Glacier looks to establish native fish in Gunsight Lake

Glacier National Park on Monday released an environmental assessment to restore pure westslope cutthroat trout and bull trout into Gunsight Lake east of the Continental Divide.

The project marks a continued effort by the Park Service to create refuges for the native fish in secure lakes in the park’s boundaries by moving the fish.

It recently did a similar project in the upper end of the Camas drainage, removing non-native Yellowstone cutthroat trout from Camas and Evangeline Lakes and re-stocking them with native westslope cutthroats.

It has also moved bull trout as well. A few years ago it moved bull trout to Grace Lake, which is protected from upstream migration by non-native species by a waterfall.

Bull Trout are listed as threatened under the Endangered Species Act and westslope cutthroats are a species of special concern.

The Gunsight Lake project follows similar protocols. First, the non-native rainbow trout will be removed from Gunsight Lake using a natural fish poison called Rotenone. Rotenone kills fish, but also breaks down in the environment quickly — usually within hours. It is not harmful to mammals or other animals.

The dead rainbows are then netted and sunk to the bottom of the lake to avoid attracting bears and other scavengers.

Then the lake would be re-stocked with native westslope cutthroat trout from drainages east of the divide.

Once the westslopes have established populations, the bull trout will be introduced a few years later— the stock also coming from native east side sources.

The reason for delaying the stocking of bull trout is that they eat westslopes. Bull trout are predatory fish.

The Rotenone treatment would extend from the lake down the outlet of the St. Mary River to Mirror Pond. Crews would set up a detoxifying station of potassium permanganate which neutralizes Rotenone from having impacts downstream.

The St. Mary River drainage from St. Mary Lake upstream to Gunsight Lake has several waterfalls that keep non-native fish from re-establishing themselves by natural migration into Gunsight Lake.

The work is scheduled to start in September. The Gunsight Lake campground would be closed from then until 2024, but the trail would only be closed about a week, perhaps longer, while the fish removal is implemented.

The project will use helicopters to ferry equipment and supplies, like boats, in and out of Gunsight Lake.

The lake is one of the most spectacular bodies of water in the park, surrounded by high peaks. The iconic Gunsight Pass is at the head of the lake.

Once the lake is successfully restocked, it would reopen to recreational fishing.

The Park Service looked at using stock instead of helicopters to transport supplies and Rotenone to the site, but it was deemed untenable.

“It is estimated that approximately 12,000 pounds of Rotenone (each barrel weighing 300 pounds, well over the weight mules or livestock can carry) and 2,500 pounds of potassium permanganate would need to be moved to Gunsight Lake in addition to the other gear required for application and detoxification,” the EA noted. “Based on these approximate weights, it is estimated that 20 mule strings of six head each would be required to get the supplies into Gunsight Lake with a lesser amount also required to move project materials back out of the site.”

The lake was historically fishless but stocked in 1916 with 35,000 non-native Yellowstone cutthroat trout and again from 1920-1936 with 224,000 rainbow trout. The rainbow trout established a self-sustaining population. These fish are able to migrate downstream and hybridize with native westslope cutthroat trout.

Gunsight Lake by trail is about six miles from the Going-to-the-Sun Road.

The EA is available for public review and comment for 30 days on the National Park Service (NPS) Planning, Environment & Public Comment website at https://parkplanning.nps.gov/GunsightLake.