al. 2005, p. 565). Adults emerge
from overwintering sites immediately following snowmelt, and will even
move over ice to reach breeding sites (Pope 1999a, pp. 46-47;
Vredenburg et al. 2005, p. 565). Mountain yellow-legged frogs deposit
their eggs underwater in clusters, which they attach to rocks, gravel,
or vegetation, or which they deposit under banks (Wright and Wright
1949, p. 431; Stebbins 1951,
[[Page 24477]]
p. 341; Zweifel 1955, p. 243; Pope 1999a, p. 30).
Lake depth is an important attribute defining habitat suitability
for mountain yellow-legged frogs. As tadpoles must overwinter multiple
years before metamorphosis, successful breeding sites are located in
(or connected to) lakes and ponds that do not dry out in the summer,
and also are deep enough that they do not completely freeze or become
oxygen depleted (anoxic) in winter. Both adults and tadpole mountain
yellow-legged frogs overwinter for up to 9 months in the bottoms of
lakes that are at least 1.7 m (5.6 ft) deep; however, overwinter
survival may be greater in lakes that are at least 2.5 m (8.2 ft) deep
(Bradford 1983, p. 1179; Vredenburg et al. 2005, p. 565).
Bradford (1983, p. 1173) found that mountain yellow-legged frog
die-offs sometimes result from oxygen depletion during winter in lakes
less than 4 m (13 ft) in depth. However, tadpoles may survive for
months in nearly anoxic conditions when shallow lakes are frozen to the
bottom. More recent work reported populations of mountain yellow-legged
frogs overwintering in lakes less than 1.5 m (5 ft) deep that were
assumed to have frozen to the bottom, and yet healthy frogs emerged the
following July (Matthews and Pope 1999, pp. 622-623; Pope 1999a, pp.
42-43). Radio telemetry indicated that the frogs were utilizing rock
crevices, holes, and ledges near shore, where water depths ranged from
0.2 m (0.7 ft) to 1.5 m (5 ft) (Matthews and Pope 1999, p. 619). The
granite surrounding these overwintering habitats probably insulates
mountain yellow-legged frogs from extreme winter temperatures, provided
there is an adequate supply of oxygen (Matthews and Pope 1999, p. 622).
In lakes and ponds that do not freeze to the bottom in winter, mountain
yellow-legged frogs may overwinter in the shelter of bedrock crevices
as a behavioral response to the presence of introduced fishes
(Vredenburg et al. 2005, p. 565).
Mountain yellow-legged frog tadpoles maintain a relatively high
body temperature by selecting warmer microhabitats (Bradford 1984, p.
973). During winter, tadpoles remain in warmer water below the
thermocline (the transition layer between thermally stratified water).
After spring overturn (thaw and thermal mixing of the water), they
behaviorally modulate their body temperature by moving to shallow, near
shore water when warmer days raise surface water temperatures. During
the late afternoon and evening, mountain yellow-legged frogs retreat to
offshore waters that are less subject to night cooling (Bradford 1984,
p. 974).
Available evidence suggests that mountain yellow-legged frogs
display strong site fidelity and return to the same overwintering and
summer habitats from year to year (Pope 1999a, p. 45). In aquatic
habitats of high mountain lakes, mountain yellow-legged frog adults
typically move only a few hundred meters (few hundred yards) (Matthews
and Pope 1999, p. 623; Pope 1999a, p. 45), but single-season distances
of up to 3.3 kilometers (km) (2.05 miles (mi)) have been recorded along
streams (Wengert 2008, p. 18). Adults tend to move between selected
breeding, feeding, and overwintering habitats during the course of the
year. Though typically found near water, overland movements by adults
of over 66 m (217 ft) have been routinely recorded (Pope 1999a, p. 45);
the farthest reported distance of a mountain yellow-legged frog from
water is 400 m (1,300 ft) (Vredenburg 2002, p. 4). Along stream
habitats, adults have been observed greater than 22 m (71 ft) from the
water during the overwintering period (Wengert 2008, p. 20).
Almost no data exist on the dispersal of juvenile mountain yellow-
legged frogs away from breeding sites; however, juveniles that may be
dispersing to permanent water have been observed in small intermittent
streams (Bradford 1991, p. 176). Regionally, mountain yellow-legged
frogs are thought to exhibit a metapopulation structure (Bradford et
al. 1993, p. 886; Drost and Fellers 1996, p. 424). Metapopulations are
spatially separated population subunits within migratory distance of
one another such that individuals may interbreed among subunits and
populations may become reestablished if they are extirpated (Hanski and
Simberloff 1997, p. 6).
Historical Range and Distribution
Mountain yellow-legged frogs were historically abundant and
ubiquitous across much of the higher elevations within the Sierra
Nevada. Grinnell and Storer (1924, p. 664) reported the Sierra Nevada
yellow-legged frog to be the most common amphibian surveyed in the
Yosemite area. It is difficult to know the precise historical ranges of
the Sierra Nevada yellow-legged frog and the mountain yellow-legged
frog, because projections must be inferred from museum collections that
do not reflect systematic surveys, and survey information predating
significant rangewide reduction is very limited. However, projections
of historical ranges are available using predictive habitat modeling
based on recent research (Knapp, unpubl. data).
The Sierra Nevada yellow-legged frog historically occurred in
Nevada on the slopes of Mount Rose in Washoe County and likely in the
vicinity of Lake Tahoe in Douglas County (Linsdale 1940, pp. 208-210;
Zweifel 1955, p. 231; Jennings 1984, p. 52). The historical range of
the Sierra Nevada yellow-legged frog extends in California from north
of the Feather River, in Butte and Plumas Counties, to the south at the
Monarch Divide, in Fresno County, west of the Sierra Nevada crest. East
of the Sierra Nevada crest, the historical range of the Sierra Nevada
yellow-legged frog extends from the Glass Mountains of Mono County,
through Inyo County, to areas north of Lake Tahoe.
The northern DPS of the mountain yellow-legged frog ranges from the
Monarch Divide in Fresno County southward through the headwaters of the
Kern River Watershed. The ranges of the two frog species within the
mountain yellow-legged complex therefore meet each other roughly along
the Monarch Divide to the north, and along the crest of the Sierra
Nevada to the east.
Current Range and Distribution
Since the time of the mountain yellow-legged frog observations of
Grinnell and Storer (1924, pp. 664-665), a number of researchers have
reported disappearances of these species from a large fraction of their
historical ranges in the Sierra Nevada (Hayes and Jennings 1986, p.
490; Bradford 1989, p. 775; Bradford et al. 1994a, pp. 323-327;
Jennings and Hayes 1994, p. 78; Jennings 1995, p. 133; Stebbins and
Cohen 1995, pp. 225-226; Drost and Fellers 1996, p. 414; Jennings 1996,
pp. 934-935; Knapp and Matthews 2000, p. 428; Vredenburg et al. 2005,
p. 564).
The current distributions of the Sierra Nevada yellow-legged frog
and the northern DPS of the mountain yellow-legged frog are restricted
primarily to publicly managed lands at high elevations, including
streams, lakes, ponds, and meadow wetlands located within National
Forests and National Parks. National Forests with extant (surviving)
populations of mountain yellow-legged frogs include the Plumas National
Forest, Tahoe National Forest, Humboldt-Toiyabe National Forest, Lake
Tahoe Basin Management Unit, Eldorado National Forest, Stanislaus
National Forest, Sierra National Forest, Sequoia National Forest, and
Inyo National Forest. National Parks with extant populations of
mountain yellow-legged frogs include Yosemite National
[[Page 24478]]
Park, Kings Canyon National Park, and Sequoia National Park.
The most pronounced declines within the mountain yellow-legged frog
complex have occurred north of Lake Tahoe in the northernmost 125-km
(78-mi) portion of the range (Sierra Nevada yellow-legged frog) and
south of Sequoia and Kings Canyon National Parks in Tulare County, in
the southernmost 50-km (31-mi) portion, where only a few populations of
the northern DPS of the mountain yellow-legged frog remain (Fellers
1994, p. 5; Jennings and Hayes 1994, pp. 74-78). Mountain yellow-legged
frog populations have persisted in greater density in the National
Parks of the Sierra Nevada as compared to the surrounding U.S. Forest
Service (USFS) lands, and the populations that do occur in the National
Parks generally exhibit higher abundances than those on USFS lands
(Bradford et al. 1994a, p. 323; Knapp and Matthews 2000, p. 430).
Population Estimates and Status
Monitoring efforts and research studies have documented substantial
declines of mountain yellow-legged frog populations in the Sierra
Nevada. The number of extant populations has declined greatly over the
last few decades. Remaining populations are patchily scattered
throughout the historical range (Jennings and Hayes 1994, pp. 74-78;
Jennings 1995, p. 133; Jennings 1996, p. 936). In the northernmost
portion of the range (Butte and Plumas Counties), only a few Sierra
Nevada yellow-legged frog populations have been documented since 1970
(Jennings and Hayes 1994, pp. 74-78; CDFG et al., unpubl. data).
Declines have also been noted in the central and southern Sierra Nevada
(Drost and Fellers 1996, p. 420). In the south (Sierra, Sequoia, and
Inyo National Forests; and Sequoia, Kings Canyon, and Yosemite National
Parks), modest to relatively large populations (for example, breeding
populations of approximately 40 to more than 200 adults) of mountain
yellow-legged frogs do remain; however, in recent years some of the
largest of these populations have been extirpated (Bradford 1991, p.
176; Bradford et al. 1994a, pp. 325-326; Knapp 2002a, p. 10).
Davidson et al. (2002, p. 1591) reviewed 255 previously documented
mountain yellow-legged frog locations (based on Jennings and Hayes
1994, pp. 74-78) throughout the historical range and concluded that 83
percent of these sites no longer support frog populations. Vredenburg
et al. (2007, pp. 369-371) compared recent survey records (1995-2004)
with museum records from 1899-1994 and reported that 92.5 percent of
historical Sierra Nevada yellow-legged frog populations and 92.3
percent of populations of the northern DPS of mountain yellow-legged
frog are now extirpated.
CDFG (2011b, pp. 17-20) used historical localities from museum
records covering the same time interval (1899-1994), but updated recent
locality information with additional survey data (1995-2010) to
significantly increase proportional coverage from the Vredenburg et al.
(2007) study. These more recent surveys failed to detect any extant
frog population (within 1 km (0.63 mi), a metric used to capture
interbreeding individuals within metapopulations) at 220 of 318
historical Sierra Nevada yellow-legged frog localities and 94 of 109
historical mountain yellow-legged frog localities (in the Sierran
portion of their range). This calculates to an estimated loss of 69
percent of Sierra Nevada yellow-legged frog metapopulations and 86
percent of northern DPS of the mountain yellow-legged frog
metapopulations from historical occurrences.
In addition to comparisons based on individual localities, CDFG
(2011b, pp. 20-25) compared historical and recent population status at
the watershed scale. This is a rough index of the geographic extent of
the species through their respective ranges. Within the Sierra Nevada,
44 percent of watersheds historically utilized by Sierra Nevada yellow-
legged frogs, and 59 percent of watersheds historically utilized by
northern DPS mountain yellow-legged frogs, no longer support extant
populations. However, as recent survey efforts generally are more
thorough than historical ones (they target all aquatic habitats in each
surveyed watershed), this watershed-level comparison likely
underestimates rangewide declines in total populations because several
individual populations may be lost even though a watershed is counted
as recently occupied if a single individual (at any life stage) is
observed within the entire watershed (CDFG 2011b, p. 20). Furthermore,
remaining populations are generally very small. Many watersheds support
only a single extant metapopulation, which occupies one to several
adjacent water bodies (CDFG 2011b, p. 20).
Rangewide, declines of mountain yellow-legged frog populations were
estimated at around one-half of historical populations by the end of
the 1980s (Bradford et al. 1994a, p. 323). Between 1988 and 1991,
Bradford et al. (1994a, pp. 323-327) resurveyed sites known
historically (1955 through 1979 surveys) to support mountain yellow-
legged frogs. They did not detect frogs at 27 historical sites on the
Kaweah River, and they detected frogs at 52 percent of historical sites
within Sequoia and Kings Canyon National Parks and 12.5 percent of
historical sites outside of Sequoia and Kings Canyon National Parks.
When both species are combined, this resurvey effort detected mountain
yellow-legged frogs at 19.4 percent of historical sites (Bradford et
al. 1994a, pp. 324-325).
Available information discussed below indicates that the rates of
population decline have not abated, and they have likely accelerated
during the 1990s into the 2000s. Drost and Fellers (1996, p. 417)
repeated Grinnell and Storer's early 20th century surveys, and reported
frog presence at 2 of 14 historical sites. The two positive sightings
consisted of a single tadpole at one site and a single adult female at
another. They identified 17 additional sites with suitable mountain
yellow-legged frog habitat, and in those surveys, they detected three
additional populations. In 2002, Knapp (2002a, p. 10) resurveyed 302
water bodies known to be occupied by mountain yellow-legged frogs
between 1995 and 1997, and 744 sites where frogs were not previously
detected. Knapp found frogs at 59 percent of the previously occupied
sites, whereas 8 percent of previously unoccupied sites were
recolonized. These data suggest an extirpation rate five to six times
higher than the colonization rate within this study area. The
documented extirpations appeared to occur non-randomly across the
landscape, were typically spatially clumped, and involved the
disappearance of all or nearly all of the mountain yellow-legged frog
populations in a watershed (Knapp 2002a, p. 9). CDFG (2011b, p. 20)
assessed data from sites where multiple surveys were completed since
1995 (at least 5 years apart). They found that the Sierra Nevada
yellow-legged frog was not detected at 45 percent of sites where they
previously had been confirmed, while the mountain yellow-legged frog
(rangewide, including southern California) was no longer detectable at
81 percent of historically occupied sites.
The USFS conducts a rangewide, long-term monitoring program for the
Sierra Nevada yellow-legged frog and the northern DPS of the mountain
yellow-legged frog known as the Sierra Nevada Amphibian Monitoring
Program (SNAMPH). This monitoring effort provides unbiased estimates by
using an integrated unequal probability design, and it provides numbers
for robust statistical comparisons across 5-year
[[Page 24479]]
monitoring cycles spanning 208 watersheds (Brown et al. 2011, pp. 3-4).
The results of this assessment indicate that breeding activity for the
frogs is limited to 4 percent of watersheds rangewide, and the species
have declined in both distribution and abundance from historical
records. For the recent historical record (positive surveys during
1990-2002 versus 2006-2009), breeding was found in about half (48
percent) of the survey sites. When compared to data prior to 1990,
recent frog occurrence is limited to 3 percent of watersheds for which
data exist. Moreover, relative abundances were low; an estimated 9
percent of populations were large (numbering more than 100 frogs or 500
tadpoles); about 90 percent of the watersheds had fewer than 10 adults,
while 80 percent had fewer than 10 subadults and 100 tadpoles (Brown et
al. 2011, p. 24).
To summarize population trends over the available historical
record, estimates range from losses between 69 to 93 percent of Sierra
Nevada yellow-legged frog populations and 86 to 92 percent of northern
DPS of the mountain yellow-legged frog. Rangewide reduction has
diminished the number of watersheds that support mountain yellow-legged
frogs somewhere between the conservative estimates of 44 percent in the
case of Sierra Nevada yellow-legged frogs and at least 59 percent in
the case of northern DPS of the mountain yellow-legged frogs, to as
high as 97 percent of watersheds for the mountain yellow-legged frog
complex across the Sierra Nevada. Remaining populations are much
smaller relative to historical norms, and the density of populations
per watershed has declined greatly; as a result, many watersheds
currently support single metapopulations at low abundances.
Distinct Population Segment (DPS) Analysis
Under the Act, we must consider for listing any species,
subspecies, or, for vertebrates, any DPS of these taxa if there is
sufficient information to indicate that such action may be warranted.
To implement the measures prescribed by the Act, we, along with the
National Marine Fisheries Service (National Oceanic and Atmospheric
Administration--Fisheries), developed a joint policy that addresses the
recognition of DPSes for potential listing actions (61 FR 4722). The
policy allows for a more refined application of the Act that better
reflects the biological needs of the taxon being considered and avoids
the inclusion of entities that do not require the Act's protective
measures.
Under our DPS Policy, we use two elements to assess whether a
population segment under consideration for listing may be recognized as
a DPS: (1) The population segment's discreteness from the remainder of
the species to which it belongs and (2) the significance of the
population segment to the species to which it belongs. If we determine
that a population segment being considered for listing is a DPS, then
the level of threat to the population is evaluated based on the five
listing factors established by the Act to determine if listing it as
either endangered or threatened is warranted.
The newly recognized species, the Sierra Nevada yellow-legged frog
(Rana sierrae), is confirmed by genetic analysis as distinct from
populations of mountain yellow-legged frogs (R. muscosa) extant in the
southern Sierra Nevada (Vredenburg et al. 2007, p. 367). Other
distinguishing features have already been mentioned (see ``Taxonomy''
above). We are not conducting a DPS assessment in this proposed rule
for the Sierra Nevada yellow-legged frog because we have determined the
species is warranted for listing across its entire range. It is our
intent to discuss below only those topics directly relevant to the
identification and determination of the northern DPS of the mountain
yellow-legged frog.
Discreteness
Under our DPS Policy, a population segment of a vertebrate species
may be considered discrete if it satisfies either one of the following
two conditions: (1) It is markedly separated from other populations of
the same taxon as a consequence of physical, physiological, ecological,
or behavioral factors (quantitative measures of genetic or
morphological discontinuity may provide evidence of this separation);
or (2) it is delimited by international governmental boundaries within
which significant differences in control of exploitation, management of
habitat, conservation, status, or regulatory mechanisms exist.
The proposed DPS, the northern DPS of the mountain yellow-legged
frog (northern DPS of Rana muscosa), satisfies the first condition for
discreteness, the marked separation from other populations. The range
of these mountain yellow-legged frogs is divided by a natural
geographic barrier, the Tehachapi Mountains, which physically isolates
populations in the southern Sierra Nevada from those in the mountains
of southern California. The distance of the geographic separation is
about 225 km (140 mi). Between the two population segments, there
remains no connectivity through the presence of contiguous habitat
sufficient for the migration, growth, rearing, or reproduction of
dispersing frogs. Genetic discreteness is also well-supported in the
scientific literature (see ``Taxonomy'' above). Therefore, we find
these two population segments are discrete.
Significance
Under our DPS Policy, once we have determined that a population
segment is discrete, we consider its biological and ecological
significance to the larger taxon to which it belongs. This
consideration may include, but is not limited to: (1) Evidence of the
persistence of the discrete population segment in an ecological setting
that is unusual or unique for the taxon, (2) evidence that loss of the
population segment would result in a significant gap in the range of
the taxon, (3) evidence that the population segment represents the only
surviving natural occurrence of a taxon that may be more abundant
elsewhere as an introduced population outside its historical range, or
(4) evidence that the discrete population segment differs markedly from
other populations of the species in its genetic characteristics.
We have found substantial evidence that three of four significance
criteria are met by the northern DPS of the mountain yellow-legged frog
in the Sierra Nevada. These include ecological uniqueness, its loss
would result in a significant gap in the range of the taxon, and
genetic uniqueness (reflecting significant reproductive isolation over
time). There are no introduced populations of mountain yellow-legged
frogs outside of the species' historical range.
One of the most striking differences between northern DPS mountain
yellow-legged frogs and southern California mountain yellow-legged
frogs is the ecological settings they occupy. Zweifel (1955, pp. 237-
241) observed that the frogs in southern California are typically found
in steep gradient streams in the chaparral belt, even though they may
range into small meadow streams at higher elevations. In contrast,
northern DPS frogs are most abundant in high-elevation lakes and slow-
moving portions of streams in the Sierra Nevada. The rugged canyons of
the arid mountain ranges of southern California bear little resemblance
to the alpine lakes and streams of the Sierra Nevada. The significantly
different ecological settings between mountain yellow-legged frogs in
southern California and those in the Sierra
[[Page 24480]]
Nevada distinguish these populations from each other.
Furthermore, the northern DPS populations of the mountain yellow-
legged frog are significant because a catastrophic reduction in
abundance of the species as a whole would occur if the populations
constituting the northern range of the species were extirpated. The
northern DPS mountain yellow-legged frogs comprise the main
distribution of the species at the northern limits of the species'
range. Loss of the northern DPS would be significant, as it would
eliminate the species from a large portion of its range and would
reduce the species to 9 small, isolated sites in southern California
(USFWS, Jul 2012, pp. 11-12).
Finally, the northern DPS populations of mountain yellow-legged
frog are biologically and ecologically significant based on genetic
criteria. Vredenburg et al. (2007, p. 361) identified that two of three
distinct genetic clades (groups of distinct lineage) constitute the
northern range of the mountain yellow-legged frog found in the Sierra
Nevada, with the remaining single clade represented by the endangered
southern California DPS of the mountain yellow-legged frog.
Based on the differences between the ecological settings for the
mountain yellow-legged frogs found in southern California (steep
gradient streams) and the frogs found in the Sierra Nevada (high-
elevation lakes and slow-moving portions of streams), the importance of
the northern population found in the Sierra Nevada to the entire range
of this species, and the genetic composition of northern clades
reflecting isolation over a substantial period of time (more than 1
mybp), mountain yellow-legged frogs found in the Sierra Nevada
mountains meet the significance criteria under our Policy Regarding the
Recognition of Distinct Vertebrate Population Segments (61 FR 4722).
Summary of Factors Affecting the Species
Section 4 of the Act (16 U.S.C. 1533), and its implementing
regulations at 50 CFR part 424, set forth the procedures for adding
species to the Federal Lists of Endangered and Threatened Wildlife and
Plants. Under section 4(a)(1) of the Act, we may list a species based
on any of the following five factors: (A) The present or threatened
destruction, modification, or curtailment of its habitat or range; (B)
overutilization for commercial, recreational, scientific, or
educational purposes; (C) disease or predation; (D) the inadequacy of
existing regulatory mechanisms; and (E) other natural or manmade
factors affecting its continued existence. Listing actions may be
warranted based on any of the above threat factors, singly or in
combination. Each of these factors is discussed below. The following
analysis is applicable to both the Sierra Nevada yellow-legged frog
(Rana sierrae) and the Northern Distinct Population Segment of the
mountain yellow-legged frog (Rana muscosa).
Factor A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range
Habitat Destruction
A number of hypotheses, including habitat loss, have been proposed
for recent global amphibian declines (Bradford et al. 1993, p. 883;
Corn 1994, p. 62; Alford and Richards 1999, p. 4). However, physical
habitat destruction does not appear to be the primary factor associated
with the decline of mountain yellow-legged frogs. Mountain yellow-
legged frogs occur at high elevations in the Sierra Nevada, which have
not had the types or extent of large-scale habitat conversion and
physical disturbance that have occurred at lower elevations (Knapp and
Matthews 2000, p. 429). Thus, direct habitat destruction or
modification associated with intensive human activities has not been
implicated in the decline of this species (Davidson et al. 2002, p.
1597).
However, other human activities have played a role in the
modification of mountain yellow-legged frog habitats and the
curtailment of their range. The aggregation of these threats has
degraded and fragmented habitats rangewide to a significant extent.
These threats include: Recreational activities, fish introductions (see
also Factor C below), dams and water diversions, livestock grazing,
timber management, road construction and maintenance, and fire
management activities. Such activities have degraded habitat in ways
that have reduced their capacity to sustain viable populations and have
fragmented and isolated mountain yellow-legged frog populations from
each other.
Recreation
Recreational activities take place throughout the Sierra Nevada and
have significant negative impacts on many plant and animal species and
their habitats (U.S. Department of Agriculture (USDA) 2001a, pp. 483-
493). High-elevation wilderness areas, where much of the increased
recreational activity occurs, are naturally stressed ecosystems because
of intense solar exposure; extremes in temperatures, precipitation
levels, and wind; short growing seasons; and shallow, nutrient-poor
soil. Such habitats are typically not resilient to disturbance
(Schoenherr 1992, p. 167; Cole and Landres 1996, p. 170).
Recreational foot traffic in riparian areas tramples the
vegetation, compacts the soils, and can physically damage the
streambanks (Kondolf et al. 1996, pp. 1018-1020). Hiking, horse,
bicycle, or off-highway motor vehicle trails compact soils within
riparian habitat (Kondolf et al. 1996, p. 1019), and can lower the
water table and cause increased erosion. The recreational activity of
anglers at high mountain lakes can be locally intense in the Sierra
Nevada, with most regions reporting a level of use greater than the
fragile lakeshore environments can withstand (Bahls 1992, p. 190).
However, studies have not been conducted to determine the extent to
which recreational activities are directly contributing to the decline
of the mountain yellow-legged frog complex, and direct effects from
recreation have not been implicated as a major cause of the decline of
these species. Nevertheless, recreational activities are the fastest
growing use of National Forests. As such, their impacts on the mountain
yellow-legged frog complex are likely to continue and to increase (USDA
2001b, p. 213). Currently, recreational activities are considered a
threat of low significance to the species' habitat overall.
Habitat Modification Due to Introduction of Trout to Historically
Fishless Areas
One habitat feature that is documented to have a significant
detrimental impact to mountain yellow-legged frog populations is the
presence of trout from current and historical stocking for the
maintenance of a sport fishery. To further angling success and
opportunity, trout stocking programs in the Sierra Nevada started in
the late 19th century (Bahls 1992, p. 185; Pister 2001, p. 280). This
anthropogenic activity has community-level effects and constitutes the
primary detrimental impact to mountain yellow-legged frog habitat and
species viability.
Prior to extensive trout planting programs, almost all streams and
lakes in the Sierra Nevada at elevations above 1,800 m (6,000 ft) were
fishless. Several native fish species occur naturally in aquatic
habitats below this elevation in the Sierra Nevada (Knapp 1996, pp. 12-
14; Moyle et al. 1996, p. 354; Moyle 2002, p. 25). Natural barriers
prevented fish from colonizing the higher elevation headwaters of the
Sierra Nevada watershed (Moyle et al. 1996, p. 354). The upper reaches
of the Kern
[[Page 24481]]
River, where native fish such as the Little Kern golden trout
(Oncorhynchus mykiss whitei) and California golden trout (O. m.
aguabonita) evolved, represent the only major exception to the 1,800-m
(6,000-ft) elevation limit for fishes within the range of the mountain
yellow-legged frog in the Sierra Nevada (Moyle 2002, p. 25).
Additionally, prior to extensive planting, native Paiute cutthroat (O.
clarki seleneris) and Lahontan cutthroat (O. c. henshawi) also occurred
within the range of the mountain yellow-legged frog in the Sierra
Nevada, but were limited in their distribution (Moyle 2002, pp. 288-
289).
Some of the first practitioners of trout stocking in the Sierra
Nevada were the Sierra Club, local sportsmen's clubs, private citizens,
and the U.S. military (Knapp 1996, p. 8; Pister 2001, p. 280). As more
hatcheries were built, and the management of the trout fishery became
better organized, fish planting continued for the purpose of increased
angler opportunities and success (Pister 2001, p. 281). After World War
II, the method of transporting trout to high-elevation areas changed
from packstock to aircraft, which allowed stocking in more remote lakes
and in greater numbers. With the advent of aerial stocking, trout
planting expanded to new areas, with higher efficiency.
Brook trout (Salvelinus fontinalis), brown trout (Salmo trutta),
rainbow trout (Oncorhynchus mykiss), and other trout species
assemblages have been planted in most streams and lakes of the Sierra
Nevada (Knapp 1996, p. 8; Moyle 2002, p. 25). National Forests in the
Sierra Nevada have a higher proportion of lakes with fish occupancy
than do National Parks (Knapp 1996, p. 3). This is primarily because
the National Park Service (NPS) adopted a policy that greatly reduced
fish stocking within their jurisdictional boundaries in the late 1970s.
Fish stocking was terminated altogether in Sierra Nevada National Parks
in 1991 (Knapp 1996, p. 9). CDFG continues to stock trout in National
Forest water bodies, but has recently reduced the number of stocked
water bodies to reduce impacts to native amphibians (ICF Jones & Stokes
2010, pp. ES-1-ES-16). Stocking decisions are based on criteria
outlined in the Environmental Impact Report for the Hatchery and
Stocking Program (ICF Jones & Stokes 2010, Appendix K).
