(NPS / Dylan Schneider)

CASPER, Wyo. — Yellowstone National Park is working to remove nonnative lake trout in order to allow populations of native cutthroat trout to recover.

They removed 282,960 fish between May and October this year. Over 3.4 million have been removed since 1994.

“The number of lake trout caught in nets continues to steadily decline, from 4.4 per net in 2017, and 3.1 per net in 2018, to just 2.9 per net in 2019,” Yellowstone officials said in a Friday, Nov. 22 announcement.

Netting less fish in the removal efforts suggests that the park’s efforts are working.

“In order to predict the success of the removal effort and set benchmarks for gillnetting in the future, Yellowstone National Park and Michigan State University collaborate to generate statistical models of the lake trout population,” the park adds. “The models suggest there are 73% less lake trout ages six and older in Yellowstone Lake now than were present at the population’s peak in 2011.”

“This is critical because older, larger lake trout have the highest reproductive potential and consume the most cutthroat trout. The models also indicate that the invasive species has been in decline since 2012.”

The park’s monitoring efforts also indicate that the number of cutthroat trout are on the rise.

“Cutthroat that inhabit the lake migrate more than 30 miles up into the Upper Yellowstone and Thorofare streams where they spawn and then return to the lake,” Yellowstone says. “This July, fisheries staff found large numbers and sizes of cutthroat in these backcountry streams.”

“Ten years ago, few cutthroat were present. This long distance migration highlights the spatial extent to which the recovery of the cutthroat impacts Yellowstone.”

At least five more years will be needed to reach the goal of reducing lake trout populations to below 100,000, the park says. Current techniques won’t be able to completely eradicate that species.

“Yellowstone fishery biologists continue to explore alternatives to gillnetting that will augment lake trout suppression, increase efficacy, and reduce costs,” the release adds. “For example, over the last few years, biologists tested a method to suppress the population by killing lake trout eggs on spawning sites.”

“One technique involved placing plant-based organic pellets on spawning sites to facilitate decomposition and loss of dissolved oxygen. This method killed eggs within two days. Since the results are promising, the park intends to expand the technique in the future.”

Over $20 million have been spent in the past two decades in Yellowstone’s work to recover cutthroat trout populations.



“Much of that funding has come from the generosity of donations through Yellowstone Forever,” the release adds. “Native cutthroat trout are the park’s most ecologically important fish and the most highly regarded by visiting anglers.”

“It is an important food source for grizzly bears, birds of prey, and other wildlife. The cutthroat decline resulted in several of these species being displaced from Yellowstone Lake or having to use alternate food sources during certain times of the year.”

More about Yellowstone’s work is available from their 2015 – 2018 YCR Fish Report and Native Fish Conservation Program.