Combining Migration History, River Conditions, and Fish Condition to Examine Cross‐Life‐Stage Effects on Marine Survival in Chinook Salmon

AbstractWe examined delayed effects (or carryover effects) on marine survival from the freshwater experiences of migrating Chinook Salmon Oncorhynchus tshawytscha. Juvenile Chinook Salmon that differed in their freshwater experience in passing hydroelectric power dams of the Columbia and Snake rivers (Pacific Northwest) as run-of-the-river or barged fish were tested in challenge experiments at 23.5°C to determine the freshwater survival index m (i.e., the time to 80% mortality). Seasonal patterns of m were best predicted by (1) an index of migration timing (t) at the exit of the hydropower system and a barge index (B) or (2) a temperature exposure index (θ; i.e., 7-d average of river temperatures experienced prior to collection). Other predictors tested included river flow, wet mass, and Fulton’s condition factor. Predicted m (mpred) based on t and B or based on θ was then related to seasonal patterns of marine survival. Significant relationships between mpred and marine survival provide support for the h...