Fish stocking as a practice has been widespread throughout the
range of both species of mountain yellow-legged frogs. Knapp and
Matthews (2000, p. 428) indicated that 65 percent of the water bodies
that were 1 ha (2.5 ac) or larger in National Forests they studied were
stocked with fish on a regular basis. Over 90 percent of the total
water body surface area in the John Muir Wilderness was occupied by
nonnative trout (Knapp and Matthews 2000, p. 434).
Another detrimental feature of fish stocking is that fish often
persist in water bodies even after stocking ceases. Lakes larger than 1
ha (2.5 ac) within Sierra Nevada National Parks were estimated to have
from 35 to 50 percent nonnative fish occupancy, only a 29 to 44 percent
decrease since fish stocking was terminated around 2 decades before the
study (Knapp 1996, p. 1). Though data on fish occupancy in streams are
lacking throughout the Sierra Nevada, Knapp (1996, p. 11) estimated
that 60 percent of the streams in Yosemite National Park were still
occupied by introduced trout.
Trout both compete for limited resources and directly prey on
mountain yellow-legged frog tadpoles and adults (see Factor C below).
The presence of these fish decimates frog populations through
competition and predation (see below). The impact of introduced trout
was greatest in the past, as it eliminated frogs across a large expanse
of their historical range. Fundamentally, this has removed deeper lakes
from being mountain yellow-legged frog habitat at a landscape scale,
because fish now populate these areas instead of frogs. Moreover,
introduced trout continue to limit species viability because remaining
populations are now isolated, and functional dispersal barriers make
emigration difficult. Finally, the few frogs that do successfully
emigrate will move to inhospitable, fish-occupied habitat where they
are often outcompeted or preyed upon by trout. These factors make
recolonization of extirpated sites unlikely.
The body of scientific research has demonstrated that introduced
trout have negatively impacted mountain yellow-legged frogs over much
of the Sierra Nevada (Grinnell and Storer 1924, p. 664; Bradford 1989,
pp. 775-778; Bradford et al. 1993, pp. 882-888; Knapp 1994, p. 3; Drost
and Fellers 1996, p. 422; Knapp 1996, pp. 13-15; Knapp and Matthews
2000, p. 428; Knapp et al. 2001, p. 401). Fish stocking programs have
negative ecological implications because fish eat aquatic flora and
fauna, including amphibians and invertebrates (Bahls 1992, p. 191;
Erman 1996, p. 992; Matthews et al. 2001, pp. 1135-1136; Pilliod and
Peterson 2001, p. 329; Schindler et al. 2001, p. 309; Moyle 2002, p.
58; Epanchin et al. 2010, p. 2406). Finlay and Vredenburg (2007, p.
2187) documented that the same benthic (bottom-dwelling) invertebrate
resource base sustains the growth of both frogs and trout, suggesting
that competition with trout for prey is an important factor that may
contribute to the decline of the mountain yellow-legged frog.
Knapp and Matthews (2000, p. 428) surveyed more than 1,700 water
bodies, and concluded that a strong negative correlation exists between
introduced trout and mountain yellow-legged frogs (Knapp and Matthews
2000, p. 435). Consistent with this finding are the results of an
analysis of the distribution of mountain yellow-legged frog tadpoles,
which indicate that the presence and abundance of this life stage are
reduced dramatically in fish-stocked lakes (Knapp et al. 2001, p. 408).
Knapp (2005a, pp. 265-279) also compared the distribution of nonnative
trout with the distributions of several amphibian and reptile species
in 2,239 lakes and ponds in Yosemite National Park, and found that
mountain yellow-legged frogs were five times less likely to be detected
in waters where trout were present. Even though stocking within the
National Park ceased in 1991, more than 50 percent of water bodies
deeper than 4 m (13 ft) and 75 percent deeper than 16 m (52 ft) still
contained trout populations in 2000-2002 (Knapp 2005a, p. 270). Both
trout and mountain yellow-legged frogs utilize deeper water bodies.
Based on the results from Knapp (2005a), the reduced detection of frogs
in trout-occupied waters indicates that trout are excluding mountain
yellow-legged frogs from some of the best aquatic habitat.
Several aspects of the mountain yellow-legged frog's life history
may exacerbate its vulnerability to extirpation by trout (Bradford
1989, pp. 777-778; Bradford et al. 1993, pp. 886-888; Knapp 1996, p.
14; Knapp and Matthews 2000, p. 435). Mountain yellow-legged frogs are
aquatic and found mainly in lakes. This increases the probability that
they will encounter introduced fishes whose distribution has been
greatly expanded throughout the Sierra Nevada. The multiple-year
tadpole stage of the mountain yellow-legged frog necessitates their use
of permanent water bodies deep enough to not freeze solid during
multiple winters (unless there is some other refuge from freezing and
oxygen depletion, such as submerged crevices). Also, overwintering
adults must avoid oxygen depletion when the water is covered by ice
(Mullally and Cunningham 1956a, p. 194; Bradford 1983, p. 1179; Knapp
and Matthews 2000, pp. 435-436). This functionally restricts tadpoles
to the same water bodies most suitable for fishes (Knapp 1996, p. 14),
and the consequences of predation and
[[Page 24482]]
competition thereby isolate mountain yellow-legged frogs to fishless,
marginal habitats (Bradford et al. 1993, pp. 886-887; Knapp and
Matthews 2000, p. 435).
Mountain yellow-legged frogs and trout (native and nonnative) do
co-occur at some sites, but these co-occurrences are probably mountain
yellow-legged frog population sinks (areas with negative population
growth rates in the absence of immigration) (Bradford et al. 1998, p.
2489; Knapp and Matthews 2000, p. 436). Mountain yellow-legged frogs
have also been extirpated at some fishless bodies of water (Bradford
1991, p. 176; Drost and Fellers 1996, p. 422). A possible explanation
is the isolation and fragmentation of remaining populations due to
introduced fishes in the streams that once provided mountain yellow-
legged frogs with dispersal and recolonization routes; these remote
populations are now non-functional as metapopulations (Bradford 1991,
p. 176; Bradford et al. 1993, p. 887). Based on a survey of 95 basins
within Sequoia and Kings Canyon National Parks, Bradford et al. (1993,
pp. 885-886) estimated that the introduction of fishes into the study
area resulted in an approximately 10-fold increase in habitat
fragmentation between populations of mountain yellow-legged frogs.
Knapp and Matthews (2000, p. 436) believe that this fragmentation has
further isolated mountain yellow-legged frogs within the already
marginal habitat left unused by fishes.
Fragmentation of mountain yellow-legged frog habitat renders
metapopulations more vulnerable to extirpation from random events (such
as disease) (Wilcox 1980, pp. 114-115; Bradford et al. 1993, p. 887;
Hanski and Simberloff 1997, p. 21; Knapp and Matthews 2000, p. 436).
Isolated population locations may have higher extinction rates because
trout prevent successful recolonization and dispersal to and from these
sites (Bradford et al. 1993, p. 887; Blaustein et al. 1994a, p. 7;
Knapp and Matthews 2000, p. 436). Amphibians may be unable to
recolonize unoccupied sites following local extinctions because of
physiological constraints, the tendency to move only short distances,
and high site fidelity (Blaustein et al. 1994a, p. 8). Finally, frogs
that do attempt recolonization may emigrate into fish-occupied habitat
and perish, rendering sites with such metapopulation dynamics less able
to sustain frog populations.
Although fish stocking has been curtailed within many occupied
basins, the impacts to frog populations persist due to the presence of
self-sustaining fish populations in some of the best habitat that
normally would have sustained mountain yellow-legged frogs. The
fragmentation that persists across the range of these frog species
renders them more vulnerable to other population stressors, and
recovery is slow, if not impossible, without costly and physically
difficult direct human intervention (such as physical and chemical
trout removal). While most of the impacts occurred historically, the
impact upon the biogeographic (population/metapopulation) integrity of
the species will be long-lasting. Currently, habitat degradation and
fragmentation by fish is considered a highly significant and prevalent
threat to persistence and recovery of the species.
Dams and Water Diversions
Numerous reservoirs have been constructed within the ranges of the
mountain yellow-legged frog complex. These include Huntington Lake,
Florence Lake, Lake Thomas A. Edison, Saddlebag Lake, Convict Lake,
Cherry Lake, and other reservoirs associated with Hetch Hetchy, Upper
and Lower Blue Lakes, Lake Aloha, Silver Lake, Hell Hole Reservoir,
French Meadow Reservoir, Lake Spaulding, Alpine Lake, Loon Lake, Ice
House Reservoir, and others. Dams and water diversions have altered
aquatic habitats in the Sierra Nevada (Kondolf et al. 1996, p. 1014).
The combination of these two features has reduced habitat suitability
within the range of the species by creating migration barriers and
altering local hydrology. This stressor causes considerable habitat
fragmentation and direct habitat loss in those areas where water
projects were constructed and are operating.
The extent of the impact to mountain yellow-legged frog populations
from habitat loss or modification due to these projects has not been
quantified. However, the construction of dams has affected populations
in the Sierra Nevada by altering the distribution of predators
(reservoirs are often stocked with fish species that prey on mountain
yellow-legged frogs) and affecting the effective dispersal of migrating
frogs. Mountain yellow-legged frogs cannot live in or disperse
effectively through the exposed shorelines created by reservoirs, nor
can they successfully reproduce in these environments unless there are
shallow side channels or disjunct pools free of predatory fishes
(Jennings 1996, p. 939). In this fashion, reservoirs represent
considerable dispersal barriers that further fragment the range of the
mountain yellow-legged frogs.
Dams alter the temperature and sediment load of the rivers they
impound (Cole and Landres 1996, p. 175). Dams, water diversions, and
their associated structures also alter the natural flow regime with
unseasonal and fluctuating releases of water. These features may create
habitat conditions unsuitable for native amphibians both upstream and
downstream of dams, and they may act as barriers to movement by
dispersing juvenile and migrating adult amphibians (Jennings 1996, p.
939). Where dams act as barriers to mountain yellow-legged frog
movement, they effectively prevent genetic exchange between populations
and the recolonization of vacant sites.
Water diversions may remove water from mountain yellow-legged frog
habitat and adversely impact breeding success and adult survivorship.
This results in physical reduction in habitat area and potentially
lowers water levels to the extent that the entire water column freezes
in the winter, thereby removing aquatic habitat altogether. Given the
amount of water development within the historical ranges of mountain
yellow-legged frogs, these factors likely have contributed to
population declines, and ongoing management and habitat fragmentation
will continue to pose a risk to the species. The magnitude of such
impacts would increase if long droughts become more frequent in the
future (see Factor E below) or if increasing diversions and storage
facilities are constructed and implemented to meet growing needs for
water and power. Currently, dams and water diversions are considered a
moderate, prevalent threat to persistence and recovery of the species.
Livestock Use (Grazing)
As discussed below, grazing reduces the suitability of habitat for
mountain yellow-legged frogs by reducing its capability to sustain
frogs and facilitate dispersal and migration, especially in stream
areas. The impact of this stressor to mountain yellow-legged frogs is
ongoing, but of relatively low importance as a limiting factor on
extant populations. While this stressor may have played a greater role
historically, leading in part to rangewide reduction of the species
(see below), the geographic extent of livestock grazing activity within
current mountain yellow-legged frog habitat does not encompass the
entire range of the species.
Grazing of livestock in riparian areas impacts vegetation in
multiple ways, including soil compaction, which increases runoff and
decreases water availability to plants; vegetation
[[Page 24483]]
removal, which promotes increased soil temperatures and evaporation
rates at the soil surface; and direct physical damage to the vegetation
(Kauffman and Krueger 1984, pp. 433-434; Cole and Landres 1996, pp.
171-172; Knapp and Matthews 1996, pp. 816-817). Streamside vegetation
protects and stabilizes streambanks by binding soils to resist erosion
and trap sediment (Kauffman et al. 1983, p. 683; Chaney et al. 1990, p.
2). Removal of vegetative cover within mountain yellow-legged frog
habitat decreases available habitat, exposes frogs to predation (Knapp
1993b, p.1), and increases the threat of desiccation (Jennings 1996, p.
539).
Aquatic habitat can also be degraded by grazing. Mass erosion from
trampling and hoof slide causes streambank collapse and an accelerated
rate of soil transport to streams (Meehan and Platts 1978, p. 274).
Accelerated rates of erosion lead to elevated instream sediment loads
and depositions, and changes in stream-channel morphology (Meehan and
Platts 1978, pp. 275-276; Kauffman and Krueger 1984, p. 432). Livestock
grazing may lead to diminished perennial streamflows (Armour et al.
1994, p. 10). Livestock can increase nutrient-loading in water bodies
due to urination and defecation in or near the water, and can cause
elevated bacteria levels in areas where cattle are concentrated (Meehan
and Platts 1978, p. 276; Stephenson and Street 1978, p. 156; Kauffman
and Krueger 1984, p. 432). With increased grazing intensity, these
adverse effects to the aquatic ecosystem increase proportionately
(Meehan and Platts 1978, p. 275; Clary and Kinney 2000, p. 294).
Observational data indicate that livestock negatively impact
mountain yellow-legged frogs by altering riparian habitat and trampling
individuals (Knapp 1993a, p. 1; 1993b, p. 1; 1994, p. 3; Jennings 1996,
p. 938; Carlson 2002, pers. comm.; Knapp 2002a, p. 29). Livestock tend
to concentrate along streams and wet areas where there is water and
herbaceous vegetation; grazing impacts are therefore most pronounced in
these habitats (Meehan and Platts 1978, p. 274; U.S. Government
Accounting Office (GAO) 1988, pp. 10-11; Fleischner 1994, p. 635; Menke
et al. 1996, p. 17). This concentration of livestock contributes to the
destabilization of streambanks, causing undercuts and bank failures
(Kauffman et al. 1983, p. 684; Marlow and Pogacnik 1985, pp. 282-283;
Knapp and Matthews 1996, p. 816; Moyle 2002, p. 55). Grazing activity
contributes to the downcutting of streambeds and lowers the water table
(Meehan and Platts 1978, pp. 275-276; Kauffman et al. 1983, p. 685;
Kauffman and Krueger 1984, p. 432; Bohn and Buckhouse 1985, p. 378; GAO
1988, p. 11; Armour et al. 1994, pp. 9-11; Moyle 2002, p. 55).
Livestock grazing may impact other wetland systems, including ponds
that can serve as mountain yellow-legged frog habitat. Grazing modifies
shoreline habitats by removing overhanging banks that provide shelter,
and grazing contributes to the siltation of breeding ponds. Pond
siltation has been demonstrated to reduce the depth of breeding ponds
and to cover underwater crevices, thereby making the ponds less
suitable, or unsuitable, as overwintering habitat for tadpoles and
adult mountain yellow-legged frogs (Bradford 1983, p. 1179; Pope 1999a,
pp. 43-44).
In general, historical livestock grazing within the range of the
mountain yellow-legged frog was at a high (although undocumented) level
until the establishment of National Parks (beginning in 1890) and
National Forests (beginning in 1905) (UC 1996a, p. 114; Menke et al.
1996, p. 14). Within the newly established National Parks, grazing by
cattle and sheep was replaced by that of packstock, such as horses and
burros. Within the National Forests, the amount of livestock grazing
was gradually reduced, and the types of animals shifted away from sheep
and toward cattle and packstock.
For mountain yellow-legged frogs, livestock grazing activity is
likely a minor prevalent threat to currently extant populations,
although in certain areas it may exacerbate habitat fragmentation
already facilitated by the introduction of trout. There are currently
161 active Rangeland Management Unit Allotments for grazing in USFS-
administered lands. Twenty-seven of these allotments have extant
mountain yellow-legged frog populations (based on surveys performed
after 2005). Currently, other allotments have been closed in certain
sensitive areas, and standards have been implemented in remaining
allotments to protect aquatic habitats. This threat is likely more one
of historical significance. While it may be a factor in certain
allotments with active grazing and extant populations, rangewide it is
likely not a significant risk factor as many populations persist
outside of actively grazed areas.
Packstock Use
Packstock grazing is the only grazing currently permitted in the
National Parks of the Sierra Nevada. Use of packstock in the Sierra
Nevada has increased since World War II as a result of improved road
access and increases in leisure time and disposable income (Menke et
al. 1996, p. 14). In the Sixty-Lakes Basin of Kings Canyon National
Park, packstock use is regulated in wet meadows to protect mountain
yellow-legged frog breeding habitat in bogs and lake shores from
trampling and associated degradation (Vredenburg 2002, p. 11; Werner
2002, p. 2). Packstock use is also permitted in National Forests within
the Sierra Nevada. However, there has been very little monitoring of
the impacts of such activity in this region (Menke et al. 1996, p. 14),
so its contribution to the decline of frog populations is impossible to
quantify.
Packstock use is likely a threat of low significance to mountain
yellow-legged frogs at the current time, except on a limited, site-
specific basis. As California's human population increases, the impact
of recreational activities, including packstock use and riding in the
Sierra Nevada, are projected to increase (USDA 2001a, pp. 473-474).
This activity may pose a risk to some remnant populations of frogs and,
in certain circumstances, a hindrance to recovery of populations in
heavily used lakes.
Roads and Timber Harvest
Activities that alter the terrestrial environment (such as road
construction and timber harvest) may impact amphibian populations in
the Sierra Nevada (Jennings 1996, p. 938). These impacts are
understandably in proportion to the magnitude of the alteration to the
environment, and are more pronounced in areas with less stringent
mitigation measures (that is, outside National Parks or wilderness
areas). Road construction and timber harvest were likely of greater
significance historically, and may have acted to reduce the species'
range prior to the more recent detailed studies and systematic
monitoring that have quantified and documented these losses.
Timber harvest activities remove vegetation and cause ground
disturbance and compaction, making the ground more susceptible to
erosion (Helms and Tappeiner 1996, p. 446). This erosion increases
siltation downstream that could potentially damage mountain yellow-
legged frog breeding habitat. Timber harvest may alter the annual
hydrograph (timing and volume of surface flows), possibly lowering the
water table, which could dewater riparian habitats used by mountain
yellow-legged frogs. The majority of erosion caused by timber harvests
is from logging roads (Helms and Tappeiner 1996, p. 447). Prior to the
formation of National Parks in 1890 and
[[Page 24484]]
National Forests in 1905, timber harvest was widespread and
unregulated, but primarily took place at elevations on the western
slope of the Sierra Nevada below the range of the mountain yellow-
legged frog (University of California (UC) 1996b, pp. 24-25). Between
1900 and 1950, the majority of timber harvest occurred in old-growth
forests on private land (UC 1996b, p. 25). Between 1950 and the early
1990s, there were increases in timber harvest on National Forests, and
the majority of timber harvest-associated impacts on mountain yellow-
legged frogs may therefore have taken place during this period.
Roads, including those associated with timber harvests, can
contribute to habitat fragmentation and limit amphibian movement, thus
having a negative effect on amphibian species richness (Lehtinen et al.
1999, pp. 8-9; deMaynadier and Hunter 2000, p. 56). This effect could
fragment mountain yellow-legged frog habitat if the road bisected
habitat consisting of water bodies in close proximity.
Currently, most of the mountain yellow-legged frog populations
occur in National Parks or designated wilderness areas where timber is
not harvested (Bradford et al. 1994a, p. 323; Drost and Fellers 1996,
p. 421; Knapp and Matthews 2000, p. 430). Other mountain yellow-legged
frog populations outside of these areas are located above the
timberline, so timber harvest activity is not expected to affect the
majority of extant mountain yellow-legged frog populations. There
remain some mountain yellow-legged frog populations in areas where
timber harvests occur or may occur in the future. Roads also exist
within the range of the mountain yellow-legged frog, and more may be
constructed. However, neither of these factors has been implicated as
an important contributor to the decline of this species (Jennings 1996,
pp. 921-941). It is likely a minor prevalent threat to mountain yellow-
legged frogs factored across the range of the species.
Fire and Fire Management Activities
Mountain yellow-legged frogs are generally found at high elevations
in wilderness areas and National Parks where vegetation is sparse and
fire suppression activities are infrequently implemented. Where such
activities may occur, potential impacts to the species resulting from
fire management activities include: Habitat degradation through water
drafting (taking of water) from occupied ponds and lakes, erosion and
siltation of habitat from construction of fuel breaks, and
contamination by fire retardants from chemical fire suppression.
In some areas within the current range of the mountain yellow-
legged frog, long-term fire suppression has changed the forest
structure and created conditions that increase fire severity and
intensity (McKelvey et al. 1996, pp. 1934-1935). Excessive erosion and
siltation of habitats following wildfire is a concern in shallow, lower
elevation areas below forested stands. However, prescribed fire has
been used by land managers to achieve various silvicultural objectives,
including fuel load reduction. In some systems, fire is thought to be
important in maintaining open aquatic and riparian habitats for
amphibians (Russell ASLO 1999, p. 378), although severe and intense
wildfires may reduce amphibian survival, as the moist and permeable
skin of amphibians increases their susceptibility to heat and
desiccation (Russell et al. 1999, p. 374). Amphibians may avoid direct
mortality from fire by retreating to wet habitats or sheltering in
subterranean burrows.
It is not known what impacts fire and fire management activities
have had on historical populations of mountain yellow-legged frogs.
Neither the direct nor indirect effects of prescribed fire or wildfire
on the mountain yellow-legged frog have been studied. Where fire has
occurred in southern California, the character of the habitat has been
significantly altered, leading to erosive scouring and flooding after
surface vegetation is denuded (North 2012, pers. comm.). When a large
fire does occur in occupied habitat, mountain yellow-legged frogs are
susceptible to direct mortality (leading to significantly reduced
population sizes) and indirect effects (habitat alteration and reduced
breeding habitat). It is suspected that at least one population in the
southern DPS was nearly extirpated by fire on the East Fork City Creek
(San Bernadino Mountains) in 2003 (North 2012, pers. comm.). It is
possible that fire has caused localized extirpations in the past.
However, because the species generally occupies high-elevation habitat,
fire is likely not a significant risk to this species over much of its
current range.
In summary, based on the best available scientific and commercial
information, we consider the threats of modification and curtailment of
the species' habitat and range to be significant, ongoing threats to
the Sierra Nevada yellow-legged frog and northern DPS of the mountain
yellow-legged frog. Threats from recreational foot traffic, camping,
and timber harvest and related activities are not quantified, but they
are not thought to be major drivers of frog population dynamics.
Threats of low prevalence (important limiting factors in some areas,
but not across a large part of the mountain yellow-legged frog
complex's range) include grazing and fire management activities. Dams
and water diversions likely present a moderate prevalent threat.
Habitat fragmentation and degradation (loss of habitat through
competitive exclusion) by stocked and persistent introduced trout
across the majority of the species' range are a threat of high
prevalence. This threat is a significant limiting factor to persistence
and recovery of the species rangewide.
Factor B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
There is no known commercial market for mountain yellow-legged
frogs, nor are there documented recreational or educational uses for
these species. Mountain yellow-legged frogs do not appear to be
particularly popular among amphibian and reptile collectors; however,
Federal listing could raise the value of the animals within wildlife
trade markets and increase the threat of unauthorized collection above
current levels (McCloud 2002, pers. comm.).
Scientific collection for museum specimens has resulted in the
death of numerous individuals (Zweifel 1955, p. 207; Jennings and Hayes
1994, pp. 74-78). However, this occurred at times when the populations
were at greater abundances and geographic distribution and in numbers
that likely had little influence on the overall population from which
individuals were sampled. Scientific research may cause stress to
mountain yellow-legged frogs through disturbance, including disruption
of the species' behavior, handling of individual frogs, and injuries
associated with marking and tracking individuals. However, this is a
relatively minor nuisance and not likely a negative impact to the
survival and reproduction of individuals or the viability of the
population.
Based on the best available scientific and commercial information,
we do not consider the overutilization for commercial, recreational,
scientific, or educational purposes to be a threat to the mountain
yellow-legged frog complex now or in the future.
Factor C. Disease or Predation
Predation
Researchers have observed predation of mountain yellow-legged frogs
by the mountain garter snake (Thamnophis
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elegans elegans), Brewer's blackbird (Euphagus cyanocephalus), Clark's
nutcracker (Nucifraga columbiana), coyote (Canis latrans), and black
bear (Ursus americanus) (Mullally and Cunningham 1956a, p. 193;
Bradford 1991, pp. 176-177; Jennings et al. 1992, p. 505; Feldman and
Wilkinson 2000, p. 102; Vredenburg et al. 2005, p. 565). However, none
of these has been implicated as a driver of population dynamics, so it
is presumed that such predation occurrences are incidental and do not
significantly impact frog populations (except perhaps in circumstances
where so few individuals remain that the loss of low numbers of
individuals would be of significant concern).
The most prominent predator of mountain yellow-legged frogs is
introduced trout, whose significance is well-established because it has
been repeatedly observed that nonnative fishes and frogs rarely
coexist, and it is known that introduced trout can and do prey on all
frog life stages (Grinnell and Storer 1924, p. 664; Mullally and
Cunningham 1956a, p. 190; Cory 1962a, p. 401; 1963, p. 172; Bradford
1989, pp. 775-778; Bradford and Gordon 1992, p. 65; Bradford et al.
1993, pp. 882-888; 1994a, p. 326; Drost and Fellers 1996, p. 422;
Jennings 1996, p. 940; Knapp 1996, p. 14; Knapp and Matthews 2000, p.
428; Knapp et al. 2001, p. 401; Vredenburg 2004, p. 7649). It is
estimated that 63 percent of lakes larger than 1 ha (2.5 ac) in the
Sierra Nevada contain one or more nonnative trout species, and greater
than 60 percent of streams contain nonnative trout (Knapp, 1996, pp. 1-
44), in some areas comprising greater than 90 percent of total water
body surface area (Knapp and Matthews 2000, p. 434).
The multiple-year tadpole stage of the mountain yellow-legged frog
requires submersion in the aquatic habitat year-round until
metamorphosis. Moreover, all life stages are highly aquatic, increasing
the frog's susceptibility to predation by trout (where they co-occur)
throughout its lifespan. Overwinter mortality due to predation is
especially significant because, when water bodies ice over in winter,
tadpoles are forced from shallow margins of lakes and ponds into deeper
unfrozen water where they are more vulnerable to predation; fish
encounters in such areas increase, while refuge is less available.
The predation of mountain yellow-legged frogs by fishes observed in
the early 20th century by Grinnell and Storer and the documented
declines of the 1970s (Bradford 1991, pp. 174-177; Bradford et al.
1994a, pp. 323-327; Stebbins and Cohen 1995, pp. 226-227) were not the
beginning of the mountain yellow-legged frog's decline, but rather the
end of a long decline that started soon after fish introductions to the
Sierra Nevada began in the mid-1800s (Knapp and Matthews 2000, p. 436).
Metapopulation theory (Hanski 1997, pp. 85-86) predicts this type of
time lag from habitat modification to population extinction (Knapp and
Matthews 2000, p. 436). In 2004, Vredenburg (2004, p. 7647) concluded
that introduced trout are effective predators on mountain yellow-legged
frog tadpoles and suggested that the introduction of trout is the most
likely reason for the decline of the mountain yellow-legged frog
complex. This threat is a significant, prevalent risk to mountain
yellow-legged frogs rangewide, and it will persist into the future.
Disease
Over roughly the last 2 decades, pathogens have been associated
with amphibian population declines, mass die-offs, and even extinctions
worldwide (Bradford 1991, pp. 174-177; Blaustein et al. 1994b, pp. 251-
254; Alford and Richards 1999, pp. 506; Muths et al. 2003, p. 357;
Weldon et al. 2004, p. 2100; Rachowicz et al. 2005, p. 1446; Fisher et
al. 2009, p. 292). One pathogen strongly associated with dramatic
declines on all five continents is the chytrid fungus, Batrachochytrium
dendrobatidis (Bd) (Rachowicz et al. 2005, p. 1442). This chytrid
fungus has now been reported in amphibian species worldwide (Fellers et
al. 2001, p. 945; Rachowicz et al. 2005, p. 1442). Early doubt that
this particular pathogen was responsible for worldwide die-offs has
largely been overcome by the weight of evidence documenting the
appearance, spread, and detrimental effects to affected populations
(Vredenburg et al. 2010a, p. 9689). The correlation of notable
amphibian declines with reports of outbreaks of fatal chytridiomycosis
(the disease caused by Bd) in montane areas has led to a general
association between high altitude, cooler climates, and population
extirpations associated with Bd (Fisher et al. 2009, p. 298).
