Whirling disease infects watershed

A world-class Alberta trout river has been infected by a disease that is usually fatal to the prized sport fish.

The Canadian Food Inspection Agency has advised that the entire Bow River watershed in southern Alberta has been contaminated by whirling disease. The advisory includes tributaries such as the Elbow River and continues downstream all the way to the Bow’s confluence with the South Saskatchewan River.

The provincial government is testing other rivers to see if the pathogen has turned up elsewhere, said Alberta Environment spokesman Peter Giamberardino.

“We continue to test those samples,” he said Friday. “We’ll be determining if it has spread outside of the Bow River.”

Lorne Fitch, an adjunct professor at the University of Calgary who spent 35 years as a provincial biologist, said whirling disease attacks young trout and eats away at the cartilage in their skulls.

“It impacts them in terms of how they’re able to respond to their environment,” he said. “They do actually start to twist and turn because they can’t align themselves any more. ”

The disease is hardest on native species such as the endangered cutthroat trout.

Fitch said an outbreak of whirling disease in Montana’s Madison River — another blue-ribbon fishery — killed up to 95 per cent of its trout, although numbers are starting to rebound.

Whirling disease was first observed earlier this summer in several lakes in Banff National Park. All fish hatcheries and farms in the province must now test their stock for whirling disease and implement measures to prevent it from spreading, Giamberardino said. The disease is not harmful to humans and eating infected fish presents no risk, he added.

Giamberardino said there’s no indication the infection has affected trout stocks in the Bow. No changes to fishing regulations in the popular and lucrative fishery are being contemplated, he said.