An 80 percent decline in the Madison River’s trout fishery over three years has made believers out of Montana biologists: Whirling disease can be devastating to rainbow trout.
Mega dittos come from biologists in Colorado, where several trout fisheries appear to have been decimated by the disease.
But some biologists in Idaho and Wyoming are downplaying the disease’s impact.
“We’re concerned,” said Idaho Fish and Game Department hatchery manager Bill Hutchinson.
“But this isn’t a situation where we’re saying, ‘The sky is falling, the sky is falling, boys get out there and document this disease.’ “
The whirling disease parasite has been found in fish in isolated areas of the Big Lost, the Lemhi, the upper Salmon, the middle Snake and the Pahsimeroi rivers, as well as the South Fork of the Coeur d’Alene River. But scientists have not been able to document that any fish have died of the disease in Idaho.
The whirling disease parasite is a spore that causes spinal deterioration in trout. Infected trout have trouble eating and are susceptible to predators.
Doug Mitchum, senior fish pathologist with the Wyoming Game and Fish Department, said, “People are blaming the decline of fisheries on whirling disease, but they have no scientific proof of that. It is a copout.”
Mitchum said that while spores have been found in Wyoming, the disease has not.
“There is a big difference between finding spores and the disease,” said Mitchum, who has been with the agency for 37 years. “We haven’t found a single fish with any signs of whirling disease.
“In order to have the disease, you have to have a proper combination between the fish, parasite and the environment.”
Drought and disturbance to spawning areas, however, could contribute to disease outbreaks, he said.