Estimating predation of adult sockeye salmon by American white pelicans in the Columbia River using a state-space Bayesian approach

Adult sockeye salmon (Oncorhynchus nerka) migrate past the largest breeding colony of American white pelicans (Pelecanus erythrorhynchos) in the Columbia River, USA. To investigate the magnitude of pelican predation on sockeye salmon, a state-space Bayesian model was used to estimate spatially and temporally explicit predation and survival probabilities, and to estimate the total number of salmon consumed by pelicans each year. Results show that pelican predation was a substantial source of salmon mortality in some years, with median predation probabilities ranging annually from 0.015 to 0.084, resulting in an estimate of 1328 to 47 265 fish consumed annually from 2014 to 2023. While there was evidence that predation probabilities were associated with the number of sockeye salmon returning to the Columbia River annually, there was no evidence that fish length was associated with susceptibility to predation. Additional research aimed at investigating how other biotic and abiotic factors influence sockeye salmon susceptibility to pelican predation are needed to broaden our understanding of predator–prey interactions and to determine to what degree predation limits sockeye salmon survival prior to spawning.