Research Document - 2000/058

Temperature conditions on the Scotian Shelf and in the southern Gulf of St. Lawrence during 1999 relevant to snow crab.

By K.F. Drinkwater, R.G. Pettipas, and L. Petrie

Abstract

Temperatures during 1999 are presented for the waters of Maritime Canada inhabited by snow crab. Data were available from a number of sources including groundfish surveys on the Scotian Shelf and Sydney Bight in July and on the Magdalen Shallows in the Gulf of St. Lawrence in September as well as at other times of the year from other fisheries surveys, research studies and ships-of-opportunity. Bottom temperatures in large portions of these shelf regions were between -1° and 3°C, conditions considered ideal for snow crab. However, the snow crab habitat index defined by the area of the bottom covered by waters between -1° to 3°C for each of the southern Gulf, Sydney Bight and northeastern Scotian Shelf declined from the relative high values that have persisted since the late-1980s. In all areas the habitat index was below the long-term mean for the first time in 4 years in the Gulf and in 11 years on the Bight and the Shelf. Although bottom temperatures within the snow crab fishing areas of the southern Gulf of St. Lawrence to the northeastern Scotian Shelf have been colder-than-average for most of the past 15 years, they have been warming since lows in the early to mid-1990s. This warming continued in 1999 and temperatures were above normal for the first time in a decade or more in most fishing areas. Exceptions were Areas 12 and F, where in spite of the warming they continued to have below normal average bottom temperatures, although they almost reached normal values during 1999. Temperature trends showed strong similarities between the Magdalen Shallows and the northeastern Scotian Shelf. Temperatures in LaHave and Roseway Basin where exploratory fishing for snow crab (NAFO Division 4X) was carried out in 1999 are also presented.

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