Combining Migration History, River Conditions, and Fish Condition to Examine Cross-Life-Stage Effects on Marine Survival in Chinook Salmon
We 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 hypothesis that the seasonal patterns of freshwater experiences during hydropower system passage influence the biological condition of juvenile salmon at seawater entry and consequently their seasonal pattern of marine survival to the adult stage. Because temperature is a more direct and biologically relevant variable than migration timing with a barging index offset, further investigation of temperature-related factors affecting the biological condition of anadromous fishes as they exit freshwater—and subsequently their marine survival—is warranted.
Received June 3, 2016; accepted January 5, 2017 Published online March 16, 2017