MISSOULA — Montana’s native trout are threatened by manmade problems, but they may survive longer in the safety of the Scapegoat Wilderness if a project to wipe out invasive trout is approved.
On Wednesday night, Montana Fish Wildlife & Parks fisheries biologist Patrick Uthe and retired biologist Pat Clancey highlighted the details of the proposed North Fork Blackfoot River Westslope Cutthroat Trout Conservation Project in an online public meeting. Their environmental assessment is open for public comment until Aug. 14.
The project would create a refuge for pure westslope cutthroat trout in the 67 miles of streams and three lakes above the falls on the North Fork Blackfoot River. The 50-foot-tall North Fork Falls creates a natural barrier that prevents nonnative fish from moving up into the project area, so biologists would carefully apply the natural fish poison rotenone to the streams and lakes above the falls.
The plan is to kill all the fish above the falls, so FWP can plant pure westslope cutthroat trout to rebuild a wild population, one that contains at least 90% westslope genes. The U.S. Forest Service is a partner in the project that has been at least a dozen years in the making.
“While there is precedent for this type of action, I want to highlight that it’s somewhat rare that all the building blocks align to have a project this size be very successful,” Uthe said. “The fact we have that in the North Fork project area, it’s incumbent upon us from a conservation standpoint to seize the opportunity.”
Northeast of Ovando, the North Fork Blackfoot River is a beautiful wildland stream that’s popular with fishermen who access it using the North Fork Blackfoot trail that leads to the North Fork ranger cabin and the North Fork Falls in the Scapegoat Wilderness.
As wild as the stream is, one would think it would have pure native fish. But unfortunately, as with many waterbodies, the state stocked the stream with rainbow, Yellowstone cutthroat and westslope cutthroat trout in the mid-20th century. Now, the North Fork has a mix of different hybrid trout, most of which carry no more than 17% westslope cutthroat genes.
This is the case in many Montana streams, and it doesn’t bode well for the survival of westslope cutthroat trout if nothing is done. Obviously, nonnative fish species play a role in their decline, but westslope cutthroat populations have also suffered because of habitat degradation and overfishing.
“Historically, they were broadly distributed in the upper Missouri drainage as well as all the drainages on the western side of the (Continental) Divide,” Uthe said. “Now, they occupy just over 10% of this historic range, so it’s a really significant decline.”
Now, climate change is adding to the mix because native trout need cold, clean water but higher summer temperatures are warming streams to the point where native trout can’t survive.
Saffel explained all the prep work and trial runs that have gone into calculating just how much rotenone will be required and how it will be applied.
Rotenone is produced by some tropical plants, and indigenous people have used it for centuries to catch fish. The poison kills fish by getting into their cells and affecting the cell’s ability to produce energy. Conditions such as sunlight and water chemistry and temperature can degrade the compound.
So FWP did test runs in three representative streams in 2018 to make sure they were dripping enough throughout the stream to kill fish within a certain distance but not enough to cause the concentration to rise above 4 parts per million. In lakes, boats follow a grid pattern to apply small amounts.
They’ll put the final application point far enough above the falls such that no rotenone gets into the lower reaches where bull trout live.
Because the poison has the potential to alter abundance and species composition of aquatic invertebrates over the short-term, biologists have also surveyed the streams to get baseline populations for amphibians and aquatic insects.
Saffel said potassium permanganate – a salt also used in municipal water plants – neutralizes rotenone. FWP will bring double the amount of potassium permanganate needed and have two applicators on hand in case of a problem.
FWP has successfully carried out similar projects in four streams: the South Fork Flathead in the Bob Marshall Wilderness, Silverbow Creek, Cherry Creek in the Madison Range and most recently the West Fork Bitterroot. So they’ve been able to fine-tune the process and see the results, Uthe said.
“Following eradication of the hybrid and nonnative brook trout (in Cherry Creek) and seeding the habitat with pure westslope cutthroat trout, we see exponential growth following project completion. So, really rapid recolonization of the habitat and we’re anticipating a very similar response within the North Fork project area,” Uthe said.
However, there will be one main difference between the North Fork project and the others: instead of taking place over two to three years, the biologists plan on completing the project in one summer, because the project area is in a wilderness.
As it is, FWP is still going to have to get a wilderness waiver to use a helicopter to carry the rotenone into the project area. Uthe said they chose to use a helicopter rather than packing it in on mules to avoid spilling the rotenone in sensitive areas. All the other gear will be packed in and the project will be carried out as quickly as possible, starting at the upper reaches and working down.
“From day to day, we’ll be overlapping treatment areas so we don’t have fish moving into the previously treated waters. So we’re basically creating a wall of toxicity moving down the drainage to achieve an effective fish kill,” Uthe said.
Shortly after all the reaches have been cleared of fish, biologists will plant multiple ages of westslope cutthroat trout from the Washoe Hatchery in Anaconda.
All this is planned for next summer.
“Given the logistic challenges, as well as not wanting to impact this wilderness setting more than we have to, we think it’s a good compromise to do a single-year treatment and then rely on genetic swamping to reach our objectives,” Uthe said.
One North Fork resident, Sandra, called in saying she and her neighbors were worried that the poison could affect fish in the lower reach where she lives. Clancey reiterated all the safeguards that would be in place to keep rotenone from going below the falls.
“I’ve done a lot to protect my 4 miles of the North Fork and I’m just trying to protect the fish that are here. If they’re funky fish, that’s okay,” Sandra said.
Those wishing to comment can do so on the FWP webpage, email Sharon Rose at firstname.lastname@example.org or mail comments to Sharon Rose, Region 2 FWP, 3201 Spurgin Rd., Missoula, MT 59804.