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Genetic stock composition analysis of the Chinook salmon (Oncorhynchus tshawytscha) bycatch from the 2018 Bering Sea pollock trawl fishery
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    A genetic analysis of samples from the Chinook salmon (Oncorhynchus tshawytscha) bycatch of the 2018 Bering Sea-Aleutian Island (BSAI) trawl fishery for walleye pollock (Gadus chalcogrammus) was undertaken to determine the overall stock composition of the bycatch and examine temporal changes in stock composition across seasons. 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 2018, genetic samples were collected using a systematic random sampling protocol where one out of every 10 Chinook salmon encountered was sampled. Based on analysis of 1,297 Chinook salmon bycatch samples, Coastal Western Alaska and British Columbia regions (34% and 30%, respectively) dominated the sample set with smaller contributions from North Alaska Peninsula (18%) and West Coast US (11%) regions. Temporal groupings within the pollock “A” and “B” seasons revealed changes in stock composition over the course of the year. The percentage and number of fish from the Coastal Western Alaska (35% vs. 31%) and North Alaska Peninsula (26% vs. 3%) regions was higher in the “A” season than the “B” season, whereas the contribution from the West Coast US (6% vs. 20%) and the British Columbia (27% vs. 33%) regions were higher in the “B” season. Spatial analysis showed that the stock compositions varied within season depending upon where the salmon were caught. For example, during the “B” season a higher proportion of Coastal Western Alaska Chinook salmon were intercepted in the northwestern area of the Bering Sea, and a higher proportion of southern origin Chinook salmon were intercepted in the southeastern area of the Bering Sea.
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