Stock-Specific Distribution and Abundance of Immature Sockeye Salmon in the Western Bering Sea in Summer and Fall 2002–2004

Seasonal stock-specific distribution and abundance of immature sockeye salmon (Oncorhynchus nerka) in the western Bering Sea in summer 2003 and fall 2002-2004 were determined using scale pattern analysis of Bering-Aleutian Salmon International Survey (BASIS) samples. Most (nearly 100%) of the sockeye salmon in BASIS catches were immature. Four age groups, 1.1, 1.2, 2.1 and 2.2, accounted for more than 90% of immature fish. Sockeye salmon of Asian (primarily Kamchatka) origin dominated catches throughout the region. In general, abundance of immature sockeye salmon was highest in the northwestern Bering Sea, where sockeye salmon of North American origin (primarily Bristol Bay stocks) were more abundant than in the southwestern Bering Sea. Estimated abundance of immature sockeye salmon in the western Bering Sea in 2002–2004 was high compared to estimated run sizes of adult returns, particularly in Asia. BASIS stock assessment methods may have overestimated the abundance of salmon or adult run-size statistics may be inaccurate, or both. Nevertheless, our stock-composition estimates were corroborated by other (genetic) studies. We concluded that the western Bering Sea in summer–fall is an important area of intermixing of immature sockeye salmon of Asian and North American origin. All correspondence should be addressed to A. Bugaev. e-mail: [email protected] Stock-Specific Distribution and Abundance of Immature Sockeye Salmon in the Western Bering Sea in Summer and Fall 2002–2004 Alexander V. Bugaev1 and Katherine W. Myers2 1Kamchatka Fishery and Oceanography Research Institute (KamchatNIRO), 18 Naberezhnaya Street, Petropavlovsk-Kamchatsky 683000, Russia 2School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195-5020, USA