Research Document - 2006/018

Perspectives on the marine ecology of Atlantic salmon (Salmo salar) in the Northwest Atlantic

By Reddin, D.G.

Abstract

The ecology of Atlantic salmon (Salmo salar) in the Northwest Atlantic Ocean is reviewed. Atlantic salmon spend time in freshwater and in the sea and both habitats are consequently important to its life history and survival. The importance of the Labrador Sea as a nursery area for postsmolt salmon from stocks ranging along the entire length of its freshwater habitat in North America is idenfifed from research vessels fishing in the Labrador Sea and gannet feeding studies. All sea ages of salmon are shown to be present in the Labrador Sea and probably over-winter there as well. Salmon that will be multi-sea winter in age when they return to freshwater are found annually in abundance in the Greenland area. Also, there are documented migrations of North American salmon to the eastern side of the Atlantic, although the overall numbers are thought to be low. Temperature preferences of adult and postsmolt salmon are depicted from research vessel catch rates and temperature profiles. Postsmolts appear to select a much narrower range of temperatures at sea than do adults. Postsmolts preferred temperatures from 5 to 8°C; while adults were found abundantly from 4 to 10°C. The lack of any relationships between numbers of adult salmon or their return rates to counting facilities compared to the numbers of smolts leaving rivers suggests that carrying capacity in the Northwest Atlantic is not limiting salmon abundance. Studies with data storage tags show that salmon spend much of their time in the surface waters but also dive deeper in the water column probably in search of prey. Salmon are found closer to the surface at night then during the day. Migration routes to and from the Labrador Sea and Greenland area are shown. Migration in relation to surface currents in the North Atlantic is discussed. Many studies are available showing relationships between marine climate and salmon growth and survival in the sea. The North Atlantic Oscillation Index seems to be related to salmon abundance in the Northeast Atlantic but not in the Northwest.

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