Protecting Native Fish in Glacier

Glacier National Park is well known for its stunning vistas, iconic megafauna, and pristine waters – but beneath the surface lies a hidden world locked in a perilous balance. Glacier is home to dwindling populations of westslope cutthroat trout and bull trout, which face the ever-looming threat of extirpation (local extinction) due, in large part, to competition with invasive species.

Diversity is a vital part of a robust, healthy ecosystem. The introduction of non-native or invasive species can have a butterfly effect on an entire ecosystem, drastically impacting biodiversity and disrupting a delicate ecological balance evolved over thousands of years. Native fish play a large role facilitating the transport of nutrients throughout aquatic habitats, and are a key link in Glacier’s food chain as a major food source for birds of prey and terrestrial carnivores, such as grizzly bears.

The introduction of non-native fish to Glacier began early in the park’s history when it was common practice to stock lakes for fishing – primarily with non-native fish – which continued until 1972. By the time the detrimental impact of invasive species became more widely known, the damage had already been done. Native fish in Glacier face predation, competition, and genetic hybridization from invasive lake trout, brook trout, and rainbow trout, in addition to climactic pressures that have resulted in critical changes to water temperatures and streamflow patterns. Bull trout in particular are listed as threatened under the Endangered Species Act, and Glacier National Park is home to the only populations of bull trout found east of the Continental Divide.

The Glacier Conservancy is proud to support park efforts to mitigate the impact of invasive fish species on the native populations of westslope cutthroat and bull trout in order to preserve and protect native aquatic habitats.

“We’re trying to save the genetic diversity”, says Glacier’s Aquatic Programs Manager, Chris Downs. “A diverse environment is a more stable environment”.

The Glacier Conservancy joined Downs and his seasonal fisheries team at Quartz Lake in June to learn more about how Conservancy funding is helping preserve and protect native fish in the park.

“These [smaller lakes] are the last of what we’re working with here to try to ‘stop the bleed’ at this point. Kintla Lake, Logging Lake, Lake McDonald are too big and costly to try what we’re doing here”.

The team’s primary goal at Quartz Lake is to suppress the invasive lake trout population in order to alleviate the pressures faced by native fish. The fisheries team lives at Quartz Lake for several months in the summer and fall, removing lake trout by casting and retrieving gillnets twice a day, as well as manually fishing the lake, while collecting critical data points on fish populations in the process. When lake trout are caught, a tracking device can be inserted into the body of the fish, which is then released back into the lake. These ‘Judas fish’ are tracked to likely spawning sites, allowing the team to target invasive populations for efficient removal.

The Conservancy also funds a Native Fisheries Intern through Flathead Valley Community College (FVCC), who plays an integral role in the small but mighty team at Quartz Lake. This year’s intern, Sally, represents the next generation of natural resource stewards who are equipped with the much-needed skills and experience to help preserve and protect Glacier National Park.

Downs foresees the need for lake trout suppression at Quartz Lake to continue indefinitely. Extinction of lake trout may be possible, but will be extremely difficult to achieve. Until then, long-term monitoring and management of native fish populations is essential to maintaining the work that has already been accomplished.

Downs plans to implement similar initiatives in other watersheds in Glacier, particularly on the east side of the Continental Divide where native fish populations are currently most at risk. Populations of bull trout in the St. Mary and Belly River drainages of the park have been identified as an “evolutionarily significant unit” for the recovery of the species, but are at high risk of hybridization and extirpation.

The fisheries team is planning to create a native fish refuge in Gunsight Lake to protect the genetic diversity and alleviate the pressures of invasive species and climate change on these populations. Downs and his team are moving forward with a project to remove invasive rainbow trout in Gunsight Lake using a piscicide called ‘rotenone’, with the goal of reintroducing genetically pure westslope cutthroat and bull trout by the fall of 2025. The precedent for the use of rotenone in similar projects has already been set by multiple land management agencies, including Glacier, and will not have long term impacts on the lake or surrounding area. Gunsight Lake is an ideal location for this project where it sits at the headwaters of the St. Mary river drainage; numerous waterfalls will protect the lake from invasive species re-entering the watershed, while its position upstream will help to repopulate the drainage with native fish.

“You could make an argument that we shouldn’t touch these fish, but there’s already non-native fish in there”, says Downs. “The trammeling has already been done. Why don’t we get a positive out of this situation and create a climate refuge, and a genetic refuge, and invasive species refuge”.

Conservation of native fish populations is an essential part of preserving the unique biosphere of Glacier National Park. Thanks to donor support, Glacier’s fisheries team is able to take decisive action to protect native fish from invasive species and other pressures, ensuring that Glacier’s aquatic ecosystems won’t lose the last of these biologically, culturally, and economically significant populations.