Bd affects the mouth parts and epidermal (skin) tissue of tadpoles
and metamorphosed frogs (Fellers et al. 2001, pp. 950-951). The fungus
can reproduce asexually, and can generally withstand adverse conditions
such as freezing or drought (Briggs et al. 2002, p. 38). It also may
reproduce sexually, leading to thick-walled sporangia that would be
capable of long-term survival (for distant transport and persistence in
sites even after all susceptible host animal populations are
extirpated) (Morgan et al. 2007, p. 13849). Adult frogs can acquire
this fungus from tadpoles, and it can also be transmitted between
tadpoles (Rachowicz and Vredenburg 2004, p. 80).
In California, chytridiomycosis has been detected in many amphibian
species, including mountain yellow-legged frogs (Briggs et al. 2002, p.
38; Knapp 2002b, p. 1). The earliest documented case in the mountain
yellow-legged frog complex was in 1998, at Yosemite National Park
(Fellers et al. 2001, p. 945). It is unclear how Bd was originally
transmitted to the frogs (Briggs et al. 2002, p. 39). Visual
examination of 43 tadpole specimens collected between 1955 and 1976
revealed no evidence of Bd infection; however 14 of 36 specimens
preserved between 1993 and 1999 did have abnormalities attributable to
Bd (Fellers et al. 2001, p. 947). Since at least 1976, Bd has affected
adult Yosemite toads (Green and Kagarise Sherman 2001, p. 92), whose
range overlaps with the mountain yellow-legged frogs. Therefore, it is
possible that this pathogen has affected all three amphibian species
covered in this proposed rule since at least the mid-1970s. Mountain
yellow-legged frogs may be especially vulnerable to Bd infections
because all life stages share the same aquatic habitat nearly year
round, facilitating the transmission of this fungus among individuals
at different life stages (Fellers et al. 2001, p. 951).
During the epidemic phase of chytrid infection into unexposed
populations, rapid die-offs are observed within short order for adult
and subadult lifestages (Vredenburg et al. 2010a, p. 9691), while
tadpoles are less affected at first (Vredenburg et al. 2010a, p. 9689).
In mountain yellow-legged frogs, Bd causes overwinter mortality and
mortality during metamorphosis (Briggs et al. 2002, p. 39; Rachowicz
2005, pp. 2-3); metamorphs are the most sensitive life stage to Bd
infection (Kilpatrick et al. 2009, p. 113; Vredenburg et al. 2010b, p.
3). Field and laboratory experiments indicate that Bd infection is
generally lethal to mountain yellow-legged frogs, and is likely
responsible for recent declines (Knapp 2005b; Rachowicz 2005, pers.
comm.). Rachowicz et al. (2006, p. 1671) monitored several infected and
uninfected populations in Sequoia and Kings Canyon National Parks over
multiple years, documenting dramatic declines and extirpations in only
the infected populations. Rapid die-offs of mountain yellow-legged
frogs from chytridiomycosis have been observed in more than 50 water
bodies in the southern Sierra Nevada (Briggs et al.
[[Page 24486]]
2005, p. 3151). Studies of the microscopic structure of tissue and
other evidence suggests Bd caused many of the recent extinctions in the
Sierra National Forest's John Muir Wilderness Area and in Kings Canyon
National Park, where 41 percent of the populations went extinct between
1995 and 2002 (Knapp 2002a, p. 10).
In several areas where detailed studies of the effects of Bd on the
mountain yellow-legged frog are ongoing, substantial declines have been
observed following the course of the disease infection and spread.
Survey results from 2000 in Yosemite and Sequoia-Kings Canyon National
Parks indicate that 24 percent of the mountain yellow-legged frog
populations showed signs of Bd infection (Briggs et al. 2002, p. 40).
In both 2003 and 2004, 19 percent of assayed populations in Sequoia and
Kings Canyon National Parks were infected with Bd (Rachowicz 2005, pp.
2-3). By 2005, 91 percent of assayed populations in Yosemite National
Park showed evidence of Bd infection (Knapp 2005b, pp. 1-2). Currently,
it is believed that all populations in Yosemite Park are infected with
Bd (Briggs et al. 2010, p. 9695).
The effects of Bd on host populations of the mountain yellow-legged
frog are variable, ranging from extinction, to persistence with a high
level of infection, to persistence with a low level of infection
(Briggs et al. 2002, pp. 40-41). In populations where Bd infection
first occurs, the most common outcome is epidemic spread of the disease
and population extirpation (Briggs et al. 2010, p. 9699). Die-offs are
characterized by rapid onset of high level Bd infections, followed by
death due to chytridiomycosis. Adults in persistent populations
frequently recover and are subsequently re-infected by Bd at low levels
(Briggs et al. 2010, pp. 9695-9696). However, it is apparent that even
at sites exhibiting population persistence with Bd, high mortality of
metamorphosing frogs persists, and this phenomenon may explain the
lower abundances observed in such populations (Briggs et al. 2010, p.
9699).
Vredenburg et al. (2010a, pp. 2-4) studied frog populations before,
during, and after the infection and spread of Bd in three study basins
constituting 13, 33, and 42 frog populations, then comprising the most
intact metapopulations remaining for these species throughout their
range. The spread of Bd averaged 688 m/year (yr) (2,257 ft/yr),
reaching all areas of the smaller basin in 1 year, and taking 3 to 5
years to completely infect the larger basins, progressing like a wave
across the landscape. The researchers documented die-offs following the
spread of Bd, with decreased population growth rates evident within the
first year of infection. Basinwide, metapopulations crashed from 1,680
to 22 individuals (northern DPS of the mountain yellow-legged frog) in
Milestone Basin, with 9 of 13 populations extirpated; from 2,193 to 47
individuals (northern DPS of the mountain yellow-legged frog) in Sixty
Lakes Basin, with 27 of 33 populations extirpated; and from 5,588 to
436 individuals (Sierra Nevada yellow-legged frog) in Barrett Lakes
Basin, with 33 of 42 populations extirpated. It is clear from the
evidence that Bd can and does decimate newly infected frog populations.
Moreover, this rangewide population threat is acting upon a landscape
already impacted by habitat modification and degradation by introduced
fishes (see Factor A discussion, above). As a result, remnant
populations in fishless lakes are now impacted by Bd.
Vredenburg et al. (2010a, p. 3) projected that at current
extinction rates, and given the disease dynamics of Bd (infected
tadpoles succumb to chytridiomycosis at metamorphosis), most if not all
extant populations within the recently infected basins they studied
will go extinct within the next 3 years. Available data (CDFG, unpubl.
data; Knapp 2005b; Rachowicz 2005, pers. comm.; Rachowicz et al. 2006,
p. 1671) indicate that Bd is now widespread throughout the Sierra
Nevada, and, although it has not infected all populations at this time,
it is effectively a serious and substantial threat rangewide to the
mountain yellow-legged frog complex.
Other diseases have also been reported as adversely affecting
amphibian species, and these may be present within the range of the
mountain yellow-legged frog. Bradford (1991, p. 174-177) reported an
outbreak of red-leg disease in Kings Canyon National Park, and
suggested this was a result of overcrowding within a mountain yellow-
legged frog population. Red-leg disease is caused by the bacterial
pathogen Aeromonas hydrophila, along with other pathogens. Though red-
leg disease is opportunistic and successfully attacks immune-suppressed
individuals, this pathogen appears to be highly contagious, affecting
the epidermis and digestive tract of otherwise healthy amphibians
(Shotts 1984, pp. 51-52; Carey 1993, p. 358; Carey and Bryant 1995, pp.
14-15). Although it has been observed in at least one instance
correlated to frog population decline, red-leg disease is likely not a
significant contributor to observed frog population declines rangewide,
based on the available literature.
Saprolegnia is a globally distributed fungus that commonly attacks
all life stages of fishes (especially hatchery-reared fishes), and has
recently been documented to attack and kill egg masses of western toads
(Bufo boreas) (Blaustein et al. 1994b, p. 252). This pathogen may be
introduced through fish stocking, or it may already be established in
the aquatic ecosystem. Fishes and migrating or dispersing amphibians
may be a vector for this fungus (Blaustein et al. 1994b, p. 253;
Kiesecker et al. 2001, p. 1068). Saprolegnia has been reported in the
southern DPS of the mountain yellow-legged frog (North 2012, pers.
comm.); however, its prevalence within the Sierran range of the
mountain yellow-legged frog complex and associated influence on
population dynamics (if any) are unknown.
Other pathogens of concern for amphibian species include
ranaviruses (Family Iridoviridae). Mao et al. (1999, pp. 49-50)
isolated identical iridoviruses from co-occurring populations of the
threespine stickleback (Gasterosteus aculeatus) and the red-legged frog
(Rana aurora), indicating that infection by a given virus is not
limited to a single species, and that iridoviruses can infect animals
of different taxonomic classes. This suggests that virus-hosting trout
introduced into mountain yellow-legged frog habitat may be a vector for
amphibian viruses. Recreationists also may contribute to the spread of
pathogens between water bodies and populations via clothing and fishing
equipment. However, definitive mechanisms for disease transmission to
the mountain yellow-legged frog remain unknown. No viruses were
detected in the mountain yellow-legged frogs that Fellers et al. (2001,
p. 950) analyzed for Bd. In Kings Canyon National Park, Knapp (2002a,
p. 20) found mountain yellow-legged frogs showing symptoms
preliminarily attributed to a ranavirus. To date, ranaviruses remain a
concern for the mountain yellow-legged frog complex, but there is
insufficient evidence to indicate they are negatively affecting
populations.
It is unknown whether amphibian pathogens in the high Sierra Nevada
have always coexisted with amphibian populations or if the presence of
such pathogens is a recent phenomenon. However, it has been suggested
that the susceptibility of amphibians to pathogens may have recently
increased in response to anthropogenic
[[Page 24487]]
environmental disruption (Carey 1993, pp. 355-360; Blaustein et al.
1994b, p. 253; Carey et al. 1999, p. 7). This hypothesis suggests that
environmental changes may be indirectly responsible for certain
amphibian die-offs due to immune system suppression of tadpoles or
post-metamorphic amphibians (Carey 1993, p. 358; Blaustein et al.
1994b, p. 253; Carey et al. 1999, p. 7-8). Pathogens such as Aeromonas
hydrophila, which are present in fresh water and in healthy organisms,
may become more of a threat, potentially causing localized amphibian
population die-offs when the immune systems of individuals within the
host population are suppressed (Carey 1993, p. 358; Carey and Bryant
1995, p. 14).
The contribution of Bd as an environmental stressor and limiting
factor on mountain yellow-legged frog population dynamics is currently
extremely high, and it poses a significant future threat to remnant
uninfected populations in the southern Sierra Nevada. Its effects are
most dramatic following the epidemic stage as it spreads across newly
infected habitats; massive die-off events follow the spread of the
fungus, and it is likely that survival through metamorphosis is
substantially reduced even years after the initial epidemic (Rachowicz
et al. 2006, pp. 1679-1680). The relative impact from other diseases
and the interaction of other stressors and disease on the immune
systems of mountain yellow-legged frogs remains poorly documented to
date.
In summary, based on the best available scientific and commercial
information, we consider the threats of predation and disease to be
significant, ongoing threats to the Sierra Nevada yellow-legged frog
and the northern DPS of the mountain yellow-legged frog. These threats
include amphibian pathogens (most specifically, the chytrid fungus) and
predation by introduced fishes, two primary driving forces leading to
population declines in the mountain yellow-legged frog complex. These
are highly prevalent threats, and they are predominant limiting factors
hindering population viability and precluding recovery across the
ranges of the mountain yellow-legged frog complex.
Factor D. The Inadequacy of Existing Regulatory Mechanisms
In determining whether the inadequacy of regulatory mechanisms
constitutes a threat to the mountain yellow-legged frog complex, we
analyzed the existing Federal and State laws and regulations that may
address the threats to these species or contain relevant protective
measures. Regulatory mechanisms are typically nondiscretionary and
enforceable, and may preclude the need for listing if such mechanisms
are judged to adequately address the threat(s) to the species such that
listing is not warranted. Conversely, threats on the landscape are not
addressed where existing regulatory mechanisms are not adequate (or
when existing mechanisms are not adequately implemented or enforced).
Federal
Wilderness Act
The Wilderness Act of 1964 (16 U.S.C. 1131 et seq.) established a
National Wilderness Preservation System made up of federally owned
areas designated by Congress as ``wilderness'' for the purpose of
preserving and protecting designated areas in their natural condition.
Within these areas, the Wilderness Act states, with limited exception
to administer the area as wilderness, the following: (1) New or
temporary roads cannot be built; (2) there can be no use of motor
vehicles, motorized equipment, or motorboats; (3) there can be no
landing of aircrafts; (4) there can be no form of mechanical transport;
and (5) no structure or installation may be built. A large number of
mountain yellow-legged frog locations occur within wilderness areas
managed by the USFS and NPS and, therefore, are afforded protection
from direct loss or degradation of habitat by some human activities
(such as, development, commercial timber harvest, road construction,
some fire management actions). Livestock grazing and fish stocking are
both permitted within designated wilderness areas.
National Forest Management Act of 1976
Under the National Forest Management Act of 1976, as amended (NFMA)
(16 U.S.C. 1600 et seq.), the USFS is tasked to manage National Forest
lands based on multiple-use, sustained-yield principles, and implement
land and resource management plans (LRMP) on each National Forest to
provide for a diversity of plant and animal communities. The purpose of
an LRMP is to guide and set standards for all natural resource
management activities for the life of the plan (10 to 15 years). NFMA
requires the USFS to incorporate standards and guidelines into LRMPs.
The 1982 planning regulations for implementing NFMA (47 FR 43026;
September 30, 1982), under which all existing forest plans in the
Sierra Nevada were prepared until recently, guided management of
National Forests and required that fish and wildlife habitat on
National Forest system lands be managed to maintain viable populations
of existing native and desired nonnative vertebrate species in the
planning area. A viable population is defined as a population of a
species that continues to persist over the long term with sufficient
distribution to be resilient and adaptable to stressors and likely
future environments. In order to insure that viable populations will be
maintained, habitat must be provided to support, at least, a minimum
number of reproductive individuals and that habitat must be well
distributed so that those individuals can interact with others in the
planning area.
On April 9, 2012, the USFS published a final rule (77 FR 21162)
amending 36 CFR 219 to adopt new National Forest System land management
regulations to guide the development, amendment, and revision of LRMPs
for all Forest System lands. These revised regulations, which became
effective on May 9, 2012, replace the 1982 planning rule. The 2012
planning rule requires that the USFS maintain viable populations of
species of conservation concern at the discretion of regional
foresters. This rule could thereby result in removal of the limited
protections that are currently in place for mountain yellow-legged
frogs under the Sierra Nevada Forest Plan Amendment (SNFPA), as
described below.
Sierra Nevada Forest Plan Amendment
In 2001, a record of decision was signed by the USFS for the Sierra
Nevada Forest Plan Amendment (SNFPA), based on the final environmental
impact statement for the SNFPA effort and prepared under the 1982 NFMA
planning regulations. The Record of Decision amends the USFS Pacific
Southwest Regional Guide, the Intermountain Regional Guide, and the
LRMPs for National Forests in the Sierra Nevada and Modoc Plateau. This
document affects land management on all National Forests throughout the
range of the mountain yellow-legged frog complex. The SNFPA addresses
and gives management direction on issues pertaining to old forest
ecosystems; aquatic, riparian, and meadow ecosystems; fire and fuels;
noxious weeds; and lower west-side hardwood ecosystems of the Sierra
Nevada. In January 2004, the USFS amended the SNFPA, based on the final
supplemental environmental impact statement, following a review of fire
and fuels treatments, compatibility with the National Fire Plan,
compatibility with the Herger-Feinstein Quincy Library
[[Page 24488]]
Group Forest Recovery Pilot Project, and effects of the SNFPA on
grazing, recreation, and local communities (USDA 2004, pp. 26-30).
Relevant to the mountain yellow-legged frog complex, the Record of
Decision for SNFPA aims to protect and restore aquatic, riparian, and
meadow ecosystems, and to provide for the viability of associated
native species through implementation of an aquatic management
strategy. The aquatic management strategy is a general framework with
broad policy direction. Implementation of this strategy is intended to
take place at the landscape and project levels. There are nine goals
associated with the aquatic management strategy:
(1) The maintenance and restoration of water quality to comply with
the Clean Water Act (CWA) and the Safe Drinking Water Act;
(2) The maintenance and restoration of habitat to support viable
populations of native and desired nonnative riparian-dependent species,
and to reduce negative impacts of nonnative species on native
populations;
(3) The maintenance and restoration of species diversity in
riparian areas, wetlands, and meadows to provide desired habitats and
ecological functions;
(4) The maintenance and restoration of the distribution and
function of biotic communities and biological diversity in special
aquatic habitats (such as springs, seeps, vernal pools, fens, bogs, and
marshes);
(5) The maintenance and restoration of spatial and temporal
connectivity for aquatic and riparian species within and between
watersheds to provide physically, chemically, and biologically
unobstructed movement for their survival, migration, and reproduction;
(6) The maintenance and restoration of hydrologic connectivity
between floodplains, channels, and water tables to distribute flood
flows and to sustain diverse habitats;
(7) The maintenance and restoration of watershed conditions as
measured by favorable infiltration characteristics of soils and diverse
vegetation cover to absorb and filter precipitation, and to sustain
favorable conditions of streamflows;
(8) The maintenance and restoration of instream flows sufficient to
sustain desired conditions of riparian, aquatic, wetland, and meadow
habitats, and to keep sediment regimes within the natural range of
variability; and
(9) The maintenance and restoration of the physical structure and
condition of streambanks and shorelines to minimize erosion and sustain
desired habitat diversity.
If these goals of the aquatic management strategy are pursued and
met, threats to the mountain yellow-legged frog complex resulting from
habitat alterations could be reduced. However, the aquatic management
strategy is a generalized approach that does not contain specific
implementation timeframes or objectives, and it does not provide direct
protections for the mountain yellow-legged frog. Additionally, as
described above, the April 9, 2012, final rule (77 FR 21162) that
amended 36 CFR 219 to adopt new National Forest System land management
planning regulations could result in removal of the limited protections
that are currently in place for mountain yellow-legged frogs under the
SNFPA.
Federal Power Act
The Federal Power Act of 1920, as amended (FPA) (16 U.S.C. 791 et
seq.) was enacted to regulate non-federal hydroelectric projects to
support the development of rivers for energy generation and other
beneficial uses. The FPA provides for cooperation between the Federal
Energy Regulatory Commission (Commission) and other Federal agencies in
licensing and relicensing power projects. The FPA mandates that each
license includes conditions to protect, mitigate, and enhance fish and
wildlife and their habitat affected by the project. However, the FPA
also requires that the Commission give equal consideration to competing
priorities, such as power and development, energy conservation,
protection of recreational opportunities, and preservation of other
aspects of environmental quality. Further, the FPA does not mandate
protections of habitat or enhancements for fish and wildlife species,
but provides a mechanism for resource agency recommendations that are
incorporated into a license at the discretion of the Commission.
Additionally, the FPA provides for the issuance of a license for the
duration of up to 50 years, and the FPA contains no provision for
modification of the project for the benefit of species, such as
mountain yellow-legged frogs, before a current license expires.
Numerous mountain yellow-legged frog populations occur within
developed and managed aquatic systems (such as reservoirs and water
diversions) operated for the purpose of power generation and regulated
by the FPA.
State
California Endangered Species Act
The California Endangered Species Act (CESA) (California Fish and
Game Code, section 2080 et seq.) prohibits the unauthorized take of
State-listed endangered or threatened species. CESA requires State
agencies to consult with CDFG on activities that may affect a State-
listed species, and mitigate for any adverse impacts to the species or
its habitat. Pursuant to CESA, it is unlawful to import or export,
take, possess, purchase, or sell any species or part or product of any
species listed as endangered or threatened. The State may authorize
permits for scientific, educational, or management purposes, and allow
take that is incidental to otherwise lawful activities.
Recently, the California Fish and Game Commission approved the
listing of the Sierra Nevada yellow-legged frog as a threatened species
and the mountain yellow-legged frog (Statewide) as an endangered
species under CESA (CDFG 2012, pp. 1-10). However, CDFG has not yet
officially listed these species under CESA, and therefore both species
remain candidate species under State law.
As a candidate species under CESA, the mountain yellow-legged frog
complex receives the same protections as a listed species, with
specified exceptions. However, CESA is not expected to provide adequate
protection for the mountain yellow-legged frog complex given that the
CDFG has currently approved take authorization for the Statewide
stocking program under CESA for fish hatchery and stocking activities
consistent with the joint Environmental Impact Statement/Environmental
Impact Report (ICF Jones & Stokes 2010, App. K), wildland fire response
and related vegetation management, water storage and conveyance
activities, and forest practices and timber harvest (CDFG 2011a, pp. 2-
3).
In 2001, CDFG revised fish stocking practices and implemented an
informal policy on fish stocking in the range of the Sierra Nevada
yellow-legged frog and northern DPS of the mountain yellow-legged frog.
This policy directs that: (1) Fish will not be stocked in lakes with
known populations of mountain yellow-legged frogs, nor in lakes that
have not yet been surveyed for mountain yellow-legged frog presence;
(2) waters will be stocked only with a fisheries management
justification; and (3) the number of stocked lakes will be reduced over
time. In 2001, the number of lakes stocked with fish within the range
of the mountain yellow-legged
[[Page 24489]]
frog in the Sierra Nevada was reduced by 75 percent (Milliron 2002, pp.
6-7; Pert et al. 2002, pers. comm.). Water bodies within the same basin
and 2 km (1.25 mi) from a known mountain yellow-legged frog population
will not be stocked with fish unless stocking is justified through a
management plan that considers all the aquatic resources in the basin,
or unless there is heavy angler use and no opportunity to improve the
mountain yellow-legged frog habitat (Milliron 2002a, p. 5). The
Hatchery and Stocking Program Environmental Impact Report/Environmental
Impact Statement, finalized in 2010 (ICF Jones & Stokes 2010, Appendix
K), outlines a decision approach to mitigate fish stocking effects on
Sierra amphibians that prohibits fish stocking in lakes with confirmed
presence of frogs using recognized survey protocols.
CDFG is in the process of developing management plans for basins
within the range of the Sierra Nevada yellow-legged frog and the
northern DPS of mountain yellow-legged frog (CDFG 2001, p. 1; Lockhart
2011, pers. comm.). The objectives of the basin plans specific to the
mountain yellow-legged frog include management in a manner that
maintains or restores native biodiversity and habitat quality, supports
viable populations of native species, and provides for recreational
opportunities that consider historical use patterns (CDFG 2001, p. 3).
Under this approach, some lakes are managed primarily for the mountain
yellow-legged frogs and other amphibian resources, with few or no
angling opportunities, while lakes with high demand for recreational
angling are managed primarily for angling purposes (CDFG 2001, p. 3).
Existing Federal and State laws and regulatory mechanisms currently
offer some level of protection for the mountain yellow-legged frog
complex.
Factor E. Other Natural or Manmade Factors Affecting Its Continued
Existence
The mountain yellow-legged frog is sensitive to environmental
change or degradation because it has an aquatic and terrestrial life
history and highly permeable skin that increases exposure of
individuals to substances in the water, air, and terrestrial substrates
(Blaustein and Wake 1990, p. 203; Bradford and Gordon 1992. p. 9;
Blaustein and Wake 1995, p. 52; Stebbins and Cohen 1995, pp. 227-228).
Several natural or anthropogenically influenced factors, including
contaminants, acid precipitation, ambient ultraviolet radiation, and
climate change, have been implicated as contributing to amphibian
declines (Corn 1994, pp. 62-63; Alford and Richards 1999, pp. 2-7).
These factors have been studied to varying degrees specific to the
mountain yellow-legged frog and are discussed below. There are also
documented incidences of direct mortality of, or the potential for
direct disturbance to, individuals from some activities already
discussed; in severe instances, these actions may have population-level
consequences.
Contaminants
Environmental contaminants have been suggested, and in some cases
documented, to negatively affect amphibians by causing direct mortality
(Hall and Henry 1992, pp. 66-67; Berrill et al. 1994, p. 663; 1995, pp.
1016-1018; Carey and Bryant 1995, p. 16; Relyea and Mills 2001, p.
2493); immune system suppression, which makes amphibians more
vulnerable to disease (Carey 1993, pp. 358-360; Carey and Bryant 1995,
p. 15; Carey et al. 1999, p. 9; Daszak et al. 1999, p. 741; Taylor et
al. 1999, p. 540); disruption of breeding behavior and physiology
(Berrill et al. 1994, p. 663; Carey and Bryant 1995, p. 16; Hayes et
al. 2002, p. 5479); disruption of growth or development (Hall and Henry
1992, p. 66; Berrill et al. 1993, p. 537; 1994, p. 663; Berrill et al.
1995, pp. 1016-1018; Carey and Bryant 1995, p. 8; Berrill et al. 1998,
pp. 1741-1744; Sparling et al. 2001, p. 1595; Brunelli et al. 2009, p.
135); and disruption of predator avoidance behavior (Hall and Henry
1992, p. 66; Berrill et al. 1993, p. 537; 1994, p. 663; Berrill et al.
1995, p. 1017; Carey and Bryant 1995, pp. 8-9; Berrill et al. 1998, p.
1744; Relyea and Mills 2001, p. 2493; Sparling et al. 2001, p. 1595).
Wind-borne pesticides that are deposited in the Sierra Nevada from
upwind agricultural sources have been suggested as a cause of sublethal
effects to amphibians (Cory et al. 1971, p. 3; Davidson et al. 2001,
pp. 474-475; Sparling et al. 2001, p. 1591; Davidson 2004, p. 1892;
Fellers et al. 2004, p. 2176). In 1998, more than 97 million kilograms
(215 million pounds) of pesticides were reportedly used in California
(California Department of Pesticide Regulation (CDPR) 1998, p. ix).
Originating from the agriculture in California's Central Valley, and
mainly from the San Joaquin Valley, where upwind agricultural activity
is greatest, pesticides are passively transported eastward to the high
Sierra Nevada where they have been detected in precipitation (rain and
snow), air, dry deposition, surface water, plants, fish, and amphibians
(including Pacific tree frogs (Pseudacris regilla) and mountain yellow-
legged frogs) (Cory et al. 1970, p. 204; Zabik and Seiber 1993, p. 80;
Aston and Seiber 1997, p. 1488; Datta et al. 1998, p. 829; McConnell et
al. 1998, pp. 1910-1911; LeNoir et al. 1999, p. 2721; Sparling et al.
2001, p. 1591; Angermann et al. 2002, p. 2213; Fellers et al. 2004, pp.
2173-2174).
Spatial analysis of mountain yellow-legged frog population trends
in the Sierra Nevada showed a strong positive association between
population decline and areas with greater amounts of upwind agriculture
(Davidson et al. 2002, pp. 1597-1598). Analysis of upwind pesticide use
determined that pesticides may play a role in the decline of the
mountain yellow-legged frog in pristine regions of the Sierra Nevada
(Davidson and Knapp 2007, pp. 593-594). Although pesticide detections
decrease with altitudinal gain, they have been detected at elevations
in excess of 3,200 m (10,500 ft) (Zabik and Seiber 1993, p. 88;
McConnell et al. 1998, p. 1908; LeNoir et al. 1999, p. 2721; Angermann
et al. 2002, pp. 2210-2211).
Snow core samples from the Sierra Nevada contain a variety of
contaminants from industrial and automotive sources, including excess
hydrogen ions that are indicative of acidic precipitation, nitrogen and
sulfur compounds (ammonium, nitrate, sulfite, and sulfate), and heavy
metals (lead, iron, manganese, copper, and cadmium) (Laird et al. 1986,
p. 275).
The pattern of recent frog extirpations in the southern Sierra
Nevada corresponds with the pattern of highest concentration of air
pollutants from automotive exhaust, and it has been suggested that this
may be due to increases in nitrification (or other changes) caused by
those pollutants (Jennings 1996, p. 940). Shinn et al. (2008, p. 186)
suggested that mountain amphibians may be more sensitive to nitrite
toxicity based on acute toxicity observed at low concentrations (less
than 0.5 milligrams/liter in Iberian water frogs (Pelophylax perezi)).
