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
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.
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 2013, 2014) 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 2015 from the U.S. Bering Sea walleye pollock (Gadus chalcogrammus) midwater trawl fishery and the GOA groundfish fisheries, as well as chum salmon collected in the Bering Sea during a test of a salmon excluder device. In the Bering Sea, the pollock fishery accounted for more than 97.7% of the total chum salmon taken in the groundfish fisheries (NMFS 2016a). In the GOA, the majority (42%) of the chum salmon were caught in the midwater trawl pollock fishery, with the remainder caught in other groundfish fisheries (NMFS 2016a).
National Marine Fisheries Service (NMFS) reporting areas associated with the groundfish fishery are shown in Figure 1 and are presented later to describe the spatial distribution of the chum salmon catch and genetic samples. A new data reporting tool was developed by the Pacific States Marine Fisheries Commission (PSMFC) that simplifies access to fishery information associated with the genetic samples of salmon PSC and is useful for organizing sample datasets at the finer resolution of ADF&G groundfish statistical areas (Fig. 1). The Alaska Fisheries Information Network (AKFIN1) reports developed by the PSMFC were used to construct spatial-temporal clusters of genetic samples along the outer continental shelf from the 2015 chum salmon PSC.