Research Document - 2009/084

Pre-COSEWIC review of barndoor skate (Dipturus laevis) in the Canadian Atlantic

By J.E. Simon, A. Cook, S. Rowe, and M. Simpson

Abstract

A Department of Fisheries and Oceans (DFO) review of Canadian standardized research vessel (RV) surveys, industry/science surveys and observer records in 2002 suggested that barndoor skate was sufficiently numerous to ease concerns about its conservation status. They were more widely distributed than previously thought and consistently captured at depths/locations beyond the standard research vessel surveys. This document updates the Canadian RV and industry science information, revisits earlier observer reports and looks at the US RV surveys in more detail. A review of recent biological studies revealed that growth was faster, females matured earlier (approximately 7 years), and the species is more fecund than previously thought. USA RV surveys indicate the species is most common from just south of Georges Bank to the Gulf of Maine. Canadian RV surveys indicate the species is most common on Georges Bank west to Sable Island on the Scotian Shelf and on the southern flanks of the Scotian Shelf and the Grand Banks. They are rare north of these areas. Observer reports that the species was distributed as far north as the Davis Strait were reexamined and found to be incorrect. Population estimates from the Canadian and USA RV surveys for Georges Bank and the Scotian Shelf suggests that abundance has been increasing at an annual rate on 3-14% per year since 1996. Abundance is now approaching or has exceeded estimates seen in the 1960s to mid 1970s. As the population rebounded, the species has expanded first from relatively small areas on Georges Bank, to the whole of the bank, then Northwest Atlantic Fisheries Organization (NAFO) Division 4X and recently back into Division 4W. There are no directed fisheries for barndoor skate in Canadian waters; however, the species is caught as a bycatch in other fisheries. An examination of the landings in these other fisheries suggest that the declines observed in barndoor skate abundance in the 1960s on Georges Bank were coincident with a peak in landings, but not in the other NAFO divisions. The recent increases in RV abundance on Georges Bank and the Scotian Shelf are occurring during times when groundfish landings are low. The population collapse observed in the late 1960s and 1970s appears to have been reversed and the review of these data suggests that the species has recovered to population sizes seen in the 1960s. The reasons for the collapse and subsequent recovery are uncertain but the status of this species must continue to be monitored as it has shown that it is vulnerable to significant population declines in the past.

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