Assessing superimposition of listed tule fall Chinook salmon redds using aerial and ground surveys on the White Salmon River, WA

Hatchery upriver bright (URB) fall Chinook salmon are straying into the White Salmon River (Figure 1). ESA-listed tule fall Chinook population in the White Salmon River spawns earlier (Sept – Oct) than URBs (late Oct – Nov). Tule redds at risk to superimposition which may displace eggs and reduce egg-to-fry survival.

A surprisingly high incidence of tule redds monitored were superimposed by URBs in 2022 and 2023.  Counts of redds superimposed from aerial surveys can be especially valuable for high-density spawning areas. Efficient processing of aerial imagery requires high performance computing environment. • Aerial drone surveys can provide high-resolution georeferenced imagery of a more expansive area of spawning grounds.

Next steps: Compare count estimates of redds superimposed from ground surveys with aerial surveys.  Estimate aerial observer error among four independent observers.  Prepare for 2024 aerial surveys using a Skydio X10 drone with onboard AI for obstacle avoidance.