Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8643
Title: Interannual variability in the feeding and condition of subyearling Chinook salmon off Oregon and Washington
Author: K. E. Dale, Elizabeth A. Daly, Richard D. Brodeur
Publication Year: 2016
Journal: Fisheries Oceanography
Volume: 26
Issue: 1
Pages: 1-16
Keywords: Juvenile Chinook salmon, feeding, piscivory, body condition, ocean conditions,

Chinook salmon Oncorhynchus tshawytscha is one of several economically important species of salmon found in the Northeast Pacific Ocean.  The first months at sea are believed to be the most critical for salmon survival, with the highest rate of mortality occurring during this period.  In the present study, we examined interannual diet composition and body condition trends for late-summer subyearling Chinook salmon caught off Oregon and Washington from 1998 to 2012.  Interannual variability was observed in juvenile salmon diet composition by weight of prey consumed.  Juvenile subyearling Chinook salmon were mainly piscivorous, with northern anchovy (Engraulis mordax) being especially important, making up half the diet by weight in some years.  Annual diets clustered into two groups, primarily defined by their proportion of invertebrate prey (14 vs. 39% on average).  Diet composition was found to influence adult returns, with salmon from high-invertebrate years returning in significantly larger numbers 23 years later.  However, years that had high adult returns had overall lower stomach fullness and poorer body condition as juveniles, a counterintuitive result potentially driven by the enhanced survival of less fit individuals in better ocean conditions (top-down effect).  Ocean conditions in years with a higher percentage of invertebrates in salmon diets were significantly cooler from May to August, and bottom-up processes may have led to a fall plankton community with a larger proportion of invertebrates.  Our results suggest that the plankton community assemblage during this first fall may be critical in predicting adult returns of Chinook salmon in the Pacific Northwest.

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Theme: Ecosystem approach to improve management of marine resources
Foci: Understand how climate influences ecosystem variability.
Characterize ecological interactions (e.g. predation, competition, parasitism, disease, etc.) within and among species.