​Yellowstone Trout Population Showing Signs of Life

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May 8, 2021

The Yellowstone National Park trout population is showing signs of life after a non-native species began to kill off the trout, but government scientists say that there are signs of decline after making an effort to kill off the invading fish.

Non-native lake trout were first discovered in Yellowstone Lake in 1994, after being illegally introduced to the 132-square-mile body of water that attracts visitors from around the world.

Crews have since netted and removed about 1.4 million of the fish in hopes of cutthroat trout populations rebounding. Adult lake trout in Yellowstone can top 30 pounds, living almost exclusively on a diet of cutthroat trout, according to researchers.

The netting costs about $2 million annually, drawing criticism that too much money is being spent to kill off a species that’s highly prized by anglers elsewhere.

Backers of the removal effort insist it’s worth the cost. Yellowstone cutthroattrout are considered a keystone animal in the country’s first national park, providing food for 42 birds and mammals including grizzly bears, osprey and bald eagles. Prior to the first lake trout being found, the native trout supported a recreational fishery valued at $30 million annually in the early 1990s.

Whether that fishing economy can fully rebound is uncertain.

After years of scant improvement, the netting efforts finally have begun to show progress, according to scientists from the park and the conservation group TroutUnlimited.

The population of the invasive trout is beginning to decline, a recent analysis by researchers from Montana State University indicated. Meanwhile, the numbers of young cutthroat trout are increasing, laying the groundwork for a rebound for the smaller, native fish.

“I’m very encouraged by some of our recent successes,” said David Hallac, chief of the park’s science center. “The goal is to crash the population of laketrout to a point where they are no longer adversely impacting Yellowstonecutthroat trout.”

Park officials sharply expanded the lake trout removal program in recent years, bringing in contract fishing companies that set tens of thousands of feet of gillnets to sweep up more of the fish. About half the cost of the program comes from outside sources.

Native trout sometimes inadvertently end up in the nets set for the invaders.

It’s unlikely lake trout will be wiped out entirely, meaning some level of management will be required to keep them from again crowding out native fish, said Jack Williams, senior scientist for Trout Unlimited.