Research Document - 2002/070

Distribution and abundance of Barndoor skate (Dipturus laevis) in the Canadian Atlantic based upon research vessel surveys and industry/science surveys

By J.E. Simon, K.T. Frank, D.W. Kulka

Abstract

Data derived from three principal sources in the Canadian Atlantic zone, spanning several decades, was examined for the occurrence of barndoor skate. The data reviewed included standardized research vessel (RV) surveys conducted by DFO, non-standard research vessel surveys and recent industry/science surveys. Despite the availability of over 80,000 RV and industry/science survey sets available for analysis, the frequency of occurrence of barndoor skate was very low (equal to 1.26%). In general, barndoor skates were more common in the 1950s and 1960s in comparison to later decades when they were sporadically encountered throughout the 1970s, and nearly absent during the 1980s to early 1990s. Since the mid-1990s, abundance has increased throughout the central/western Scotian Shelf and Gulf of Maine area. These patterns have been corroborated by seasonal surveys conducted by NMFS in US waters. Some persistent areas of concentration were evident, notably those associated with Georges Bank/Fundian Channel region, in the vicinity of Browns Bank, the central and slope waters of the Scotian Shelf and possibly the Laurentian Channel region. Concentrations that were evident early in data series but are not evident now include the eastern Scotian Shelf, Div. 3Ps and the southwestern slope waters of the Grand Banks. It was apparent from the industry/science surveys that barndoor skate were consistently captured at depths/locations beyond the standard research vessel surveys. This observation is in agreement with previous analyses of observed commercial fisheries data, i.e. that barndoor skate are captured in depths extending to 1000m and beyond. Limited information exists on the reproductive biology of barndoor skate, however recent studies have shown that length at first and 50% maturity is in excess of 105 cm and 110 cm respectively for both male and female barndoor skate. Length composition of barndoor skate from both RV and industry/science surveys show a wide range of sizes, indicative of both juvenile and adult fish. RV surveys appear to capture mainly juveniles. Collectively, the review of these data suggests that barndoor skate is currently sufficiently numerous to ease concerns about its conservation status.

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