Using acoustics to evaluate the effect of fishing on school characteristics of walleye pollock

Using acoustics to evaluate the effect of fishing on school characteristics of walleye pollock

H. Shen, T.J. Quinn II, V. Wespestad, M.W. Dorn, and M. Kookesh

Using acoustics to evaluate the effect of fishing on school characteristics of walleye pollockThis is part of Resiliency of Gadid Stocks to Fishing and Climate Change
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Description

Walleye pollock (Theragra chalcogramma) is the target of one of the world's largest fisheries and is an important prey species in the eastern Bering Sea (EBS) ecosystem. Little is known about the potential effects of fishing on the school characteristics and spatial distribution of walleye pollock. Few dedicated research surveys have been conducted during pollock fishing seasons, so analysis of fishery data is the only feasible approach to study these potential effects. We used acoustic data collected continuously by one fishing vessel in January-February 2003, which operated north of Unimak Island. Results from comparisons between two fishing periods showed significant changes of pollock distribution at different scales. The schools were smaller and denser during the second period. Furthermore, the spatial distribution of schools became sparser, as evidenced by the lower frequency of schools per elementary distance sampling unit and the increase in average next-neighbor distances (NNDs). However, the average NND between schools within a cluster and the average abundance of clusters did not change significantly. Variography was used to investigate the changes at scales larger than 1 nm. The increased range, nugget effect, and sill in the second period indicated changes of pollock spatial distribution; however, it is unclear whether these changes are attributable to fishing or ecological processes.

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