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Whirling Disease Update


Fri Jul 30 00:00:00 MDT 1999

Montana Fish, Wildlife & Parks has confirmed that whirling disease has been detected on four new rivers: the Gallatin near Logan; the East Gallatin, northwest of Bozeman; the Bitterroot, north of Darby; and the Yellowstone, near Livingston and at the mouth of the Shields River.

Dick Vincent, FWP's Whirling Disease Coordinator, said FWP researchers on the main stem of the Gallatin captured five, 1.5-year-old rainbow trout this spring that had deformities. The fish were submitted to the U.S. Fish and Wildlife Services Fish Health Lab in Bozeman and confirmed to have whirling disease. Vincent said the testing method could not determine the level of infection, but additional sampling results from other Gallatin locations is forthcoming.

On the East Gallatin River near Riverside Country Club, results from fish placed in "live cages" last fall show that two of 50 rainbow trout were infected. According to Vincent, the infection was "light." On a scale of one to four, the infection level was 0.04. Additional information from two more East Gallatin River sites will be available in September, Vincent said.

On the Yellowstone River, infected fish were found in two of eight test sites established last fall between Gardiner and the mouth of the Shields River. Infected trout were taken from the Yellowstone near the 9th Street Bridge at Livingston and from a site established at the mouth of the Shields River. Both of those infections were moderate to low, according to Vincent. Additional information, which will include samples from as far down the Yellowstone as the mouth of the Stillwater River, is also expected in September, Vincent said.

On the Bitterroot River, samples from trout collected at five sites between Lolo and Painted Rocks earlier this spring turned up one yearling rainbow trout with a mild rate of infection.

FWP has sampled more than 350 sites in Montana for whirling disease. At 78 sites, fish were found with varying degrees of whirling disease.

Vincent repeated some good news associated with the findings. "It's becoming more and more clear that not all streams with the whirling disease parasite will experience trout population declines," he said. "While it's impossible to predict if trout from the new sites will become more severely infected, for the time being, fish populations in those drainages appear to be healthy." -