Genetic stock composition analysis of the Chinook salmon bycatch from the 2015 Bering Sea walleye pollock (Gadus chalcogrammus) trawl fishery
A genetic analysis of samples from the Chinook salmon (Oncorhynchus tshawytscha) bycatch of the 2015 Bering Sea-Aleutian Island (BSAI) trawl fishery for walleye pollock (Gadus chalcogrammus) was undertaken to determine the overall stock composition of the bycatch. 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 2015, genetic samples from the Bering Sea were collected using a systematic random sampling protocol where one out of every 10 Chinook salmon encountered was sampled. Based on the analysis of 1,757 Chinook salmon bycatch samples collected throughout the 2015 BSAI walleye pollock trawl fishery, Coastal Western Alaska stocks dominated the sample set (40%) with smaller contributions from British Columbia (22%), West Coast U.S. (WA/OR/CA) (15%), and North Alaska Peninsula (11%) 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 Coastal Western Alaska, North Alaska Peninsula, and Upper Yukon stocks and higher contributions of West Coast U.S. (WA/OR/CA), British Columbia, NW Gulf of Alaska, and Coastal Southeast Alaska stocks during the “B” season.
The Bering Sea is known as a feeding habitat for multiple brood years of Chinook salmon (Oncorhynchus tshawytscha) originating from many different localities in North America and Asia. Determining the geographic origin and stock composition of Pacific salmon caught in federally managed fisheries is essential to understanding whether fisheries management could address conservation concerns. This report provides genetic stock identification results for the Chinook salmon bycatch samples collected from the U.S. Bering Sea-Aleutian Island (BSAI) pollock trawl fishery. National Marine Fisheries Service (NMFS) geographical statistical areas associated with the BSAI groundfish fishery (areas 509-524) are shown in Figure 1 and are used. Later in this report to describe the spatial distribution of the Chinook salmon bycatch and genetic samples.