Macias and Blaustein (2007, p. 55) observed a synergistic effect (when
the net effect of two things acting together exceeds the sum of both
alone) in the common toad (Bufo bufo) where nitrite in combination with
ultraviolet radiation (UV-B; 280 to 320 nanometers (11-12.6
microinches)) was up to seven times more lethal than mortality from
either stressor alone (the synergy was four times the summed effect
from both treatments alone in the Iberian water frog).
The correlative evidence between areas of pesticide (and other)
contamination in the Sierra Nevada and areas of amphibian decline
support
[[Page 24490]]
hypotheses that contaminants may present a risk to the mountain yellow-
legged frog and could have contributed to the species' decline
(Jennings 1996, p. 940; Sparling et al. 2001, p. 1591; Davidson et al.
2002. p. 1599; Davidson and Knapp 2007, p. 587). However, studies
confirming exposure in remote locations to ecotoxicologically relevant
concentrations of contaminants are not available to support this
hypothesis.
To the contrary, efforts to date have found fairly low
concentrations of many of the primary suspect constituents commonly
indicating agricultural and industrial pollution (organochlorines,
organophosphates/carbamates, polycyclic hydrocarbons). Bradford et al.
(2010, p. 1064) observed a rapid decline in concentrations of
endosulfan, chlorpyrifos, and DDE (among others) going out to 42 km (26
mi) linear distance from the valley floor in air, water, and tadpole
tissues. These researchers also found relatively minute variation in
concentrations among high-elevation study sites relative to the
differences observed between the San Joaquin Valley and the nearest
high-elevation sites. Essentially, sites beyond 42 km (26 mi) exhibited
very low concentrations of measured compounds, which did not
appreciably decrease with distance (Bradford et al. 2010, p. 1064).
These observations make the contaminant decline hypotheses less
tenable, and so windborne organic contaminants are currently considered
minor contributors (if at all) to observed frog declines.
Acidic deposition has been suggested to contribute to amphibian
declines in the western United States (Blaustein and Wake 1990, p. 204;
Carey 1993, p. 357; Alford and Richards 1999, pp. 4-5). Acid
precipitation has also been postulated as a cause of amphibian declines
at high elevations in the Sierra Nevada (Bradford et al. 1994b, p. 156)
because waters there are low in acid neutralizing capacity and,
therefore, are susceptible to changes in water chemistry caused by acid
deposition (Byron et al. 1991, p. 271). Extreme pH in surface waters of
the Sierra Nevada is estimated at 5.0, with most high-elevation lakes
having a pH of greater than 6 (Bradford et al. 1992, p. 374). Near Lake
Tahoe, at an elevation of approximately 2,100 m (6,900 ft),
precipitation acidity has increased significantly (Byron et al. 1991,
p. 272). In surface waters of the Sierra Nevada, acidity increases and
acid neutralizing capacity decreases during snow melt and summer
storms, though rarely does pH drop below 5.4 (Nikolaidis et al. 1991,
p. 339; Bradford and Gordon 1992, p. 73; Bradford et al. 1998, p.
2489). The mountain yellow-legged frog breeds shortly after snow melt;
therefore, its most sensitive early life stages are exposed to
acidification (Bradford and Gordon 1992, p. 9). Bradford et al. (1998,
p. 2482) found that mountain yellow-legged frog tadpoles were sensitive
to naturally acidic conditions, and that their distribution was
significantly related to lake acidity (they were not found in lakes
with a pH lower than 6).
Laboratory studies have documented sublethal effects (reduced
growth) on mountain yellow-legged frog embryos at pH 5.25 (Bradford et
al. 1992, p. 369). Survivorship of mountain yellow-legged frog embryos
and tadpoles was negatively affected as acidity increased (at
approximately pH 4.5 or lower); embryos were more sensitive to
increased acidity than tadpoles (Bradford and Gordon 1992, p. 3;
Bradford et al. 1992, pp. 374-375). Potential indirect effects via
impacts to the larger pond community were suggested by the observation
that mountain yellow-legged frogs, common microcrustaceans, and
caddisfly larvae were rare or absent at lakes with lower pH, and
community richness declined with decreasing pH (Bradford et al. 1998,
p. 2478).
However, other studies do not support this hypothesis of acid
deposition as a contributing factor to amphibian population declines in
this area (Bradford and Gordon 1992, pp. 74-77; Bradford et al. 1992,
p. 375; Corn and Vertucci 1992, p. 366; Bradford et al. 1994a, p. 326;
1994b, p. 160; Corn 1994, p. 61). The hypothesis of acidic deposition
as a cause of mountain yellow-legged frog declines has been rejected by
field experiments that failed to show differences in water chemistry
parameters between occupied and unoccupied mountain yellow-legged frog
sites (Bradford et al. 1994b, p. 160). Though acidity may have an
influence on mountain yellow-legged frog abundance or distribution, it
is unlikely to have contributed significantly to the species' decline,
given the rarity of lakes acidified either by natural or anthropogenic
sources (Bradford et al. 1998, pp. 2488-2489).
Collectively, contaminant risks to mountain yellow-legged frogs are
likely a minor risk factor across the range of the species that does
not represent a threat to the species at a population level. Frogs are
sensitive to contaminants, although exposure to contaminants from
upwind sources has not been substantiated. Localized exposure to
upgradient or directly applied compounds is of theoretical concern.
However, the overlap of extant populations and such land uses, and
contribution of these management activities to aquatic pollution, is
undocumented.
Ultraviolet Radiation
Melanic pigment on the upper surfaces of amphibian eggs and
tadpoles protects these sensitive life stages against UV-B damage, an
important protection for normal development of amphibians exposed to
sunlight, especially at high elevations in clear and shallow waters
(Perotti and Di[eacute]guez 2006, p. 2064). Blaustein et al. (1994c, p.
1793) observed decreased hatching success in several species of
amphibian embryos (the mountain yellow-legged frog was not tested)
exposed to increased UV-B radiation, and proposed that this may be a
cause of amphibian declines.
Ambient UV-B radiation has increased at north temperate latitudes
over the past 2 decades (Adams et al. 2001, p. 521). If UV-B is
contributing to amphibian population declines, the declines would
likely be greater at higher elevations and more southerly latitudes
where the thinner atmosphere allows greater penetration (Davidson et
al. 2001, p. 474; Davidson et al. 2002, p. 1589). In California, where
there is a north-to-south gradient of increasing UV-B exposure,
amphibian declines would also likely be more prevalent at southerly
latitudes (Davidson et al. 2001, p. 474; Davidson et al. 2002, p.
1589). In a spatial test of the hypothesis that UV-B has contributed to
the decline of the mountain yellow-legged frog in the Sierra Nevada,
Davidson et al. (2002, p. 1598) concluded that patterns of this
species' decline are inconsistent with the predictions of where UV-B-
related population declines would occur. Greater numbers of extant
populations of this species were present at higher elevations than at
lower elevations, and population decline was greater in the northern
portion of the species' range than it was in the southern portion.
Adams et al. (2005, p. 497) also found no evidence that the
distribution of mountain yellow-legged frogs in lakes in Sequoia and
Kings Canyon National Parks was determined by UV-B. Pahkala et al.
(2003, p. 197) even observed enhanced tadpole growth rates in two of
three amphibian species exposed to moderate amounts of UV-B. Vredenburg
et al. (2010b, p. 509) studied the effects of field level exposures of
UV-B on hatching success in mountain the yellow-legged frog, Yosemite
toad, and Pacific tree frog and found only a small increase in time to
hatching in one of three lakes for the mountain yellow-
[[Page 24491]]
legged frog. The authors suggested that amphibians occupying habitats
with high UV-B exposure may have evolved mechanisms for coping with or
avoiding the damaging UV rays. This is plausible, given that such a
field level experiment was testing a persistent population, one that
would logically be a survivor from past exposure (made up of tolerant
individuals), and this level of experimental bias is inherent to
experiments with such designs.
The UV-B hypothesis is controversial and has been the topic of much
scientific debate. Support is undermined by lack of evidence linking
experimental results to observed changes in abundance and distribution
in the wild, and also the inability of proponents to document increased
exposure in amphibian populations (Corn 2005, p. 60). In weighing the
available evidence, UV-B does not appear to be a contributing factor to
mountain yellow-legged frog population declines in the Sierra Nevada.
Climate Change
Our analyses under the Act include consideration of ongoing and
projected changes in climate. The terms ``climate'' and ``climate
change'' are defined by the Intergovernmental Panel on Climate Change
(IPCC). The term ``climate'' refers to the mean and variability of
different types of weather conditions over time, with 30 years being a
typical period for such measurements, although shorter or longer
periods also may be used (IPCC 2007a, p. 78). The term ``climate
change'' thus refers to a change in the mean or variability of one or
more measures of climate (for example, temperature or precipitation)
that persists for an extended period, typically decades or longer,
whether the change is due to natural variability, human activity, or
both (IPCC 2007a, p. 78).
Scientific measurements spanning several decades demonstrate that
changes in climate are occurring, and that the rate of change has
increased since the 1950s. Examples include warming of the global
climate system, and substantial increases in precipitation in some
regions of the world and decreases in other regions (for these and
other examples, see IPCC 2007a, p. 30 and Solomon et al. 2007, pp. 35-
54, 82-85). Results of scientific analyses presented by the IPCC show
that most of the observed increase in global average temperature since
the mid-20th century cannot be explained by natural variability in
climate, and is ``very likely'' (defined by the IPCC as 90 percent or
higher probability) due to the observed increase in greenhouse gas
(GHG) concentrations in the atmosphere as a result of human activities,
particularly carbon dioxide emissions from use of fossil fuels (IPCC
2007a, pp. 5-6 and figures SPM.3 and SPM.4; Solomon et al. 2007, pp.
21-35). Further confirmation of the role of GHGs comes from analyses by
Huber and Knutti (2011, p. 4), who concluded it is extremely likely
that approximately 75 percent of global warming since 1950 has been
caused by human activities.
Scientists use a variety of climate models, which include
consideration of natural processes and variability, as well as various
scenarios of potential levels and timing of GHG emissions, to evaluate
the causes of changes already observed and to project future changes in
temperature and other climate conditions (for example, Meehl et al.
2007, entire; Ganguly et al. 2009, pp. 11555, 15558; Prinn et al. 2011,
pp. 527, 529). All combinations of models and emissions scenarios yield
very similar projections of increases in the most common measure of
climate change, average global surface temperature (commonly known as
global warming), until about 2030. Although projections of the
magnitude and rate of warming differ after about 2030, the overall
trajectory of all the projections is one of increased global warming
through the end of this century, even for the projections based on
scenarios that assume that GHG emissions will stabilize or decline.
Thus, there is strong scientific support for projections that warming
will continue through the 21st century, and that the magnitude and rate
of change will be influenced substantially by the extent of GHG
emissions (IPCC 2007a, pp. 44-45; Meehl et al. 2007, pp. 760-764, 797-
811; Ganguly et al. 2009, pp. 15555-15558; Prinn et al. 2011, pp. 527,
529). (See IPCC 2007b, p. 8, for a summary of other global projections
of climate-related changes, such as frequency of heat waves and changes
in precipitation. Also see IPCC 2011 (entire) for a summary of
observations and projections of extreme climate events.)
Various changes in climate may have direct or indirect effects on
species. These effects may be positive, neutral, or negative, and they
may change over time, depending on the species and other relevant
considerations, such as interactions of climate with other variables
(for example, habitat fragmentation) (IPCC 2007a, pp. 8-14, 18-19).
Identifying likely effects often involves aspects of climate change
vulnerability analysis. Vulnerability refers to the degree to which a
species (or system) is susceptible to, and unable to cope with, adverse
effects of climate change, including climate variability and extremes.
Vulnerability is a function of the type, magnitude, and rate of climate
change and variation to which a species is exposed, its sensitivity,
and its adaptive capacity (IPCC 2007a, p. 89; see also Glick et al.
2011, pp. 19-22). There is no single method for conducting such
analyses that applies to all situations (Glick et al. 2011, p. 3). We
use our expert judgment and appropriate analytical approaches to weigh
relevant information, including uncertainty, in our consideration of
various aspects of climate change.
Global climate projections are informative and, in some cases, the
only or the best scientific information available for us to use.
However, projected changes in climate and related impacts can vary
substantially across and within different regions of the world (for
example, IPCC 2007a, pp. 8-12). Therefore, we use downscaled
projections when they are available and have been developed through
appropriate scientific procedures, because such projections provide
higher resolution information that is more relevant to the spatial
scales used for analyses of a given species (see Glick et al. 2011, pp.
58-61, for a discussion of downscaling). With regard to our analysis
for the Sierra Nevada of California (and western United States),
downscaled projections are available.
Variability exists in outputs from different climate models, and
uncertainty regarding future GHG emissions is also a factor in modeling
(PRBO 2011, p. 3). A general pattern that holds for many predictive
models indicates northern areas of the United States will become
wetter, and southern areas (particularly the Southwest) will become
drier. These models also predict that extreme events, such as heavier
storms, heat waves, and regional droughts, may become more frequent
(Glick et al. 2011, p. 7). Moreover, it is generally expected that the
duration and intensity of droughts will increase in the future (Glick
et al. 2011, p. 45; PRBO 2011, p. 21).
The last century has included some of the most variable climate
reversals documented, at both the annual and near-decadal scales,
including a high frequency of El Ni[ntilde]o (associated with more
severe winters) and La Ni[ntilde]a (associated with milder winters)
events (reflecting drought periods of 5 to 8 years alternating with wet
periods) (USDA 2001b, p. 33). Scientists have confirmed a longer
duration climate cycle termed the Pacific Decadal Oscillation (PDO),
which operates on cycles between 2 to 3 decades, and
[[Page 24492]]
generally is characterized by warm and dry (PDO positive) followed by
cool and wet cycles (PDO negative) (Mantua et al. 1997, pp. 1069-1079;
Zhang et al. 1997, pp. 1004-1018). Snowpack is seen to follow this
pattern--heavier in the PDO negative phase in California, and lighter
in the positive phase (Mantua et al. 1997, p. 14; Cayan et al. 1998, p.
3148; McCabe and Dettinger 2002, p. 24).
Mantua et al. (1997, pp. 15-19) observed a relationship in
population trends in Pacific salmon that mirror the PDO. The last turn
of this cycle was in 1977, towards a warm and dry phase for the western
United States. If this interdecadal trend holds, indications are that
we are currently trending back into a cooler and wetter phase in
California. Given the impacts to climate (snowpack, and therefore,
hydrology in the alpine system), and the extended duration of these
cycles relative to generation time for these species, it is logical to
presume that amphibian population trends (other things being equal)
would also tend to track these cycles. Drost and Fellers (1996, p. 423)
indicated that drought probably has an exacerbating or compounding
effect in mountain yellow-legged frog complex population declines.
For the Sierra Nevada ecoregion, climate models predict that mean
annual temperatures will increase by 1.8 to 2.4 [deg]C (3.2 to 4.3
[deg]F) by 2070, including warmer winters with earlier spring snowmelt
and higher summer temperatures. However, it is expected that
temperature and climate variability will vary based on topographic
diversity (for example, wind intensity will determine east versus west
slope variability) (PRBO 2011, p. 18). Mean annual rainfall is
projected to decrease from 9.2-33.9 cm (3.6-13.3 in) by 2070; however,
projections have high uncertainty and one study predicts the opposite
effect (PRBO 2011, p. 18). Given the varied outputs from differing
modeling assumptions, and the influence of complex topography on
microclimate patterns, it is difficult to draw general conclusions
about the effects of climate change on precipitation patterns in the
Sierra Nevada (PRBO, 2011, p. 18). Snowpack is, by all projections,
going to decrease dramatically (following the temperature rise and more
precipitation falling as rain). Higher winter streamflows, earlier
runoff, and reduced spring and summer streamflows are projected, with
increasing severity in the southern Sierra Nevada (PRBO 2011, pp. 20-
22).
Snow-dominated elevations from 2,000-2,800 m (6,560-9,190 ft) will
be the most sensitive to temperature increases, and a warming of 5
[deg]C (9 [deg]F) is projected to shift center timing (the measure when
half a stream's annual flow has passed a given point in time) to more
than 45 days earlier in the year as compared to the 1961-1990 baseline
(PRBO 2011, p. 23). Lakes, ponds, and other standing waters fed by
snowmelt or streams may dry out or be more ephemeral during the non-
winter months (PRBO 2011, p. 24). This pattern could influence ground
water transport, and springs may be similarly depleted, leading to
lower lake levels.
Vulnerability of species to climate change is a function of three
factors: Sensitivity of a species or its habitat to climate change,
exposure of individuals to such physical changes in the environment,
and their capacity to adapt to those changes (Glick et al. 2011, pp.
19-22). Critical sensitivity elements broadly applicable across
organizational levels (from species through habitats to ecosystems) are
associated with physical variables, such as hydrology (timing,
magnitude, and volume of waterflows), fire regime (frequency, extent,
and severity of fires), and wind (Glick et al. 2011, pp. 39-40).
Species-level sensitivities generally include physiological factors,
such as changes in temperature, moisture, or pH as they influence
individuals; these also include dependence on sensitive habitats,
ecological linkages to other species, and changes in phenology (timing
of key life-history events) (Glick et al. 2011, pp. 40-41).
Exposure to environmental stressors renders species vulnerable to
climate change impacts, either through direct mechanisms (for example,
physical temperature extremes or changes in solar radiation), or
indirectly through impacts upon habitat (hydrology; fire regime; or
abundance and distribution of prey, competitors, or predator species).
A species' capacity to adapt to climate change is increased by
behavioral plasticity (the ability to modify behavior to mitigate the
impacts of the stressor), dispersal ability (the ability to relocate to
meet shifting conditions), and evolutionary potential (for example,
shorter-lived species with multiple generations have more capacity to
adapt through evolution) (Glick et al. 2011, pp. 48-49).
The International Union for Conservation of Nature describes five
categories of life-history traits that render species more vulnerable
to climate change (Foden et al. 2008 in Glick et al. 2011, p. 33): (1)
Specialized habitat or microhabitat requirements, (2) narrow
environmental tolerances or thresholds that are likely to be exceeded
under climate change, (3) dependence on specific triggers or cues that
are likely to be disrupted (for example, rainfall or temperature cues
for breeding, migration, or hibernation), (4) dependence on
interactions between species that are likely to be disrupted, and (5)
inability or poor ability to disperse quickly or to colonize more
suitable range. We apply these criteria in this proposed rule to assess
the vulnerability of mountain yellow-legged frogs to climate change.
The mountain yellow-legged frog is not necessarily a habitat
specialist, although it does depend on fishless high mountain lakes
with particular properties necessary to sustain a multi-year life
cycle. As a species that inhabits areas with relative climate extremes,
some conditions may directly push mountain yellow-legged frogs past
physiological or ecological tolerance thresholds, and therefore enhance
risk from the effects of climate change. For example, the increased
severity of some winter storms may freeze lakes to greater depths than
is historically typical. Severe winters (typical of El Ni[ntilde]o
Southern Oscillation years and PDO negative decades) would force longer
hibernation times and could stress mountain yellow-legged frogs by
reducing the time available for them to feed and breed. The deeper
lakes that once supported frog populations (but now harbor introduced
trout) are no longer available as refuge for frogs in a drier climate
with possible severe cold winters. It is important to note that these
episodic stressors may be infrequent, but they are important to long-
lived species with small populations.
In summer, reduced snowpack and enhanced evapotranspiration
following higher temperatures may dry out ponds that otherwise would
have sustained rearing tadpoles (Lacan et al. 2008, p. 220), and may
also reduce fecundity (egg production) (Lacan et al. 2008, p. 222).
Lacan et al. (2008, p. 211) observed most frog breeding in the smaller,
fishless lakes of Kings Canyon National Park, lakes that are shallow
and prone to summer drying. Thus, climate change will likely reduce
available breeding habitat for mountain yellow-legged frogs and lead to
greater frequency of stranding and death of tadpoles (Corn 2005, p. 64;
Lacan et al. 2008, p. 222).
Earlier snowmelt is expected to cue breeding earlier in the year.
The advance of this primary signal for breeding phenology in montane
and boreal habitats (Corn 2005, p. 61) may have both positive and
negative effects. Additional time for growth and development may render
larger individuals more fit to overwinter;
[[Page 24493]]
however, earlier breeding may also expose young tadpoles (or eggs) to
killing frosts in more variable conditions of early spring (Corn 2005,
p. 60).
It is unclear if there are dependencies upon other species with
which mountain yellow-legged frogs interact that may be affected either
positively or negatively by climate change. Climate change may alter
invertebrate communities (PRBO 2011 p. 24). In one study, an
experimental increase in stream temperature was shown to decrease
density and biomass of invertebrates (Hogg and Williams 1996, p. 401).
Thus, climate change might have a negative impact on the mountain
yellow-legged frog prey base.
Indirect effects from climate change may lead to greater risk to
mountain yellow-legged frog population persistence. For example, fire
intensity and magnitude are projected to increase (PRBO 2011, pp. 24-
25), and therefore the contribution and influence of this stressor upon
frog habitat and populations will increase. Climate change may alter
lake productivity through changes in water chemistry, the extent and
timing of mixing, and nutrient inputs from increased fires, all of
which may influence community dynamics and composition (Melack et al.
1997, p. 971; Parker et al. 2008, p. 12927). These changes may not all
be negative; for example, water chemistry and nutrient inputs, along
with warmer summer temperatures, could increase net primary
productivity in high mountain lakes to enhance frog food sources.
Changes in temperature may also affect virulence of pathogens
(Carey 1993, p. 359), which could make mountain yellow-legged frogs
more susceptible to disease. Climate change could also affect the
distribution of pathogens and their vectors, exposing mountain yellow-
legged frogs (potentially with weakened immune systems as a result of
other environmental stressors) to new pathogens (Blaustein et al. 2001,
p. 1808). Climate change (warming) has been hypothesized as a driver
for the range shift of Bd (Pounds et al. 2006, p. 161; Bosch et al.
2007, p. 253). However, other work has indicated that survival and
transmission of Bd is more likely facilitated by cooler and wetter
conditions (Corn 2005, p. 63). Fisher et al. (2009, p. 299) present a
review of information available to date, and evaluate the competing
hypotheses regarding Bd dynamics and present some cases that suggest a
changing climate can change the host-pathogen dynamic to a more
virulent state.
The key risk factor for climate change impacts on mountain yellow-
legged frogs is likely the combined effect of reduced water levels in
high mountain lakes and ponds and the relative inability of individuals
to disperse and colonize across longer distances in order to occupy
more favorable habitat conditions (if they exist). Although such
adaptive range shifts have been observed in some plant and animal
species, they have not been reported in amphibians. The changes
observed in amphibians to date have been more associated with changes
in timing of breeding (phenology) (Corn 2005, p. 60). This reduced
adaptive capacity for mountain yellow-legged frogs is a function of
high site fidelity and the extensive habitat fragmentation due to the
introduction of fishes in many of the more productive and persistent
high mountain lake habitats and streams that constitute critical
dispersal corridors throughout much of the frog's range (see Factor C
discussion above).
An increase in the frequency, intensity, and duration of droughts
caused by climate change may have compounding effects on populations of
mountain yellow-legged frogs already in decline. In situations where
other stressors have resulted in the isolation of mountain yellow-
legged frogs in marginal habitats factors (such as introduced fish),
localized mountain yellow-legged frog population crashes or
extirpations resulting from drought may exacerbate their isolation and
preclude natural recolonization (Bradford et al. 1993, p. 887; Drost
and Fellers 1996, p. 424; Lacan et al. 2008, p. 222). Climate change
represents a substantial future threat to the persistence of mountain
yellow-legged frog populations.
Direct and Indirect Mortality
Other risk factors include direct and indirect mortality as an
unintentional consequence of activities within mountain yellow-legged
frog habitat. Recreation may threaten all life stages of the mountain
yellow-legged frog through trampling by humans, packstock, or vehicles,
including off-highway vehicles; harassment by pets; and habitat
degradation associated with these various land uses (Cole and Landres
1996, p. 170; USDA 2001b, pp. 213-214). Fire management activities
probably lead to some direct mortality and have the potential to
disrupt behavior. Fire retardant chemicals contain nitrogen compounds
and surfactants (chemical additive used to facilitate application).
Laboratory tests have shown that surfactants or ammonia byproducts can
cause mortality in fishes and aquatic invertebrates (Hamilton et al.
1996, pp. 132-144); similar effects are possible in amphibians. Calfee
and Little (2003, pp. 1529-1530) report that southern leopard frogs
(Rana sphenocephala) and boreal toads (Bufo boreas) are more tolerant
than rainbow trout (Oncorhynchus mykiss) to fire retardant chemicals;
however the acute toxicity of some compounds is enhanced by ultraviolet
light, which may harm amphibians at environmentally relevant
concentrations. Therefore, if fire retardant chemicals are dropped in
or near mountain yellow-legged frog habitat, they could have negative
effects on individuals. The prevalence of this impact is undetermined,
but this threat may be sporadically significant. Roads create the
potential for direct mortality of amphibians by vehicle strikes
(deMaynadier and Hunter 2000, p. 56) and the possible introduction of
contaminants into new areas; however, most extant populations are not
located near roads. Collectively, direct mortality risks to mountain
yellow-legged frogs are likely of sporadic significance. They may be
important incidentally on a site-specific basis, but are likely of low
prevalence across the range of the species.
Small Population Size
Remaining populations for both the Sierra Nevada yellow-legged frog
and the mountain yellow-legged frog are small in many localities (CDFG,
unpubl. data). Brown et al. (2011, p. 24) reported that about 90
percent of watersheds have fewer than 10 adults and 80 percent have
fewer than 10 subadults and 100 tadpoles. Remnant populations in the
far northern extent of the range for the Sierra Nevada yellow-legged
frog (from Lake Tahoe north) and the southern extent of the Sierran
populations of the mountain yellow-legged frog (south of Kings Canyon
National Park) currently also exhibit very low abundances (CDFG,
unpubl. data).
Compared to large populations, small populations are more
vulnerable to extirpation from environmental, demographic, and genetic
stochasticity (random natural occurrences), and unforeseen (natural or
unnatural) catastrophes (Shaffer 1981, p. 131). Environmental
stochasticity refers to annual variation in birth and death rates in
response to weather, disease, competition, predation, or other factors
external to the population (Shaffer 1981, p. 131). Small populations
may be less able to respond to natural environmental changes
(K[eacute]ry et al. 2000, p. 28), such as a prolonged drought or even a
significant natural
[[Page 24494]]
predation event. Periods of prolonged drought are more likely to have a
significant effect on mountain yellow-legged frogs because drought
conditions occur on a landscape scale and all life stages are dependent
on habitat with a perennial water source. Demographic stochasticity is
random variability in survival or reproduction among individuals within
a population (Shaffer 1981, p. 131) and could increase the risk of
extirpation of the remaining populations. Genetic stochasticity results
from changes in gene frequencies due to the founder effect (loss of
genetic variation that occurs when a new population is established by a
small number of individuals) (Reiger 1968, p. 163); random fixation
(the complete loss of one of two alleles in a population, the other
allele reaching a frequency of 100 percent) (Reiger 1968, p. 371); or
inbreeding depression (loss of fitness or vigor due to mating among
relatives) (Soul[eacute] 1980, p. 96). Additionally, small populations
generally have an increased chance of genetic drift (random changes in
gene frequencies from generation to generation that can lead to a loss
of variation) and inbreeding (Ellstrand and Elam 1993, p. 225).
Allee effects (Dennis 1989, pp. 481-538) occur when a population
loses its positive stock-recruitment relationship (when population is
in decline). In a declining population, an extinction threshold or
``Allee threshold'' (Berec et al. 2006, pp. 185-191) may be crossed,
where adults in the population either cease to breed or the population
becomes so compromised that breeding does not contribute to population
growth. Allee effects typically fall into three broad categories
(Courchamp et al. 1999, pp. 405-410): Lack of facilitation (including
low mate detection and loss of breeding cues), demographic
stochasticity, and loss of heterozygosity (a measure of genetic
variability). Environmental stochasticity amplifies Allee effects
(Dennis 1989, pp. 481-538; Dennis 2002, pp, 389-401). The Allee effects
of demographic stochasticity and loss of heterozygosity are likely as
mountain yellow-legged frog populations continue to diminish. Lack of
facilitation is a possible threat, though less probable as frogs can
vocalize to advertise presence.
