This year, fisheries biologists will get to add a new commercial gill netting boat to their operation. While the largest lake trout taken from Yellowstone Lake was 21.5 pounds, the largest cutthroat trout in the lake weighs about five pounds, and that would probably be considered a trophy. The size isn't the only difference between cutthroats and lake trout. Life expectancy for a cutthroat is about 10 years, while Mahoney says lake trout can live to be 25-40 years old. In other words, one lake trout lives through two generations of cutthroats.
Cutthroats spawn only once or twice during their entire lifetime.
Lake trout may spawn eight to 10 years in a row. On average, a lake trout has 1,000 eggs per kilogram of body weight. That means a 20-pound fish could produce 10,000 eggs. If just one percent of those eggs survive, that's 100 new lake trout born to a single fish. In addition to being eaten by the non-native lake trout, cutthroats also are being impacted by a competition that exists.