UM Research Tackles Native Trout Protection

By Guest Writer, 12-25-08

Editor’s Note: This story was provided courtesy of the University of Montana. It’s based on research being performed by the UM College of Forestry and Conservation.

A 1929 issue of Montana Wild Life, the magazine of the State Fish and Game Commission, included a picture of a bull trout under the caption “The Cannibal of Montana’s Streams.” The photo shows a trout sliced open to display 103 fingerlings that were in its belly when it was caught near the mouth of Rattlesnake Creek. Another article declared bull trout “the enemy of game fish” and described efforts to scoop them out of Flathead Lake to give smaller fish a chance.

Times have changed.

Now the bull trout is listed as “threatened” under the Endangered Species Act. In most Montana lakes and streams, anglers are required to carefully release them back into the water. And Lisa Eby, associate professor of aquatic vertebrate ecology in UM’s College of Forestry and Conservation, is looking at ways to help bull trout and other native fish thrive.

Eby said fisheries science has come a long way from its beginnings when hatcheries viewed rivers as empty channels that could hold some ideal assemblage of fish, a view she characterizes as “the Walt Disney World approach.”

“Our perceptions and our values have changed,” Eby said, adding that the new emphasis is on “an appreciation of the native systems and the native trout.” Arctic grayling. Northern pikeminnow. Pallid sturgeon. All have risen in esteem, as have other native species, such as the frogs and toads of Montana showcased in a color poster on Eby’s office door.

Many threats to Montana’s wildlife are large and well-known – climate change, habitat fragmentation, polluted waters. But small changes to the landscape – an earthen dam built for irrigation, a newly closed road, a beaver pond – can have large ramifications, too, and Eby and her graduate students have set out to quantify them.

One study in Eby’s lab looks at effects of small dams. Many of the more than 2,000 small dams in Montana no longer serve their original purpose or are showing their age. Built to last 50 or 100 years, many are reaching the end of their life spans, forcing the state to decide whether to repair or remove them.

Outside Seeley Lake, graduate student Aubree Benson tracks bull trout near two dams on the Clearwater River, a tributary of the Blackfoot. Migratory bull trout are born in creeks and streams, move to lakes where they bulk up, then return to their birthplace to spawn. Benson has radio-tagged bull trout, surgically injecting tiny transmitters that put out unique signals every two seconds. This way she can track individual fish and see whether the dams thwart migration.

Benson also snorkels the river bottom to see if bull trout gather below the dams, and she set up a fish ladder that leads to a tank where she can monitor which fish are trying to get over. The goal of the project, done in collaboration with Montana Fish, Wildlife and Parks, is to determine if the dam has a negative effect on the survival of bull trout populations.

Conventional wisdom said that removing dams helps fish, but Eby suspects that may not always be the case.

Just as attitudes toward bull trout have swung 180 degrees, so have attitudes about non-native fish. Eighty years ago, Montana Wild Life articles described heroic rescues of exotic sunfish from pools that dried up in the summer and schemes to increase numbers of non-native bass and northern pike. In the 21st century, as these newcomers have disrupted ecosystems and battered native trout populations, the question is how to stop their spread.

Some dams have kept northern pike – voracious predators of young trout – downstream. At Hungry Horse Dam near Glacier National Park, the barrier has prevented lake trout (native to the Missouri River but not the Flathead River) from reaching the reservoir.

“It’s one of the places the bull trout are thriving; the cutthroat are thriving,” Eby said. “If your dam is holding back a lot of exotics ... it might not play out that all dams are always bad.”

The study on the Clearwater will outline the trade-offs of taking down the barriers or leaving them in place.

Another of Eby’s graduate students examines different kinds of small-scale dams – those made by beavers. When beavers fell trees and build a dam, they create pools that are warmer and more biologically productive than surrounding, free-flowing waters. Because of this, beavers will sometimes be transplanted to help restore a damaged watershed.

But there is a downside. “A lot of people have noticed that brook trout will move into an area where beavers have established,” Eby said.

Brook trout, native to eastern North America but not Montana, out-compete native westslope cutthroat at lower elevations. Westslope cutthroat are stuck at the top of drainages, where the water is colder and there are fewer insects to eat.

In Beaverhead-Deerlodge National Forest in Southwest Montana, Magnus McCaffrey compares watersheds with beavers to watersheds without. He captures brook trout and cutthroat at the start of the summer, marking them with tags – 8 mm transponders with individual codes. He then recaptures them several months later, scans the tags to determine the identity of the fish, and tallies growth and survival rates.

McCaffrey’s study is designed to see whether beaver dams let brook trout gain a finhold higher in the watershed and if there is anything managers can do about it.

A third project looks at westslope cutthroat in the Jocko River, just north of Arlee. As if westslope cutthroat didn’t have enough problems with brook trout, they also have trouble with rainbows. Before stocking, rainbows and cutthroat only co-existed in a few watersheds in Western Montana and their breeding schedules kept them from mating. But rainbow trout that have been stocked in traditional cutthroat areas interbreed with them and produce fertile offspring.

Right now small dams along the river keep the hybrids from entering some streams. Working with the Confederated Salish and Kootenai Tribes, graduate student Matthew Corsi mapped the location of hybrids along the Jocko. He’s now comparing hybrids to pure westslope cutthroats, looking at the timing of migration, measuring how large they are as 1-year-olds and counting eggs to measure fecundity.

“Are they less fit? Do they respond differently? It’s an unknown now,” said Eby. Answers to these questions might point to whether hybrids should be kept out or let pass as if they were pure cutthroats. “If you pass fish that look like cutthroats, what is the long-term sustainability versus what are the genetic consequences?” Eby asks.

These studies center on questions raised with increasing frequency in Montana and throughout the West. How do you conserve native species in the face of constant competition for water and the influx of invasive species?

“Everyone in the lab, whether they are working on amphibians or fish, are looking at how landscapes or riverscapes affect fish populations and communities to give us more information to solve some of these contemporary problems,” Eby said.

Wildlife managers are as eager to know the answers as the scientists. As Eby said, “They’re interesting questions not only from a biological point of view, but they’re useful, too.”