Whirling Disease Killing In Ever-Widening Circles

The whirling disease threat to American trout has been raised to a possible “biological Chernobyl,” leading Alberta, a huge province of Canada, to shut its border to live trout from the United States, effective Oct. 1, to protect its own streams.

“Recent studies implicate whirling disease in the significant decline of wild trout populations in Montana, Utah and Colorado,” Alberta’s environmental protection department said in a statement announcing the decision in April.

Ty Lund, the environmental minister, said, “This will help us ensure that our grandchildren enjoy the same opportunity to fish for trout in some of the finest trout-fishing rivers in the world.”

At the largest scientific gathering to date on the whirling disease parasite, held earlier this year in Logan, Utah, the news was uniformly bad.

It was Kevin Thompson of Colorado State University who said we could face a “biological Chernobyl” as the whirling disease parasite from Europe, first found in a Pennsylvania stream in the late 1950s, is now in at least 22 states and expanding. No foreseeable hope of a reversal was offered at the conference.

Karl Johnson, a scientist and fly fisher who heads the Whirling Disease Foundation based in Bozeman, Mont, was blunt: “Before it’s done,” he said of the killer of young trout, “most of the streams in the lower 48 states, if they have wild trout, will probably become infected.”

Growing evidence bolsters the worst-case scenario: A combination of biological and environmental factors, feared but not yet scientifically defined, could suddenly surge in a mildly infected stream and begin the demise of most of the susceptible species of trout. It happened to the rainbow trout on the world-class Madison River in Montana from 1993 to 1995.

Barry Nehring of the Colorado Division of Wildlife called this scenario a “harmonic convergence” of various factors. He said this happened at the South Platte River, where at some sites the rainbow trout density has dropped some 95 percent from 1989 to 1996.

“Wild rainbow trout populations throughout 180 to 200 miles of Colorado’s premier trout streams are experiencing the severely debilitating effects of whirling disease,” he said.

Officials from states with many of the nation’s top trout streams - like Colorado, Utah, Idaho, Montana, Wyoming and Washington - reported that the hardy whirling disease spores are infecting more and more fish and waterways. However, they are not finding a corresponding increase in dead or sick trout.

This puzzling result supports the convergence theory: That once a stream is infected, a still-to-be-defined set of circumstances can throw off the balance and spur a whirling disease trout kill.