What is the upper thermal tolerance limit of larval Pacific Lamprey? Annual Report: 2020

Lampreys are obligate ectotherms and directly influenced by the ambient water temperature.  In species other than Pacific Lamprey, evidence exists that lethal water temperatures for larvae occur near 27.0-31.0°C (e.g. Potter and Beamish 1975; Arakawa and Yanai 2021).  Although few studies have addressed Pacific Lamprey, recent investigations indicated the ultimate upper incipient lethal temperature (UUILT) for larvae exceeds 27.5°C (Uh and Whitesel unpublished data) and provided preliminary evidence that larvae have the ability to occupy natural areas warmer than 27.5°C (Whitesel and Sankovich 2021).  How climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.

Learn more about climate change will ultimately influence the status of Pacific Lamprey is uncertain (see Wang et al. 2020).  Currently, many of the locations where Pacific Lamprey rear naturally experience maximum water temperatures near 26.0°C.  With predictions that during the next 25-35 years air temperatures in the Pacific Northwest may rise 2-5°C (Wu et al. 2012), maximum water temperatures where some Pacific Lamprey exist now may exceed the lethal limit for larvae.  Whether the UUILT derived from laboratory experiments reflects the natural distribution of larval Pacific Lamprey, or there are effects at warm but sublethal temperatures, is not well understood.  We propose to continue an evaluation of i) whether larval Pacific Lamprey occupy streams where water temperatures exceed 27.5°C, ii) whether larvae occupy areas these areas at a similar rate to areas where temperatures do not exceed 27.5°C, iii) whether burrowing may provide refuge from warm water and iv) whether sub lethally warm temperatures influence larvae.