OREGON STATE UNIVERSITY

OSU researcher studying beaver impact on desert trout

03/16/2000

CORVALLIS - Is the state's largest rodent the friend or foe of an isolated population of endangered trout?

A graduate student in Oregon State University's Department of Fisheries and Wildlife is closing in on the answer with his two-year study of Willow Creek in Oregon's lonesome southeastern corner.

"We don't know for sure yet whether the study will show that the presence of beavers is harmful, neutral or beneficial to the fish, and when we do we won't know how far beyond Willow Creek whatever we determine may be true," said Andrew Talabere, who is conducting the research for his master's degree. "But," he added, "we do know that this study is going to give us another tool to use in the potential recovery of these threatened fish."

Talabere is talking about Lahontan cutthroat trout, the only fish in Willow Creek. The federal government listed the Lahontan cutthroats in that tiny stream and nearby White Horse Creek as threatened in 1991.

Willow Creek is only 18 miles long. It starts in southeastern Oregon's Trout Creek Mountains near the Oregon-Nevada border and runs almost due north toward Steens Mountain. It ends in a marshy area that is a shallow lake during wet climatic periods. A person could jump across the creek in spots.

Several years ago researchers with the Oregon Department of Fish and Wildlife noted that the area right around the banks of Willow and White Horse creeks, damaged in decades past by livestock, wild horses and weather factors such as droughts, was improving. They suspected the improvement could be attributed, at least in part, to a change in how the federal land the creek runs through was managed.

The Bureau of Land Management was working cooperatively with ranchers, environmentalists and state resource managers. The improvement included the return of willows and other trees around the streams, and there seemed to be a related rise in beaver activity, including the number of dams.

Talabere began his field research in 1998 under the supervision of OSU fisheries ecologist Bill Liss and aquatic ecologist Bob Gresswell.

In recent years there has been increasing interest in how beaver ponds affect fish distribution, Talabere noted.

"Some work on this had been done in the Midwest and west of the Cascades. But none had been done in this kind of desert ecosystem.

"There's a lot of concern that beaver ponds increase the water temperature, both because of an increase in the surface area of the stream and because beavers cut down trees, removing shade," he added. Basically, what the OSU graduate student did during two fields seasons was measure shade and other physical characteristics along the stream, and survey the fish in the creek.

For comparison, Talabere and assistants conducted identical studies in stretches of the creek with beaver ponds and in stretches without beaver influences. They also placed special devices in some of the study areas to monitor the water temperature over time.

There is a difference in the beaver pond complexes between the temperature of the water going in and coming out, Talabere says. "The water heats up a degree or so in complexes in our higher-elevation study areas," he said, " and two or three degrees in lower-elevation complexes. But it did that in the study stretches without beaver activity, too."

He hasn't finished analyzing the amount of shade by the creek, but he suspects there is more where beavers are active.

"When I go out to Willow Creek beaver ponds in March," Talabere said, "some of them tend to look like war zones. Clearcut. All stumps. But by July it's all grown back, and more. There have been beavers in North America for three to four million years and willows even longer. They've evolved together."

"This is highly speculative at this point," said Talabere, "but there appear to be more large fish in the beaver complexes (we studied). If that's true, and I haven't analyzed all the data yet, it means the beaver ponds are providing either more food that allows fish to get larger, or greater habitat area. Ultimately what it means for the population is that you grow more large fish per unit of stream and get more reproduction."

The research is featured in an article in the Winter 2000 issue of Oregon's Agricultural Progress, a magazine published by OSU's Agricultural Experiment Station. Copies are available by writing: Jeanne Bush, EESC, 422 Kerr Administration, OSU, Corvallis, OR 97331-2119, or calling Bush at 541-737-3717.

Talabere said he expects to complete his report on what he learned in the study of Willow Creek by July 2000.