Yellowstone Lake Trout Suppression

Tyler Klippel, a private netting contractor from Fredonia, Wisconsin, untangles lake trout from a gill net aboard a National Park Service fishing boat on Yellowstone Lake last September. Numbers of netted lake trout are down nearly 40 percent, suggesting a potential population crash of the invasive species.

A quarter-century after a Yellowstone Lake angler’s exotic catch first alarmed fisheries managers, the population of the non-native lake trout finally appears to be crashing.

Yellowstone National Park and its partners have netted lake trout since the turn of the century, and for the past seven summers have spent millions of dollars annually catching and killing the fish. But the overall hauls, in terms of total numbers of lake trout caught, continued to climb.

Then this summer the catch abruptly fell off.

“In 2018 so far, we’ve caught basically 155,000 lake trout,” Yellowstone fisheries chief Todd Koel said, “and that’s 63,000 less than this time last year.”

“That’s huge,” he said. “It’s a real signal that this population is finally crashing. It’s what our science has predicted and the population modeling has predicted, and now we’ve finally started seeing it on the ground, which is great.”

The lake trout killing is the centerpiece of a long-term fight to help Yellowstone’s native cutthroat trout recover from a predation-driven crash of their own.

The mackinaw catch declined 37 percent year over year, Koel said, even though there was a concurrent increase in the level of netting pressure.

Almost all the difference comes from smaller fish, which aren’t turning up in small-mesh gill nets in as high of numbers. A year ago, nearly 350,000 of the 400,000 caught and killed were classified as small fish, those perhaps a foot or so long, Koel said.

“There have been less and less large lake trout out there for many, many years,” he said. “Now we’re seeing declines in the smaller fish.”

The lack of 2- and 3-year-old mackinaw showing up in gill nets suggests that the slaying of larger lake trout slowed down reproduction several years ago. This “recruitment,” in biologist speak, is declining.

The National Park Service had been predicting the crash of Yellowstone’s lake trout population for several years. Entirely eliminating lake trout in the 136-square-mile lake is believed to be an impossibility, and so the suppression efforts, in some form, will likely continue in perpetuity.

A 2015 Montana State University dissertation predicted that it would take another 14 years of intensive lake trout killing to rebound native cutthroat trout to conservation goals sought by managers.

Koel affirmed that there’s no plan to ease up on the program.

“We have no intention of letting off on the netting pressure at all,” he said. “In fact, we’ve been talking about increasing it more. We want to put the nail in the coffin of these lake trout.”

The resources enabling the intensive lake trout killing regime keep coming in. Yellowstone’s netting program runs about $2 million a year, a cost that’s about evenly accounted for by entrance gate collections and the supporting park organization Yellowstone Forever.

Koel and his contracted fishing crews recently received a one-time infusion of capital to bolster the campaign. California philanthropists Julia and George Argyros in late June granted the National Park Foundation $500,000 to help with the effort.

“Because of my passion for fishing, I understand the importance of native species and how we can all help with their preservation,” Argyros Family Foundation President Julia Argyros said in a statement. “My family and I are honored to support these critical efforts to save the cutthroat trout at Yellowstone National Park.”

The gift, Koel said, was unexpected, but useful and welcome.

“It’s the largest single family gift that I’ve ever seen,” he said.

Contact Mike Koshmrl at 732-7067, or @JHNGenviro.

Mike has reported on the Greater Yellowstone Ecosystem's wildlife, wildlands and the agencies that manage them since 2012. A native Minnesotan, he arrived in the West to study environmental journalism at the University of Colorado.

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