Life Cycle Modeling Approach to Estimating Dam Operation Effects on Juvenile Salmon Survival

The Snake River, which drains into the Columbia River, is home to many Pacific salmon stocks. Many Snake River chinook salmon stocks are endangered or listed, and a considerable amount of the debate about recovery strategies revolves around hydroelectric dam operations. A life cycle model was built to estimate the effect of dam operations on juvenile survival during outmigration for the purpose of exploring operational alternatives. The dynamics of multiple stocks were combined into a single statistical population to cross-validate survival trends between stocks, and to infer juvenile production where stock-specific juvenile abundance data were not available. Dam passage variables and ocean environmental variables were used to predict variability in juvenile outmigration survival and ocean survival. Results show that when dam operations are pooled with ocean temperatures and upwelling indices, the most consistent predictor of mortality leading up to the first year of overwinter ocean residency is the dam operation variable. Furthermore, combining stocks into a common statistical group makes it possible to predict juvenile production parameters where juvenile data were not available.