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NOAA Technical Memorandum NMFS-AFSC-244

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Genetic stock composition analysis of Chinook salmon bycatch samples from the 2011 Bering Sea and Gulf of Alaska trawl fisheries

Abstract

A genetic analysis of samples from the Chinook salmon (Oncorhynchus tshawytscha) bycatch of the 2011 Bering Sea-Aleutian Island (BSAI) and Gulf of Alaska (GOA) pollock trawl fisheries was undertaken to determine the stock composition of the sample set. Samples were genotyped for 43 single nucleotide polymorphism (SNP) DNA markers and results were estimated using the Alaska Department of Fish and Game (ADF&G) SNP baseline. In 2011, genetic samples from the Bering Sea were collected using a systematic random sampling protocol from one out of every 10 Chinook salmon encountered. Based on the analysis of 2,473 Chinook salmon bycatch samples collected throughout the 2011 BSAI walleye pollock (Theragra chalcogramma) trawl fishery, Coastal Western Alaska stocks dominated the sample set (68%) with smaller contributions from North Alaska Peninsula (9%), British Columbia (8%), and U.S. west coast (6%) stocks. Analysis of temporal groupings within the pollock “A” and “B” seasons revealed changes in stock composition during the course of the year with lower contributions of North Alaska Peninsula and Yukon River stocks during the “B” season. Genetic samples were also collected from Chinook salmon taken in the bycatch of the 2011 Gulf of Alaska (GOA) pollock trawl fisheries. In contrast with the Bering Sea, genetic samples were collected opportunistically in the GOA during 2011; consequently, the resulting stock composition estimates should be considered as stock compositions of the sample set rather than a representative composition of the entire GOA Chinook salmon bycatch. Based on the analysis of 240 Chinook salmon bycatch samples, British Columbia (40%) and U.S. west coast (26%) stocks comprised the largest stock groups with smaller contributions from Northwest GOA (15%) and Coastal Southeast Alaska (14%) stocks.

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