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Marine Ecology and Stock Assessment Program

Growth Rate Potential of Juvenile Chum Salmon on the Eastern Bering Sea Shelf

Spatial and temporal variation in growing conditions for juvenile salmon may determine the survival of salmon after their first year at sea. To assess this aspect of habitat quality, a spatially explicit bioenergetics model was used to predict juvenile chum salmon (Oncorhynchus keta) growth rate potential (GRP) on the eastern Bering Sea shelf during years with cold and warm spring sea surface temperatures (SSTs).

Annual averages of juvenile chum salmon GRP were generally lower among years and regions with cold spring SSTs. In addition, juvenile chum salmon GRP was generally higher in offshore than in nearshore regions of the eastern Bering Sea shelf during years with warm SSTs; however, the distribution (catch per unit effort) of juvenile chum salmon was not significantly (P < 0.05) related to GRP.

Shifts from warm to cold SSTs in the northern region do not appear to affect summer abundance of juvenile Yukon River chum salmon, whereas the abundance of juvenile Kuskokwim River chum salmon drops precipitously during years with cold SSTs.

From this result, we hypothesize that size-selective predation is highest on juvenile Kuskokwim chum salmon during cold years, but that predation is not as great a factor for juvenile Yukon River chum salmon.

Although not addressed in this study, we also hypothesize that the smaller Yukon River chum salmon captured during years with cold SSTs likely incur higher size-selective mortality during winter.

By Ed Farley

Juvenile Pink and Chum Salmon Distribution, Diet, and Growth in the Northern Bering and Chukchi Seas

Loss of nonseasonal sea ice and a general warming trend in the Bering Sea has altered the composition, distribution, and abundance of marine organisms inhabiting the region. Juvenile pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon were found in significant numbers throughout the Chukchi Sea and Bering Strait regions during early autumn 2007, reflecting significant utilization of Arctic marine habitat by Pacific salmon.

Linear models of juvenile pink and chum salmon body size corrected for Day of Year were parameterized to estimate daily growth rates and habitat-specific differences in body size using 6 years of survey data. Model results revealed that juvenile pink salmon inhabiting the eastern Bering Sea grew at an average rate of 1.17 mm per day and juvenile chum salmon grew at a rate of 1.21 mm per day.

The U.S. Bering-Aleutian Salmon International Study (BASIS) survey area was expanded northward to include the Chukchi Sea during 2007, where larger juvenile pink and chum salmon were found in higher abundances relative to pink and chum salmon inhabiting the eastern Bering Sea. Food habits analyses revealed that juvenile pink and chum salmon fed upon high energy prey in the Chukchi Sea, and that the majority of chum salmon encountered there were from either Alaskan or Russian stocks.

By Jamal Moss

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