Trout Disease Hits Blue-Ribbon Stream

Whirling disease has made its way to Rock Creek, the world-class trout fishery east of Missoula, state fisheries managers reported Tuesday.

A sample of 17 young rainbow trout taken from the upper river in November found all of the fish infected with the disease. Thirty-nine of 40 brown trout were infected.

“We have a very serious rate of infection - and it’s in the upper stream,” said Dennis Workman, regional fisheries manager for the state Department of Fish, Wildlife and Parks in Missoula.

“This is a tough blow,” he said. “I had hoped that Rock Creek might escape. It’s our blue-ribbon stream.”

Between 1992 and 1996, young rainbow trout numbers dropped by 78 percent in the middle portion of the stream. “That’s a horrendous drop,” FWP fisheries biologist Don Peters said. “It’s inordinate.”

In the upper river, the young rainbow trout population declined by 73 percent between 1986 and 1989 - and has not rebounded. The fishery in upper Rock Creek is 80 percent rainbow trout.

Rainbows are the salmonids most susceptible to the parasite that causes whirling disease.