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

Seasonal stock-specific distribution and abundance of Chinook salmon (Oncorhynchus tshawytscha) were determined using scale pattern analysis of Bering-Aleutian Salmon International Survey (BASIS) samples and catch data collected in the western Bering Sea in summer 2003 and fall 2002–2004. Chinook salmon were sparsely distributed in this region, which greatly limited the number of samples available for stock identification research. Research trawl catches of immature Chinook salmon were highest in northern areas, and catches throughout the region were dominated by fish in their second ocean summer. Estimated percentages of immature Chinook salmon of North American (Alaska) origin (50.2–71.2%) were consistently higher than those of Asian (Russia) origin. The highest estimated abundance of immature Chinook salmon was in summer 2003 (~21 million North American and ~20 million Asian fish). These estimates were extraordinarily high compared to adult returns to Asia and North America in 2004–2006, and we concluded that BASIS stock assessment methods overestimated the abundance of this species. Nevertheless, our results provided the first quantitative evidence of the extensive distribution of immature Chinook salmon of North American origin in the western Bering Sea in summer and fall. We concluded that the western Bering Sea ecosystem is an important summer–fall foraging area for immature Chinook salmon of both Asian and North American origin. All correspondence should be addressed to A. Bugaev. e-mail: [email protected] Stock-Specific Distribution and Abundance of Immature Chinook 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, Petropavlovsk-Kamchatsky 683000, Russia 2School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195-5020, USA