Lake tributaries in Yellowstone National Park allow unique study of whirling disease

BOZEMAN, MONT--The tributaries of Yellowstone Lake in Yellowstone National Park remind fisheries biologist Beth MacConnell of the three bears: Some tributaries may be too hot for the parasite that causes whirling disease; some may be too cold, and some might be just right.

Just what temperatures allow the infection to flourish is what MacConnell and other scientists hope to find out in a unique study this year in Yellowstone National Park.

Whirling disease attacks the cartilage of young fish, causing them to swirl in a circular pattern and fall victim to predators. The disease mainly affects rainbow trout and was discovered in Montana in 1994 and in Yellowstone National Park in 1998.

In Yellowstone Lake, 20 percent of adult native Yellowstone cutthroat are infected with the disease, MacConnell said. But scientists don�t know if all of the lake�s tributaries are infected or which ones support ideal conditions for the disease.

MacConnell is a Montana Fish, Wildlife and Parks biologist in Bozeman, Mont., and a member of the whirling disease steering committee for the Montana University Water Center based at Montana State University. The Yellowstone study will be conducted by Todd Koel, the park�s fisheries and aquatic sciences chief.

The Yellowstone study and 12 others in eight western states are the latest whirling disease projects funded with $700,000 from the National Partnership for the Management of Wild and Native Coldwater Fisheries. The partnership, created in 1995, is administered by the Montana Water Center and funded by the U.S. Fish and Wildlife Service.

"Gradually the whole effort is moving from basic biology to field and applied research," said Water Center director Gretchen Rupp. "The overall purpose of the partnership is to devise and test methods for controlling whirling disease in nature. We�re not there yet, but we have a much better understanding of the biology of the [parasite] than we did a few years ago."

The 10 or more Yellowstone Lake tributaries under study differ in temperature, with some warming quickly in the spring and early summer while others warm more slowly. Still others may stay too cool year around for the parasite to complete its cycle and cause disease, MacConnell said.

"Thermally we have a lot of variety there, so it�s a good outdoor laboratory," MacConnell said.

From other studies, scientists know that the parasite is most active when water temperatures reach between 48 degrees and 60 degrees Fahrenheit, said Dick Vincent, whirling disease research coordinator for Montana Department of Fish and Wildlife and Parks. Young fish--three months or younger--are the most vulnerable to infection.

"Our hypothesis is that temperature is a factor in whether the disease remains benign or becomes acute," Vincent said.

In addition to varying temperatures among lake tributaries, the Yellowstone study also offers scientists the chance to study whirling disease in a population of native fish, Vincent said. Previous studies primarily focused on rainbow trout, which were introduced to this region about 100 years ago.

Other whirling disease projects funded by the national partnership this year include an ongoing MSU study of the Missouri River between Holter Dam and Cascade, Mont. Scientists want to know whether trout populations from healthy tributaries can keep the overall fish numbers from collapsing in the main stem.

Another study, led by the University of Montana, focuses on the Rock Creek drainage near Missoula. Scientists at MSU are studying the aquatic worm in which the parasite lives before infecting fish.

California, Colorado, Idaho, Oregon, Utah, Wyoming and New Mexico also have projects funded this year by the partnership. Twenty-three states have whirling disease, which is thought to have come to the U.S. nearly 50 years ago in a shipment of processed fish from Denmark.