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Research Document - 2004/113

Changes in Distribution and Habitat Associations of Wolffish (Anarhichidae) in the Grand Banks and Labrador Shelf

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

Abstract

The Species at Risk Act (SARA) recognizes habitat for species designated at risk as an important component for their survival and recovery. In this study, we review the available information on habitat requirements for three species of wolffish in the western Atlantic. Specifically, the life history and ecology of wolffish are reviewed, their current and historic distributions are described and distributions are modeled in relation to available habitat information. The results are interpreted in relation to critical habitat requirements of the Species at Risk Act. The three wolffish species are at the center of their distribution, reaching highest density and covering the largest area on the northeast Newfoundland and Labrador Shelf. There they distribute over a wide range of depths, from about 25 m to > 1 400 m., A. denticulatus occupying the widest range, A. lupus the narrowest. We show that temperature is an important feature of wolffish habitat. All three species are associated with a narrow thermal range of above average bottom temperatures, mainly 1.5-4.5°C, absent where temperatures are < 0°C. Based on the results of this study, wolffish may be classified as “temperature keepers” – they maintain a similar temperature range by changing their distribution, in this case a reduction, co-occurring with a period of reduced abundance. The distribution of wolffish is also related to sediment type. Analysis of bottom type data using ROXANN data indicated that A. minor and A. lupus were widely distributed on various sediment types. A. denticulatus, however, did occupy sand/shell hash, gravely sand and rock sediments more frequently. A. lupus in near-shore areas avoided sediments that can be stirred up such as muddy substrates. The area where wolffish were concentrated corresponds to the most heavily fished grounds along the outer shelf. The rate of decline at the unfished locations was observed to be similar or higher than in the most intensely fished areas. Thus, there is no evidence of cropping down by the fisheries. However, changes in ambient temperature resulted in a greater proportion of the wolffish being concentrated on the outer shelf where fishing intensity was greatest, thus making them more vulnerable to capture.

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