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Killing one fish to save another in Yellowstone


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Commercial fishermen manage up to 40 miles of net on any given day at Yellowstone Lake in Yellowstone National Park. | Kris Millgate, Tight Line Media

YELLOWSTONE NATIONAL PARK — White-breasted gulls are following a slow-moving boat in Yellowstone Lake. The crew on board is up to something fishy.

It’s four fishermen letting out an awful lot of net. The net sinks into the lake’s deep depths in a large S-curve created by the swerve of the captain’s turns. The crew manages up to 40 miles of netting. That netting collects 300,000 lake trout every summer.

“We are aggressively netting non-native lake trout in Yellowstone Lake to reduce their predation on our native cutthroat,” says Todd Koel, Yellowstone National Park native fish conservation leader.

An angler turned in an unusual catch in 1994. It was a fish that wasn’t supposed to be in Yellowstone Lake — a lake trout. The surprise catch hooked biologists with an unexpected problem. They had an invader in a fishery carefully monitored for the persistence of the park’s coveted native fish, Yellowstone cutthroat trout.


Todd Koel, Yellowstone National Park native fish conservation leader, explains the park’s gillnetting operation while motoring to the commercial fishing boat on Yellowstone Lake. | Kris Millgate, Tight Line Media

“We’re not going to allow that in Yellowstone National Park,” Koel says. “This place is much more than that. We’re way better than that.”

Lake trout have aggressive appetites. They made quick work of eating native swimmers. By mid 2000s, 90 to 95 percent of the native Yellowstone cutthroat trout in Yellowstone Lake were gone.

“The problem is lake trout are like large wolves on the landscape, only in the lake,” Koel says. “Large, highly predatory, fish-eating machines essentially.”

The park’s fisheries biologists are fighting those fish-eating machines with intensity. The goal is a lake trout population crash. That’s what the commercial fishing boat from the Great Lakes region is for. The crew, with gulls in their wake, put out gillnets as fast as they bring fish in. They work the waters from May to October. They fill stacks of black bins with dead lake trout. Cut open any of the dead fish and there’s up to eight cutthroat trout inside.

“It is disappointing when we find the lake trout with all the cutthroat in the their stomach,” Koel says. “But then again, it’s also satisfying because this is a lake trout that’s no longer swimming around in the lake. It’s gone.”

Dead lake trout are dumped back into the lake to decompose adding nutrients.


The Yellowstone National Park fisheries department oversees a gillnetting operation that kills 300,000 non-native lake trout annually in Yellowstone Lake. Yellowstone Lake is home to native Yellowstone cutthroat trout, which are declining because of lake trout. | Kris Millgate, Tight Line Media

Gillnetting started in 2009. This year is a significant milestone. It’s the halfway mark. If the program is working, researchers should know it by now. There should be signs of turn around. Those signs are subtle, but they exist and for wallets and wildlife that’s encouraging.

“This fish is more than just a fish. It’s a vital part of the economy in this area. It represents about $30 million annually,” says Dave Sweet, Wyoming Trout Unlimited Yellowstone Lake special project manager. “Plus, it’s a keystone species in this ecosystem. At one time, it was part of the diet of some 40 other animals in this ecosystem.”

Those animals left the lake when the cutthroat disappeared. Now they’re coming back. This spring, grizzlies keyed in on spawning cutties and more fishermen showed up opening day than the park has seen in at least five years. The cutthroat are coming back, but success isn’t a given until the lake trout crash and stay crashed.

“There are much stronger pulses of fish returning to lake ecosystem than we saw before,” Koel says. “All signs are up for the cutthroat trout.”

Outdoor journalist Kris Millgate is based in Idaho Falls, Idaho. See her work at