The extinction risk of a species represented by few small
populations is magnified when those populations are isolated from one
another. This is especially true for species whose populations normally
function in a metapopulation structure, whereby dispersal or migration
of individuals to new or formerly occupied areas is necessary.
Connectivity between these populations is essential to increase the
number of reproductively active individuals in a population; mitigate
the genetic, demographic, and environmental effects of small population
size; and recolonize extirpated areas. Additionally, fewer populations
increase the risk of extinction.
The combination of low numbers with the other extant stressors of
disease, fish persistence, and potential for climate extremes could
have adverse consequences for the mountain yellow-legged frog complex
as populations approach the Allee threshold. Small population size is
currently a significant threat to most populations of mountain yellow-
legged frogs across the range of the species.
Cumulative Impacts of Extant Threats
Stressors may act additively or synergistically. An additive effect
would mean that an accumulation of otherwise low threat factors acting
in combination may collectively result in individual losses that are
meaningful at the population level. A synergistic effect is one where
the interaction of one or more stressors together leads to effects
greater than the sum of those individual factors combined. Further, the
cumulative effect of multiple added stressors can erode population
viability over successive generations and act as a chronic strain on
the viability of a species, resulting in a progressive loss of
populations over time. Such interactive effects from compounded
stressors thereby act synergistically to curtail the viability of frog
metapopulations and increase the risks of extinction.
It is difficult to predict the precise impact of the cumulative
threat represented by the relatively novel Bd epidemic across a
landscape already fragmented by fish stocking. The singular threat of
the Bd epidemic wave in the uninfected populations of the mountain
yellow-legged frog complex in the southern Sierra Nevada could
extirpate those populations as the lethal pathogen spreads. A
compounding effect of disease-caused extirpation is that recolonization
may never occur because streams connecting extirpated sites to extant
populations now contain introduced fishes, which act as barriers to
frog movement within metapopulations. This isolates the remaining
populations of mountain yellow-legged frogs from one another (Bradford
1991, p. 176; Bradford et al. 1993, p. 887). It is logical to presume
that the small, fragmented populations left in the recent wake of Bd
spread through the majority of the range of the Sierra Nevada yellow-
legged frog may experience further extirpations as surviving adults
eventually die, and recruitment into the breeding pool from the Bd-
positive subadult class is significantly reduced. These may be
exacerbated by the present and growing threat of climate change,
although this effect may take years to materialize.
In summary, based on the best available scientific and commercial
information, we consider other natural and manmade factors to be
substantial ongoing threats to the Sierra Nevada yellow-legged frog and
the northern DPS of the mountain yellow-legged frog. These include
high, prevalent risk associated with climate change and small
population sizes, and the associated risk from the additive or
synergistic effects of these two stressors interacting with other
acknowledged threats, including habitat fragmentation and degradation
(see Factor A), disease (see Factor C), or other threats currently
present but with low relative contribution in isolation.
Proposed Determination for the Sierra Nevada Yellow-legged Frog
We have carefully assessed the best scientific information
available regarding the past, present, and future threats to the Sierra
Nevada yellow-legged frog.
There has been a rangewide decline in the geographic extent of
populations, and losses of populations have continued in recent
decades. There are now fewer, increasingly isolated populations
maintaining viable recruitment (entry of post-metamorphic frogs into
the breeding population). Coupled with the observation that remnant
populations are also numerically smaller (in some cases consisting of
few individuals), this reduction in occupancy and population density
across the landscape suggests significant losses in metapopulation
viability and high attendant risk to the overall population. The
impacts of the declines on population resilience are two-fold: (1) The
geographic extent and number of populations are reduced across the
landscape, resulting in fewer and more isolated populations (the
species is less able to withstand population stressors and unfavorable
conditions exist for genetic exchange or dispersal to unoccupied areas
(habitat fragmentation)); and (2) species abundance (in any given
population) is reduced, making local extirpations much more likely
(decreased population viability). Knapp et al. (2007b, pp. 1-2)
estimated a 10 percent decline per year in the number of remaining
mountain yellow-legged frog populations, and argued for the listing of
the species as
[[Page 24495]]
endangered based on this observed rate of population loss.
The best available science indicates the cause of the decline of
the Sierra Nevada yellow-legged frog is the introduction of fishes to
its habitat (Factor A, C) to support recreational angling. Water bodies
throughout this range have been intensively stocked with introduced
fish (principally trout). It is a threat of significant influence, and
although it more directly impacted populations historically, it remains
prevalent today because fish persist in many high-elevation habitats
even where stocking has ceased. Competitive exclusion and predation by
fish have reduced frog populations in stocked habitats, and left
remnant populations isolated. It is important to recognize that
throughout the vast majority of its range, Sierra Nevada yellow-legged
frogs did not co-evolve with any species of fish, as they predominantly
occur in water bodies above natural fish barriers. Further, the
introduction of fish has generally restricted remaining Sierra Nevada
yellow-legged frog populations to more marginal habitats, thereby
increasing the likelihood of localized extinctions. Recolonization in
these situations is difficult for a highly aquatic species with high
site fidelity and unfavorable dispersal conditions. Climate change is
likely to exacerbate these other threats and further threaten
population resilience.
Historical grazing activities may have modified the habitat of the
Sierra Nevada yellow-legged frog throughout much of its range (Factor
A). Grazing pressure has been significantly reduced from historical
levels, although grazing may continue to contribute to some localized
degradation and loss of suitable habitat. The effects of recreation,
dams and water diversions, roads, timber harvests, and fire management
activities on the Sierra Nevada yellow-legged frog are not well-
studied, and although they may negatively affect frog populations and
their habitat, these effects have not been implicated as primary
factors in the decline of this species. However, these activities may
be factors of secondary importance in the decline of the Sierra Nevada
yellow-legged frog and the modification of its habitat. Although these
threat factors are of relatively lower current magnitude and imminence,
part of their lesser studied, more uncertain contribution to population
dynamics may be a function of timing. Historical losses may already be
realized in areas where impacts are greater, and these would not be
documented in studies that have mostly been conducted over the last 2
to 3 decades amongst surviving populations. During this same time
interval, management practices by Federal agencies with jurisdiction
within the current range of the Sierra Nevada yellow-legged frog have
generally improved.
Sierra Nevada yellow-legged frogs are vulnerable to multiple
pathogens, whose effects range from low levels of infection within
persistent populations to disease-induced extirpation of entire
populations. The Bd epidemic has caused localized extirpations of
Sierra Nevada yellow-legged frog populations and associated significant
declines in numbers of individuals. Though Bd was only recently
discovered to affect the Sierra Nevada yellow-legged frog, it appears
to infect populations at much higher rates than other diseases. The
imminence of this risk to currently uninfected habitats is immediate,
and the potential effects severe. The already-realized effects to the
survival of sensitive amphibian life stages in Bd-positive areas are
well-documented. Although some populations survive the initial Bd wave,
survival rates of metamorphs and population viability are markedly
reduced relative to historical (pre-Bd) norms.
The main and interactive effects of these various risk factors have
acted to reduce Sierra Nevada yellow-legged frog populations to a small
fraction of its historical range and reduce population abundances
significantly throughout most of its range. Remaining areas in the
southern Sierra Nevada that have yet to be impacted by Bd are at
immediate and severe risk.
Given the life history of this species, dispersal, recolonization,
and genetic exchange are largely precluded by the fragmentation of
habitat common throughout its current range as a result of fish
introductions. Frogs that may disperse are susceptible to hostile
conditions in many circumstances. In essence, Sierra Nevada yellow-
legged frogs have been marginalized by historical fish introductions
and, likely, other land management activities. Populations have
recently been decimated by Bd, and the accumulation of other stressors
(such as anticipated reduction of required aquatic breeding habitats
with climate change and more extreme weather) upon a fragmented
landscape make adaptation and recovery a highly improbable scenario
without active intervention. The cumulative risk from these stressors
to the persistence of the Sierra Nevada yellow-legged frog throughout
its range is significant.
The Act defines an endangered species as any species that is ``in
danger of extinction throughout all or a significant portion of its
range'' and a threatened species as any species ``that is likely to
become endangered throughout all or a significant portion of its range
within the foreseeable future.'' We find that the Sierra Nevada yellow-
legged frog is presently in danger of extinction throughout its entire
range, based on the immediacy, severity, and scope of the threats
described above. Specifically, these include habitat degradation and
fragmentation under Factor A, predation and disease under Factor C, and
climate change and the interaction of these various stressors
cumulatively impacting small remnant populations under Factor E. There
has been a rangewide reduction in abundance and geographic extent of
surviving populations of the Sierra Nevada yellow-legged frog following
decades of fish stocking, habitat fragmentation, and, most recently, a
disease epidemic. Surviving populations are smaller and more isolated,
and recruitment in Bd-positive populations is much reduced relative to
historical norms. This combination of population stressors makes
species persistence precarious throughout the currently occupied range
in the Sierra Nevada.
We have carefully assessed the best scientific and commercial
information available regarding the past, present, and future threats
to the species, and have determined that the Sierra Nevada yellow-
legged frog meets the definition of endangered under the Act, rather
than threatened. This is because significant threats are occurring now
and will occur in the future, at a high magnitude and across the
species' entire range, making the species in danger of extinction at
the present time. The rate of population decline remains high in the
wake of chytrid epidemics, and core areas are at high, imminent risk.
Population declines are expected to continue as maturing tadpoles
succumb to Bd infection, and fragmented populations at very low
abundances will face significant obstacles to recovery.
Under the Act and our implementing regulations, a species may
warrant listing if it is endangered or threatened throughout all or a
significant portion of its range. The Sierra Nevada yellow-legged frog
proposed for listing in this rule is restricted in its range, and the
threats occur throughout the remaining occupied habitat. Therefore, we
assessed the status of this species throughout its entire range. The
threats to the survival of the species occur throughout the species'
range and are not restricted to any particular
[[Page 24496]]
significant portion of that range. Accordingly, our assessment and
proposed determination applies to the species throughout its entire
range.
Proposed Determination for the Northern DPS of the Mountain Yellow-
legged Frog
We have carefully assessed the best scientific information
available regarding the past, present, and future threats to the
northern DPS of the mountain yellow-legged frog.
There has been a rangewide decline in the geographic extent of
populations, and losses of populations have continued in recent
decades. There are now fewer, increasingly isolated populations
maintaining viable recruitment (entry of post-metamorphic frogs into
the breeding population). Coupled with the observation that remnant
populations are also numerically smaller (in some cases consisting of
few individuals), this reduction in occupancy and population density
across the landscape suggests significant losses in metapopulation
viability and high attendant risk to the overall population. The
impacts of the declines on population resilience are two-fold: (1) The
geographic extent and number of populations are reduced across the
landscape, resulting in fewer and more isolated populations (the
species is less able to withstand population stressors and unfavorable
conditions exist for genetic exchange or dispersal to unoccupied areas
(habitat fragmentation)); and (2) species abundance (in any given
population) is reduced, making local extirpations much more likely
(decreased population viability). Knapp et al. (2007b, pp. 1-2)
estimated a 10 percent decline per year in the number of remaining
mountain yellow-legged frog populations, and argued for the listing of
the species as endangered based on this observed rate of population
loss.
The best available science indicates the cause of the decline of
the northern DPS of the mountain yellow-legged frog is the introduction
of fishes to its habitat (Factor A, C) to support recreational angling.
Water bodies throughout this range have been intensively stocked with
introduced fish (principally trout). It is a threat of significant
influence, and although it more directly impacted populations
historically, it remains prevalent today because fish persist in many
high-elevation habitats even where stocking has ceased. Competitive
exclusion and predation by fish have reduced frog populations in
stocked habitats, and left remnant populations isolated. It is
important to recognize that throughout the vast majority of their
range, mountain yellow-legged frogs did not co-evolve with any species
of fish, as they predominantly occur in water bodies above natural fish
barriers. Further, the introduction of fish has generally restricted
remaining mountain yellow-legged frog populations to more marginal
habitats, thereby increasing the likelihood of localized extinctions.
Recolonization in these situations is difficult for a highly aquatic
species with high site fidelity and unfavorable dispersal conditions.
Climate change is likely to exacerbate these other threats and further
threaten population resilience.
Historical grazing activities may have modified the habitat of the
mountain yellow-legged frog throughout much of its range (Factor A).
Grazing pressure has been significantly reduced from historical levels,
although grazing may continue to contribute to some localized
degradation and loss of suitable habitat. The effects of recreation,
dams and water diversions, roads, timber harvests, and fire management
activities on the mountain yellow-legged frog are not well-studied, and
although they may negatively affect frog populations and their habitat,
these effects have not been implicated as primary factors in the
decline of this species. However, these activities may be factors of
secondary importance in the decline of the mountain yellow-legged frog
and the modification of its habitat. Although these threat factors are
of relatively lower current magnitude and imminence, part of their
lesser studied, more uncertain contribution to population dynamics may
be a function of timing. Historical losses may already be realized in
areas where impacts are greater, and these would not be documented in
studies that have mostly been conducted over the last 2 to 3 decades
amongst surviving populations. During this same time interval,
management practices by Federal agencies with jurisdiction within the
current range of the mountain yellow-legged frog have generally
improved.
Mountain yellow-legged frogs are vulnerable to multiple pathogens,
whose effects range from low levels of infection within persistent
populations to disease-induced extirpation of entire populations. The
Bd epidemic has caused localized extirpations of mountain yellow-legged
frog populations and associated significant declines in numbers of
individuals. Though Bd was only recently discovered to affect the
mountain yellow-legged frog, it appears to infect populations at much
higher rates than other diseases. The imminence of this risk to
currently uninfected habitats is immediate, and the potential effects
severe. The already-realized effects to the survival of sensitive
amphibian life stages in Bd-positive areas are well-documented.
Although some populations survive the initial Bd wave, survival rates
of metamorphs and population viability are markedly reduced relative to
historical (pre-Bd) norms.
The main and interactive effects of these various risk factors have
acted to reduce the northern DPS of the mountain yellow-legged frog
populations to a small fraction of its historical range and reduce
population abundances significantly throughout most of its range.
Remaining areas in the southern Sierra Nevada that have yet to be
impacted by Bd are at immediate and severe risk.
Given the life history of this species, dispersal, recolonization,
and genetic exchange are largely precluded by the fragmentation of
habitat common throughout its current range as a result of fish
introductions. Frogs that may disperse are susceptible to hostile
conditions in many circumstances. In essence, mountain yellow-legged
frogs have been marginalized by historical fish introductions and,
likely, other land management activities. Populations have recently
been decimated by Bd, and the accumulation of other stressors (such as
anticipated reduction of required aquatic breeding habitats with
climate change and more extreme weather) upon a fragmented landscape
make adaptation and recovery a highly improbable scenario without
active intervention. The cumulative risk from these stressors to the
persistence of the mountain yellow-legged frog throughout its range is
significant.
The Act defines an endangered species as any species that is ``in
danger of extinction throughout all or a significant portion of its
range'' and a threatened species as any species ``that is likely to
become endangered throughout all or a significant portion of its range
within the foreseeable future.'' We find that the northern DPS of the
mountain yellow-legged frog is presently in danger of extinction
throughout its entire range, based on the immediacy, severity, and
scope of the threats described above. Specifically, these include
habitat degradation and fragmentation under Factor A, predation and
disease under Factor C, and climate change and the interaction of these
various stressors cumulatively impacting small remnant populations
under Factor E. There has been a rangewide reduction in abundance and
geographic extent of surviving populations of the northern DPS of the
[[Page 24497]]
mountain yellow-legged frog following decades of fish stocking, habitat
fragmentation, and, most recently, a disease epidemic. Surviving
populations are smaller and more isolated, and recruitment in Bd-
positive populations is much reduced relative to historical norms. This
combination of population stressors makes species persistence
precarious throughout the currently occupied range in the Sierra
Nevada.
We have carefully assessed the best scientific and commercial
information available regarding the past, present, and future threats
to the species, and have determined that the northern DPS of the
mountain yellow-legged frog, already endangered in the southern part of
its range, meets the definition of endangered under the Act, rather
than threatened. This is because significant threats are occurring now
and will occur in the future, at a high magnitude and across the
species' entire range, making the species in danger of extinction at
the present time. The rate of population decline remains high in the
wake of chytrid epidemics, and core areas are at high, imminent risk.
The recent rates of decline for these populations are even higher than
declines in the Sierra Nevada yellow-legged frog, and as Bd infects
remaining core areas, population viability will be significantly
reduced, and extirpations or significant population declines are
expected. Population declines are further expected to continue as
maturing tadpoles succumb to Bd infection, and fragmented populations
at very low abundances will face significant obstacles to recovery.
Therefore, on the basis of the best available scientific and commercial
information, and the threats posed to these species under the listing
factors above, we propose listing the northern DPS of the mountain
yellow-legged frog as endangered in accordance with sections 3(6) and
4(a)(1) of the Act.
Under the Act and our implementing regulations, a species may
warrant listing if it is endangered or threatened throughout all or a
significant portion of its range. The northern DPS of the mountain
yellow-legged frog proposed for listing in this rule is restricted in
its range, and the threats occur throughout the remaining occupied
habitat. Therefore, we assessed the status of this DPS throughout its
entire range in the Sierra Nevada of California. The threats to the
survival of this DPS occur throughout its range in the southern Sierra
Nevada and are not restricted to any particular significant portion of
that range. Accordingly, our assessment and proposed determination
applies to the DPS throughout its entire range.
Status for Yosemite Toad
Background
In this section of the proposed rule, it is our intent to discuss
only those topics directly relevant to the listing of the Yosemite toad
(Anaxyrus canorus) as threatened.
Taxonomy
The Yosemite toad (Anaxyrus canorus; formerly Bufo canorus) was
originally described by Camp (1916, pp. 59-62), and given the common
name Yosemite Park toad. The word ``canorus'' means ``tuneful'' in
Latin, referring to the male's sustained melodious trill, which
attracts mates during the early spring breeding season. Later, Grinnell
and Storer (1924, pp. 657-660) referred to this species as the Yosemite
toad when the species' range was found to extend beyond the boundaries
of Yosemite National Park.
When he described the species, Camp noted similarities in
appearance of the Yosemite toad and the western toad (Camp 1916, pp.
59-62). Based on general appearance, structure, and distribution, it
appeared that the western toad and the Yosemite toad were closely
related (Myers 1942, p. 10; Stebbins 1951, pp. 245-248; Mullally 1956b,
pp. 133-135; Savage 1958, pp. 251-253). The close relationship between
the western toad and the Yosemite toad is also supported by studies of
bone structure (Tihen 1962, pp. 1-50) and by the survivorship of hybrid
toads produced by artificially crossing the two species (Blair 1959,
pp. 427-453; 1963, pp. 1-16; 1964, pp. 181-192).
Camp (1916, pp. 59-62), using characteristics of the skull,
concluded that Bufo boreas, B. canorus, and B. nestor (extinct) were
more closely related to one another than to other North American toads
(Family Bufonidae), and that these species comprised the most primitive
group of Bufo in North America. Blair (1972, pp. 93-95) grouped B.
boreas, B. canorus, black toads (B. exsul), and Amargosa toads (B.
nelsoni) together taxonomically as the ``boreas group.'' Subsequently,
Frost et al. (2006, p. 297) divided the paraphyletic genus ``Bufo''
into three separate genera, assigning the North American toads to the
genus Anaxyrus. This taxonomic distinction has been recently adopted by
the American Society of Ichthyologists and Herpetologists, the
Herpetologists' League, and the Society for the Study of Amphibians and
Reptiles (Crother et al. 2008. p. 3).
Feder (1977, pp. 43-55) found Yosemite toads to be the most
genetically distinct member of the boreas group based on samples from a
limited geographic range. However, Yosemite toads hybridize with
western toads in the northern part of their range (Karlstrom 1962, p.
84; Morton and Sokolski 1978, pp. 52-55). A genetic analysis of a
segment of mitochondrial DNA from Yosemite toads was performed by
Shaffer et al. (2000, pp. 245-257) using 372 toads from Yosemite and
Kings Canyon National Parks. These data showed significant genetic
differences in Yosemite toads between the two National Parks. They
observed that genetic divergence among regionally proximate populations
of Yosemite toads was high, implying low rates of genetic exchange.
Their data also suggest that black toads are a nested subgroup within
Yosemite toads, rather than a separate species, and that a group of
western toad populations in the Oregon Cascades appears more closely
related to Yosemite toads than their current classification would
indicate. However, sufficient molecular evidence to change the
taxonomic classification of these three species is not yet available.
Stephens (2001, pp. 1-62) examined mitochondrial DNA from 8
Yosemite toads (selected to represent the range of variability found in
the Shaffer et al. (2000, pp. 245-257) study) and 173 western toads.
This study indicated that Bufo in the Sierra Nevada occurs in northern
and southern evolutionary groups, each of which includes both Yosemite
toads and western toads (that is, toads of both species are more
closely related to each other within an evolutionary group than they
are to members of their own species in the other evolutionary group).
Goebel et al. (2008, p. 223) also concluded that the Yosemite toad is
paraphyletic, split between a northwest and southwest haplotype group.
Further genetic analysis of Yosemite toads is needed to fully
understand the evolutionary history and appropriate taxonomic status of
the Yosemite toad (Stephens 2001, pp. 1-62). Current information
indicates that the range is segregated between northern and southern
evolutionary groups. This information also indicates that genetic
introgression (movement of genes into the native gene pool to create
hybrid populations) is occurring from a closely related counterpart
(likely over an extended period), possibly associated with range
expansion and overlap with the western toad following reproductive
isolation that occurred during the Pleistocene glaciation (Feder 1977,
p. 43). It therefore appears that natural hybridization has occurred
where
[[Page 24498]]
Yosemite toad and western toad ranges overlap. We have assessed the
available information, and have determined that the Yosemite toad is a
valid species, following its current classification by the American
Society of Ichthyologists and Herpetologists, the Herpetologists'
League, and the Society for the Study of Amphibians and Reptiles
(Crother et al. 2008, p. 3).
Species Description
The Yosemite toad is moderately sized, with a snout-urostyle length
(measured from the tip of the snout to the posterior edge of the
urostyle, a bony structure at the posterior end of the spinal column)
of 30-71 mm (1.2-2.8 in) with rounded to slightly oval paratoid glands
(a pair of glands, one on each side of the head, that produce toxins)
(Karlstrom 1962, pp. 21-23). The paratoid glands are less than the
width of a gland apart (Stebbins 1985, pp. 71-72). A thin mid-dorsal
stripe (on the middle of the back) is present in juveniles of both
sexes. The stripe disappears or is reduced with age; this process takes
place more quickly in males (Jennings and Hayes 1994, pp. 50-53). The
iris of the eye is dark brown with gold iridophores (reflective pigment
cells) (Jennings and Hayes 1994, pp. 50-53).
Male Yosemite toads are smaller than female Yosemite toads, with
less conspicuous warts (Stebbins 1951, p. 246). Differences in
coloration between males and females are more pronounced in the
Yosemite toad than in any other North American frog or toad (Stebbins
1951, p. 246). Females have black spots or blotches edged with white or
cream set against a grey, tan, or brown background color (Jennings and
Hayes 1994, pp. 50-53). Males have a nearly uniform dorsal coloration
of yellow-green to olive drab to darker greenish brown (Jennings and
Hayes 1994, pp. 50-53). Karlstrom (1962, pp. 80-81) suggested that
differences in coloration between the sexes evolved because they
provide the Yosemite toad with protective coloration (camouflage). The
uniform coloration of the adult males matches and blends with the silt
and grasses that they frequent during the breeding season, whereas the
young and females with disruptive coloration tend to use a wider range
of habitats with broken backgrounds; thus, coloration may help conceal
individual toads from predators.
Habitat and Life History
Yosemite toads are found in wet meadow habitats and lake shores
surrounded by lodgepole (Pinus contorta) or whitebark (P. albicaulis)
pines (Camp 1916, pp. 59-62). They are most often found in areas with
thick meadow vegetation or patches of low willows (Salix spp.)
(Mullally 1953, pp. 182-183). Liang (2010, p. 81) observed Yosemite
toads most frequently associated with (in order of preference): wet
meadows, alpine-dwarf scrub, red fir (Abies magnifica), water,
lodgepole pine, and subalpine conifer habitats.
Yosemite toads were found as often at large as at small sites
(Liang 2010, p. 19), suggesting that this species is capable of
successfully utilizing small habitat patches. Liang also found that
population persistence was greater at higher elevations, with an
affinity for relatively flat sites with a southwesterly aspect (Liang
2010, p. 20). These areas receive higher solar radiation and are
capable of sustaining hydric (wet), seasonally ponded, and mesic
(moist) breeding and rearing habitat. The Yosemite toad is more common
in areas with less variation in mean annual temperature, or more
temperate sites with less climate variation (Liang 2010, pp. 21-22).
Adults are thought to be long-lived, and this factor allows for
persistence in variable conditions and more marginal habitats where
only periodic good years allow high reproductive success (USFS et al.
2009, p. 27). Females have been documented to reach 15 years of age,
and males as many as 12 years (Kagarise Sherman and Morton 1993, p.
195); however the average longevity of the Yosemite toad in the wild is
not known. Jennings and Hayes (1994, p. 52) indicated that females
begin breeding at ages four to six, while males begin breeding at ages
three to five.
Adults tend to breed at a single site and appear to have high site-
fidelity (Liang 2010, p. 99), although individuals will move between
breeding areas (Liang 2010, p. 52). Breeding habitat includes the edges
of wet meadows and slow-flowing streams (Jennings and Hayes 1994, pp.
50-53). Tadpoles have also been observed in shallow ponds and shallow
areas of lakes (Mullally 1953, pp. 182-183).
Males exit burrows first, and spend more time in breeding pools
than females, who do not breed every year (Kagarise Sherman and Morton,
1993, p. 196). It is suggested that higher lipid storage in females,
which enhances overwinter survival, also precludes the energetic
expense of breeding every year (Morton 1981, p. 237). The Yosemite toad
is a prolific breeder, laying many eggs immediately at snowmelt. This
is accomplished in a short period of time, coinciding with water levels
in meadow habitats and ephemeral pools they use for breeding. Female
toads lay approximately 700-2,000 eggs in two strings (one from each
ovary) (USFS et al. 2009, p. 21). Females may split their egg clutches
within the same pool, or even between different pools, and may lay eggs
communally with other toads (USFS et al. 2009, p.22).
Eggs hatch within 3-15 days, depending on ambient water
temperatures (Kagarise Sherman 1980, pp. 46-47; Jennings and Hayes
1994, p. 52). Tadpoles typically metamorphose around 40-50 days after
fertilization, and are not known to overwinter (Jennings and Hayes
1994. p. 52). Tadpoles are black in color, tend to congregate together
(Brattstrom 1962, pp. 38-46) in warm shallow waters during the day
(Cunningham 1963, pp. 60-61), and then retreat to deeper waters at
night (Mullaly 1953, p. 182). Rearing through metamorphosis takes
approximately 5-7 weeks after eggs are laid (USFS et al. 2009, p. 25).
Reproductive success is dependent on the persistence of tadpole
rearing sites and conditions for breeding, egg deposition, hatching,
and rearing to metamorphosis (USFS et al. 2009, p. 23). Given their
association with shallow, ephemeral habitats, Yosemite toads are
susceptible to droughts and weather extremes. Abiotic factors leading
to mortality (such as freezing or desiccation) appear to be more
significant during the early life stages of toads, while biotic factors
(such as predation) are probably more prominent factors during later
life stages (USFS et al. 2009, p. 30). However, since adult toads lead
a much more inconspicuous lifestyle, direct observation of adult
mortality is difficult and it is usually not possible to determine
causes of adult mortality.
Adult Yosemite toads are most often observed near water, but only
occasionally in water (Mullally and Cunningham 1956b, pp. 57-67). Moist
upland areas such as seeps and springheads are important summer non-
breeding habitats for adult toads (Martin 2002, pp. 1-3). The majority
of their life is spent in the upland habitats proximate to their
breeding meadows. They use rodent burrows for overwintering and
probably for temporary refuge during the summer (Jennings and Hayes
1994, pp. 50-53), and they spend most of their time in burrows (Liang
2010, p. 95). They also use spaces under surface objects, including
logs and rocks, for temporary refuge (Stebbins 1951, pp. 245-248;
Karlstrom 1962, pp. 9-10). Males and females also likely inhabit
different areas and habitats when not breeding, and females tend to
move farther from
[[Page 24499]]
breeding ponds than males (USFS et al. 2009, p. 28).
