Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4551
Title: Winter ichthyoplankton biomass as a predictor of early summer prey fields and survival of juvenile salmon in the northern California Current
Author: Elizabeth A. Daly, Richard D. Brodeur, Toby D. Auth, W. T. Peterson
Publication Year: 2013
Journal: Marine Ecology Progress Series
Volume: 484
Pages: 203-217
Keywords: salmon, ocean ecology, ichthyoplankton, feeding,salmon,ocean conditions,Ichthyoplankton,feeding
Abstract:

Diets of juvenile coho Oncorhynchus kisutch and Chinook O. tshawytscha salmon are made up primarily of winterspawning fish taxa in the late-larval and early juvenile stages that are undersampled in plankton and larger trawl nets. Although we have no direct measure of the availability of fish prey important to juvenile salmon during early marine residence, we do have data on the larval stage of their prey that may be used as a surrogate for the later stages.  Data on these prey items were obtained from ichthyoplankton samples collected along the Newport Oregon Hydrographic line (44.65°N) during JanuaryMarch 19982010.  We explored winter biomass of prey fish larvae as a potential indicator of marine feeding conditions for young salmon the following spring.  The proportion of total winter ichthyoplankton biomass considered to be common salmon fish prey fluctuated from 13.9% in 2006 to 95.0% in 2000.  The relationship between biomass of fish larvae in winter and subsequent coho salmon survival was highly significant (R2 = 50.0, p = 0.004).  When the two outlier years of 1998 (El Niño) and 1999 (La Niña) were removed, this relationship was also highly significant for spring Chinook (R2 = 70.7, p = 0.0002) and significant for fall Chinook salmon (R2 = 34.0, p = 0.03) returns.  Winter larval fish composition showed a high degree of overlap with juvenile salmon diets during May, but less overlap in June.  Larval fishes appeared to be an early and costeffective indicator of ocean ecosystem conditions and future juvenile salmon survival.