Genetic stock composition analysis of the Chinook salmon bycatch samples from the 2015 Gulf of Alaska trawl fisheries

A genetic analysis of samples from the Chinook salmon (Oncorhynchus tshawytscha) bycatch of the 2015 Gulf of Alaska (GOA) trawl fisheries for walleye pollock (Gadus chalcogrammus), rockfish (Sebastes spp.), and arrowtooth flounder (Atheresthes stomias) was undertaken to determine the stock composition of the sample sets. 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 were collected from Chinook salmon taken in the bycatch of the Gulf of Alaska (GOA) pollock trawl fisheries using a simple random sample protocol with trip being the primary unit. This is the second year for this sampling protocol and resulted in the largest available genetic sample set to date with 17.8% of the salmon bycatch successfully genotyped. Based on the analysis of 2,414 Chinook salmon bycatch samples, British Columbia (51%), West Coast U.S. (32%), Coastal Southeast Alaska (14%), and Northwest Gulf of Alaska stocks (3%) comprised the largest stock groups. In 2015, genetic samples from the bycatch of the GOA rockfish catcher vessel (CV) fishery were collected by the fishing industry using a census sampling protocol where every Chinook salmon encountered was sampled. Based on the genotyping of 635 Chinook salmon bycatch samples collected from the 2015 GOA rockfish CV trawl fishery in NMFS Statistical Areas 620 and 630, West Coast U.S. stocks (WA/OR/CA) represented the largest stock grouping (73%) with smaller contributions from British Columbia (19%), Coastal Southeast Alaska (5%), and Northwest GOA (3%) stocks. Based on the genotyping of 300 Chinook salmon bycatch samples collected throughout the 2015 GOA arrowtooth flounder trawl fishery from the catcherprocessors (CP), West Coast U.S. stocks (WA/OR/CA) represented the largest stock grouping.