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NOAA Technical Memorandum NMFS-AFSC-345

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Genetic stock composition analysis of chum salmon from the prohibited species catch of the 2015 Bering Sea walleye pollock trawl fishery and Gulf of Alaska groundfish fisheries

Abstract

A genetic analysis of the prohibited species catch (PSC) of chum salmon (Oncorhynchus keta) collected during 2015 from the federally managed walleye pollock (Gadus chalcogrammus) trawl fishery in the Bering Sea and from the federal groundfish fisheries in the Gulf of Alaska (GOA) was undertaken to determine the overall stock composition of the sample sets. Additionally, a genetic analysis was conducted of chum salmon collected in the southeastern Bering Sea during a test of a salmon excluder device. Samples were genotyped for 11 microsatellite markers from which stock contributions were estimated using the current chum salmon microsatellite baseline. In 2015, one genetic sample was collected for every 30.5 chum salmon caught in the Bering Sea midwater trawl fishery. The evaluation of sampling in the Bering Sea based on time, location, and vessel indicated that the genetic samples were representative of the total chum salmon PSC in the Bering Sea. The small set of chum salmon samples (142) from the A-season were mostly from Northeast Asia (41%) and Eastern GOA/PNW (47%) stocks. Based on the analysis of 1,836 chum salmon collected throughout the  B-season, the largest stock group in the catch was Eastern GOA/Pacific Northwest (PNW) (51%), followed by Northeast Asia (17%), Western Alaska (16%), Southeast Asia (10%), Upper/Middle Yukon (4%), and Southwest Alaska (< 2%) stocks. The regional stock estimates for the 2015 chum salmon caught in the Bering Sea differed from most previous years, with contributions from Eastern GOA/PNW stocks surpassing those from Northeast Asia and Southeast Asia stocks. Of the 131 chum salmon samples from the GOA groundfish fisheries, the highest proportion was from Eastern GOA/PNW (88%) stocks. As with the Bering Sea fishery samples, the highest proportion of the 549 excluder device test samples were also from Eastern GOA/PNW (51%) stocks and included fish from multiple geographic regions despite being collected at small spatial and temporal scales.



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