Book Description
Surveys of the semi-demersal gadoid walleye pollock (Theragra chalcogramma) are conducted in summer on the eastern Bering Sea shelf by the Alaska Fisheries Science Center. The demersal portion of the stock is surveyed annually as part of a multispecies bottom trawl (BT) survey of groundfish and crab, while the midwater portion of the stock is surveyed biennially using acoustics and midwater trawling. Recently, an acoustic acoustic vessel-of-opportunity (AVO) index of midwater pollock biomass was developed with acoustic data collected by BT survey vessels for use during years in which AT survey data were not available. The AVO index was used in the Bering Sea walleye pollock stock assessment for the first time in 2010 and was fully incorporated in 2011. This document reports and discusses AVO index results for summers 2010 and 2011. Comparison of 2010 AVO and AT survey results provided additional confirmation that the AVO index is a good proxy for the abundance and distribution of midwater walleye pollock. Both AT and AVO time series suggested a rough doubling of midwater pollock biomass in the U.S. EEZ from summer 2009 to 2010, and a small decline in biomass from summer 2010 to 2011. Most of the change from 2010 to 2011 occurred on the shelf north and west of the Pribilof Islands, where the great majority of midwater pollock biomass was located in both years.
