AFSC/ABL: 2007 Chum Salmon Bycatch Sample Analysis Bering Sea

A genetic analysis of samples from the chum salmon (Oncorhynchus keta) bycatch of the 2007 Bering Sea walleye pollock (Theragra chalcogramma) trawl fishery was undertaken to determine the overall stock composition of the sample set. Samples were genotyped for eleven microsatellite markers and results were estimated using the current chum salmon microsatellite baseline. In 2007, genetic samples were collected opportunistically as part of a special project, but sample biases have the potential to affect stock composition analysis results. Consequently, stock composition estimates apply to the sample set and may not represent the entire chum salmon bycatch. Based on the analysis of 1,279 chum salmon bycatch samples collected throughout the 2007 Bering Sea trawl fishery, North Asian (35%), East Asian (34%), and Eastern Gulf of Alaska/Pacific Northwest (16%) stocks dominated the sample set, with smaller contributions from Western Alaska (10%) and Upper/Middle Yukon River (5%) stocks. The estimates for the 2007 chum salmon bycatch sample set were similar to the 2005, 2006, and 2009 chum salmon bycatch estimates, suggesting consistency of the regional stock contributions across years. Analysis of temporal groupings within the groundfish B season revealed changes in stock composition during the course of the season with decreasing contribution of Upper/Middle Yukon stocks over time, but leaves unanswered whether these changes are due to temporal or spatial differences in the sample set.