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NOAA Technical Memorandum NMFS-AFSC-270

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Genetic stock composition analysis of Chinook salmon bycatch samples from the 2012 Bering Sea and Gulf of Alaska trawl fisheries

Abstract

A genetic analysis of samples from the Chinook salmon (Oncorhynchus tshawytscha) bycatch of the 2012 Bering Sea-Aleutian Island (BSAI) and Gulf of Alaska (GOA) trawl fisheries for walleye pollock (Gadus chalcogrammus) 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 2012, 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 1,111 Chinook salmon bycatch samples collected throughout the 2012 BSAI walleye pollock trawl fishery, Coastal Western Alaska stocks dominated the sample set (63%) with smaller contributions from North Alaska Peninsula (11%), British Columbia (10%), and West Coast U.S. (OR/CA/WA) (7%) 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 higher contributions of British Columbia and West Coast U.S. stocks during the “B” season.

Genetic samples were also collected from Chinook salmon taken in the bycatch of the 2012 Gulf of Alaska (GOA) pollock trawl fisheries. In contrast with the Bering Sea, genetic samples were collected opportunistically in the GOA during 2012; 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 948 Chinook salmon bycatch samples, British Columbia (49%), West Coast U.S. (28%), and Coastal Southeast Alaska (20%) stocks comprised the largest stock groups.

We also produced stock composition estimates of Chinook salmon from tests of salmon excluder devices performed in February 2012 in an area north of Unimak Pass in the Bering Sea. Stock composition results showed that the majority of the 249 Chinook salmon collected in the 2012 excluder device test originated from Coastal Western Alaska (69%) and the North Alaska Peninsula (12.4%). These were very similar to the stock composition estimates from the 2012 BSAI “A” season.


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