Non-Native Lake Trout Numbers Declining, Yellowstone Officials Say

Nov 26, 2019

Yellowstone National Park says it’s making progress reducing the number of non-native lake trout. 

Park and contract crews caught and killed over 280,000 lake trout from Yellowstone Lake between May and October, according to a press release Friday. The total tally is less than last year and the year before that, which is a good thing.

Catching fewer lake trout means the non-native fish population is shrinking and the last genetically pure Yellowstone cutthroat trout population has a better chance of recovering.

Yellowstone cutthroats are the linchpin in a complex food web that includes animals as small as zooplankton and as large as grizzly bears. When lake trout showed up in Lake Yellowstone in the 1990s and started feasting on cutthroats, the native fish population plummeted and the whole food web was disrupted.

Through rigorous gillnetting and millions of dollars, park staff and contractors have managed to catch and kill over 3 million adult lake trout since 2012, reducing the population by 70 percent.

Yellowstone fisheries biologist Todd Koel said in earlier reporting that there are still probably about half-a-million adult lake trout in Yellowstone Lake, but the cutthroat population is on the upswing.

A panel of expert fishery scientists in May estimated that at least five more years of aggressive gillnetting and other suppression tactics are needed to get the lake trout population below 100,000. They emphasized that lake trout cannot be completely eradicated and will continue to require annual removal and monitoring into the future.

Researchers have been experimenting with dropping plant-based pellets on spawning sites to smother lake trout eggs to knock out the next generation.