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Modeling Estuary and Ocean Survival of Pacific Salmon Using a Temporally-Stratified Mark-Recapture-Recovery Approach that Accounts for Avian Predation and Age of Return

James Faulkner, Steven Smith

NOAA Fisheries, 2725 Montlake Blvd E, Seattle, WA 98112

Current methods for modeling smolt-to-adult returns of salmon as functions of ocean conditions do not directly account for losses of individual fish to predation, and often do not account for age of return. We present an approach for modeling survival in the estuary and ocean of juvenile migrating salmon using a Bayesian mark-recapture-recovery framework that accounts for mortality from avian predation using tags recovered from avian nesting colonies. The model estimates travel time to the ocean for daily groups of juvenile fish migrating past the final dam using live detections of these fish in the estuary. This allows effects of conditions experienced in the estuary and early ocean to be modeled at a finer time scale than conditions experienced in the open ocean, and allows estimation of time-dependent tag recovery and predation probabilities on the avian colonies when data on tag deposition and detection are available from the colonies. The model further incorporates age at return, which allows estimates of effects of conditions on survival for each year in the ocean. We use simulations to show that accounting for tag recoveries from avian predation and incorporating age of return reduces bias and improves precision of parameter estimates.