Glacier Park Pitches Native Trout Preservation Project on Gunsight Lake

If approved, fisheries managers would remove non-native rainbow trout from the alpine lake using a fish toxicant and replace them with genetically pure strains of westslope cutthroat and bull trout

By Tristan Scott
Gunsight Lake. Courtesy Glacier National Park

Glacier National Park fisheries managers are proposing a conservation project aimed at restoring genetically pure populations of native westslope cutthroat trout and bull trout to Gunsight Lake, an emerald-hued alpine gem located north of Mount Jackson at the headwaters of the St. Mary River, which is the last drainage east of the U.S. Continental Divide to support native bulls.

The impetus for the proposal, according to fisheries biologists with Glacier Park, as well as other state, tribal and federal natural resource management agencies, is rooted in the mounting threats to native populations of bulls and cutts in the St. Mary. A tributary of the South Saskatchewan River drainage, the St. Mary populations of native trout are losing their genetic purity due to hybridization with non-native rainbow trout, which radiate outward from infested lakes, including Gunsight.

Meanwhile, climate change presents additional threats that could compound the stressors faced by bull trout and westslope cutthroat trout in the St. Mary drainage, according to biologists, including changes in stream flow and warmer water temperatures that favor non-native species.

Park officials are currently seeking input from the public to inform the project, with comments due by Oct. 26.

According to the proposal, Gunsight Lake is a prime candidate for the removal of non-natives and the translocation native fish species because it features geographic barriers that can stave off natural invasions, including several waterfalls located downstream.

Situated in an alpine cirque and flanked by high peaks — Fusillade Mountain rises to the north and Gunsight Mountain to the west, while the towering monolith of Mount Jackson looms more than 4,700 feet above the lake’s surface to the north — Gunsight Lake was historically fishless; however, in 1916 park officials stocked it with 35,000 non-native cutthroat trout, and then again from 1920-1936, this time with 224,000 rainbow trout. The rainbow trout established a self-sustaining population in the lake while migrating downstream to the St. Mary River, where they hybridize with native cutthroat and bull trout, a species of special significance because they’re listed as threatened under the Endangered Species Act (ESA).

To re-establish the native trout populations and curb the trend of hybridization, Glacier National Park is proposing to remove non-native rainbow trout from Gunsight Lake using a fish toxicant, such as rotenone, and establish the lake as secure habitat for native westslope cutthroat trout and bull trout.

“This would remove an ongoing risk to native fish downstream and provide secure habitat to native fish that are at risk from hybridization and climate change,” according to Chris Downs, the park’s aquatic and physical science programs leader. “Once removed, non-native fish would not be able to reinvade Gunsight Lake since several waterfalls downstream are barriers to upstream fish migration.”

Given its high elevation, Gunsight Lake also has a high likelihood of sustaining the cold-water habitat necessary for westslope cutthroat and bull trout to persist in a changing climate, according to park officials.

While rotenone and other fish toxicants degrade naturally with sunlight and water movement, detoxification would be hastened with a neutralizing agent, according to the proposal.

“The toxicant would be detoxified before it reaches downstream native fish populations,” the proposal states, emphasizing that native fish, including westslope cutthroat trout and bull trout, are not currently present in Gunsight Lake.

The fish toxicant would be applied to the lake from motorized watercraft, such as an inflatable boat with an outboard motor or other small motorboat, and to the stream from drip stations and backpack sprayers. Application would occur during low water in late summer or early fall to reduce the amount of water treated and the likelihood of non-target organisms, such as larval amphibians, being present, the proposal states.

The treatment area would be temporarily closed to the pubic during application and detoxification. Following the removal of the non-native rainbow trout, genetically pure strains of westslope cutthroat trout and bull trout would be translocated (i.e. stocked) in Gunsight Lake.

Translocated fish would be live-harvested from donor populations within the St. Mary drainage or other drainages with similar evolutionary pressures; to maximize the survival of

eggs and juvenile fish, eggs from donor fish would likely be taken to a hatchery for rearing, according to the proposal.

“Some donor fish may need to be moved to a hatchery for spawning while others could be directly translocated to Gunsight Lake,” the proposal states.

Helicopter flights would likely be required to transport materials, equipment, and live fish for translocation, officials stated.

If approved, the project may begin in the late summer or fall of 2023.

In 2019, Glacier National Park, in partnership with Montana Fish, Wildlife and Parks (FWP) and the U.S. Fish and Wildlife Service (FWS), and the nonprofit Glacier National Park Conservancy, undertook a similar project in the Camas Creek drainage west of the Continental Divide. In that project, biologists successfully removed non-native Yellowstone cutthroat trout from Camas and Evangeline lakes and translocated native westslope cutthroat trout and bull trout to both lakes.

More information on the proposed project may be found on the NPS Planning, Environment, and Public Comment (PEPC) website. Comments can be posted on the PEPC site or sent by mail to Superintendent, Glacier National Park, Attn:  Gunsight Lake EA, PO Box 128, West Glacier, Montana, 59936.

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