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Study Could Help Wildlife Managers Predict Illegal Fish Introductions

Westslope cutthroat trout.
Montana Fish, Wildlife & Parks
Westslope cutthroat trout

A recent study found a way to identify lakes and other bodies of water in northwest Montana that are at high risk of illegal fish introductions, which can threaten native species. The study will allow state fish managers to improve patrols in high risk areas.

Standing next to Foy’s Lake southwest of Kalispell, Montana Fish, Wildlife and Parks fisheries biologist Sam Bourret explains that there was a recent report of a northern pike in the lake. According to Montana FWP, northern pike are only native to Montana "in the Saskatchewan River drainage on the east side of Glacier Park." As a top predator, their presence can lead to fewer native species like the threatened bull trout or westslope cutthroat trout.

Reports like these help managers’ efforts to eradicate non-native species before they get a foothold.

"But in the end, it is hard to detect illegal fish introductions before they establish a population, because there is so many water bodies; over 900 just in this Region 1 in northwest Montana."

Bourett says a more visible law enforcement presence from FWP can be a deterrent to anglers, who he calls “bucket biologists,” illegally dumping fish to then catch for sport. But with so many water bodies in just this one corner of the state, it can be hard to know where to start.

Bourett worked on a study to identify which lakes are at high risk of introductions. Co-author and FWP contract fisheries scientist Niall Clancy explains that the study used a unique data set documenting illegal fish introductions in the northwest corner of the state dating back to 1953.

Clancy says, "we found that the variables that really made a water body at-risk of illegal introductions was the elevation the lake was at -- kind of a proxy for how easy it is to access that lake -- what the human population is like around that lake, and then the angling pressure, how many people fish there every year."

Understanding what factors may have led to past illegal fish dumps can help identify what lakes are at risk now.

One of the five high-risk water bodies identified by the study is the Hungry Horse Reservoir. Clancy says the reservoir is connected to the South Fork of the Flathead River, which is one of the largest interconnected habitats for iconic native fish species in Western Montana. Fish he says the state can’t afford to lose to invasive species.

Trout Unlimited Montana Executive Director David Brooks sits on the governor’s invasive species council. He applauds FWP’s efforts to identify water bodies at risk for non-native fish introductions, but adds that the state could further reduce risk by implementing stricter regulations on private ponds, which he says could be a source of non-native fish and other invasive species making their way into area water bodies.

"There’s a whole host of issues around this with private ponds," Brooks says. "One fix to consider would be not permitting any new private ponds in this state."

He says so far, Trout Unlimited has not had much success lobbying the state Legislature for stricter controls on private ponds filled with non-native fish.

Correction - 06/11/20

We updated this story to clarify that northern pike in Montana are only native in the Saskatchewan River drainage on the east side of Glacier Park. An earlier version of the story said the fish were not native in Montana.

Aaron graduated from the University of Minnesota School of Journalism in 2015 after interning at Minnesota Public Radio. He landed his first reporting gig in Wrangell, Alaska where he enjoyed the remote Alaskan lifestyle and eventually moved back to the road system as the KBBI News Director in Homer, Alaska. He joined the MTPR team in 2019. Aaron now reports on all things in northwest Montana and statewide health care.
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