Science Advisory Report 2005/063

Recovery Potential Assessment for Winter Skate in the southern Gulf of St. Lawrence North Atlantic Fisheries Organization (NAFO) Division 4T)

Summary

• Winter skate in the southern Gulf of St. Lawrence are designated as endangered by Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and are being considered for listing on Schedule 1 of Canada’s Species-at-Risk Act.
• Catch rates of adult winter skate in the DFO annual research survey have declined steadily since the early 1980s and are currently at the lowest level on record. Catch rates of juveniles increased in the survey from the early 1970s to the mid 1980s but have since also declined to low levels.
• Catch rates of winter skate in the DFONorthumberland Strait survey (conducted since 2000) declined by over 50% between 2001 and 2004.
• There is no directed fishery for winter skate in the southern Gulf. Estimated bycatch in fisheries for groundfish and shrimp declined throughout the 1970s and early 1980s, and has been very low (<50 t) since the early 1990s. Bycatch of winter skate in the scallop fishery is likely but its magnitude is unknown.
• A population model was used to estimate trends in mortality. The estimated exploitation rate declined steadily from the early 1970s to very low levels by the early 1990s. Natural mortality of juveniles appeared to be higher in the 1970s than in years since then. In contrast, natural mortality of adults appeared to increase in the 1980s and 1990s.
• The decline in winter skate abundance appears to be caused by this increase in adult natural mortality (or unknown human-induced mortality that is interpreted as natural mortality in the models).
• The increase in adult mortality occurred during a period of increasing grey seal abundance.
• Winter skate abundance is projected to continue to decline even with no bycatch in fisheries. Bycatch at the most recent level (10 t) has a negligible effect on the rate of decline but slightly higher bycatch (50 t) would substantially accelerate the decline.

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