The news from the Madison River is all good these days - the rainbow trout population is rebounding, though the biologist who used to be in charge of whirling disease in Montana isn't really sure why.

(As an added journalistic bonus, he retired last year and now raises dauchshunds). From the Associated Press:

In the 1990s, whirling disease slashed the rainbow trout population by 90 percent compared to levels measured in the 1960s and '70s.

Now, after a succession of rebound years, rainbows under 10 inches have "pretty well recovered to pre-whirling levels" and the population of those larger is about 60 percent of what it was before the disease, said Dick Vincent, whirling-disease coordinator for the Montana Department of Fish, Wildlife and Parks until his retirement last winter.

Vincent has now embarked on a new career as a breeder of dachshunds, but the agency says Vincent remains the authority on whirling disease in Montana.

Rainbows in the blue-ribbon Madison River, where guides this summer charge about $425 per boat for a day of fishing, have developed considerable resistance to the disease, a parasitic condition often characterized by a tail-chasing whirl. How that resistance came about is unknown, Vincent said.

Later in the report, Vincent wonders if whirling-resistant trout genes didn't find their way into the Madison's population via reservoir trout:

Vincent said he suspects, but cannot prove, that whirling-disease resistance in Madison River fish is tied to disease-resistant trout that were in southwestern Montana's Willow Creek Reservoir, somehow ended up in the Madison years ago and shared favorable genes with fish there.

Dave Kumlien of the Bozeman-based Whirling Disease Foundation, part of the conservation group Trout Unlimited, said developments on the Madison are encouraging but "we're not entirely sure the population is recovered. The infection level in the river is still quite high."

However it's happening, it's good news for anglers - and a sign that whirling disease may eventually not the pack the punch it has the past.