Factors Affecting Spatiotemporal Variation in Survival of Endangered Winter‐Run Chinook Salmon Out‐migrating from the Sacramento River

Among four extant and declining runs of Chinook Salmon Oncorhynchus tshawytscha in California’s Central Valley, none has declined as precipitously the Sacramento River winter run. Migratory winter-run employ a life history strategy to reside feed stopover habitats on their way from freshwaters ocean. run, ocean, that have been affected by anthropogenic disturbance. Using acoustic telemetry, we examined conditions influenced reach-specific movement survival out-migrating juveniles during prolonged, multi-year drought 2013 2016, followed one wettest years record (2017). We modeled how time-varying individual riverine covariates habitat features smolt survival. Model selection favored model with mean annual flow, intra-annual deviations flow at reach scale, channel characteristics, travel time. Mean had strongest positive effect A negative interaction between indicated within-year scale larger effects low-flow years. These factors resulted higher pulse flows or high flows. Changes behavior response small-scale changes velocity were negatively associated Covariates revetment wooded bank positively survival, but these fixed changed depending whether they situated upper lower part river. Fish exhibited density-dependent behavior, slowed downstream migration river wet extending most critically dry year. This paper contributes two key findings for natural resource managers interested management targeted restoration. The first is new insight into magnitude affects fish. second density dependence influences where used. Despite this, identified an area fish consistently all