Echo integration-trawl survey of walleye pollock (Theragra chalcogramma) in the southeast Aleutian Basin during February and March, 1994

Abstract

Results from the winter 1994 echo integration-trawl survey of spawning walleye pollock (Theragra chalcogramma) near Bogoslof Island, covering an area between 166°W. and about 170°W. long., from the Aleutian chain north to 54°30' N. lat. are presented. The eastern part of the survey area was inhabited mainly by non-spawning pollock from the 1989 year class that formed echo sign layers at depths of about 200-500 m. In the middle of the region, over deeper water, older pollock from a number of year classes and 1989 year class pollock formed dense spawning aggregations at depths of around 300-600 m. Although some pollock eggs were collected in one of five bongo net tows, little evidence of pollock spawning was observed before the end of the survey on 9 March. Despite some recruitment of the 1989 year class and the near absence of commercial fishing in the central and southeast Aleutian Basin, estimated spawning biomass declined from its winter 1993 level of about 0.63 million metric tons (t) to about 0.49 million t. The decline was most likely due to the natural mortality of aging year classes, which had supported the Bogoslof area spawning population at least since 1988.


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