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Research Document 2004/002

Temperature Conditions on the Scotian Shelf and in the southern Gulf of St. Lawrence during 2003 Relevant to Snow Crab.

By Chassé, J., K.F. Drinkwater, R.G. Pettipas, W.M. Petrie

Abstract

Temperatures during 2003 are presented for the waters of Maritime Canada inhabited by snow crab. Data were available from a number of sources including snow crab and groundfish surveys on the Scotian Shelf and the Magdalen Shallows in the Southern Gulf of St. Lawrence. Bottom temperatures within the snow crab fishing areas of the southern Gulf of St. Lawrence were generally cooler-than-average in 2003 except for the shallower regions where warmer-than-normal conditions were observed. Over the central Magdalen Shallows, temperatures decreased in 2003 compared to 2002 and there was more water with temperatures <0°C. In the northeastern Scotian Shelf, bottom waters were significantly colder than the long-term average (1971-2000) having cooled relative to observations in 2002. A snow crab habitat index, defined by the area of the bottom covered by waters between
-1° to 3°C, was calculated for each of the southern Gulf, Sydney Bight and northeastern Scotian Shelf regions. The index for the Gulf rose compared to 2002, but it is still below the long-term mean value. On the Scotian Shelf, the index increased by 50% and it is above its long-term average with the highest value of the timeseries. In Sydney Bight the habitat index also increased compared to 2002 and is significantly above its long-term mean. The crabs caught during the annual snow crab surveys were found in colder waters in 2003 than in 2002, which is believed to reflect in large part the availability of cooler temperatures.

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