Using Acoustics to Evaluate the Effect of Fishing on School Characteristics of Walleye Pollock

Abstract

Walleye pollock (Theragra chalcogramma) is the target of one of the world's largest sheries and is an important prey species in the eastern Bering Sea (EBS) ecosystem. Little is known about the potential e ects of shing on the school characteristics and spatial distribution of walleye pollock. Few dedicated research surveys have been conducted during pollock shing seasons, so analysis of shery data is the only feasible approach to study these potential e ects. We used acoustic data collected continuously by one shing vessel in January-February 2003, which operated north of Unimak Island. Results from comparisons between two shing periods showed signi cant changes of pollock distribution at di erent 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 signi cantly. Variography was used to investigate the changes at scales larger than 1 nm. The increased range, nugget e ect, and sill in the second period indicated changes of pollock spatial distribution; however, it is unclear whether these changes are attributable to shing or ecological processes.

Ichthyophonus‐infected walleye pollock Theragra chalcogramma (Pallas) in the eastern Bering Sea: a potential reservoir of infections in the North Pacific

“…The extensive range and prevalence of this trophically transmitted parasite in all pollock year classes is an important finding because this host is a key prey species in the eastern Bering Sea (Livingston ) and the target of one of the world's largest commercial fisheries (Shen et al . ). Although the limited data presented here only allow us to speculate on the dynamics of this parasite in this system, it does offer a foundation for future research.…”

“…Pollock is not only a key prey item linking many marine predators in Alaskan waters (Livingston ), but is also the target of one of the largest fisheries in the world (Shen et al . ). A portion of the pollock caught in Alaska is processed and inspected at sea (Wilen & Richardson ), and fish waste material, offal, is discharged into the ocean (Bluhm & Bechtel ).…”