Whirling Disease Could Spread

A nervous-system infection that has devastated the rainbow trout population in a stretch of Montana’s Madison River might affect the trophy rainbow fishery on the Henry’s Fork of the Snake River.

“Theoretically, it could be a threat,” said Mark Gamblin, Region 6 fisheries manager for the Idaho Department of Fish and Game. “I don’t want to downplay the threat, but I don’t want to lead the public to think a catastrophe is imminent.”

The rainbow trout population in a 50-mile stretch of the Madison River between Quake Lake and Ennis Lake has declined more than 90 percent since 1991, said Dick Vincent, a fisheries manager for Montana Fish, Wildlife and Parks.

“It’s almost unheard of for a disease to have a population level effect like the one in the Madison River in wild populations of fish in nature,” Gamblin said.

Whirling disease, which spread to the United State from Europe in 1956, has been found in 18 states, including Colorado, Utah and Idaho. It often is associated with hatchery fish, which makes the Montana outbreak surprising.

Idaho biologists fear the disease can be spread by birds, mud on boats and trailers or bait buckets.

Idaho Fish and Game is running monthly tests on fish from the Henry’s Fork throughout the winter to determine whether the parasite already is present. Gamblin said results should be in by early February.