Assessment of walleye pollock stocks in the eastern North Pacific Ocean: an integrated analysis using research survey and commercial fisheries data
Walleye pollock (Theragra chalcogramma) is the single most abundant fish species in the North Pacific Ocean. Concentrations of this species, which occur in the eastern Bering Sea and western Gulf of Alaska, support the largest single-species commercial fishery in the world. Exploitation of these stocks began in the early 1960s primarily by foreign national fleets. Currently the fishery is in a transitional phase. Over a relatively short time a combination of events dramatically reshaped the fishery from a multispecies foreign bottom-trawl fishery to a joint-venture fishery and finally to an expanding domestic presence. In the process, patterns and methods of fishing have changed as have the fishery parameters estimated from assessment models.
In the past, fishery assessments were based on limited non-directed bottom-trawl survey c.p.u.e., fishery c.p.u.e., and length-frequency analysis. Beginning in 1979, the use of hydroacoustic surveys allowed the assessment of the midwater portion of the stock which normally was not available to the bottom-trawl surveys or the commercial fishery. The hydroacoustic survey provided data which made it possible to tune sequential population models. Also described are current assessment methods which allow direct integration of hydroacoustic survey information into separable fishery assessment models. With an integrated approach, estimated abundance levels are more consistent with survey estimates. The hydroacoustic surveys in coming years will be especially important to the estimation of new tuning parameters.
This paper reviews past catch, management, and assessment results. Also presented are results from current assessments. In particular we emphasize how survey results, especially results from hydroacoustic surveys, can be integrated with age-structured fishery assessment models to examine the validity of assumptions inherent in each method.
