Distribution and migration of Atlantic salmon, Salmo salar L., in the sea.

Atlantic salmon are distributed over large areas in the North Atlantic Ocean during ther migrations between fresh water and their feeding grounds at sea. -the are observed from Connecticut to Ungava Bay in North America, -and in Europe from northern Portugal to the border between Europe and Asia in northern Russia.
Atlantic salmon are also present around the British Isles, Ireland, Iceland and Greenland. In some Oceanic Areas, for example in the Norwegian Sea, north of the Faroe Islands and between West Greenland and Labrador, the number of immature salmon has been sufficiently large to encourage commercial fisheries (Millz 1993). Atlantic salmon may spend 1-5 years in the ocean until the become sexually mature. Depending on the population and duration of marine residence, the weight may range from 1 to 30 kg.
Many studies have shown that Atlantic salmon home the stream they left as smolts (Malloch 1910, Carlin 1969, Swain 1982, Hansen et al 1993, Potter & Russel 1994, Youngson et al. 1994). The mechanisms underlying salmon orientation on the ocean are still a matter of controversy (Quinn 1990) but it is generally accepted that salmon smolts imprint on, or learn the odour of, their home river (Carlin 1969, Hasler & Scholz 1983, Dittman & Quinn 1996), and use that information in the final (estuarine and riverine) stages of homeward migration. Ocean migrations, however, appear to be guided by compass and perhaps also map navigational systems (Dittman & Quinn 1996).
Hansen & Quinn (in press) described and discussed som important characteristics of the Atlantic salmon during the marine phase. In this paper we briefly review some of the information available on stock composition of pre-adult salmon in the ocean and discuss mechanisms controlling migration of homing salmon.