Fish Disease Devastates Famous Montana River

A year after its discovery in the Madison River, whirling disease has shed some of its mystery, but the fish malady is still stomping one of North America’s most valuable and famous fisheries.

The disease, caused by a parasitic infection, is blamed for a 90 percent decline in the Madison’s rainbow trout population.

It poses no threat to humans, and exists in several western states. Whirling disease is so named because it causes fish to swim in a tail-chasing motion, making them more susceptible to predators and less likely to feed.

The disease has everyone from fishing guides to real estate agents agitated. Trout fishing is big business in Montana.

Over the past year, the state Fish, Wildlife and Parks Department did groundwork research on the disease in the Madison.

One study found angling pressure may adversely affect rainbow trout living in infected waters.

To conduct the study, FWP closed a section of the Madison and compared it to an open-fishing section.

Vincent said he wants another year to conduct the study.

“It could have been a fluke,” he said. “We need to try it one more year. We want to make sure it is the correct interpretation.”

If FWP biologists reach the same conclusions after another year of study, FWP would create a list of options for anglers to consider, such as closing sections of rivers or entire rivers for long periods of time, having rotational closures or closing waterways during times of high fishing pressure.

Other FWP discoveries:

Although the adult rainbow trout population declined in 1995, there were enough adult fish in the upper river to spawn and seed the river with young fish.

This fall, rainbow trout were found with disfigured heads, crooked jaws, snubbed-nose snouts and black tails.

Brown trout appear unaffected by the disease.

Yearling trout - hatched in the spring of 1994 - have more than doubled their population over estimates made last September, but that is still about one-fourth the historical population.