River environment effects on adult migration phenology and rate of spring-run Chinook Salmon.

This article investigates how river environmental factors influence the migration phenology and upstream movement rates of adult spring-run Chinook Salmon (Oncorhynchus tshawytscha) in Oregon’s Willamette River basin, a population threatened by climate warming and habitat changes. Using a 23-year time series of daily salmon counts at Willamette Falls and radiotelemetry data from 909 tagged adults, the study found that salmon runs migrated earlier in years with warmer water temperatures and lower river discharge, with May conditions best predicting median run timing. Tagged salmon moved faster upstream under warmer, low-flow conditions and in low-gradient main-stem reaches, while individual fish traits had limited influence on migration rates after accounting for environmental variables. These findings align with patterns observed in other Pacific Northwest and Yukon River populations and suggest that climate-driven shifts toward earlier migration may increase freshwater residency time, posing uncertain risks to spring-run Chinook Salmon conservation.