Research Document - 2002/073

Barndoor skate in the Northwest Atlantic off Canada: Distribution in relation to temperature and depth based on commercial fisheries data

By D.W. Kulka, K. Frank, K., and J. Simon

Abstract

Commercial fisheries data were used to examine the distribution of barndoor skate in Canadian waters. Bycatch in the commercial fisheries shows that the distribution of barndoor skate extends much further north than indicated by survey data, indicating their presence along the shelf edge as far north as Lat. 620 N. Between 1980 and 2001, over all areas and depths fished, barndoor skate were taken in 7 commercial gears, primarily in otter trawls and longlines in 1 set in 200 on average. Percent occurrence was used to define relative abundance in relation to temperature and depth. Spatial differences in catch rates (based on weight) reflected local density or perhaps the presence of larger (heavier) fish. Barndoor skate are widespread in terms of depth across its entire range although their depth distribution varied among areas. On the western Scotian Shelf, both catch rates and percent occurrence of barndoor skate were about 10 times higher at depths exceeding 450 m. Considering that ninety-nine percent of survey sets in this area were prosecuted at depths < 450 m, this indicates that the surveys cover only a fringe of the total distribution in that area. Thus, indices based on surveys underestimate abundance and may not reflect population trends. They may represent shifts distribution into and out of the surveyed area rather than trends in abundance. In terms of bottom temperature, very few barndoor skate were taken where temperature was < 1.50C even though substantial proportion of the fishing effort occurred there. To the north, barndoor skate were associated mainly with temperatures of 2-4.50 C, to the south, 4-90 C. The difference between the two areas likely relates to different depths (and associated temperature ranges) fished.

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