Since first discovered in Swan Lake in 1998, non-native lake trout have been a constant source of controversy and debate. Following the proliferation of lake trout in Flathead Lake and its surrounding tributaries, including the Swan, native bull trout populations have plunged in Northwest Montana.
Montana Fish, Wildlife and Parks is seeking a five-year extension of an experimental project using gill nets to remove spawning adult lake trout during the fall with the hopes that native species could begin rebounding. A summary report of an existing three-year project and the state’s proposal are open to public comment and review until June 15. The proposed extension would continue an experiment involving state biologists and professional fishery consultants. FWP and Swan Valley Bull Trout Working Group members would conduct gill netting along known spawning sites during the fall for five years. The project would cost roughly $86,000 a year as it did the last three years, according to FWP.
FWP Fisheries Biologist Leo Rosenthal, one of the project leaders, said it remains unclear how effective gill netting has been in accomplishing the project’s overall goal — benefitting bull trout and kokanee salmon — but another five years would provide almost two life cycles for the fish and provide a clearer answer.
“What we’re trying to find is what are some long-term, cost-effective management tools we can have to reduce this lake trout population?” Rosenthal told board members at a recent Flathead Wildlife Inc. meeting in Kalispell. “This research project is not a long-term management plan for Swan Lake. This was a three-year project and now we want to complete it and see it through.”
From 2009-11, a total of 21,330 lake trout were removed from Swan. The number of fish caught per net increased the first two years before decreasing, leading biologists to believe that netting efforts were effectively reducing recruitment of young lake trout. Other research found juvenile lake trout were successfully reduced, too. Rosenthal said past eradication efforts across the nation have shown that inflicting mortality rates greater than 50 percent of the population have led to sizeable declines or even collapses of some populations.
But what would that mean for bull trout and kokanee? Roughly 4 percent of the fish caught in gill nets the last three years were bull trout, pike or other unintentional bycatches. Including two years prior to the official netting experiment, a total of 1,523 bull trout have been unintentionally netted on Swan. On average, more than half of those were released alive, Rosenthal said.
“Ideally, if this project is successful, you would want at a minimum to see the bull trout stop declining from where they’ve been going and start to increase and the same for kokanee,” Rosenthal said.
Swan Lake was historically a haven for native bull trout. In 1998, there were an estimated 829 bull trout redds, the name given to spawning beds. But by 2011, that number had dropped to 312. The alarming decline in juvenile and adult bull trout, as well as kokanee, led to a campaign against the assumed culprit.
But the battle has evolved. State and tribal agencies are focused on defending native species, primarily bull trout, which have been federally listed as threatened since ‘98. But today the large lake trout population is being championed as a popular game fish that benefits the sport and its surrounding communities.
“I’m a passionate lake trout fisherman on Flathead. I’d rather catch a lake trout instead of a bull trout because there’s more opportunity,” said Doug Bolender, a board member for Flathead Wildlife Inc., a local nonprofit conservation organization. “I like to tug on my line. I don’t care if it’s a sucker. I don’t care if it’s a lake trout. I want to tug on my line.”
Bolender and others questioned the feasibility of eliminating lake trout in Swan. Past studies have shown that the lake trout population began with only three fish – is it realistic that gill netting will put a dent in populations if that’s the case? Rosenthal responded that total elimination of lake trout is not the goal, nor is it realistic.
The bigger concern involved ramifications that could extend beyond Swan Lake. The Confederated Salish and Kootenai Tribes are currently examining ways to rejuvenate native species by eliminating non-native ones in Flathead Lake.
“If the tribe starts dunking nets in that lake, we’re done,” Bolender said.
A larger scale of gill netting on Flathead would remove hundreds of thousands of game fish, he said, which “would ruin the largest freshwater lake west of the Mississippi. That will be a travesty. That would never be forgotten.”
Tom McDonald, manager for the CSKT wildlife, recreation and conservation division, said the tribe is currently drafting an environmental impact statement for removing lake trout on Flathead. There are no definite plans yet, he said, but the tribe is watching the Swan Lake project.
“Flathead Lake is way different than Swan Lake, but there are some things we can learn from the efforts on Swan. We learn from every experiment,” he said. “We’re using the best science. We’re looking at all the research we have done. We’re putting together some alternatives that are well meaning and based on sound and good science.”
And what about Bolender and others’ concern that removing lake trout could ruin Flathead as a popular fishery?
“The top predator (lake trout) has become one of the most abundant fish,” McDonald said of lake trout. “That’s just not a good scenario.”
If left alone, lake trout could overrun the lake and diminish any diversity, he said.
“That’s worst-case scenario, but without that diversity, can that be sustained long term with just non-native fish?” he asked. “Long term, if they wipe out all the other fish, maybe they can’t adapt. They could be gone. Then we don’t have anything.”
To read the FWP Swan Lake three-year summary and proposed extension plan, visit fwp.mt.gov/news/publicNotices/environmentalAssessments/restorationAndRehab/pn_0106.html.