Factors affecting the survival of Chinook salmon (Oncorhynchus tshawytscha) embryos in upper and middle Columbia River watersheds, Washington State, USA

A greater understanding of environmental effects on salmon survival during incubation can aid in prediction and facilitate population modeling at local and regional scales. Four basin-scale studies of Chinook salmon egg-to-fry survival were conducted between 2009 and 2021in spawning in tributaries of the upper and middle Columbia River; each study population is currently supplemented or have a recent history of supplementation, and most listed under the U.S. Endangered Species Act. Together, these studies provided a unique opportunity to assess factors influential to egg-to-fry survival, such as fine sediment infiltration and substrate scour, in the context of differences in survival among rivers and study years. We detected a 16.8% decrease in the odds of survival for every 1-cm increase in substrate scour, a 1.0% decrease in the survival odds with each one-unit change in the percentage of accumulated fines, distinct differences in survival within and among rivers (from 30.5% to 82.5%), and subtle effects of parentage in the presence of environmental factors. The causal and predictive relationships provided here will inform conservation, restoration, and further research.