Yosemite toads can move farther than 1 km (0.63 mi) from their
breeding meadows (average movement is 275 m (902 ft)), and they utilize
terrestrial environments extensively (Liang 2010, p. 85). The average
distance traveled by females is twice as far as males, and home ranges
for females are 1.5 times greater than those for males (Liang 2010, p.
94). Movement into the upland terrestrial environment following
breeding does not follow a predictable path, and toads tend to traverse
longer distances at night, perhaps to minimize evaporative water loss
(Liang 2010, p. 98). Martin (2008, p. 123) radio-tracked adult toads
during the active season and found that on average toads traveled a
total linear distance of of 494 m (1,620 ft) within the season, with
minimum travel distance of 78 m (256 ft) and maximum of 1.76 km (1.09
mi).
Historical Range and Distribution
The historical range of the Yosemite toad in the Sierra Nevada
extended from the Blue Lakes region north of Ebbetts Pass (Alpine
County) to just south of Kaiser Pass in the Evolution Lake/Darwin
Canyon area (Fresno County) (Jennings and Hayes 1994, pp. 50-53).
Yosemite toad habitat historically spanned elevations from 1,460 to
3,630 m (4,790 to 11,910 ft) (Stebbins 1985, pp. 72; Stephens 2001, p.
12).
Current Range and Distribution
The current range of the Yosemite toad, at least in terms of
overall geographic extent, remains largely similar to the historical
range defined above (USFS et al. 2009, p. 41). However, within that
range, toad habitats have been degraded and may be decreasing in area
as a result of conifer encroachment and livestock grazing (see Factor A
below). The vast majority of the Yosemite toad's range is within
Federal land. Figure 2, Estimated Range of Yosemite Toad, displays a
range map for the species.
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Population Estimates and Status
Baseline data on the number and size of historical Yosemite toad
populations are limited, and historic records are largely based on
accounts from field notes, or pieced together through museum
collections. Systematic survey information across the range of the
species largely follows the designation of the Yosemite toad as a
candidate species under the Act. From these recent inventories,
Yosemite toads have been found at 469 localities collectively on six
National Forests (more sites than previously known), indicating that
the species is still widespread throughout its range (USFS et al. 2009,
p. 40). These inventories were conducted to determine toad presence or
absence (they were not censuses), and the referenced figure does not
explicitly compare historic sites to recent surveys. Moreover, single-
visit surveys of toads are unreliable as indices of abundance because
timing is so critical to the presence of detectable life stages (USFS
et al. 2009, p. 41; Liang 2010, p. 10). Given these considerations,
conclusions about population trends, abundance, or extirpation rates
are not possible relative to this specific dataset.
One pair of studies allows us to compare current distribution with
historic distributions and indicates that large reductions have
occurred. In 1915 and 1919, Grinnell and Storer (1924, pp. 657-660)
surveyed for vertebrates at 40 sites along a 143-km (89-mi) west-to-
east transect across the Sierra Nevada, through Yosemite National Park,
and found Yosemite toads at 13 of those sites. Drost and Fellers (1996,
pp. 414-425) conducted more thorough surveys, specifically for
amphibians, at 38 of the Grinnell and Storer sites plus additional
nearby sites in 1992. Drost and Fellers found that Yosemite toads were
absent from 6 of 13 sites where they had been
[[Page 24501]]
found in the original Grinnell and Storer survey. Moreover, at the
sites where they were present, Yosemite toads occurred in very low
numbers relative to general abundance reported in the historical record
(Grinnell and Storer 1924, pp. 657-660). Specifically, by the early
1990s, the species was either undetectable or had declined in numbers
at 9 of 13 (69 percent) of the Grinnell and Storer (1924, pp. 657-660)
sites.
Another study comparing historic and current occurrences also found
a large decline in Yosemite toad distribution. In 1990, David Martin
surveyed 75 sites throughout the range of the Yosemite toad for which
there were historical records of the species' presence. This study
found that 47 percent of historically occupied sites showed no evidence
of any life stage of the species (Stebbins and Cohen 1995, pp. 213-
215). This result suggests a rangewide decline to about one half of
historical sites, based on occupancy alone.
A third study comparing historic and recent surveys indicates
declines in Yosemite toad distribution. Jennings and Hayes (1994, pp.
50-53) reviewed the current status of Yosemite toads using museum
records of historic and recent sightings, published data, and
unpublished data and field notes from biologists working with the
species. They estimated a loss of over 50 percent of former Yosemite
toad locations throughout the range of the species (based on 144
specific sites).
The only long-term, site-specific population study for Yosemite
toads documented a dramatic decline over 2 decades of monitoring.
Kagarise Sherman and Morton (1993, pp. 186-198) studied Yosemite toads
at Tioga Pass Meadow (Mono County, California) from 1971 through 1991
(with the most intensive monitoring through 1982). They documented a
decline in the average number of males entering the breeding pools from
258 to 28 during the mid-1970s through 1982. During the same time
period, the number of females varied between 45 and 100, but there was
no apparent trend in number observed. During the 1980s, it appeared
that both males and females continued to decline, and breeding activity
became sporadic. By 1991, they found only one male and two egg masses.
The researchers also found similar population declines in local
nonbreeding habitat.
Kagarise Sherman and Morton (1993, pp. 186-198) also conducted
occasional surveys of six other populations in the eastern Sierra
Nevada. Five of these populations showed long-term declines that were
evident beginning between 1978 through 1981, while the sixth population
held relatively steady until the final survey in 1990, at which time it
dropped. In 1991, E.L. Karlstrom revisited the site where he had
studied a breeding population of Yosemite toads from 1954 to 1958 (just
south of Tioga Pass Meadow within Yosemite National Park), and found no
evidence of toads or signs of breeding (Kagarise Sherman and Morton
1993, pp. 190).
The most reliable information about Yosemite toad population status
and trends is the USFS SNAMPH. This study is designed to provide
statistical comparisons across 5-year monitoring cycles with at 134
watersheds (Brown et al. 2011, pp. 3-4). This approach allows
researchers to assess trends for the entire range of the toad, rather
than make year-to-year comparisons at limited survey sites (C. Brown
2012, pers. comm.). The results of this assessment indicate the species
has declined from historical levels, with Yosemite toads occurring in
only 12 percent of watersheds where they existed prior to 1990. This
study also found that breeding currently occurs in an estimated 22
percent of watersheds within their current estimated range.
Additionally, the study found that breeding was occurring in 81 percent
of the watersheds that were occupied from 1990-2001, suggesting that
the number of locations where breeding occurs has continued to decline
(Brown et al. 2011, p. 4).
Moreover, overall abundances in the intensively monitored
watersheds were very low (fewer than 20 males per meadow per year)
relative to other historically reported abundances of the species
(Brown et al. 2011, p. 4). Brown et al. (2011, p. 35) suggest that
populations are now very small across the range of the species. They
found only 18 percent of occupied survey watersheds rangewide had
``large'' populations during their monitoring over the past decade
(more than 1,000 tadpoles or 100 of any other lifestage detected at the
time of survey). The researchers interpret this data, in combination
with documented local population declines from other studies (see
above), to support the hypothesis that population declines have
occurred rangewide (Brown et al. 2012, p. 11).
Summary of Factors Affecting the Species
Section 4 of the Act (16 U.S.C. 1533), and its implementing
regulations at 50 CFR part 424, set forth the procedures for adding
species to the Federal Lists of Endangered and Threatened Wildlife and
Plants. Under section 4(a)(1) of the Act, we may list a species based
on any of the following five factors: (A) The present or threatened
destruction, modification, or curtailment of its habitat or range; (B)
overutilization for commercial, recreational, scientific, or
educational purposes; (C) disease or predation; (D) the inadequacy of
existing regulatory mechanisms; and (E) other natural or manmade
factors affecting its continued existence. Listing actions may be
warranted based on any of the above threat factors, singly or in
combination. Each of these factors is discussed below.
Factor A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range
The habitat comprising the current range of the Yosemite toad is
generally characterized by low levels of physical disturbance (there is
little to no current development pressure). However, these areas are
also generally more sensitive to perturbation and take longer to
recover from disturbances due to reduced growing seasons and harsher
environmental conditions. Past management and development activity has
played a role in the degradation of certain habitat features within the
Sierra Nevada. Anthropogenic activities within these habitats include
grazing, timber harvest, fuels management, recreation, and water
development. Collectively, these factors continue to degrade habitat
conditions for the toad, although the contribution of this factor to
population dynamics has probably lessened over time, perhaps because
toad populations disappear from impacted areas first, but also through
improved management practices implemented in recent decades.
Meadow Habitat Loss and Degradation
Some of the threat factors associated with grazing activities for
the mountain yellow-legged frogs (see their Summary of Factors
Affecting the Species section, above) also apply to Yosemite toads.
However, there are differences based on the Yosemite toad's affinity
for meadow and pool habitats versus the lakes and streams frequented by
mountain yellow-legged frogs. Meadow habitat quality in the Western
United States, and specifically the Sierra Nevada, has been degraded by
various stressors over the last century (Stillwater Sciences 2008, pp.
1-53; Halpern et al. 2010, pp. 717-732; Vale 1987, pp. 1-18; Ratliff
1985, pp. i-48). These various stressors have contributed to erosion
and stream incision, leading to meadow dewatering and encroachment by
invasive vegetation (Menke et al. 1996, pp. 25-28; Linquist 2000, p.
2). The legacy of these impacts remains extant to this day
[[Page 24502]]
in the ecosystems of the high Sierra Nevada (Vankat and Major 1978, pp.
386-397).
Given the reliance of the Yosemite toad on these meadow and pool
habitats for breeding, rearing, and adult survival, it is logical to
conclude that the various stressors have had an indirect effect on the
viability of Yosemite toad populations via degradation of their
habitat. Loss of connectivity of habitats leads to further isolation
and population fragmentation. Due to constraints of their physiology,
low mobility, and higher site fidelity, many amphibian populations may
be unable to recolonize after local extirpations (Blaustein et al.
1994a, p. 60).
Since the existence of meadows is largely dependent on their
hydrologic setting, most meadow degradation is due fundamentally to
hydrologic alterations (Stillwater Sciences 2008, p. 13). There are
many drivers of hydrologic alterations in meadow ecosystems. Historic
water development and ongoing management has physically changed the
underlying hydrologic landscape. Diversion and irrigation ditches
formed a vast network that altered local and regional stream hydrology.
Timber harvest and associated road construction further affected
erosion and sediment delivery patterns in rivers and meadow streams.
Changes in the pre-settlement fire regime, fire suppression, and an
increase in the frequency of large wildfires due to excessive fuel
buildup, introduced additional disturbance pressure to the meadows of
the Sierra Nevada (Stillwater Sciences 2008, p. 13). Many meadows now
have downcut stream courses, compacted soils, altered plant community
compositions, and diminished wildlife and aquatic habitats (SNEP 1996,
pp. 120-121). Meadow dewatering by these changes within the watershed
has facilitated these shifts in the vegetative community. Finally,
climate variability has also played a role in the conifer encroachment.
Land uses causing channel erosion threaten Sierra Nevada meadows.
These threats include erosive activities within the watershed upslope
of the meadow, along with impacts from land use directly in the meadows
themselves. Compaction of meadow soils by roads and/or intensive
trampling (for example, overgrazing) can reduce infiltration,
accelerate surface run-off, and thereby lead to channel incision (Menke
et al. 1996, pp. 25-28). Mining, overgrazing, timber harvesting, and
railroad and road construction and maintenance have contributed to
watershed degradation, resulting in accelerated erosion, sedimentation
in streams and reservoirs, meadow dewatering, and degraded terrestrial
and aquatic habitats (Linquist 2000, p. 2). Deep incision has been
documented in several meadows in the Sierra Nevada. One example is
Halstead Meadow in Sequoia National Park, where headcutting exceeds 10
feet in many areas and is resulting in widening channels, erosion in
additional meadows, and a lowered water table (Cooper 2006, p. 1).
The hydrologic effects of stream incision on the groundwater system
may significantly impact groundwater storage, affecting late summer
soil moisture and facilitating vegetation change (Bergmann 2004, pp.
24-31). For example, in the Last Chance Watershed in the northern
Sierra Nevada, logging, overgrazing, and road/railroad construction
have caused stream incision, resulting in dewatering of riparian meadow
sediments and a succession from native wet meadow vegetation to
sagebrush and dryland grasses (Loehide and Gorelick 2007, p. 2). A
woody shrub (Artemisia rothrockii) is invading meadows as channel
incision causes shallow-water-dependent herbs to die back, allowing
shrub seedlings to establish in disturbed areas during wet years
(Darrouzet-Nardi et al. 2006, p. 31).
Mountain meadows in the western United States and Sierra Nevada
have also been progressively colonized by trees (Thompson 2007, p. 3;
Vale 1987, p. 6), with an apparent pattern of encroachment during two
distinct periods in the late 1800s and mid 1900s (Halpern et al. 2010,
p. 717). This trend has been attributed to a number of factors,
including climate, changes in fire regime, and cessation of sheep
grazing (Halpern et al. 2010, pp. 717-718; Vale 1987, pp. 10-13), but
analyses are limited to correlational comparisons and research results
are mixed, so the fundamental contribution of each potential driver
remains uncertain. We discuss the contribution of these factors to
habitat loss and degradation for the Yosemite toad below.
Livestock Use (Grazing) Effects to Meadow Habitat
Grazing of livestock in Sierra Nevada meadows and riparian areas
(rivers, streams, and adjacent upland areas that directly affect them)
began in the mid-1700s with the European settlement of California
(Menke et al. 1996, p. 7). Following the gold rush of the mid-1800s,
grazing increased to a level exceeding the carrying capacity of the
available range, causing significant impacts to meadow and riparian
ecosystems (Meehan and Platts 1978, p. 275; Menke et al. 1996, p. 7).
By the turn of the 20th century, high Sierra Nevada meadows were
converted to summer rangelands for grazing cattle, sheep, horses,
goats, and pigs, although the alpine areas were mainly grazed by sheep
(Beesley 1996, pp. 7-8; Menke et al. 1996, p. 14). Stocking rates of
both cattle and sheep in Sierra meadows in the late 19th and early 20th
centuries were very heavy (Kosco and Bartolome 1981, pp. 248-250), and
grazing severely degraded many meadows (Ratliff 1985, pp. 26-31; Menke
et al. 1996, p. 14). Grazing impacts occurred rangewide, as cattle and
sheep were driven virtually everywhere in the Sierra Nevada where
forage was available (Kinney 1996, pp. 37-42; Menke et al. 1996, p.
14).
Grazing within the National Forests has continued into modern
times, with reduction in activity (motivated by resource concerns,
conflicts with other uses, and deteriorating range conditions)
beginning in the 1920s. A brief wartime increase in the 1940s followed,
before activity continued to be scaled back beginning in the 1950s
through the early 1970s. However, despite these reductions, grazing
still exceeded sustainable capacity in many areas (Menke et al. 1996,
p. 9; UC 1996a, p. 115). Currently, approximately 33 percent of the
estimated range of the Yosemite toad is within active USFS grazing
allotments (USFS 2008, geospatial data). While stocking rates have been
reduced or eliminated in most areas, many meadows remain disturbed from
the historical period of heavy grazing, with legacy effects including
eroded channels, non-vegetated patches from heavy trampling and
grazing, altered plant composition, and reduced plant production
(Vankat and Major 1978, pp. 386-397; Ratliff 1985, pp. ii-iii).
Livestock grazing in the Sierra Nevada has been widespread for so
long that, in most places, no ungrazed areas are available to
illustrate the natural condition of the habitat (Kattelmann and Embury
1996, pp. 16-18). Dull (1999, p. 899) conducted stratigraphic pollen
analysis (identification of pollen in sedimentary layers) in mountain
meadows of the Kern Plateau, and found significant vegetation changes
attributable to sheep and cattle grazing by 1900 (though fire regime
change was also implicated; see below). This degradation is widespread
across the Sierra Nevada. Cooper 2006 (p. 1) reports that 50 to 80
percent of grazed meadows now dominated by dry meadow plants were
formerly wet meadows (Cooper 2006, p. 1).
Overgrazing has been associated with accelerated erosion and
gullying of
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meadows (Kattelmann 1996, p. 13), which leads to siltation and more
rapid succession of meadows. Grazing can cause erosion by disturbing
the ground, damaging and reducing vegetative cover, and destroying peat
layers in meadows, which lowers the groundwater table and summer flows
(Armour et al. 1994, pp. 9-12; Martin 2002, pp. 1-3; Kauffman and
Krueger 1984, pp. 431-434). Downcut channels, no longer connected to
the historic, wide floodplains of the meadow, instead are confined
within narrow, incised channels. Downstream, formerly perennial (year-
round) streams often become intermittent or dry due to loss of water
storage capacity in the meadow aquifers that formerly sustained them
(Lindquist et al. 1997, pp. 7-8). Many examples exist like the one at
Cottonwood Creek (in the Feather River watershed) where overgrazing of
meadow vegetation and soil erosion of streambanks led to meadow channel
incision (Linquist 2000, pp. 1-7; Odion et al. 1988, pp. 277-292,
Schoenherr 1992, pp. 167-227).
Heavy grazing can alter vegetative species composition and
contribute to lodgepole pine (Pinus contorta) invasion (Ratliff 1985,
pp. 33-36). Lowering of the water table facilitates encroachment of
conifers into meadows. Gully formation and lowering of water tables,
changes in the composition of herbaceous vegetation, increases in the
density of forested stands, and the expansion of trees into areas that
formerly were treeless have been documented in California Wilderness
areas and National Parks (Cole and Landres 1996, p. 171). This invasion
has been attributed to sheep grazing, though the phenomenon has been
observed on both ungrazed meadows and on meadows grazed continually
since about 1900 (Ratliff 1985, p. 35), suggesting an interaction with
other drivers (see ``Fire Management Regime Effects to Meadow
Habitats'' and ``Climate Effects to Meadow Habitat'' below).
Due to the long history (Menke et al. 1996, Ch. 22 pp. 1-52) of
livestock and packstock grazing in the Sierra Nevada and the lack of
historical Yosemite toad population size estimates, it is impossible to
establish a reliable quantitative estimate for the historical
significance and contribution of grazing on Yosemite toad populations.
However, because of the documented negative effects of livestock on
Yosemite toad habitat, and the documented direct mortality caused by
livestock, the decline of some populations of Yosemite toad has been
attributed to the effects of livestock grazing (Jennings and Hayes
1994, pp. 50-53; Jennings 1996, pp. 921-944). Because Yosemite toad
breeding habitat is in shallow waters at high elevation, the habitat is
believed to be more vulnerable to changes in hydrology caused by
grazing (Knapp 2002c, p. 1; Martin 2002, pp. 1-3; USFS et al. 2009, p.
62).
The influence of grazing on toad populations in recent history is
uncertain, despite more available data on land use and Yosemite toad
occurrence. In 2005, the USFS began a long-term study to assess the
effects of grazing on Yosemite toads (Allen Diaz et al. 2010, pp. 1-
45). The researchers assessed: (1) Whether livestock grazing under
SNFPA Riparian Standards and Guidelines has a measurable effect on
Yosemite toad populations and (2) effects of livestock grazing
intensity on key habitat components that affect survival and
recruitment of Yosemite toad populations. SNFPA standards and
guidelines limit livestock utilization of grass and grass-like plants
to a maximum of 40 percent (or a minimum 4-inch stubble height) (USDA
2004, p. 56). This study did not detect an effect from grazing activity
on young-of-year toad density or breeding pool occupancy, water
quality, or cover (when grazing under SNFPA Riparian Standards and
Guidelines) (Allen Diaz et al. 2010, p. 1).
However, the design of these studies did not include direct
measurements of toad survival (for example, mark-recapture analysis of
population trends), and the design was limited in numbers of years and
treatment replicates. It is plausible that for longer-lived species
with irregular female breeding activity over the time course of this
particular study, statistical power was not sufficient to discern a
treatment effect. Further, there may be a time lag between effect and
discernible impacts, and significant confounding variability in known
drivers such as interannual variation in climate.
Additionally, the experimental design in the Allen Diaz study
tested the hypothesis that forest management guidelines (at 40 percent
use threshold) were impacting toad populations, and this limited some
analyses and experimental design to sites with lower treatment
intensities. Researchers reported annual utilization by cattle ranging
from 10-48 percent, while individual meadow use ranged from 0-76
percent (the SNFPA allowable use is capped at 40 percent) (Allen Diaz
et al. 2010, p. 5). As a result of the study design, the Allen Diaz
study does not provide sufficient information on the impacts of grazing
on Yosemite toads above the prescribed management guidelines. It is
also not clear to what extent brief episodes of intense use (such as in
cattle gathering areas) have as negative impacts on toads, or over what
percentage of the grazed meadow landscape such heavier usage may occur.
The researchers observed significant variation in young-of-year
occupancy in pools between meadows and years, and within meadows over
years (Allen Diaz et al. 2010, p. 7). This variability would likely
mask treatment effects, unless the grazing variable was a dominant
factor driving site occupancy, and the magnitude of the effect was
quite severe. Further, Lind et al. (2011, pp. 12-14) report
statistically significant negative (inverse) relationships for tadpole
density and grazing intensity (tadpole densities decreased when percent
use exceeded between 30 and 40 percent). This result supports the
hypothesis that grazing at intensities approaching and above the 40
percent threshold can negatively affect Yosemite toad populations.
Allen Diaz et al. (2010, p. 2) found that toad occupancy is
strongly driven by meadow wetness (hydrology) and suggested attention
should focus on contemporary factors directly impacting meadow wetness,
such as climate, fire regime changes, and conifer encroachment (see
Factor A above). Lind et al. (2011, pp. 12-14) noted a positive
relationship between meadow dryness and livestock use (cattle prefer
drier meadows), and also found that the proportion of Yosemite toad-
occupied pools and tadpole and young-of-year densities declined in
drier sites (toads prefer wetter meadows). The researchers suggest that
this provides for some segregation of toad and livestock use in meadow
habitats, so that at least direct mortality threats may be mitigated by
behavioral isolation.
The available grazing studies focus on breeding habitat (wet
meadows) and do not consider impacts to upland habitats. The USFS
grazing guidelines for protection of meadow habitats of the Yosemite
toad include fencing breeding meadows, but they do not necessarily
protect upland habitat. Grazing removes vegetative cover, and surveys
have shown reductions in the number of Yosemite toads in an area after
the herbaceous cover was grazed (Martin 2008, p. 298). Grazing can also
degrade or destroy moist upland areas used as nonbreeding habitat by
Yosemite toads (Martin 2008, pp. 159), especially when nearby meadow
and riparian areas have been fenced to exclude livestock. Livestock may
also collapse rodent burrows used by Yosemite toads as cover and
hibernation sites (Martin 2008, p. 159) or disturb toads and
[[Page 24504]]
disrupt their behavior. Martin (2008, pp. 305-306) observed that
grazing significantly reduced vegetation height, and since these areas
are not protected by current grazing guidelines, deduced that cattle
grazing is having a negative effect on terrestrial life stage
survivorship in Yosemite toads. This problem was exacerbated as fenced
areas effectively shifted grazing activity to upland areas actively
used by terrestrial life stages of the Yosemite toad (Martin 2008, p.
306). Based on the limitations of the study as described above, we find
the initial results from Allen Diaz et al. (2010, pp. 1-45) to be
inconclusive to discern the impacts of grazing on Yosemite toad
populations rangewide.
Although we lack definitive data to assess the link between
Yosemite toad population dynamics and habitat degradation by livestock
grazing activity (see Factor E below), in light of the documented
impacts to meadow habitats (including effects on local hydrology) from
grazing activity in general, we consider this threat prevalent with
moderate impacts to the Yosemite toad and a potential limiting factor
in population recovery rangewide. In addition, given the potential for
negative impacts from heavy use, and the vulnerability of toad habitat
should grazing management practices change with new management plans,
we expect this threat to continue into the future.
Roads and Timber Harvest Effects to Meadow Habitat
Road construction and use, along with timber harvest activity, may
impact Yosemite toad habitat via fragmentation, ground disturbance, and
soil compaction or erosion (Helms and Tappeiner 1996, pp. 439-476).
These activities, similar to overgrazing, may lead to increased rates
of siltation and succession of wet meadows, contributing to the loss of
breeding habitats for the Yosemite toad.
Prior to the formation of National Parks and National Forests,
timber harvest was widespread and unregulated in the Sierra Nevada;
however, most cutting occurred below the current elevation range of the
Yosemite toad (University of California at Davis (UCD) UC 1996b, pp.
17-45). Between 1900 and 1950, most timber harvest occurred in old
growth forests on private land (UC 1996b, pp. 17-45). The majority of
roads in National Forests of the Sierra Nevada were built between 1950
and 1990, to support major increases in timber harvest on National
Forests and also at higher elevations (USDA 2001a, p. 445).
It is plausible to hypothesize that the majority of timber harvest,
road development, and associated management impacts (see ``Fire
Management Regime Effects to Meadow Habitats'' below) to Yosemite toads
would have taken place during this expansion period in the latter half
of the 20th century. However, the magnitude (and perhaps even whether
it is positive or negative) of this effect would likely be a function
of site-specific parameters, and the level of intensity of each
particular land use. In contrast to overharvest, it is also possible
that moderate harvest activity adjacent to meadow habitats could
benefit meadows and upland habitat by discouraging encroachment and
opening the forest canopy (Liang et al. 2010, p. 16). Despite this
possibility, there is no evidence that the current level of timber
harvest occurring within watersheds currently inhabited by the Yosemite
toad is adversely affecting habitat. Therefore the best available
scientific and commercial information does not indicate whether ongoing
road construction and maintenance or timber harvest are significant
threats to the Yosemite toad.
Fire Management Regime Effects to Meadow Habitats
Fire management refers to activities over the past century to
combat forest fires. Historically, it is known that American Indians
regularly burned the mountains (Parsons and Botti 1996, p. 29), and in
the latter 19th century, the active use of fire to eliminate tree
canopy in favor of forage plants continued by sheepherders (Kilgore and
Taylor 1979, p. 139). Beginning in the 20th century, land management in
the Sierra Nevada shifted to focus on fire suppression as a guiding
policy (UC 2007, p. 10).
Long-term fire suppression has influenced forest structure and
altered ecosystem dynamics in the Sierra Nevada. In general, the time
between fires is now much longer than it was historically, and live and
dead fuels are more abundant and continuous (USDA 2001a, p. 35). It is
not clear how this has precisely affected Yosemite toad populations;
however Liang et al. (2010, p. 16) observed that toads were less likely
to occur in areas where the fire regime was significantly altered from
historical conditions, and suggested that the toads are affected by
some unknown or unmeasured factors related to fire management.
Evidence indicates that fire plays a significant role in the
evolution and maintenance of meadows of the Sierra Nevada. Under
natural conditions, conifers are excluded from meadows by fire and
saturated soils. Small fires thin and/or destroy encroaching conifers,
while large fires are believed to determine the meadow-forest boundary
(Vankat and Major 1978, p. 394; Parsons and DeBenedetti 1979, pp. 29-
31). Fire is thought to be important in maintaining open aquatic and
riparian habitats for amphibians in some systems (Russel et al. 1999,
pp. 374-384), and fire suppression may have thereby contributed to
conifer encroachment on meadows (Chang 1996, pp. 1071-1099; NPS 2002,
p. 1).
While no definitive studies have confirmed a link between fire
management and rangewide population decline of the Yosemite toad,
circumstantial evidence to date suggests that historic fire suppression
has been a factor underlying meadow encroachment that has reduced the
suitability of these areas to sustain the life history of the Yosemite
toad. Given this link and based on the best available information, we
find it likely that habitat modification due to reduced fire frequency
is an extant threat to Yosemite toad habitat, acting with moderate
prevalence.
Recreation Effects to Meadow Habitat
Recreational activities take place throughout the Sierra Nevada,
and they can have significant negative impacts on wildlife and their
habitats (USDA 2001a, pp. 221, 453-500). Recreation can cause
considerable impact to western U.S. Wilderness Areas and National Parks
even with light use, with recovery only occurring after considerable
periods of non-use (USFS et al. 2009, p. 66). Heavy foot traffic in
riparian areas tramples vegetation, compacts soils, and can physically
damage streambanks. Trails (foot, horse, bicycle, or off-highway motor
vehicle) compact the soil, displace vegetation, and increase erosion,
thereby potentially lowering the water table (Kondolph et al. 1996, pp.
