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COSEWIC assessment and status report on the Atlantic Salmon (Lake Ontario population) in Canada

Species Information

Name and classification 

The Atlantic salmon (Salmo salar) or saumon atlantique is in the family Salmonidae which includes Atlantic and Pacific salmon, trout, charr, grayling and whitefishes (Mills 1989).  Atlantic salmon have several other common names in English and French, many of which refer to the geographical location of a population or a specific life stage.  Names such as black salmon, grilse, grilt, kelt, grayling, smolt, slink, fiddler, and parr are all lifestage references (Scott & Crossman 1973).  Populations which spend their entire life cycle in freshwater are often referred to as lake Atlantic salmon, non-anadromous salmon, ouananiche, sebago, freshwater salmon or saumon d'eau douce (Scott & Crossman 1973, MacCrimmon & Gots 1979).  They have been found in lakes in New Brunswick, Quebec, Newfoundland, Ontario (Lake Ontario; and an introduction into Trout Lake, Ontario), and the New England states.  



The most complete description of Atlantic salmon can be found in Scott and Crossman (1973) where they are described as having a "trout-like" body with an average length of about 18 inches (457 mm), somewhat compressed laterally, with the greatest body depth usually at the dorsal fin origin or slightly posterior to it (Figure 1).  The sea salmon has a blue-green back, silvery sides and a white belly (Carcao 1986).  There are several X-shaped and round spots mostly above the lateral line (Carcao 1986).  When a marine salmon reenters freshwater it loses the silvery guanine coat replacing it with hues of greenish or reddish brown and large spots that are edged with white (Scott & Crossman1973, Carcao 1986).  Juvenile salmon or salmon parr display parr marks or pigmented vertical bands with a single red spot between each parr mark along the lateral line (Scott & Crossman 1973).  When parr become smolts and go to sea, the parr marks are lost and the fish become silvery (Scott & Crossman 1973).  Adult Lake Ontario salmon and other freshwater salmon were reported to be darker than the "true" salmon found on the east coast and in the British Isles (Dymond 1965).


Designatable units 

Approximately 40 tributaries of Lake Ontario were known to support runs of Atlantic salmon (Parsons 1973).  The Credit River was "reputed to be the best salmon river in Upper Canada" (Wilmot 1879).  Scales obtained from two adult museum specimens indicate an exclusively freshwater growth history, suggesting that the salmon that originally inhabited Lake Ontario was most likely a non-anadromous (freshwater) form (Blair 1938). 

Some authors have suggested that prior to the construction of the R.H. Saunders dam in 1958 in the St. Lawrence River, Atlantic salmon would have been able to migrate to the Atlantic Ocean, aside from the distance of 2400 km (Carcao 1986).  However, there is compelling evidence that Lake Ontario Atlantic salmon were isolated from the sea and did not mix with other non-anadromous populations.  The spring date of runs into Lake Ontario tributaries occurred earlier than possible for adult Atlantic salmon to have returned from the ocean. Two runs occurred, one in spring (March/April) and one in fall (Sep/Oct).  Wilmot (1879) reported that salmon appeared in the Humber River in April, and the earliest recorded date in the year for the capture of salmon was March 17.  Anadromous individuals are unlikely to have been capable of moving into Lake Ontario so soon after the ice left the St. Lawrence and arrive in the prime condition noted in the Oswego River in New York, and in the Credit and Humber Rivers in Canada (Webster 1982).  It is therefore highly likely that the Lake Ontario Atlantic salmon population was geographically and reproductively isolated from other Atlantic salmon populations in North America.  Ongoing genetic studies to test this hypothesis are constrained by small sample sizes (historic mounts).

Figure 1.  The Atlantic Salmon. Source: A.H. Leim and W.B. Scott. Fishes of the Atlantic coast of Canada. (1966)

Figure 1.  The Atlantic Salmon. Source: A.H. Leim and W.B. Scott. Fishes of the Atlantic coast of Canada. (1966)