Evaluation of mitigation goals for spring/summer Chinook Salmon hatchery programs in the Snake River basin

Abstract Objective Hatcheries are a persistent feature of freshwater fisheries management in North America. Many salmon hatcheries in the Columbia River basin were established to mitigate the effects of hydroelectric development on fisheries. We examined the ability of Snake River hatchery programs to achieve adult spring/summer Chinook Salmon Oncorhynchus tshawytscha mitigation goals. Methods We developed a life cycle model incorporating smolt release number, smolt survival from release to the first dam encountered (Srel), and the smolt-to-adult return rate (SAR) in the most recent two decades. We used the model to determine the Srel and SAR necessary to achieve mitigation goals and to investigate the effect of increasing hatchery production on achieving mitigation goals or at least implementing a targeted fishery. Results We found that hatchery programs would have achieved goals for 21 of 177 total releases under current hatchery operational parameters. The minimum SAR to achieve return goals at maximal postrelease survival (Srel = 1.0) varied among hatcheries from 0.3% to 1.0%, and programs exceeded minimum SAR thresholds in approximately 30% of the releases analyzed. At current production and observed Srel, the SAR needs to increase 2-fold to over 10-fold relative to the recent past to consistently achieve return goals depending on the hatchery. If the SAR remains similar to that observed in the recent past, hatchery programs need to increase smolt production by 300–1,200%. Finally, we lowered the goal to “implementing a targeted sport fishery” and found that less than half could reliably support a minimal recreational fishery under current survival rates and that three programs may not support a fishery even with substantial production increases. Conclusions Our analysis demonstrates that goals cannot be achieved under current conditions with the existing hatchery system. Evaluating the linkage between smolt production and the SAR is crucial to understanding the potential of hatchery stocks, identifying management options to consistently meet goals, and informing strategic decision making.