|Document Type:||Contract Report|
|Title:||Passage and survival of adult Snake River sockeye salmon within and upstream from the Federal Columbia River Power System|
|Author/Editor:||Lisa G. Crozier, Brian J. Burke, Benjamin P. Sandford, Gordon A. Axel, Beth L. Sanderson|
|Publisher:||National Marine Fisheries Service|
|Contracting Agency:||U.S. Army Corps of Engineers. Walla Walla, Washington|
Snake River sockeye salmon (Oncorhynchus nerka) are among the most endangered of all Pacific salmon, with production primarily from captive broodstock since 1990. The adult migration presents an especially significant challenge to recovery of this population because they must migrate through various fisheries, pass over 8 hydroelectric dams, and travel over 1,500 km to reach native spawning areas. Survival for adult Snake River sockeye salmon from Bonneville Dam to the Sawtooth Weir ranged from 13% to 60% between 2008 and 2013. To increase the number of spawners for natural production and broodstock for the hatchery program, one potential management strategy is to collect adult sockeye salmon at Lower Granite Dam when in-river survival is relatively unfavorable and transport them to the Sawtooth Valley. We analyzed existing PIT-tag data from 920 fish (all detected at Bonneville Dam from 2008 through 2013) to determine whether we could identify river conditions unfavorable for migration success, and explored the implications of potential triggers for transportation. Specifically, we evaluated the extent to which migration success varied with juvenile history (e.g., hatchery origin, juvenile transportation, and age of adult return), migration characteristics (e.g., arrival timing, travel time, fallback), and river environment (temperature, flow, spill and the percentage of dissolved gas) in river reaches from Bonneville Dam to the Sawtooth Valley. We explored triggers for transportation by comparing the survival rates of various proportions of the population based on different types of triggers (date and temperature), locations of potential transport (Bonneville, Ice Harbor, or Lower Granite Dam) and threshold values for each trigger above which to initiate transportation.
Fallback affected a relatively small percentage of the fish at McNary Dam (~3-6% of fish fell back at least once) and Bonneville Dam (4-15%), but increasing percentages at Ice Harbor Dam (7-18%) and Lower Granite Dam (6-38%). The percent of fish falling back peaked at Lower Granite Dam in 2012 (38%) followed by 2013 (33%). Because some fish fell back multiple times, the absolute number of fallbacks was much higher, especially at Lower Granite Dam (45-49 fallbacks per 100 fish in 2010, 2012 and 2013). In 2013 in particular, fish that had been transported as juveniles fell back at Bonneville, The Dalles, and McNary Dams at higher rates than fish that were not transported. Summing fallbacks at these three dams, transported fish exhibited 50 fallbacks per 100 fish, whereas in-river juvenile migrants exhibited 12 fallbacks per 100 fish. However, this effect was weak or absent in other years, so further investigation is needed to determine whether this factor was confounded with something else. Temperature and/or flow correlated strongly with the probability of falling back, but dissolved gas and fish history also influenced fallback risk.
The most important predictors of survival across reaches and years based on the effect magnitude of their effect were thermal exposure and fish travel time. Dramatically higher temperature exposure contributed to high fallback rates and low survival in 2013. In the Columbia River, juvenile transportation and fishery catch also strongly influenced survival. In comparison to Upper Columbia River sockeye, Snake River sockeye had lower conversion rates from Bonneville Dam to McNary Dam. Snake River sockeye migrated 3-5 days later, but the stocks had similar travel times.
Migration survival varied strongly as a function of temperature. Survival dropped below 50% when the river surpassed 18°C. In most years, no particular trigger or threshold produced a dramatic or strongly non-linear advantage over others, but a ≤18°C threshold temperature at Bonneville, Ice Harbor or Lower Granite Dam noticeably improved in-river survival in ou
|Theme:||Recovery and rebuilding of marine and coastal species|
Develop methods to use physiological, biological and behavioral information to predict population-level processes.