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

Greater understanding of environmental effects to 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 years 2009 and 2021 in spawning tributaries of the upper and middle Columbia River. Each of the four basins support Chinook salmon populations that are either currently hatchery-supplemented or have a recent history of supplementation, and most are 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.