Distribution, Growth, and Feeding of Sockeye Salmon in the Western Bering Sea

Abstract

The Pacific Research Institute of Fisheries and Oceanography (TINRO) in Vladivostok, Russia, conducted 12 major biological surveys in the western Bering Sea in 1986–1995. During these surveys, sockeye salmon Oncorhynchus nerka were sampled with a new pelagic trawl. We used salmon catch, age and growth, and diet data from the TINRO surveys to evaluate the role of sockeye salmon in the structure and function of pelagic communities in the western Bering Sea. Estimates of abundance (numbers and biomass) showed large annual and seasonal fluctuations in the western Bering Sea. Immature and maturing sockeye salmon migrated to the western Bering Sea in late spring from their winter (December–May) feeding grounds in the North Pacific Ocean. Maturing sockeye salmon were distributed in the western Bering Sea from June to early August before returning to their natal spawning rivers. In late August, smolts (age n.0, where the n indicates an ocean-age cohort and zero indicates the number of ocean annuli) began to move from coastal to offshore waters, where the largest numbers occurred in September–November. We inferred from catch data that most of the other age-groups of sockeye salmon left the western Bering Sea by the end of November and moved southward to the North Pacific Ocean. The analyses indicated that sockeye salmon fed in the seasonal thermocline layers, where they were important consumers of interzonal zooplankton and micronektonic organisms. The dietary ration of sockeye salmon was high. The high growth rates of sockeye salmon in the western Bering Sea were comparable to those in the North Pacific Ocean. The wide distribution, numerous trophic linkages, high rations, and high growth rate of sockeye salmon establish their important role in pelagic communities of the western Bering Sea.