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The relationships between predatory fish, forage fishes, and juvenile salmonid marine survival off the Columbia River: a simple trophic model analysis

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  • A trophic model that simulates interactions between a predatory fish (Pacific hake, Merluccius productus), forage fish, and juvenile salmon off the Columbia River was constructed to identify if trophic interactions could account for marine mortality of Columbia River juvenile salmon. The model estimates the number of juvenile salmon that are eaten annually by Pacific hake off the Columbia River for a given hake and forage fish population. Model results indicate that the presence of high numbers of Pacific hake could account for high mortality of some juvenile salmonid species/stocks leaving the Columbia River, and that this mortality would be much reduced when forage fish are abundant. Estimates of hake and forage fish abundance, based on field data collected from 1998–2005, were used in the model to derive annual estimates of the number of salmon possibly eaten by hake. A multiple regression analysis using the output from the trophic model and average May/June Columbia River flows accounted for much of the annual variation in Columbia River fall Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon marine survival (p < 0.05, R2 > 60%), but not spring or summer Chinook salmon. For these two stocks, average May/June sea-surface temperature was the best predictor of marine survival. Results support the hypothesis that for some Columbia River salmon species/stocks, marine survival is predation-driven and affected by the interaction between the abundance of Pacific hake, forage fish, Columbia River flows, and possibly ocean turbidity. Future modeling work should include predation estimates of other large fishes, marine mammals, and sea birds.
  • Previously published in California Cooperative Oceanic Fisheries Investigations, Progress Report v. 48 (2007); access courtesy of publisher and authors.
  • Keywords: Juvenile salmonid, Predatory fish, Forage fish
  • Keywords: Juvenile salmonid, Predatory fish, Forage fish
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  • Reports of California Cooperative Oceanic Fisheries Investigations v.48, p.92-105
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  • 0575-3317

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