Bull trout require the coldest water temperatures of any salmonid species in the United States, which makes Northwest Montana’s cold, clear, glacially carved networks of lakes and streams a marquee habitat for the native fish.
In Glacier National Park, however, bull trout have been pushed to the brink of extirpation by non-native lake trout, which have invaded 10 of 17 lake systems inside the park west of the Continental Divide.
But in 2009, biologists with the U.S. Geological Survey in partnership with Glacier National Park pioneered a new effort to suppress lake trout in remote backcountry lakes and reintroduce dwindling native trout populations.
Recent results show strong evidence of success, and indicate that the efforts could be applied to other invaded habitats and broader ranges, according to a study published in the journal “Fisheries Management and Ecology.”
“This is the first study in the region to show that suppression efforts in a remote backcountry lake can be successful,” said Clint Muhlfeld, an aquatic biologist with the USGS. “If we can overharvest the oceans and the Great Lakes, it makes sense that we can overfish these small, isolated bathtub lakes in the Rocky Mountains. All it takes is a level of sufficient effort to tip that balance back in favor of our native species.”
In 2009, biologists with Glacier Park and the USGS began an experimental project on Quartz Lake, located in the park’s remote northwest corner, where lake trout invasion was still in its early stages. The aim was to reduce or eliminate lake trout by gillnetting, a project that required a 25-foot boat to be helicoptered in and all of the supplies to be hauled in by biologists and mules.
Muhlfeld and his team first located so-called “Judas fish,” captured and radio-tagged them, then tracked the fish to spawning areas in order to capture and remove the densest concentrations of spawning lake trout.
In eight years, the project has shown evidence of success in significantly reducing lake trout while maintaining and growing bull trout populations, and is hailed as one of the first successful projects of its kind and a leading example that lake trout suppression, once thought to be futile, is possible.
Now, biologists with both agencies have received approval to continue the federal program on Quartz, which is now being overseen by Chris Downs, fisheries biologist for Glacier National Park, and have applied a similar method of lake trout removal to Logging Lake, which was once among the most robust bull trout fisheries in the park but is now on the cusp of blinking out due to lake trout invasion.
Downs said that while the stabilizing bull trout population on Quartz Lake is a sign of success, more netting and monitoring is critical to determining whether lake trout respond to suppression.
“There certainly are some positive signs in the stability of the native fish community, so that’s certainly a positive. It’s going to take additional years of netting removal to get a better handle on how the lake trout population will ultimately respond to the suppression-removal pressure we’ve been applying,” he said. “There’s no doubt there are fewer large lake trout in there which is another good sign, but we need to see how things play out.”
A second element to the Logging Lake project involves translocation of bull trout — the first of its kind in the upper Columbia basin — where biologists moved 130 bull trout from Logging Lake to a safe haven called Grace Lake, an upstream body of water that is protected from lake trout invasion by a waterfall, which serves as a natural barrier.
“We are continuing to knock back the lake trout population in Logging Lake and rescue bull trout, but they are almost extinct at this point,” Muhlfeld said. “The lake trout are fully established in Logging. We are continuing to monitor how the juvenile bull trout that we salvaged are doing, and we do have data showing that some are still alive. But we have seen no evidence of spawning.”
To that end, Muhlfeld and Downs have embarked on a program to raise juvenile bull trout at the Creston National Fish Hatchery using fertilized eggs from Quartz Lake, and transfer the fish to Logging Lake and Grace Lake in an effort to reestablish healthy populations while continuing to suppress lake trout.
“We saw the writing on the wall and knew that if we allowed lake trout to invade, they would take over,” Muhlfeld said. “It’s just a matter of time before the conversion takes place, and we were able to prevent that from happening.”