Madison River Trout Under Attack

A disease with the potential to devastate Montana’s world-class rainbow trout fishing was confirmed recently in the upper reaches of the Madison River.

Myxobolus cerebralis, better known as whirling disease, apparently had killed 90 percent of the rainbows in a 50-mile stretch of the fabled stream since 1990.

Whirling disease, which already has wreaked havoc in Colorado trout, can eventually cause major dieoffs in young rainbows, said Colorado state fish pathologist Pete Walker.

“Since about 1986, it has stormed the western United states,” he said. “It overwhelmed us before we ever knew it was here.”

The disease apparently was spread through Colorado by private fish hatcheries that released diseased fish, he said.

Migratory birds eat infected fish and could have brought the parasite in their wastes, said Rick Barrows, a U.S. Fish and Wildlife Service nutritionist.

The Montana fisheries biologist who first suspected the disease, however, still believes it was brought to Montana with illegally planted hatchery fish.

“I’m convinced it’s not birds,” said Dick Vincent, a regional fisheries manager for Montana Department of Fish, Wildlife and Parks. Vincent contends hatchery fish were illegally planted in the Madison in the late 1980s. He has a photograph of a trout caught near the West Fork in 1989 bearing what he says are scars of a hatchery environment.

Montana biologists fear there’s no way to stop the disease from spreading to rainbow stocks in the Gallatin, Jefferson, Big Hole, Beaverhead and Missouri rivers.

Whirling disease attacks the cartilage of young trout, making the fish more vulnerable to disease and predators. The name comes from the tail-chasing behavior of infected fish. The disease is not a threat to human health, Walker said.

The disease has been found in 18 states, including California, Idaho and Utah.

Previously, the closest population of infected trout to Montana was in Idaho’s Salmon River.

“There’s really very little we can do about it,” Walker said. “You either switch to another kind of fish or you start stocking.”

That’s a bitter pill for Montana, since it has been a leader among the many western states that have weaned from hatchery production to build hardier naturally reproducing rainbow populations.