Relative Importance of River Flow, Ocean Conditions, and Hatchery Practices on Early Ocean Growth and Overall Survival of Central Valley Fall Run Chinook Salmon

Pacific salmon species encounter a diversity of environments across space and time, making it difficult to determine which factors influence overall survival. As improving survival is a primary goal of managers, environmental complexity presents a challenge for managing these migratory species. Pacific salmon populations have been declining and many are heavily supported by hatchery operations which use coded wire tags (CWTs) to monitor harvest and ocean return rates. There are many variables that may influence salmon survival including river flows during juvenile outmigration, ocean conditions, and hatchery practices. We use a dataset of recaptured CWT juvenile hatchery fall run Chinook salmon from the California Central Valley to estimate early ocean growth and cohort survival. We also determined values for oceanographic variables, river flows, and hatchery practices derived from the fishes CWT release group for each individual fish.  We then built models to describe early ocean growth and overall survival. We used AIC model selection to determine which factors; river flow, ocean conditions, or hatchery practices; significantly impact growth and survival. Studies have shown early ocean growth to positively correlate with overall survival, and we also examine this by determining whether the same factors are important in both models.