Genetic Stock Composition Analysis of Chum Salmon from the Prohibited Species Catch of the 2016 Bering Sea Walleye Pollock Trawl Fishery and Gulf of Alaska Groundfish Fisheries
A genetic analysis of the prohibited species catch (PSC) of chum salmon (Oncorhynchus keta) collected during 2016 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. Samples were genotyped for 11 microsatellite markers from which stock contributions were estimated using the current chum salmon microsatellite baseline. In 2016, one genetic sample was collected for every 30.6 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 majority of the 114 chum salmon samples from the A-season were from Northeast Asia (37%) and Eastern GOA/Pacific Northwest (PNW) (37%) stocks. Based on the analysis of 2,701 chum salmon collected throughout the B-season, the largest stock groups in the catch were Eastern GOA/PNW (35%) and Northeast Asia (31%), followed by Western Alaska (19%), Southeast Asia (9%), Upper/Middle Yukon (5%), and Southwest Alaska (< 2%) stocks. The chum salmon caught in the Bering Sea in 2016 shared general patterns of stock distribution with those from past years, but differed by some finer-scale spatiotemporal strata. Of the 473 chum salmon samples from the GOA groundfish fisheries, the highest proportion was from Eastern GOA/PNW (93%) stocks, similar to previous years.
Pacific salmon (Oncorhynchus spp.) are prohibited species in the federally managed Bering Sea and Gulf of Alaska (GOA) groundfish fisheries, which are subject to complex management rules (NPMFC 2017a,b) that are in part designed to reduce prohibited species catch (PSC). It is important to understand the stock composition of Pacific salmon caught in these fisheries, which take place in areas that are known feeding habitat for multiple brood years of chum salmon (O. keta) from many different localities in North America and Asia (Myers et al. 2007, Davis et al. 2009, Urawa et al. 2009). Determining the geographic origin of salmon caught in federally managed fisheries is essential to understanding the effects that fishing has on chum salmon stocks, especially those with conservation concerns (NPFMC 2012).
In this report, we present the genetic stock composition estimates for the samples of chum salmon PSC collected during 2016 from the U.S. Bering Sea walleye pollock (Gadus chalcogrammus) trawl fishery and the GOA groundfish fisheries. In the Bering Sea, the pollock fishery accounted for more than 98.8% of the total chum salmon taken in the groundfish fisheries (NMFS 2017). In the GOA, the majority (56%) of the chum salmon were caught in the pollock trawl fishery, with the remainder caught in other groundfish fisheries (NMFS 2016).