Migration Timing of Columbia River Spring Chinook Salmon: Effects of Temperature, River Discharge, and Ocean Environment

Abstract In an effort to improve run timing forecasts for Columbia River spring Chinook salmon Oncorhynchus tshawytscha , we examined relationships among regional ocean climate indices, in‐river environmental conditions, and full run and stock‐specific migration timing metrics. Results consistently indicated that adult Chinook salmon arrived earliest in years with low river discharge or warm water temperatures and arrived latest in years of cold water temperatures and high flows. As single predictors, in‐river conditions generally explained more interannual variability in salmon return timing than did air temperature, the Pacific Decadal Oscillation, or the North Pacific Index. However, best‐fit multiple‐regression models included a combination of in‐river and climate predictors. While spatial and temporal scales of the analyses were relatively coarse (i.e., monthly values were used for all predictors), clear patterns emerged that can be used to improve pre‐ and in‐season run timing forecasting models for Columbia River spring Chinook salmon. We recommend continued refinement of climate‐based and environmental predictive tools to help manage anadromous fish stocks, including the threatened and endangered populations of the Columbia River basin.