The National Park Service is trying to get rid of lake trout, which were discovered in Yellowstone Lake in 1994. Lake trout is an invasive predator species that feeds on cutthroats.

“They’re a wonderful fish, but they just don’t belong here,” Phil Doepke, a fisheries biologist who has been part of the cutthroat-trout conservation effort for 14 seasons, told the Powell Tribune in Wyoming.

Computer modeling indicates the lake trout population will collapse within 10 years, said Todd Koel, the park’s senior fisheries biologist told the paper in an update on the effort. “Lake trout are in decline, but it doesn’t happen overnight,” he said.  More via AP:

Researchers use nets to remove lake trout. They have removed 2.6 million pounds (1.2 million kilograms) since 1996, including more than 366,000 pounds (166,000 kilograms) last year.

They also locate and destroy lake trout eggs at spawn sites.

Biologists are finding more efficient ways to remove lake trout every season, Koel said. They now implant transmitters in individual lake trout, called Judas fish, and release them to study their patterns.

“The Judas fish lead us to their friends, and then we kill them,” Koel said.

Small aircraft search for the transmitter-equipped fish, covering the entire 22-mile (35-kilometer) lake in about two hours, far faster than boats. “I’m hopeful we can shift completely to flights to find fish soon,” Koel said.

Recreational anglers also help. The fishing season opened in late May, and anglers can catch as many lake trout as they like – and they’re not allowed to throw any back.

“Catch them, kill them and eat them,” Yellowstone National Park Superintendent Dan Wenk said.

More than 50,000 visitors buy the required Yellowstone fishing permit each year.