News & Features

FWP Approves Nonnative Trout Suppression in Swan River Tributary

Collaborative project aims to boost native cutthroat, bull trout populations

In its latest effort to boost native westslope cutthroat and bull trout populations in Northwest Montana, the state Fish, Wildlife and Parks will begin removing nonnative trout species through electrofishing in Cooney Creek, a tributary of the upper Swan River north of Condon and one of the best strongholds of the native fish in the entire drainage.

Following a public comment period, FWP is moving forward with the project to capture and remove all brook and rainbow trout in Cooney Creek’s core westslope cutthroat trout habitat. The project will be in collaboration with the University of Montana and MPG Ranch, a privately owned conservation ranch in the Swan Valley. Funding for the project is primarily provided by MPG Ranch with labor assistance from FWP. UM will conduct electronic DNA testing to monitor the genetic purity of the native fish, which to date have not hybridized.

“Protecting these native trout populations is of the utmost importance, as rainbow trout have recently been observed in the stream. Rainbow trout threaten to compromise the westslope cutthroat population through hybridization,” according to FWP’s environmental assessment for the suppression project. “Initiating this project is important, as it immediately begins to remove the threats of nonnative fish species while agencies explore alternatives for a barrier to prevent re-colonization of nonnative fish.”

According to Leo Rosenthal, one of the architects of the project, freshwater fisheries are in decline throughout North America. In Montana, two native species particularly at risk are westslope cutthroat trout and bull trout. Competition and hybridization between nonnative trout has caused declines of native westslope and bull trout across their historic range.

The Swan Valley was once home to robust populations of native trout; however, populations of bull trout and genetically pure westslope cutthroat trout have become reduced in abundance and distribution due to the proliferation of nonnative species.

“We have taken genetic samples in Cooney Creek since 2008 and we have never detected hybridization in that stream,” Rosenthal said. “But just recently we started detecting a few rainbow trout, so we know that rainbows are now present in the system. But we have never detected any hybridization between rainbows and native cutthroat in this system, which is one of the best cutthroat populations in the drainage.”

Currently, the Swan River drainage contains less than 20 pure populations of westslope cutthroat trout.

Hybridization is particularly concerning because it diminishes the unique genetic signature of a species, causing extirpation, according to the environmental assessment.

Widespread hybridization between rainbow and westslope cutthroat trout has been documented in the Flathead River drainage, and in portions of the Swan River basin. To mitigate the problem, FWP’s 2013-2018 Statewide Fisheries Management Plan recommends “isolation of westslope cutthroat trout populations if hybridization is a threat and habitat is sufficient to allow persistence” for the area encompassing Cooney Creek.

In the South Fork Flathead River, for example, FWP biologists, including Rosenthal, conducted the largest conservation project in the country aimed at restoring native cutts, eliminating nonnative species populating the alpine lakes above Hungry Horse Dam and replenishing them with genetically pure populations of Montana’s state fish. Those fish then radiate out of the mountain lakes and into the South Fork Flathead River.

Native westslope cutthroats found in the South Fork and elsewhere are precious gems for fisheries managers, as each fish is equipped with the genes and genetic wiring of its ancestors, traits developed specifically for certain drainages and long-term survival in a harsh northern Montana climate.

Westslope cutthroat trout have lived in post-glacial western Montana for thousands of years, during which time the species has been able to survive catastrophic fires, massive floods and severe droughts.

Yet less than 10 percent of the species’ historic range still exists, and the fish is considered a state-listed “species of concern” in Montana and “threatened” in Alberta.

With that in mind, FWP set out in 2007 to preserve and restore the westslope fishery in the pristine South Fork, which meanders through a large swath of protected wilderness, the Bob Marshall Wilderness Area.

The project helped usher in a new era of fisheries management, rooted in a growing recognition that landscape-scale conservation efforts were needed to re-establish, jumpstart and bolster genetically pure populations, which have come under siege from stream siltation, dams, over-fishing, and competition from — and hybridization with — introduced nonnative fish such as rainbow and brook trout.

While the South Fork Flathead Cutthroat Conservation Project employed a piscicide called rotenone to kill off the nonnative populations, the Cooney Creek project uses electrofishing to parse out natives from invasives.

Electrofishing is a common tool used to collect fish for fish surveys. During collection, fish are netted and kept alive in buckets or in-stream pens to be sorted and measured. All native fish will be released alive to the stream after collection. Brook and rainbow trout, however, will be killed.

“This fits right in with the management plan that we have for the Swan,” Rosenthal said. “We always have that dual mission at FWP to provide recreational and sport fishing opportunities while also conserving our native fish. And in the Swan we are down to very few. This is the last best chance for cutthroat and bull trout conservation in that drainage.”

FWP published the environmental assessment in July and accepted public input for 30 days. The agency received 11 written comments by mail or email and one comment by phone. Of the comments received, nine supported the proposed action, two individuals opposed the proposed action, and one individual expressed concern over a variety of issues. Responses to comments are available online with the decision notice at fwp.mt.gov/news/publicNotices.

The biggest concern centered on the project’s efficacy given that there is no downstream barrier between the section of Cooney Creek where biologists will target through suppression and the Swan River; without a barrier, nonnative trout will repopulate the upstream habitat, critics said.

Rosenthal said that the success of the project will ultimately depend on the creation of a future barrier to prevent repopulation of nonnative species, and the agency is working on funding one in the future. Still, given the recent presence of rainbow trout in Cooney Creek, he said the time to act is now.

“In a perfect world we’d have the barrier in place, but with the immediacy of rainbow trout showing up we wanted to start right away,” Rosenthal said.

Suppression by electrofishing is anticipated to occur annually during the summer months beginning in 2019. In addition to the removals of rainbow trout and brook trout, biologists will continue to collect environmental DNA samples to determine rainbow trout distribution throughout the project area.

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