Estimating impacts of the pollock fishery bycatch on western Alaska Chinook salmon.

Chinook salmon (Oncorhynchus tshawytscha) are taken as bycatch in the Bering Sea pollock (Gadus chalcogrammus) fishery, with recently revised managementmeasures in place to limit theoverall Chinook salmon catch.Historicalimpact of the bycatch onregional salmon stocks ismade difficult because, until recently, sampling for the stockcomposition of the bycatchwas patchy and diverse in approaches. In this study, extensive observer data on the biological attributes (size and age composition) of the bycatch were used to estimate the impact on specific regional stock groups (RSGs), as defined given available genetic stock identification estimates. Our model provides estimates of the impact on Chinook salmon RSGs, given seasonal and spatial variability in the bycatch, and accounts for observed in-river age compositions, uncertainty in age-specific oceanic natural mortality of Chinook salmon, and between-year variability in genetic information. The upper Yukon River stock is transboundary and subject to heightened management interest and international management agreements on escapement goals. Our study updates results from an earlier analysis used to develop the management regulations that went into place in 2011. It shows that the new data result in slight changes in previous estimates, and that the lower overall Chinook salmon bycatch since 2008 has resulted in lower impacts to the main western Alaskan RSGs. [ABSTRACT FROM AUTHOR]