Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9102
Title: Competing tradeoffs between increasing marine mammal predation and fisheries harvest of Chinook salmon
Author: Brandon Chasco, I. C. Kaplan, Austen Thomas, Alejandro Acevedo-Gutierrez, D. P. Noren, Michael J. Ford, M. B. Hanson, J. Scordino, Kristin Marshall, Andrew O. Shelton, C. D. Matkin, Brian J. Burke, E. J. Ward
Publication Year: 2017
Journal: Scientific Reports
Keywords: Chinook salmon,killer whale,harbor seal,California sea lion,Steller sea lion,predation

Many marine mammal predators, particularly pinnipeds, have increased in abundance in recent decades, generating new challenges for balancing human uses with recovery goals via ecosystem-based management. We used a spatio-temporal bioenergetics model of the Northeast Pacific Ocean to quantify how predation by three species of pinnipeds and killer whales (Orcinus orca) on Chinook salmon (Oncorhynchus tshawytscha) has changed since the 1970s along the west coast of North America, and how this compares to salmon caught by commercial and recreational fisheries. We find that from 1975 to 2015, biomass of Chinook salmon consumed by pinnipeds and killer whales increased from 6,100 to 15,200 metric tons (from 5 to 31.5 million individual salmon). Though there is variation across the seven regions in our model, overall, killer whales consume the largest biomass of Chinook salmon, but harbor seals (Phoca vitulina) consume the largest number of individuals. The decrease in adult Chinook salmon harvest from 1975-2015 was 16,400 to 9,600 metric tons. Thus, Chinook salmon mortality increased in the past 30 years despite catch reductions by fisheries, due to consumption by recovering pinnipeds and endangered killer whales. Long-term management strategies for Chinook salmon may need to consider potential conflicts between rebounding predators or endangered predators and prey.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.
Describe the relationships between human activities and species recovery, rebuilding and sustainability.