Defending One of the Last Strongholds

The South Fork Flathead River is home to the strongest population of westslope cutthroat trout in Montana, if not the entire West. State biologists are doing everything they can to protect the species, even if it means eradicating hundreds of other nonnative fish

By Dillon Tabish

Koessler Lake is a backcountry reservoir of crystalline water fed from the wild South Fork Flathead River, hidden in the mountains amid the towering Swan Range north of Seeley Lake.

Its remote, isolated setting inside the western boundaries of the Bob Marshall Wilderness makes it ideal for secluded fish populations.

In other words, it’s a perfect place to protect a world-class, genetically pure species.

As part of an ambitious 10-year conservation project aimed at protecting the South Fork’s revered westslope cutthroat trout fishery, state biologists are targeting Koessler Lake as the next site to undergo a rare population restoration.

Regional biologists with the Montana Fish, Wildlife and Parks Department are planning to eradicate the lake’s existing nonnative Yellowstone cutthroat and other westslope hybrids this fall before replanting the lake with pure cutts. Koessler Lake is scheduled for rotenone treatment in September, and the following spring roughly 8,600 genetically pure cutthroat fry will be planted, along with some 1-year-olds.

The fry will come from a local source within the South Fork drainage, which is considered home to the strongest, most vibrant westslope population in Montana, if not the entire West.

A species first described in the nation’s vernacular by Lewis and Clark during their famed expedition in 1805, westslope cutthroat are among western Montana’s original salmonid inhabitants. They are a subspecies of cutthroat and designated the state’s official fish, treasured for their sport and beauty.

“Westslope cutthroat are a big part of Montana’s cultural heritage,” Bruce Farling, the executive director of Montana Trout Unlimited, told the New York Times earlier this year in an ode to the iconic fish.

Yet only roughly 10 percent of the species’ historic range still exists, and the fish is considered a “species of concern” in Montana and “threatened” in Alberta.

With that in mind, FWP set out nearly 10 years ago to preserve and restore the westslope fishery in the pristine South Fork, which meanders through a large swath of protected wilderness.

The South Fork Flathead Cutthroat Conservation Project has been systematically removing non-native fish and replacing them with pure westslope cutthroat since 2007. FWP identified 21 lakes in the Bob Marshall Wilderness and Jewel Basin, and 12 mountain lakes have been successfully chemically treated. An additional six lakes were genetically swamped and may not require chemical treatment, according to FWP.

Only three lakes remain on the original list of 21: Koessler, Handkerchief and Sunburst. Handkerchief is slated for treatment and repopulation next year and Sunburst is up in 2016.

“This project is one of a kind. It’s sort of using cutting edge techniques,” said FWP biologist and project leader Matt Boyer. “There’s not really anything quite like it. Certainly not at this scale and certainly not with an eye toward genetic conservation.”

Almost 500,000 westslope cutthroat have been stocked in the lakes involved in the cutthroat conservation project, according to FWP.

The project has not been without its detractors, particularly when it was originally announced that lakes would be filled with pesticide. However, as Boyer has described it before, the project has focused intensely on making sure the habitat remains strong and contains everything it had before, except for the nuisance hybrids and non-native fish.

Rotenone is a naturally occurring substance that derives from the roots of tropical plants in the bean family, commonly found in southern Asia and South America. It has been used for centuries to capture fish and fisheries managers in the U.S. began using the substance in the 1930s as a natural pesticide to eliminate undesirable fish populations. The substance only affects living species with gills.

“One of the biggest surprises, and it’s a pleasant surprise, is the support from some of the user groups. In fact, some individuals who rightly so were skeptical at the outset of this project through time have become staunch supporters,” Boyer said.

Hybridization has drastically watered down the pure species within the drainage, Boyer said, and the project’s goal is to maintain a strong genuine fishery.

The project is funded by Bonneville Power Administration and in collaboration with the U.S. Forest Service.

FWP is asking the state Fish and Wildlife Commission to lift the bag limit of three fish per day leading up to the eradication in September.

In the fall, a helicopter will deliver the rotenone to Koessler and the pesticide will be administered. The lake will sit through winter and begin naturally regenerating itself in spring. That’s when biologists will pack in the frys and begin the restoration process.

“The rewarding part has been the restocking of the fish and being able to go back to those lakes and monitoring the growth and seeing that they’re already naturally reproducing in the lakes,” Boyer said. “It’s a world class fishery. The South Fork is an amazing resource and this is our state fish. We’re doing what we can to conserve it for future Montanans and other anglers.”

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