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The effects of physical and biological oceanographic factors on marine growth of Fraser river sockeye salmon Cox, Sean Patrick


The average size at maturity of sockeye salmon (Oncorhynchus nerka) in the northeast Pacific Ocean varies considerably from year to year: It is generally accepted that the majority of variation in size at maturity of sockeye salmon is due to variation in marine growth. However, few studies have shown strong linkages between specific oceanographic factors such as temperature, ocean currents, zooplankton production, and salmon abundance and the ultimate size of returning Fraser River sockeye. Using size at maturity data specific for ten Fraser River sockeye stocks I demonstrate that i.) the amount of variation in size at maturity that is due to environment is detectable in spawning ground length samples and ii.) mean size at maturity declined in almost every stock over the period 1954-1993.1 also show that variation in marine growth is strongly associated with changes in sockeye salmon abundance and sea surface temperature in the northeast Pacific Ocean. Marine growth was not correlated to sockeye salmon abundance over the period 1959-1975; however the two were strongly associated during the period 1978- 1992. Annual scale growth increments support the assumption that critical periods for density dependent growth occur during the time when Early Stuart sockeye salmon are present in the Central Gulf of Alaska. If present levels of salmon abundance are maintained during future warmer climates, major declines in size at maturity of sockeye salmon are likely to result due to the combined effects of high temperature, high abundance, and possibly a reduction in the standing crop of prey.

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