Evaluating the Suitability of Potential Donor Stocks of Chinook Salmon for Reintroduction to the US-Canada Transboundary Reach of the Columbia River

Anadromous salmon have been extirpated from the Columbia River basin upstream from Grand Coulee Dam for 75 years. Multiple life histories of Chinook salmon were abundant upstream of this point, and adults spawned in the US-Canada Transboundary Reach, what is now one of the last remaining free-flowing stretches of the extensively dammed river. Restoration of a self-sustaining population to the Transboundary Reach would benefit from determining the suitability of potential donor stocks to survive and complete their life-cycle in this novel environment. In this study, unique life-cycle timing, life history attributes, behavioural and physical adaptations of several distinct Columbia basin donor stocks were determined from literature review. Each donor stock was scored based on whether these adaptations were advantageous or allowed stocks to avoid environmental stressors and critical life-cycle timing incompatibilities. Donor stocks were then ranked in order to determine their relative suitability in the novel reintroduction reach, as well as downstream reaches they must migrate through to complete their life-cycles. The model identified several common life-cycle timing tradeoffs and limitations relating to prespawn holding, emergence timing or juvenile travel time. Opportunities for environmental modification were preliminarily identified, which may improve the suitability of the river for reintroduced populations.