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Atlantic Salmon Biology

Atlantic Salmon (Salmo salar) are a large, silvery species of salmon with small black spots over most of the body, with the colour changing to a deep bronze when spawning. Colour can be highly variable, however, with brown, green, or blue shades possible on the back, and sometimes during spawning reddish spots are seen on the head and body. Use either this or this fact sheet to help you distinguish Atlantic Salmon from other salmon and trout species in Lake Ontario.

Atlantic Salmon

Average sizes of 28-30 inches and 8-12 pounds were probably typical in the historical population of Lake Ontario. A 35 inch, 24.3 pound fish caught in 1989 is the Ontario record for the species, and came from New York’s put-grow-take program for Atlantic Salmon. Old records suggest fish up to almost 45 pounds were occasionally caught.

Most Atlantic Salmon populations are sea-running, with adults returning to their natal freshwater stream and spawning in the fall. Young Atlantic Salmon spend 1-7 years in the river before migrating to the sea to grow to adulthood. Other populations, including Lake Ontario’s former population, are fully or partially landlocked, living as adults in freshwater lakes and spawning in the lake’s tributaries. Historically, 40 tributaries of Lake Ontario supported runs of Atlantic Salmon. Unlike many west-coast salmon species, Atlantic Salmon survive spawning and return to the lake/ocean until the next spawning season, though the number of repeat spawners is highly variable across rivers.  Like other salmon, Atlantic Salmon return to spawn in the same river where they themselves hatched.

When they existed in Lake Ontario, adult Atlantic Salmon were top predators in the lake, along with Lake Trout and Burbot. They fed primarily upon lake herring, and probably slimy sculpins; they also feed upon alewife and rainbow smelt in the current Lake Ontario ecosystem. Before reaching maturity, Atlantic Salmon feed on invertebrates as well as fish.

Sea-running Atlantic Salmon are found from the Arctic Circle to Portugal, from northern Quebec and the northeastern coast of North America to Iceland, Greenland, and northern Europe, anywhere there is a tributary leading to the North Atlantic Ocean and Baltic Sea. North American landlocked populations are found in Newfoundland and Labrador, Quebec, Michigan, Vermont and Maine. A stocked population exists in Trout Lake, Ontario.

Range for Atlantic Salmon. Red=extirpated population (locally extinct), dark yellow=extant (existing), light yellow=probably extant. Source: IUCN

Atlantic Salmon migration and feeding routes. Source: Atlantic Salmon Federation

The Atlantic Salmon of Lake Ontario were the only native population of the species in Ontario, as Niagara Falls prevented their migration into Lake Erie. The story of their original relationship with humans and how they were extirpated (became locally extinct) continues in the Early History of Atlantic Salmon in Ontario.