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Why Lake Trout are a Problem

Why Lake Trout are a Problem

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Lake trout were introduced into Flathead Lake in 1905, but substantial catches were not recorded until the 1940s, and for the next 50 years, the population grew slowly. Then, in the period from 1968 to 1976, Mysis (or opossum shrimp) were introduced into the basin. The shrimp provided abundant food for juvenile lake trout, greatly expanding the lake trout population.

While Mysis and other invertebrates make up two-thirds of the lake trout diet in Flathead Lake, lake trout also eat fish, which represent the remaining third of their diet. Lake trout prey on nearly all fish species in Flathead Lake, and they have hit bull trout and westslope cutthroat trout hard. Bull trout were listed as a Threatened species under the Endangered Species Act in 1998, and populations in the Flathead Basin have declined to the point that many experts are concerned that bull trout could become extinct in the basin. Westslope cutthroat trout have declined by roughly two thirds since monitoring began in 1981.

HoldingFish2
Lake trout were introduced into Flathead Lake in 1905, but substantial catches were not recorded until the 1940s, and for the next 50 years, the population grew slowly. Then, in the period from 1968 to 1976, Mysis (or opossum shrimp) were introduced into the basin. The shrimp provided abundant food for juvenile lake trout, greatly expanding the lake trout population.

While Mysis and other invertebrates make up two-thirds of the lake trout diet in Flathead Lake, lake trout also eat fish, which represent the remaining third of their diet. Lake trout prey on nearly all fish species in Flathead Lake, and they have hit bull trout and westslope cutthroat trout hard. Bull trout were listed as a Threatened species under the Endangered Species Act in 1998, and populations in the Flathead Basin have declined to the point that many experts are concerned that bull trout could become extinct in the basin. Westslope cutthroat trout have declined by roughly two thirds since monitoring began in 1981.

HoldingFish2
Lake trout were introduced into Flathead Lake in 1905, but substantial catches were not recorded until the 1940s, and for the next 50 years, the population grew slowly. Then, in the period from 1968 to 1976, Mysis (or opossum shrimp) were introduced into the basin. The shrimp provided abundant food for juvenile lake trout, greatly expanding the lake trout population.

While Mysis and other invertebrates make up two-thirds of the lake trout diet in Flathead Lake, lake trout also eat fish, which represent the remaining third of their diet. Lake trout prey on nearly all fish species in Flathead Lake, and they have hit bull trout and westslope cutthroat trout hard. Bull trout were listed as a Threatened species under the Endangered Species Act in 1998, and populations in the Flathead Basin have declined to the point that many experts are concerned that bull trout could become extinct in the basin. Westslope cutthroat trout have declined by roughly two thirds since monitoring began in 1981.

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Research indicates that bull trout and westslope cutthroat trout declines are the result of lake trout increases. Because increases in the lake trout population have put native trout at risk, there is a need to reduce the risk through the gillnetting program the Tribes have implemented.

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Native Fish Keepers, Inc.
408 6th Ave. East
Polson, MT 59860
© 2017 Confederated Salish and Kootenai Tribes

Native Fish Keepers, Inc.
408 6th Ave. East
Polson, MT 59860
© 2017 Confederated Salish and Kootenai Tribes

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