Research Document 1998/120

Marine environmental conditions in the Northwest Atlantic during 1997 potentially impacting Atlantic salmon (Salmo salar)

By K. Drinkwater

Abstract

Marine environmental conditions during 1997 in the Northwest Atlantic that could potentially impact eastern Canadian Atlantic salmon stocks are reviewed from available atmospheric and oceanographic datasets. The Labrador Sea is of particular interest because it is the overwintering site for most of these stocks. In the Labrador Sea, environmental conditions were cooler than in 1996 but generally warmer than the early 1990s. During 1997 above normal winter air temperatures were observed, however, the first half of the winter was very warm while the second half was very cold. The spring air temperatures also tended to be below normal. The air temperatures are linked to the strength of the North Atlantic Oscillation (NAO) which is a measure of the large scale atmospheric circulation pattern. The NAO index increased relative to 1996 but was well below that of the early 1990s. A low NAO index is associated with weaker NW winds over the Labrador Sea and warmer air and sea temperatures. Some of the inner Bay of Fundy salmon stocks are known to overwinter in the Gulf of Maine instead of migrating to the Labrador Sea. In the Gulf of Maine, in situ measurements of surface temperatures were above normal in the winter, cooled in the spring and were generally above normal through the rest of the year. Seasonal sea surface temperature patterns were extracted from the MCSST data set. Anomalies in various regions varied in sign throughout the year, but much of the offshore North Atlantic and Labrador Sea was warmer than normal for most of the year. Over the continental shelves, the Grand Banks was relatively warm while the Scotian Shelf/Gulf of Maine region was characterized by both positive and negative anomalies as was the Gulf of St. Lawrence.

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