Pollock Conservation Cooperative Research Center
2001 Awarded Research Projects
Factors affecting nearshore survival and production of juvenile sockeye salmon from Kvichak Bay
Stephen Jewett, Paul Rasanowski
Award: $36,000
Estimated Completion: April 14, 2002
Abstract
Low returns of sockeye salmon to Bristol Bay in 1997 and 1998, and the failure of the peak sockeye salmon run on the Kvichak River in 2000 has generated great concern for the health and continued viability of the Kvichak River stock of sockeye salmon. These events, in tum, have spurred a renewed interest in determining factors that affect survival of sockeye salmon throughout their life cycle, and particularly the early marine phase of that cycle. In this study we provide detailed information on important habitats utilized by juvenile salmon as they migrate from the Kvichak River into and through Kvichak Bay, define their migratory route through Kvichak Bay, and assess food resources available during that migration.
In 2001, during the period of sockeye smolt outmigration (mid May to mid June), juvenile sockeye salmon were sampled along several transects from shore up to 50 km offshore. Abundances of sockeye tended to decrease from shallow, nearshore areas with higher temperatures, higher turbidity, and lower salinities to deeper, offshore areas with colder, more saline, and less turbid waters. Bottom depth, temperature, salinity, Secchi depth, and distance from shore are all strongly confounded, thus their potential effects on the distribution of salmon are difficult to separate. Sockeye abundances were not correlated with total zooplankton density or biomass, however, sockeye were correlated with selected zooplankters, such as the calanoid copepods Eurytemora and Epilabidocera. Eurytemora was the most important prey item, in terms of frequency of occurrence and number eaten. Mysid crustaceans dominated the prey in terms of biomass. There is some evidence that fish nearshore are feeding less than fish offshore in deeper, less turbid water.
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