Research Document - 2003/022

Annual Trends in Abundance and Bycatch Removals of Blue Hake (Antimora rostrata Günther 1878) in the Northwest Atlantic

By D.W. Kulka, M.R. Simpson

Abstract

Blue hake form a continuous distribution in slope waters off North America and into the northeast Atlantic. In fact, it has been found to inhabit most of the world's slope waters that have been surveyed. Our study examines annual trends in a) mortality attributable to fishing and b) trends in abundance. Trends in deepwater fisheries that captured blue hake as a bycatch were examined and fisheries observer data are used to estimate amounts of blue hake captured in the fisheries. On average, 84 t (since 1980) and 16 t (since 1993) have been removed annually as bycatch in the slope fisheries off Canada since 1985, primarily from the grenadier and Greenland halibut directed fisheries. Given the greater deepwater effort in the 1960's and 1970's catches were greater during that period (estimated peak catch was 887 t in 1971). Catch rate increased steadily out to the maximum depths fished for commercial gear and peaked at about 1 400 m for survey trawls although depths greater than 1 200 m were poorly sampled. Deep (1 371-2 286 m) longline survey sets from the 1960s (and catches from depths in excess of
3 000 m in USA waters to the south) indicated that blue hake are distributed well beyond depths commercially fished. In terms of using standard surveys to estimate abundance, 95% of survey sets containing blue hake occurred at depths greater than 600 m while < 5 % of survey sets occurred at those depths. In addition, maximum depth surveyed changed from year to year (deeper in recent years). Thus, only a fringe of the blue hake population in Canadian waters falls within the survey area. Most of the population is well beyond depths surveyed (or fished). The limitations and the difficulties associated with using a shelf based survey to study changes in the abundance of a slope species are discussed.

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