1009-1026).
Packstock use has similar effects to those discussed for livestock
grazing, although this risk factor is potentially more problematic as
this land use typically takes place in more remote and higher elevation
areas occupied by Yosemite toads, and packstock tend to graze in many
of the same locations that the toads prefer (USFS et al. 2009, p. 65).
Currently, there are very few studies on the effects of packstock
grazing on amphibians, especially in the Sierra Nevada. It is not clear
how well studies on livestock grazing can be extrapolated to packstock,
and even then, shorter-term experiments may not show effects if
landscapes have already
[[Page 24505]]
been pushed beyond a threshold of effect (Brooks 2012, pers. comm.).
However, current guidelines in the National Parks limit trips to 20-25
animals, regulated under conditional use permits (Brooks 2012, pers.
comm.). In general, National Parks and commercial users are reducing
their usage, so packstock impacts, if they occur, are declining within
the National Parks (Berlow 2012, pers. comm.).
The effects of recreational activities on the Yosemite toad are not
quantified, but they may have impacts in certain areas and under
certain conditions. For example, where foot traffic or vehicle activity
adjacent to occupied meadows is more prevalent, erosion and channel
incision could result. The cumulative impact to the species from
localized threats associated with recreational impacts is not possible
to quantify, but we do know that recreation is the fastest growing use
of National Forests (USDA 2001a, pp. 453-500). The relative sensitivity
of high-elevation sites to recreational use makes them vulnerable to
disturbance, and the significance of this impact is expected to
increase into the future as recreational use continues to increase.
Nevertheless, collectively at this time, we consider recreational
activities to be a low prevalence threat across the range of the
Yosemite toad.
Dams and Water Diversions Effects to Meadow Habitat
Diversion and irrigation ditches form a vast network that altered
local and regional stream hydrology in the Sierra Nevada (SNEP 1996, p.
120). Several artificial lakes are located in or above Yosemite toad
habitat, most notably Edison, Florence, Huntington, Courtright, and
Wishon Reservoirs. By altering the timing and magnitude of water flows,
these reservoirs have caused changes in hydrology that may have altered
Yosemite toad habitat. Changes in water flows have increased water
levels upstream of the reservoirs, which may have reduced the
suitability of shallow water habitats necessary for egg laying and
allowed fish competitors into those habitats. Moreover, water level
declines caused by drawdown of reservoirs can lead to the mortality of
eggs and tadpoles by stranding and desiccation.
The artificial lakes (reservoirs) mentioned above were probably
created within, and inundated, Yosemite toad habitat, and most native
Sierra Nevada amphibians cannot live in or move through reservoirs
(Jennings 1996, pp. 921-944). Therefore, reservoirs represent both a
loss of habitat and a barrier to dispersal and gene flow. These factors
have likely contributed to the decline of the Yosemite toad and
continue to pose a risk to the species. Impacts due to increasing
effects from climate change, or new water supply development in
response to such effects, may exacerbate this risk in the future. The
contribution of reservoir construction and operation to population
losses was likely of high historical significance in these developed
areas, but less so in the current extent of the Yosemite toad's
(remnant) range. Therefore, currently, we consider this threat to be of
low prevalence to the Yosemite toad across its range.
Climate Effects to Meadow Habitat
Different studies indicate that multiple drivers are behind the
phenomenon of conifer encroachment on meadows. The first factor
affecting the rate of conifer encroachment on meadow habitats, fire
suppression, was discussed above. Climate variability is another factor
affecting the rate of conifer encroachment on meadow habitats. A study
by Franklin et al. (1971, p. 215) concluded that fire had little
influence on meadow maintenance of their study area, while another
study concluded that climate change is a more likely explanation for
encroachment of trees into the adjacent meadow at their site, rather
than fire suppression or changes in grazing intensity (Dyer and
Moffett, 1999, pp. 444).
Climatic variability is strongly correlated with encroachment of
dry subalpine meadows (Jakubos and Romme 1993, p. 382). In the Sierra
Nevada, most lodgepole pine seedlings become established during years
of low snowpack when soil meadow moisture is reduced (Wood 1975, p.
129). The length of the snow-free period may be the most critical
variable in tree invasion of subalpine meadows (Franklin et al. 1971,
pp. 222), with the establishment of a good seed crop, followed by an
early snowmelt, resulting in significant tree establishment. It is
apparent that periods of low snowpack and early melt may in fact be
necessary for seedling establishment (Ratliff, 1985, p. 35). Millar et
al. (2004, p. 181) reported that increased temperature, coupled with
reduced moisture availability in relation to large-scale temporal
shifts in climate, facilitated the invasion of 10 subapline meadows
studied in the Sierra Nevada.
Our analyses under the Act include consideration of ongoing and
projected changes in climate. The terms ``climate'' and ``climate
change'' are defined by the Intergovernmental Panel on Climate Change
(IPCC). ``Climate'' refers to the mean and variability of different
types of weather conditions over time, with 30 years being a typical
period for such measurements, although shorter or longer periods also
may be used (IPCC 2007, p. 78). The term ``climate change'' thus refers
to a change in the mean or variability of one or more measures of
climate (for example, temperature or precipitation) that persists for
an extended period, typically decades or longer, whether the change is
due to natural variability, human activity, or both (IPCC 2007, p. 78).
Various types of changes in climate can have direct or indirect effects
on species. These effects may be positive, neutral, or negative, and
they may change over time, depending on the species and other relevant
considerations, such as the effects of interactions of climate with
other variables (for example, habitat fragmentation) (IPCC 2007, pp. 8-
14, 18-19). In our analyses, we use our expert judgment to weigh
relevant information, including uncertainty, in our consideration of
various aspects of climate change.
For the Sierra Nevada ecoregion, climate models predict that mean
annual temperatures will increase by 1.8 to 2.4 [deg]C (3.2 to 4.3
[deg]F) by 2070, including warmer winters with earlier spring snowmelt
and higher summer temperatures (PRBO 2011, p. 18). Additionally, mean
annual rainfall is projected to decrease from the current average by
some 9.2-33.9 cm (3.6-13.3 in) by 2070 (PRBO 2011, p. 18). However,
projections have high uncertainty and one study predicts the opposite
effect (PRBO 2011, p. 18). Snowpack is, by all projections, going to
decrease dramatically (following the temperature rise and increase in
precipitation falling as rain) (PRBO 2011, p. 19). Higher winter
streamflows, earlier runoff, and reduced spring and summer streamflows
are projected, with increasing severity in the southern Sierra Nevada
(PRBO 2011, pp. 20-22).
Snow-dominated elevations from 2,000-2,800 m (6,560-9,190 ft) will
be the most sensitive to temperature increases (PRBO 2011, p. 23).
Meadows fed by snowmelt may dry out or be more ephemeral during the
non-winter months (PRBO 2011, p. 24). This pattern could influence
ground water transport, and springs may be similarly depleted, leading
to lower water levels in available breeding habitat and decreased area
of suitable habitat for rearing tadpoles of Yosemite toads.
Historically, drought has contributed to the decline of the
Yosemite toad (Kagarise Sherman and Morton 1993, p. 186; Jennings and
Hayes 1994, pp. 50-53). Climate change itself may also have contributed
to that decline if greenhouse
[[Page 24506]]
gas emissions have contributed to the intensity of droughts and
severity of occasional extreme cold winters during the last several
decades. Extended and more severe droughts pose an ongoing, rangewide
risk to the species. Less water, specifically less water as snow, means
less and lower quality habitat for Yosemite toads. However, it is
difficult to discern the effects of climate change on Yosemite toad
populations without focused, long-term study.
Davidson et al. (2002, p. 1598) analyzed geographic decline
patterns in Yosemite toad. They compared known areas of extirpation
against a hypothesized model for climate change that would predict
greater numbers of extirpations at lower altitudes, and in more
southern latitudes. The researchers did not observe a pattern in the
available historic data to support the climate change hypothesis as a
driver of historic population losses, although they acknowledge that
climate change may be a contributor in more complex or subtle ways.
Additionally, this study was limited by small sample size, and it is
possible that climate change effects on the Yosemite toad (a long-lived
species) may not become evident for many years (USFS et al. 2009, p.
48). Finally, Davidson et al. (2002, p. 1598) did find an increase in
occupancy with elevation (greater densities of populations at
altitude), and it is suggested that this observation is consistent with
a pattern that would fit a response to climate change (USFS et al.
2009, p. 48). However, this observation would also be consistent if the
features of these particular habitats (such as at higher elevation)
were more suited to the special ecological requirements of the toad, or
if other stressors acting on populations at lower elevations were
responsible for the declines. We therefore find these results
inconclusive.
The breeding ecology and life history of the Yosemite toad are that
of a habitat specialist, as it utilizes pool and meadow habitats during
the onset of snowmelt and carefully times its reproduction to fit
available conditions within ephemeral breeding sites. The most striking
documented declines in Yosemite toad populations in the historical
record are correlated with extreme climate episodes (drought) (Kagarise
Sherman and Morton 1993, pp. 186-198). Given these observations, it is
likely that climate change (see also discussion in mountain yellow-
legged frog's Summary of Factors Affecting the Species, under Factor E)
poses a significant risk to the Yosemite toad now and in the future. It
is quite possible that these impacts are occurring currently, and have
occurred over the last few decades. However, it is difficult in short
time intervals to discern the degree of effect from climate change
within the variability of natural climate cycles.
In summary, based on the best available scientific and commercial
information, we consider the threats of destruction, modification, and
curtailment of the species' habitat and range to be significant ongoing
threats to the Yosemite toad. The legacy effects of past land uses have
altered meadow communities through the mechanism of stream incision by
permanently reducing habitat quantity and quality unless active and
costly restoration is implemented. Climate change is a current threat
of high magnitude. Threats considered of moderate magnitude include
livestock grazing and fire management regime. Threats considered
currently low magnitude include roads and timber harvest, dams and
water diversions, and recreational land uses.
Factor B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
We do not have any scientific or commercial information to indicate
that overutilization for commercial, recreational, or scientific
purposes poses a threat to the Yosemite toad. There is no known
commercial market for Yosemite toads, and there is also no documented
recreational or educational use for Yosemite toads.
Scientific research may cause some stress to Yosemite toads through
disturbance and disruption of behavior, handling, and injuries
associated with marking individuals. This activity has resulted in the
known death of a few individuals through accidental trampling (Green
and Kagarise Sherman 2001, pp. 92-103), irradiation from radioactive
tags (Karlstrom 1957, pp. 187-195), and collection for museum specimens
(Jennings and Hayes 1994, pp. 50-53). However, there is currently
relatively little research effort on this species, and scientists as a
general rule take actions to mitigate harm to their study species.
Therefore, scientific research is not a threat to the Yosemite toad. It
is anticipated that further research into the genetics and life history
of the Yosemite toad and broader methodological censuses will provide a
net conservation benefit to this under-studied species.
Based on the best available scientific and commercial information,
we do not consider the overutilization for commercial, recreational,
scientific, or educational purposes to be a threat to the Yosemite
toad.
Factor C. Disease or Predation
Predation
Prior to the trout stocking of high Sierra Nevada lakes, which
began over a century ago, fish were entirely absent from most of this
region (Bradford 1989, pp. 775-778). Observations regarding the effects
of introduced fishes on the Yosemite toad are mixed. However, re-
surveys of historical Yosemite toad sites have shown that the species
has disappeared from several lakes where they formerly bred, and these
areas are now occupied by fish (Stebbins and Cohen 1995, pp. 213-215;
Martin 2002, p. 1).
Drost and Fellers (1994, pp. 414-425) suggested that Yosemite toads
are less vulnerable to fish predation than frogs because they breed
primarily in ephemeral waters that do not support fish. Further,
Jennings and Hayes (1994, pp. 50-53) stated that the palatability of
Yosemite toad tadpoles to fish predators is unknown, but often assumed
to be low based on the unpalatability of western toads (Drost and
Fellers 1994, pp. 414-425; Kiesecker et al. 1996, pp. 1237-1245), to
which Yosemite toads are closely related. Grasso (2005, p. 1) observed
brook trout swimming near, but the trout ignored Yosemite toad
tadpoles, suggesting that tadpoles are unpalatable. The study also
found that subadult Yosemite toads were not consumed by brook trout
(Grasso 2005, p. 1), although the sublethal effects of trout
``sampling'' (mouthing and ejecting tadpoles) and the palatability of
subadults to other trout species are unknown. Martin (2002, p. 1)
observed brook trout preying on Yosemite toad tadpoles, and also saw
them ``pick at'' Yosemite toad eggs (which later became infected with
fungus). In addition, metamorph western toads have been observed in
golden trout stomach contents (Knapp 2002c, p. 1). Nevertheless, Grasso
et al. (2010, p. 457) concluded that early life stages of the Yosemite
toad likely possess chemical defenses that provide sufficient
protection from native trout predation.
The observed predation of Yosemite toad tadpoles by trout (Martin
1992, p.1) indicates that introduced fishes may pose a predation risk
to the species in some situations, which may be accentuated during
drought years. At a site where Yosemite toads normally breed in small
meadow ponds, they have been observed to successfully switch breeding
activities to stream habitat containing fish during years of low water
(Strand 2002, p. 1). Thus,
[[Page 24507]]
drought conditions may increase the toads' exposure to predatory fish,
and place them in habitats where they compete with fish for
invertebrate prey. Additionally, although the number of lake breeding
sites used by Yosemite toads is small relative to the number of
ephemeral sites, lake sites may be especially important because they
are more likely to be habitable during years with low water (Knapp
2002c, p. 1).
Overall, the data and available literature suggest that direct
mortality from fish predation is likely not an important factor driving
Yosemite toad population dynamics. This does not discount other
indirect impacts, such as the possibility that fish may be effective
disease vectors (see below). Yosemite toad use of more ephemeral
breeding habitats (which are less habitable to fish species as they
cannot tolerate drying or freezing) minimizes the interaction of fish
and toad tadpoles. Further, where fish and toads co-occur, it is
possible that food depletion (outcompetition) by fish negatively
affects Yosemite toads (USFS et al. 2009, p. 58).
Other predators may also have an effect on Yosemite toad
populations. Kagarise Sherman and Morton (1993, p. 194) reported
evidence of toad predation by common ravens (Corvus corax) and
concluded this was the responsible factor in the elimination of toads
from one site. These researchers also confirmed, as reported in other
studies, predation on Yosemite toad by Clark's nutcrackers (Nucifraga
columbiana). The significance of avian predation may increase if the
abundance of common ravens within the current range of the Yosemite
toad increases as it has in nearby regions (Camp et al. 1993, p. 138;
Boarman et al. 1995, p. 1; Kelly et al. 2002, p. 202). However, the
degree to which avian predation may be affecting Yosemite toad
populations has not been quantified.
Disease
Although not all vectors have been confirmed in the Sierra Nevada,
introduced fishes, humans, pets, livestock, packstock, vehicles, and
wild animals may all act to facilitate disease transmission between
amphibian populations. Infection of both fish and amphibians by a
common disease has been documented with viral (Mao et al. 1999, pp. 45-
52) and fungal pathogens in the western United States (Blaustein et al.
1994b, pp. 251-254). Mass die-offs of amphibians in the western United
States and around the world have been attributed to Bd fungal
infections of metamorphs and adults (Carey et al. 1999, pp. 1-14),
Saprolegnia fungal infections of eggs (Blaustein et al. 1994b, pp. 251-
254), ranavirus infections, and bacterial infections (Carey et al.
1999, pp. 1-14).
Various diseases are confirmed to be lethal to Yosemite toads
(Green and Kagarise Sherman 2001, pp. 92-103), and recent research has
elucidated the potential role of Bd infection as a threat to Yosemite
toad populations (Dodge and Vredenburg 2012, p.1). These various
diseases and infections, in concert with other factors, have likely
contributed to the decline of the Yosemite toad (Kagarise Sherman and
Morton 1993, pp. 193-194), and may continue to pose a risk to the
species (Dodge and Vredenburg 2012, p. 1).
Die-offs in Yosemite toad populations have been documented in the
literature, and an interaction with diseases in these events has been
confirmed. However, no single cause has been validated by field
studies. Tissue samples from dead or dying adult Yosemite toads and
healthy tadpoles were collected during a die-off at Tioga Pass Meadow
and Saddlebag Lake and analyzed for disease (Green and Kagarise Sherman
2001, pp. 92-103). Six infections were found in the adults, including
infection with Bd, bacillary bacterial septicemia (red-leg disease),
Dermosporidium (a fungus), myxozoa spp. (parasitic cnidarians),
Rhabdias spp. (parasitic roundworms), and several species of trematode
(parasitic flatworms). Despite positive detections, no single
infectious disease was found in more than 25 percent of individuals,
and some dead toads showed no signs of infection to explain their
death. Further, no evidence of infection was found in tadpoles. A meta-
analysis of red-leg disease also revealed that the disease is a
secondary infection that may be associated with a suite of different
pathogens, and so actual causes of decline in these instances were
ambiguous (Kagarise Sherman and Morton 1993, p. 194). The authors
concluded that the die-off was caused by suppression of the immune
system caused by an undiagnosed viral infection or chemical
contamination that made the toads susceptible to the variety of
diagnosed infections.
Saprolegnia ferax, a species of water mold that commonly infects
fish in hatcheries, caused a massive lethal infection of eggs of
western toads at a site in Oregon (Blaustein et al. 1994b, pp. 252). It
is unclear whether this event was caused by the introduction of the
fungal pathogen via fish stocking, or if the fungus was already present
and the eggs' ability to resist infection was inhibited by some unknown
environmental factor (Blaustein et al. 1994b, pp. 253). Subsequent
laboratory experiments have shown that the fungus could be passed from
hatchery fish to western toads (Kiesecker et al. 2001, pp. 1064-1070).
Fungal growth on Yosemite toad eggs has been observed in the field, but
the fungus was not identified and it was unclear whether the fungus was
the source of the egg mortality (Kagarise Sherman 1980, p. 46). Field
studies conducted in Yosemite National Park found that an undetermined
species of water mold infected only the egg masses that contained dead
embryos of Yosemite toads (Sadinski 2004, pp. 33-34). The researchers
also observed that the water mold became established on egg masses only
after embryo death, and subsequently spread, causing the mortality of
additional embryos of Yosemite toads.
Sadinski (2004, p. 35) discovered that mortality of Yosemite toad
embryos may be attributed to an unidentified species of a free-living
flatworm (Turbellaria spp.). In Yosemite National Park, these worms
were observed to penetrate Yosemite toad egg masses and feed directly
on the embryos. In some locations, Turbellaria spp. reached such large
densities that they consumed all the embryos within a Yosemite toad egg
mass. Predation also facilitated the colonization and spread of water
mold on egg masses, leading to further embryo mortality. Further
studies would be needed to determine which species of Turbellaria feeds
on Yosemite toad eggs, and the extent of this impact on Yosemite toad
populations.
Until recently, the contribution of Bd infection to Yosemite toad
population declines was relatively unknown. Although the toad is
hypothetically susceptible due to co-occurrence with the mountain
yellow-legged frog, it is suspected that the spread and growth of Bd in
the warmer pool habitats, occupied for a much shorter time relative to
the frog, renders individuals less prone to epidemic outbreaks (USFS et
al. 2009, p. 50). Fellers et al. (2011, p. 391) documented the
occurrence of Bd infection in Yosemite National Park toads over at
least a couple of decades, and they note population persistence in
spite of the continued presence of the pathogen. In a survey of 196
museum specimens, Dodge and Vredenburg (2012, p. 1) report the first
presence of Bd infection in Yosemite toads beginning in 1961, with the
pathogen becoming highly prevalent during the recorded declines of the
late 1970s, before it peaked in the 1990s at 85 percent positive
incidence. In live specimen sampling, Dodge and Vredenburg (2012, p. 1)
collected 1,266 swabs of Yosemite toads between 2006 and 2011, and
found Bd infection
[[Page 24508]]
intensities at 17-26 percent (with juvenile toads most affected). The
results from these studies support the hypothesis that Bd infection and
chytridiomycosis have played an important role in Yosemite toad
population dynamics over the period of their recent recorded decline.
Carey (1993, pp. 355-361) developed a model to explain the
disappearance of boreal toads (Bufo boreas boreas) in the Rocky
Mountains, suggesting immune system suppression from extreme winter
stress (``winter stress syndrome'') could have contributed to the
decline in that species. This model may also fit Yosemite toad die-offs
observed by Kagarise Sherman and Morton (1993, pp. 186-198), given the
close relationship between the two toads, and their occupation of
similar habitats. However, an analysis of immune system suppression and
the potential role of winter stress relative to Yosemite toad
population trends is not available at this time. Yet, the decline
pattern observed in the Carey study is mirrored by the pattern in the
Yosemite toad (heavy mortality exhibited in males first) (Knapp 2012,
pers. comm.). This observation, in concert with the recent results from
museum swabs (Dodge and Vredenburg 2012, p. 1), provides a correlative
link to the timing of the recorded Yosemite toad declines and Bd
infection intensities.
Although disease as a threat factor to the Yosemite toad is
relatively less documented, there is evidence for Bd infection related
to historical die-offs in Yosemite toads. Much of the historic research
documenting Yosemite toad declines predated our awareness of Bd as a
major amphibian pathogen. Additionally, the life history of the
Yosemite toad, as a rapid breeder during early snowmelt, limits the
opportunities to observe population crashes in the context of varied
environmental stressors. Currently available evidence indicates that Bd
was likely a significant factor contributing to the recent historical
declines observed in Yosemite toad populations (Dodge and Vredenburg
2012, p. 1). Although infection intensities are currently lower than
some peak historic measurements, this threat remains a potential factor
to date that may continue to reduce survival through metamorphosis, and
therefore recruitment to the breeding population (Knapp 2012, pers.
comm.). Additionally, the interaction of disease and other stressors,
such as climate extremes, is not well understood in the Yosemite toad.
Research does suggest that the combination of these threats represents
a factor in the historical decline of the species (Kagarise Sherman and
Morton 1993, p. 186).
In summary, based on the best available scientific and commercial
information, we consider disease to be a threat to the Yosemite toad
that has a moderate, ongoing effect on populations of the species
rangewide. The threat most specifically includes the amphibian
pathogen, Bd. Based on the best available scientific and commercial
information, we are uncertain about the impacts of avian predation on
Yosemite toads at this time, and therefore do not consider it to be a
listing factor. Although definitive empirical data quantifying the
contribution of disease to Yosemite toad population declines are not
currently available, the concurrence of population declines with the
prevalence and spread of Bd across the Sierra Nevada support the
assertion that disease has played a role in the observed trend.
Further, Bd infection, even at lower intensities, may interact with
climate extremes and continue to depress recruitment of yearling and
subadult Yosemite toads to breeding Yosemite toad populations. We
suspect this threat was historically significant, that it is currently
having a moderate influence on toad populations, and we expect it to be
a future concern.
Factor D. The Inadequacy of Existing Regulatory Mechanisms
In determining whether the inadequacy of regulatory mechanisms
constitutes a threat to the Yosemite toad, we analyzed the existing
Federal and State laws and regulations that may address the threats to
the species or contain relevant protective measures. Regulatory
mechanisms are typically nondiscretionary and enforceable, and may
preclude the need for listing if such mechanisms are judged to
adequately address the threat(s) to the species such that listing is
not warranted. Conversely, threats on the landscape are not addressed
by existing regulatory mechanisms where the existing mechanisms are not
adequate (or not adequately implemented or enforced).
We discussed the applicable State and Federal laws and regulations,
including the Wilderness Act, NFMA above (see Factor D discussion for
mountain yellow-legged frog complex). In general, the same
administrative policies and statutes are in effect for the Yosemite
toad. This section additionally addresses regulatory mechanisms with a
specific emphasis on the Yosemite toad.
Taylor Grazing Act of 1934
In response to overgrazing of available rangelands by livestock
from the 1800s to the 1930s, Congress passed the Taylor Grazing Act in
1934 (43 U.S.C. 315 et seq.). This action was an effort to stop the
damage to the remaining public lands as a result of overgrazing and
soil depletion, to provide coordination for grazing on public lands,
and to attempt to stabilize the livestock industry (Meehan and Platts
1978, p. 275; Public Lands Council et al. v. Babbitt Secretary of the
Interior et al. (167 F. 3d 1287)). Although passage of the Taylor
Grazing Act resulted in reduced grazing in some areas, it did not
reduce grazing severity, and localized use remained high, precluding
regeneration of many meadow areas (Beesley 1996, p. 14; Menke et al.
1996, p. 14; Public Lands Council et al. v. Babbitt Secretary of the
Interior et al. (167 F. 3d 1287)).
Existing Federal and State laws and regulatory mechanisms currently
offer some level of protection for the Yosemite toad. Specifically,
these include the Wilderness Act, the NFMA, the SNFPA, and the FPA (see
Factor D discussion for mountain yellow-legged frog complex). Based on
the best available scientific and commercial information, we do not
consider the inadequacy of existing regulatory mechanisms to be a
threat to the Yosemite toad.
Factor E. Other Natural or Manmade Factors Affecting Its Continued
Existence
The Yosemite toad is sensitive to environmental change or
degradation due to its life history, biology, and existence in
ephemeral habitats characterized by climate extremes and low
productivity. It is also sensitive to anthropogenically influenced
factors. For example, contaminants, acid precipitation, ambient
ultraviolet radiation, and climate change have been implicated as
contributing to amphibian declines (Corn 1994, pp. 62-63; Alford and
Richards 1999, pp. 2-7). These factors are discussed in the context of
the mountain yellow-legged frog above (see Factor E discussion for
mountain yellow-legged frog complex), and are largely applicable to the
Yosemite toad. The following discussion will focus on potential threat
factors specifically studied in the Yosemite toad, or areas where the
prevalence of the threat may differ based on the unique life history,
population status, demographics, or biological factors specific to
Yosemite toad populations.
Contaminants
The Yosemite toad is likely exposed to a variety of pesticides and
other chemicals throughout its range. This includes those imported via
aerial drift and precipitation (see ``Contaminants''
[[Page 24509]]
discussion for mountain yellow-legged frog complex). But, given their
life history that includes significant time in upland habitats, there
are also locally applied pesticides that may have more of an impact on
the terrestrial life stages of Yosemite toads. In order of their
application rate, the most commonly used locally applied pesticides for
forest resource management are: glyphosate, triclopyr, clopyralid,
hexazinone, aminopyralid, chlorsulfuron, imazapyr, and aluminum
phosphide (applied to rodent burrows) (USFS et al. 2009, p. 63).
Large amounts of ammonia-based fire retardants and surfactant-based
fire-suppressant foams, including ammonium phosphate, ammonium sulfate,
and sodium ferrocyanide, are applied to areas managed by the USFS
(National Forests and Wilderness Areas) that may be inhabited by
Yosemite toads when wildfires occur within their range (USFS et al.
2009, p. 54). Fire retardant chemicals contain nitrogen compounds and
surfactants. Applied surfactants and dyes include: R-11, Hasten,
Syltac, highlight blue, bas-oil red, and colorfast purple (USFS et al.
2009, p. 63). Laboratory tests of these chemicals have shown that they
cause mortality in fish and aquatic invertebrates (Hamilton et al.
1996, pp. 132-144); similar effects are possible in amphibians. Calfee
and Little (2003, pp. 1529-1530) report that southern leopard frogs
(Rana sphenocephala) and boreal toads (Bufo boreas) are more tolerant
than rainbow trout (Oncorhynchus mykiss) to fire retardant chemicals.
However, the acute toxicity of some compounds is enhanced by
ultraviolet light, which may harm amphibians at environmentally
relevant concentrations. Therefore, if fire retardant chemicals are
dropped in or near Yosemite toad habitat, they may have negative
effects on individual toads. Yosemite toad populations span wilderness
areas and sparsely vegetated, high-elevation habitats. As fire is
infrequent in these areas, fire retardant chemicals are likely not a
threat through much of the species' range (USFS et al. 2009, p. 55).
The risk to Yosemite toad from locally applied pesticides,
surfactants, and dyes is not known. However, most of the use of these
chemicals also largely occurs below the current elevational range of
the toad, so this risk factor is likewise limited in scale.
