In 2011, an estimated 25,499 Chinook salmon were taken in the bycatch of BSAI pollock trawl fisheries (NMFS 2012), of which 7,136 were estimated from the trawl “A” season and 18,363 were estimated for the “B” season. Since 1991, the year with the highest overall Chinook bycatch in the BSAI was 2007 (Fig. 2) when an estimated 121,770 fish were taken. The genetic sample set for the 2011 “A” season Chinook salmon bycatch was 695 fish, corresponding to a sampling rate of 9.7%. The genetic sample set for the 2011 “B” season Chinook bycatch was 1,778 fish, corresponding to a sampling rate of 9.7%. The annual sampling rate for the entire year was 9.7%. There were more Chinook salmon taken in the “B” season than in the “A” season for the first time since 2005.

2011 was the first year systematic random sampling was employed for collecting genetic tissue from the Bering Sea Chinook salmon bycatch and Figure 4 shows that the resulting Chinook salmon bycatch samples were collected in proportion through time and space with the total catch. The sample spatial and temporal distribution was excellent in 2011 compared to previous years when samples were collected more opportunistically.

From the 2011 Chinook salmon bycatch, a total of 2,756 samples were analyzed of which 2,720 samples were successfully genotyped for 35 or more of the 43 SNP loci, a success rate of 98.7%.

Results suggest that 85% of the 695 samples from the “A” season originated from Alaskan river systems flowing into the Bering Sea with the Coastal Western Alaska stock contributing the most (54%), followed by the North Alaska Peninsula (22%), and Upper Yukon (7%). The other major contributor was British Columbia (7%) (Table 1).

For the “B” season, over 79% of the 1,778 samples originated from Alaskan river systems flowing into the Bering Sea with the Coastal Western Alaska region contributing the most (74%). This was followed by British Columbia (8%) and the U.S. west coast stock (6%)

For the entire year, an estimated 81% of the bycatch samples were estimated to be from Alaskan river systems flowing into the Bering Sea with the Coastal Western Alaska stock contributing the most (68%), trailed by the North Alaska Peninsula (9%). Other contributors were British Columbia (8%), and U.S. west coast (6%) (Table 3). The “overall” and “B” season stock compositions were similar, which was anticipated given that 72% of the samples were from the “B” season. In 2011, 72% of the Chinook salmon bycatch was from the “B” season of the Bering Sea pollock fishery.

Full report here....

http://www.afsc.noaa.gov/Publications/AFSC-TM/NOAA-TM-AFSC-244.pdf