The potential damage a lake trout population can cause to cutthroat is enormous.
For starters, a lake trout lives through two or three generations of a cutthroat. A lake trout may live for 25-40 years, a cutthroat, maybe 10 years.
“Lake trout are so long-lived,” says Pat Bigelow, fisheries biologist. “A seven-year-old cutthroat is sort of an old fish. If you have seven years of serious impact on the juveniles coming up, you could lose your whole population.”
A big lake trout taken from Yellowstone Lake weighs 21.5 pounds. A big cutthroat in the lake – maybe even a trophy catch – would weigh about five pounds.
As soon as a lake trout reaches four years old, it begins eating cutthroats, which make up half of its diet. A couple of years later, it eats cutthroats almost exclusively. Typically, a mature lake trout will eat 50 cutthroats a year. The non-native lake trout are not only eating several cutthroats a year, but they compete with the native fish for the same food sources. Lake and cutthroat trout both feed on leaches, amphipods, and lake midges.
A life cycle for domination
Lake trout are a reproductive bunch, spawning eight to 10 years in a row, each time yielding 1,000 eggs per kilogram of body weight. This means a 20-pound lake trout could produce 10,000 eggs. If just one percent of those eggs survive, you’re talking 100 new lake trout born to a single fish in one year. On the other hand, a cutthroat may spawn only once or twice during its lifetime.
It doesn’t take a calculator to conclude that lake trout will do serious damage in a short amount of time if left unchecked at Yellowstone Lake.
A panel of fisheries experts that met in 1995 to assess the lake trout’s presence and likely impacts on Yellowstone cutthroat population estimated that, with effective suppression of lake trout numbers, the cutthroat population decline might be held to 10 to 20 percent of present levels. Without some control of lake trout, the experts predicted the cutthroat population would be reduced by 70 percent in 100 years.
Other impacts
The cutthroat population is valued ecologically, economically and socially. Cutthroat trout live and spawn in shallow streams and waters, providing prey for at least 42 species of birds and mammals. Grizzly bears, otters, eagles, white pelicans and osprey are just a handful of the animals that stand to lose a valuable food source if the Yellowstone Lake population is diminished.
Furthermore, the cutthroat trout in the lake help generate $36 million in revenues resulting from the world-class sport fishing found in Yellowstone and surrounding communities. Anglers come from all over the world to fish for these native wild fish.
