Lake trout

(Salvelinus namaycush)

Order: Salmoniformes Family: Salmonidae Subfamily: Salmoninae

Foto: Lauri Urho

Description: The lake trout varies in colour from almost silver to green or brownish grey and is covered with yellowish spots. It is a large-mouthed fish and, unlike the charr (Salvelinus alpinus), never has a red belly.

Origin and distribution: The lake trout is native to Canada, Alaska, the northeastern United States and the Great Lakes region. It was introduced into Europe over 100 years ago, and into Finland in 1955. Since then lake trout have been stocked in many lakes in this country, since 1972 mainly in Inarijärvi, in the north, the intention being to compensate for Arctic charr catches lost due to water level regulation. The spawning grounds of lake trout are deeper than those of Arctic charr, and it was assumed that they would be able to reproduce naturally in the lake.

Reproduction: Lake trout reach sexual maturity at age of 5─8 years of age. They spawn in the autumn on clean gravel bottoms at 2─30 m depth. Mature fish weighing 2 to 5 kg have been caught in Lake Inarijärvi, but there is no evidence of spawning success. The stock is dependent on regular stocking, and the broodstock is kept in a governmental fish hatchery.

Diet, growth and migrations: In their early life stages, lake trout feed on zooplankton and bottom fauna. At a length of 20 cm they start to prey on fish, including nine-spined stickleback (Pungitius pungitius), vendace (Coregonus albula) and, in Inarijärvi, dwarf whitefish (Coregonus lavaretus) in particular. Lake trout grow slowly and live to a great age, even 30─40 years. According to tagging experiments conducted in Lake Inarijärvi, fish released at 30 cm reach a length of 50 cm in 4─5 years. Lake trout caught in Inarijärvi commonly weigh from 0.7 to 2 kg, though weights of over 7 kg are not unknown.

Fishing and catches: There is no evidence of natural reproduction of lake trout in Inarijärvi. During the last 10 years the number of stocked fish has been small compared with the size of releases in the 1980s. In the mid-1990s, the annual catch totalled about 5 tonnes, about 12 tonnes in 2001-2002, and 8 tonnes in 2003.

Vulnerability, threats and management: Lake trout grow slowly, and young fish often get tangled in gillnets by their teeth. Finland’s Fishing Act does not prescribe a minimum allowable catch size for lake trout.

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