Changes in the Abundance and Size of Skates in the Southern Gulf of St. Lawrence, 1971-2002

Abstract

Three species of skates commonly occur in the southern Gulf of St. Lawrence: thorny skate Amblyraja radiata, winter skate Leucoraja ocellata, and smooth skate Malacoraja senta. Trends in their abundance and size are described using data from annual bottom-trawl surveys conducted each September since 1971. Biomass and the abundance of mature skates decreased over the 1971–2002 period, by 80–90% for thorny and winter skates, and to a lesser degree for smooth skates. Abundance of juvenile thorny and smooth skates increased from the mid-1980s to a peak in the mid-1990s, and then declined in the late1990s. Mean length decreased by 20–30% during the 1980s for each of the three species. The increase in the abundance of juvenile skates in the 1990s coincided with a collapse in the biomass of large-bodied demersal teleost fishes, a dramatic decline in fishing effort, a cooling of the cold intermediate layer in the southern Gulf and decreasing abundance of mature skates. The decline in the abundance of large skates may be an effect of fishing, though reported landings of skates have been low. These results for the southern Gulf of St. Lawrence contrast those observed on Georges Bank and in the North Sea, where small elasmobranch species that were not targeted by fisheries increased in biomass as the biomass of heavily exploited groundfish stocks declined.