The effect of contamination from other environmental pollutants is
not well-studied. Preliminary research indicates that Yosemite toad
tadpoles in grazed areas take longer to metamorphose and produce
smaller metamorphs than those in areas being rested from grazing,
potentially due to high bacterial and nutrient levels in the grazed
areas (Martin 2002, pp. 1-3; Martin 2008, p. 157). Finally, water
quality may be affected by the introduction of chemicals and wastes
from camp use (USFS et al. 2009, p. 68), which would logically have
greater influence on the more aquatic life stages. However, given the
early season breeding for this species, the coincidence of recreational
use wastes and tadpoles is likely relatively minor.
Acid precipitation has been hypothesized as a cause of amphibian
declines (including toads) in the Sierra Nevada because waters there
are extremely low in acid-neutralizing capacity, and therefore
susceptible to changes in water chemistry due to acidic deposition
(Bradford et al. 1994b, pp. 155-161). In addition to raising the
acidity of water bodies, acid deposition may also cause increases in
dissolved aluminum (from soils), which may be toxic to amphibians
(Bradford et al. 1992, 271-275). In laboratory experiments (Bradford et
al. 1992, pp. 369-377; Bradford and Gordon 1992, pp. 75-76), high
acidity and high aluminum concentrations did not have significant
effects on survival of Yosemite toad embryos or newly hatched tadpoles.
However, at pH 5.0 and at high aluminum concentrations, Yosemite toad
embryos hatched earlier and the tadpoles showed a reduction in body
size.
In a complementary field study of 235 amphibian breeding sites,
Bradford et al. (1994, pp. 155-161) concluded that acid precipitation
is an unlikely cause of decline in Yosemite toad populations. However,
researchers suggest this risk factor should still be considered in
conservation efforts because of the possibility of sublethal effects,
of its interaction with other factors, and of the potential for more
severe acid deposition in the future (Bradford et al. 1992, p. 375;
USFS et al. 2009, p. 44). Overall, we consider acid deposition a low
risk to the species at this time, and likely not a significant threat
into the future (see discussion under Factor E for mountain yellow-
legged frogs above).
In summary, a number of studies have investigated the potential
threats of a number of contaminants, such as pesticides, fire
retardants, and acid precipitation. Based on the best available
commercial and scientific information, we do not believe that
contaminants pose a significant threat to populations of the Yosemite
toad.
Ultraviolet Radiation
Ambient UV-B radiation has increased at north temperate latitudes
in the past 2 decades (Adams et al. 2001, pp. 519-525). Ambient levels
of UV-B were demonstrated to cause significant decreases in survival of
western toad eggs in field experiments (Blaustein 1994, pp. 32-39). In
a laboratory experiment (Kats et al. 2000, pp. 921-931), western toad
metamorphs exposed to levels of UV-B below those found in ambient
sunlight showed a lower alarm response to chemical cues of injured
toads than metamorphs that were completely shielded from UV-B. This
indicates that ambient levels of UV-B may cause sublethal effects on
toad behavior that could increase their vulnerability to predation. In
a field experiment (Kiesecker and Blaustein 1995, pp. 11049-11052), the
combined effects of exposure to ambient levels of UV-B radiation and
exposure to a pathogenic fungus (Saprolegnia) were shown to cause
significantly higher mortality of western toad embryos than either
factor alone.
Sadinski et al. (1997, pp. 1-8) observed a high percentage of
embryo mortality in Yosemite toads at six breeding sites in Yosemite
National Park, but in a subsequent field experiment this mortality did
not appear to be related to UV-B (Sadinski 2004, p. 37). In spatial
analyses of extant and extinct populations, higher elevation was
positively correlated with extant Yosemite toad populations. This is
counter to what would be expected if UV-B were the primary cause of
decline (Davidson 2002, p. 15), as sites at higher elevations would be
expected to receive more solar radiation due to the thinner atmosphere.
UV-B at high elevations in the Sierra Nevada has increased less than 5
percent in the past several decades (Jennings 1996, pp. 921-944). These
data further indicate that UV-B has likely not contributed
significantly to the decline of Yosemite toads. Based on the best
available commercial and scientific information, this threat factor is
currently considered a low risk to the species.
Climate Change Effects on Individuals
As discussed above in Factor A, climate change can result in
detrimental impacts to Yosemite toad habitat. Climate variability could
also negatively impact populations through alteration of the frequency,
duration, and magnitude of either droughts or severe winters (USFS et
al. 2009, p. 47). Yosemite toads breed and their tadpoles develop in
shallow meadow and ephemeral habitats, where mortality from
[[Page 24510]]
desiccation and freezing can be very high, often causing complete loss
of an annual cohort (USFS et al. 2009, p. 10). Kagarise Sherman and
Morton (1993, pp. 192-193) documented in a long-term population study
that Yosemite toad hatching success and survival were subject to a
balance between the snowpack water contribution to breeding pools and
the periodicity and character of breeding season storms and post-
breeding climate (whether it is cold or warm). When it is too cold,
eggs and tadpoles are lost to freezing. This poses a risk as earlier
snowmelt is expected to cue breeding earlier in the year, exposing
young tadpoles (or eggs) to killing frosts in more variable conditions
of early spring (Corn 2005, p. 60). When it is too warm, tadpoles are
lost to pool desiccation. Alterations in the annual and seasonal
hydrologic cycles that influence water volume and persistence in
Yosemite toad breeding areas can thereby impact breeding success. The
threat of climate change on individuals is significant, and is of high
prevalence now and into the future.
Other Sources of Direct and Indirect Mortality
Direct and indirect mortality of Yosemite toads has occurred as a
result of livestock grazing. Recently metamorphosed (juvenile) toads
congregate in large numbers in mesic meadow habitats, and are at
highest risk for trampling because their presence coincides with
grazing activity (USFS et al. 2009, p. 61). Cattle have been observed
to trample Yosemite toad eggs, and new metamorphs and subadult toads
can fall into deep hoof prints and die (Martin 2008, p. 158). Martin
(2008, p. 158) also witnessed some 60 subadult and metamorph toad
deaths during the movement of 25 cattle across a stream channel
bordered by willows within a meadow complex. Adult Yosemite toads
trampled to death by cattle have also been observed (Martin 2002, pp.
1-3). This risk factor is likely of sporadic significance, and is of
greatest concern where active grazing allotments coincide with breeding
meadows. However, it is difficult to determine the degree of this
impact without quantitative data.
Trampling and collapse of rodent burrows by recreationists, pets,
and vehicles could lead to direct mortality of terrestrial life stages
of the Yosemite toad. Recreational activity may also disturb toads and
disrupt their behavior (Karlstrom 1962, pp. 3-34). Recreational anglers
may be a source of introduced pathogens and parasites, and they have
been observed using toads and tadpoles as bait (USFS et al. 2009, p.
66). However, Kagarise Sherman and Morton (1993, p. 196) did not find a
relationship between the distance from the nearest road and the
declines in their study populations, suggesting that human activity was
not the cause of decline in that situation. Recreational activity may
be of conservation concern, and this may increase with greater activity
in mountain meadows. However, current available information does not
indicate that recreational activity is a significant stressor for
Yosemite toads.
Fire management practices over the last century have created the
potential for severe fires in the Sierra Nevada. Wildfires do pose a
potential direct mortality threat to Yosemite toads, although
amphibians in general are thought to retreat to moist or subterranean
refuges and thereby suffer low mortality during natural fires (Russel
et al. 1999, pp. 374-384). However, data on the direct and indirect
effects of fire on Yosemite toads are lacking.
USFS et al. (2009, p. 74) suggested that the negative effects of
roads that have been documented in other amphibians, in concert with
the substantial road network across a portion of the Yosemite toad's
range, indicate this risk factor may be potentially significant to the
species. Roads may facilitate direct mortality of amphibians through
vehicle strikes (DeMaynadier and Hunter 2000, pp. 56-65). Levels of
timber harvest and road construction have declined substantially since
implementation of the California Spotted Owl Sierran Province Interim
Guidelines in 1993, and some existing roads have been decommissioned or
are scheduled to be decommissioned (USDA 2001a, p. 445). Therefore, the
risks posed by new roads and timber harvests have declined, but those
already existing still may pose risks to the species and its habitat.
Collectively, direct mortality from land uses within the Yosemite toad
range may have a population-level impact. However, we are aware of no
studies that have quantified or estimated the prevalence of this
particular threat to be able to assess its impact to frog populations.
At the current time, direct and indirect mortality from roads are not
considered to be a significant factor affecting the Yosemite toad.
Small Population Size
Although it is believed that the range of the Yosemite toad has not
significantly contracted, the majority of populations across this area
have been extirpated, and this loss has been significant relative to
the historical condition (reflecting multitudes of populations within
many watersheds across their geographic range) (see ``Population
Estimates and Status'' above). Further, the populations that remain are
small, numbering less than 20 males in most cases (Brown et al. 2011,
p. 4). This situation renders these remnant populations susceptible to
risks inherent to small populations (see Factor E discussion, ``Small
Population Size,'' for mountain yellow-legged frogs, above) including
inbreeding depression and genetic drift, along with a higher
probability of extirpation from unpredictable events such as severe
storms or extended droughts.
Traill et al. (2009, p. 32) argued for a benchmark viable
population size of 5,000 adult individuals (and 500 to prevent
inbreeding) for a broad range of taxa, although this type of blanket
figure has been disputed as an approach to conservation (Flather et al.
2011, pp. 307-308). Another estimate, specific to amphibians, is that
populations of at least 100 individuals are less susceptible to
demographic stochasticity (Schad 2007, p. 10). Amphibian species with
highly fluctuating population size, high frequencies of local
extinctions, and living in changeable environments may be especially
susceptible to curtailment of dispersal and restriction of habitat
(Green 2003, p. 331). These conditions are all likely applicable to the
Yosemite toad.
Therefore, based on the best available commercial and scientific
information, we conclude that small population size is a prevalent and
significant threat to the species viability of the Yosemite toad across
its range, especially in concert with other extant stressors (such as
climate change).
Cumulative Impacts of Extant Threats
Interactive effects or cumulative impacts from multiple additive
stressors acting upon Yosemite toad populations over time are evident
by the documented declines in populations and abundance across the
range of the species. Although no single causative factor linked to
population declines in Yosemite toads has been confirmed in the
literature (excepting perhaps extreme climate conditions such as
droughts) (Kagarise Sherman and Morton 1993, p. 186; Jennings and Hayes
1994, pp. 50-53), there has been a decline in population abundance and
numbers of extant populations inhabiting the landscape (Brown et al.
2012, pp. 115-131; Kagarise Sherman and Morton 1993, pp. 186-198). This
pattern of decline suggests a factor or combination of factors common
throughout the range of the toad. The available literature (Kagarise
Sherman
[[Page 24511]]
and Morton 1993, pp. 186-198; Jennings and Hayes 1994, pp. 50-53; USFS
et al. 2009, pp. 1-133; Martin 2008, pp. i-393) supports the contention
that a combination of factors has interacted and is responsible for the
decline observed in Yosemite toad populations over the past few
decades.
Disease has been documented in Yosemite toad populations, and
recent data documenting historic trends in Bd infection intensity are
compelling (Dodge and Vredenburg 2012, p. 1), but disease has not been
definitively tied to the observed rangewide decline. There is
considerable evidence that various stressors, mediated via impacts to
meadow hydrology following upslope land management practices over the
last century, have detrimentally affected the quantity and quality of
breeding meadows. Many of these stressors, such as grazing, have likely
been more significant in the past than under current management
standards. However, legacy effects remain and meadows tend not to
recover without active intervention once excessive stream incision in
their watershed is set in motion (Vankat and Major 1978, pp. 386-397).
Certain stressors may be of concern, such as increasing recreational
impacts and avian predation upon terrestrial life stages of toads,
although we do not have sufficient data to document the magnitude of
these particular stressors.
Given the evidence supporting the role of climate in reducing
populations and potentially leading to the extirpation of many of the
populations studied through the 1970s and into the early 1990s
(Kagarise Sherman and Morton 1993, pp. 186-198), it is likely that this
factor is either a primary driver, or at least a significant
contributing factor in the declines that have been observed. Climate
models predict increasing drought intensity and changes to the
hydroperiod based on reduced snowpack, along with greater climate
variability in the future (PRBO 2011, pp. 18-25). It is likely that
these changes will exacerbate stress to the habitat specialist Yosemite
toad through a pronounced impact on its ephemeral aquatic habitat, and
also through an increase in the frequency of freezing and drying events
that kill exposed Yosemite toad eggs and tadpoles. These changes and
the resultant impacts will effectively reduce breeding success of
remnant populations already at low abundance and still in decline. If
an interaction such as winter stress and disease (Carey 1993, pp. 355-
362) is the underlying mechanism for Yosemite toad declines, then the
enhanced influence of climate change as a stressor may tip the balance
further towards higher incidence and increased disease virulence, which
would also lead to greater population declines and extirpations.
Proposed Determination
We have carefully assessed the best scientific and commercial
information available regarding the past, present, and future threats
to the Yosemite toad. The Yosemite toad is the most narrowly
distributed, Sierra Nevada endemic, pond-breeding amphibian (Shaffer et
al. 2000, p. 246). Although it apparently still persists throughout a
large portion of its historical range, it has been reduced to an
estimated 12 percent of historical watersheds. In addition, remnant
populations are predominantly small.
Yosemite toad populations are subject to threats from habitat
degradation associated with land uses that negatively influence meadow
hydrology, fostering meadow dewatering, and conifer and other invasive
plant encroachment. These activities include grazing, the fire
management regime of the past century, historic timber management
activities, and associated road construction. The impacts from these
threats are cumulatively of moderate magnitude, and their legacy
impacts on meadow habitats act as a constraint upon extant populations
now and are expected to hinder persistence and recovery into the
future. Disease are threats of conservation concern that have likely
also had an effect on populations leading to historical population
decline, and these threats are operating currently and will continue to
do so into the future, likely with impacts of moderate magnitude
effects on Yosemite toad populations.
The direct, interactive, and cumulative effects of these various
risk factors have acted to reduce the geographic extent and abundance
of this species throughout its habitat in the Sierra Nevada. The
combined effect of these stressors acting upon small remnant
populations of Yosemite toads is of significant conservation concern.
The Yosemite toad has a life history and ecology that make it sensitive
to drought and anticipated weather extremes associated with climate
change. Climate change is expected to become increasingly significant
to the Yosemite toad and its habitat in the future throughout its
range. Therefore, climate change represents a threat that has a high
magnitude of impact as an indirect stressor via habitat loss and
degradation, and as a direct stressor via enhanced risk of climate
extremes to all life stages of toads.
The Act defines an endangered species as any species that is ``in
danger of extinction throughout all or a significant portion of its
range'' and a threatened species as any species ``that is likely to
become endangered throughout all or a significant portion of its range
within the foreseeable future.'' We find that the Yosemite toad is
likely to become endangered throughout all or a significant portion of
its range within the foreseeable future, based on the immediacy,
severity, and scope of the threats described above. These include
habitat loss associated with degradation of meadow hydrology following
stream incision consequent to the cumulative effects of historic land
management activities, notably livestock grazing, and also the
anticipated hydrologic effects upon habitat from climate change under
listing Factor A. Additionally, we find that disease under listing
Factor C was likely a contributor to the recent historic decline of the
Yosemite toad, and may remain an important factor limiting recruitment
in remnant populations. We also find that the Yosemite toad is likely
to become endangered through the direct effects of climate change
impacting small remnant populations under Factor E, likely compounded
with the cumulative effect of other threat factors (such as disease).
We have carefully assessed the best scientific and commercial
information available regarding the past, present, and future threats
to the species, and have determined that the Yosemite toad meets the
definition of threatened under the Act, rather than endangered. This is
because the impacts from the threats are occurring now at moderate
magnitude, but are likely to become of high magnitude in the
foreseeable future across the species' entire range, making the species
likely to become in danger of extinction. While population decline has
been widespread, the rate of decline is not so severe to indicate
extinction is imminent, but this rate could increase as stressors such
as climate change impact small remnant populations. Further, the
geographic extent of the species remains rather widespread throughout
its historic range, conferring some measure of ecological and
geographic redundancy. Therefore, on the basis of the best available
scientific and commercial information, we propose listing the Yosemite
toad as threatened in accordance with sections 3(20) and 4(a)(1) of the
Act.
The term ``threatened species'' means any species (or subspecies
or, for vertebrates, distinct population segments) that is likely to
become an
[[Page 24512]]
endangered species within the foreseeable future throughout all or a
significant portion of its range. The Act does not define the term
``foreseeable future'' but it likely describes the extent to which the
Service could reasonably rely on predictions about the future in making
determinations about the future conservation status of the species. In
considering the foreseeable future as it relates to the status of the
Yosemite Toad, we considered the historical data to identify any
relevant existing trends that might allow for reliable prediction of
the future (in the form of extrapolating the trends). We also
considered how current stressors are affecting the species and whether
we could reliably predict any future trends in those stressors that
might affect the species recognizing that our ability to make reliable
predictions for the future is limited by the quantity and quality of
available data. Thus the foreseeable future includes the species
response to these stressors and any trends.
Under the Act and our implementing regulations, a species may
warrant listing if it is endangered or threatened throughout all or a
significant portion of its range. The Yosemite toad proposed for
listing in this rule is highly restricted in its range and the threats
occur throughout its range. Therefore, we assessed the status of the
species throughout its entire range. The threats to the survival of the
species occur throughout the species' range and are not restricted to
any particular significant portion of that range. Accordingly, our
assessment and proposed determination applies to the species throughout
its entire range.
Available Conservation Measures
Conservation measures provided to species listed as endangered or
threatened under the Act include recognition, recovery actions,
requirements for Federal protection, and prohibitions against certain
practices. Recognition through listing results in public awareness and
conservation by Federal, State, tribal, and local agencies, private
organizations, and individuals. The Act encourages cooperation with the
States and requires that recovery actions be carried out for all listed
species. The protection required by Federal agencies and the
prohibitions against certain activities are discussed, in part, above.
The primary purpose of the Act is the conservation of endangered
and threatened species and the ecosystems upon which they depend. The
ultimate goal of such conservation efforts is the recovery of these
listed species, so that they no longer need the protective measures of
the Act. Subsection 4(f) of the Act requires the Service to develop and
implement recovery plans for the conservation of endangered and
threatened species. The recovery planning process involves the
identification of actions that are necessary to halt or reverse the
species' decline by addressing the threats to its survival and
recovery. The goal of this process is to restore listed species to a
point where they are secure, self-sustaining, and functioning
components of their ecosystems.
Recovery planning includes the development of a recovery outline
shortly after a species is listed, preparation of a draft and final
recovery plan, and revisions to the plan as significant new information
becomes available. The recovery outline guides the immediate
implementation of urgent recovery actions and describes the process to
be used to develop a recovery plan. The recovery plan identifies site-
specific management actions that will achieve recovery of the species,
measurable criteria that determine when a species may be downlisted or
delisted, and methods for monitoring recovery progress. Recovery plans
also establish a framework for agencies to coordinate their recovery
efforts and provide estimates of the cost of implementing recovery
tasks. Recovery teams (comprised of species experts, Federal and State
agencies, nongovernmental organizations, and stakeholders) are often
established to develop recovery plans. When completed, the recovery
outline, draft recovery plan, and final recovery plan will be available
on our Web site (http://www.fws.gov/endangered), or from our Sacramento
Fish and Wildlife Office (see FOR FURTHER INFORMATION CONTACT).
Implementation of recovery actions generally requires the
participation of a broad range of partners, including other Federal
agencies, States, tribal, nongovernmental organizations, businesses,
and private landowners. Examples of recovery actions include habitat
restoration (for example, restoration of native vegetation), research,
captive propagation and reintroduction, and outreach and education. The
recovery of many listed species cannot be accomplished solely on
Federal lands because their range may occur primarily or solely on non-
Federal lands. To achieve recovery of these species requires
cooperative conservation efforts on private, State, and tribal lands.
If these species are listed, funding for recovery actions will be
available from a variety of sources, including Federal budgets, State
programs, and cost-share grants for non-Federal landowners, the
academic community, and nongovernmental organizations. In addition,
pursuant to section 6 of the Act, the State of California would be
eligible for Federal funds to implement management actions that promote
the protection and recovery of the Sierra Nevada yellow-legged frog,
the northern DPS of the mountain yellow-legged frog, and the Yosemite
toad. Information on our grant programs that are available to aid
species recovery can be found at: http://www.fws.gov/grants.
Although the Sierra Nevada mountain yellow-legged frog, the
northern DPS of the mountain yellow-legged frog, and the Yosemite toad
are only proposed for listing under the Act at this time, please let us
know if you are interested in participating in recovery efforts for
this species. Additionally, we invite you to submit any new information
on these species whenever it becomes available and any information you
may have for recovery planning purposes (see FOR FURTHER INFORMATION
CONTACT).
The Act and its implementing regulations set forth a series of
general prohibitions and exceptions that apply to all endangered
wildlife. The prohibitions of section 9(a)(2) of the Act, codified at
50 CFR 17.21 for endangered wildlife, in part, make it illegal for any
person subject to the jurisdiction of the United States to take
(includes harass, harm, pursue, hunt, shoot, wound, kill, trap,
capture, or collect; or to attempt any of these), import, export, ship
in interstate commerce in the course of commercial activity, or sell or
offer for sale in interstate or foreign commerce any listed species.
Under the Lacey Act (18 U.S.C. 42-43; 16 U.S.C. 3371-3378), it is also
illegal to possess, sell, deliver, carry, transport, or ship any such
wildlife that has been taken illegally. Certain exceptions apply to
agents of the Service and State conservation agencies.
We may issue permits to carry out otherwise prohibited activities
involving endangered and threatened wildlife species under certain
circumstances. Regulations governing permits are codified at 50 CFR
17.22 for endangered species, and at 17.32 for threatened species. With
regard to endangered wildlife, a permit must be issued for the
following purposes: for scientific purposes, to enhance the propagation
or survival of the species, and for incidental take in connection with
otherwise lawful activities.
It is our policy, as published in the Federal Register on July 1,
1994 (59 FR 34272), to identify to the maximum extent practicable at
the time a species is listed, those activities that would or would not
constitute a violation of
[[Page 24513]]
section 9 of the Act. The intent of this policy is to increase public
awareness of the effect of a proposed listing on proposed and ongoing
activities within the range of species proposed for listing. The
following activities could potentially result in a violation of section
9 of the Act; this list is not comprehensive:
(1) Unauthorized collecting, handling, possessing, selling,
delivering, carrying, or transporting of the species, including import
or export across State lines and international boundaries, except for
properly documented antique specimens of these taxa at least 100 years
old, as defined by section 10(h)(1) of the Act;
(2) Introduction of species that compete with or prey upon the
Sierra Nevada yellow-legged frog, the northern DPS of the mountain
yellow-legged frog, or the Yosemite toad;
(3) The unauthorized release of biological control agents that
attack any life stage of these species;
(4) Unauthorized modification of the mountain meadow habitats or
associated upland areas important for the breeding, rearing, and
survival of these species; and
(5) Unauthorized discharge of chemicals or fill material into any
waters in which the Sierra Nevada yellow-legged frog, the northern DPS
of the mountain yellow-legged frog, or the Yosemite toad are known to
occur.
Questions regarding whether specific activities would constitute a
violation of section 9 of the Act should be directed to the Sacramento
Fish and Wildlife Office (see FOR FURTHER INFORMATION CONTACT).
Requests for copies of the regulations concerning listed animals and
general inquiries regarding prohibitions and permits may be addressed
to the U.S. Fish and Wildlife Service, Endangered Species Permits, 2800
Cottage Way, Suite W-2606, Sacramento, CA 95825-1846 (telephone 916-
414-6464; facsimile 916-414-6486).
Peer Review
In accordance with our joint policy on peer review published in the
Federal Register on July 1, 1994 (59 FR 34270), we will seek the expert
opinions of at least three appropriate and independent specialists
regarding this proposed rule. The purpose of such review is to ensure
that our proposed actions are based on scientifically sound data,
assumptions, and analyses. We have invited these peer reviewers to
comment, during the public comment period, on the specific assumptions
and conclusions in this proposed listing.
We will consider all comments and information we receive during the
comment period on this proposed rule during preparation of a final
determination. Accordingly, the final decision may differ from this
proposal.
Public Hearings
Section 4(b)(5) of the Act provides for one or more public hearings
on this proposal, if requested. Requests must be received within 45
days after the date of publication of this proposed rule in the Federal
Register. Such requests must be sent to the address shown in the FOR
FURTHER INFORMATION CONTACT. We will schedule public hearings on this
proposal, if any are requested, and announce the dates, times, and
places of those hearings, as well as how to obtain reasonable
accommodations, in the Federal Register and local newspapers at least
15 days before the hearing.
Required Determinations
Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.)
This rule does not contain any new collections of information that
require approval by OMB under the Paperwork Reduction Act of 1995 (44
U.S.C. 3501 et seq.). This rule will not impose recordkeeping or
reporting requirements on State or local governments, individuals,
businesses, or organizations. An agency may not conduct or sponsor, and
a person is not required to respond to, a collection of information
unless it displays a currently valid OMB control number.
National Environmental Policy Act (42 U.S.C. 4321 et seq.)
We have determined that environmental assessments and environmental
impact statements, as defined under the authority of the National
Environmental Policy Act (NEPA; 42 U.S.C. 4321 et seq.), need not be
prepared in connection with listing a species as endangered or
threatened under the Endangered Species Act. We published a notice
outlining our reasons for this determination in the Federal Register on
October 25, 1983 (48 FR 49244).
Clarity of the Rule
We are required by Executive Orders 12866 and 12988 and by the
Presidential Memorandum of June 1, 1998, to write all rules in plain
language. This means that each rule we publish must:
(1) Be logically organized;
(2) Use the active voice to address readers directly;
(3) Use clear language rather than jargon;
(4) Be divided into short sections and sentences; and
(5) Use lists and tables wherever possible.
If you feel that we have not met these requirements, send us
comments by one of the methods listed in the ADDRESSES section. To
better help us revise the rule, your comments should be as specific as
possible. For example, you should tell us the numbers of the sections
or paragraphs that are unclearly written, which sections or sentences
are too long, the sections where you feel lists or tables would be
useful, etc.
References Cited
A complete list of references cited in this rulemaking is available
on the Internet at http://www.regulations.gov and upon request from the
Sacramento Fish and Wildlife Office (see FOR FURTHER INFORMATION
CONTACT).
Authors
The primary authors of this package are the staff members of the
Sacramento Fish and Wildlife Office.
List of Subjects in 50 CFR Part 17
Endangered and threatened species, Exports, Imports, Reporting and
recordkeeping requirements, Transportation.
Proposed Regulation Promulgation
Accordingly, we propose to amend part 17, subchapter B of chapter
I, title 50 of the Code of Federal Regulations, as set forth below:
PART 17--[AMENDED]
0
1. The authority citation for part 17 continues to read as follows:
Authority: 16 U.S.C. 1361-1407; 1531-1544; and 4201-4245, unless
otherwise noted.
0
2. Amend Sec. 17.11(h) by adding entries for ``Frog, mountain yellow-
legged (northern California DPS)'', ``Frog, Sierra Nevada yellow-
legged'', and ``Toad, Yosemite'' to the List of Endangered and
Threatened Wildlife in alphabetical order under AMPHIBIANS to read as
follows:
Sec. 17.11 Endangered and threatened wildlife.
* * * * *
(h) * * *
[[Page 24514]]
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Species Vertebrate
-------------------------------------------------------- population where Critical Special
Historical range endangered or Status When listed habitat rules
Common name Scientific name threatened
--------------------------------------------------------------------------------------------------------------------------------------------------------
* * * * * * *
AMPHIBIANS
* * * * * * *
Frog, mountain yellow-legged Rana muscosa........ U.S.A. (CA)........ Entire............. E ........... NA NA
(northern California DPS).
* * * * * * *
Frog, Sierra Nevada yellow-legged Rana sierrae........ U.S.A. (CA, NV).... Entire............. E ........... NA NA
* * * * * * *
Toad, Yosemite................... Anaxyrus canorus.... U.S.A. (CA)........ Entire............. T ........... NA NA
* * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------
Dated: March 15, 2013.
Rowan Gould,
Director, U.S. Fish and Wildlife Service.
[FR Doc. 2013-09600 Filed 4-24-13; 8:45 am]
BILLING CODE 4310-55-P