| Summary: | 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. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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