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Ontogenetic shifts in diets of juvenile and subadult coho and chinook salmon in coastal marine waters: important for marine survival?

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  • Successfully shifting to a more piscivorous diet may be an important factor in the growth and survival of juvenile coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha during their first summer in the northern California Current. Nonmetric multidimensional scaling and cluster analysis of diets by size showed several distinct groupings as the salmon grew during their first marine summer. These size-based diet differences were clearly driven by increased rates of piscivory for both species. Fish prey composition, feeding intensity, and fish prey-predator length ratios all significantly increased for coho salmon at approximately 240 mm fork length when they changed from diets dominated by juvenile rockfishes Sebastes spp., the larvae of crabs Cancer spp., and adult euphausiids to one of predominantly juvenile forage fish. As Chinook salmon grew, they gradually increased the proportional contribution (by weight) of fish prey in their diets-from 55% in the smallest length-class examined (80-100 mm) to 95% in the largest one (. 375 mm). Chinook salmon fed in the same marine environments as coho salmon and consistently ate more and longer fish prey at a given size than coho salmon but had lower overall feeding intensity, perhaps owing to a higher level of prey selection. Relating subsequent interannual adult salmon returns to juvenile diets showed mixed results. During lower-survival years, coho salmon ate fewer and smaller fish prey, while subyearling Chinook salmon had less total food and more empty stomachs. We did not find consistent trophic patterns for yearling Chinook salmon in relation to their ultimate survival.
  • Keywords: Oncorhynchus tshawytscha, Oncorhynchus kisutch, diet
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  • Daly, E. A., Brodeur, R. D., & Weitkamp, L. A. (2009, November). Ontogenetic shifts in diets of juvenile and subadult coho and chinook salmon in coastal marine waters: important for marine survival? Transactions of the American Fisheries Society, 138(6), 1420-1438.
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  • 138
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  • Funding was provided by the Bonneville Power Administration and the U.S. Global Ocean Ecosystems (GLOBEC) Northeast Pacific Program. This is contribution 636 of the U.S. GLOBEC Program.
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