Invasive Smallmouth Bass Threaten Trout on Montana’s Famous Bitterroot River

It is unknown if this fish emigrated from existing river populations, escaped from private ponds, or was illegally
introduced, Montana FWP said.

On July 5, a trout angler netted a smallmouth bass in western Montana’s Bitterroot River, marking the first-ever sighting of a smallie in the well-known coldwater trout stream. Before that, the closest documented reports of locally-invasive smallmouth bass occurred nearly 70 miles away in the Clearwater River system and 80 miles downstream in the Clark Fork River near St. Regis, Montana. 

Upon confirming the report, Montana Fish Wildlife & Parks (FWP) combed the area for evidence of additional smallmouth. None were picked up in those surveys, but FWP staffers determined that the area could be suitable habitat for the species to establish a “self-sustaining” population, given rising river temperatures and ample underwater structure. 

Smallmouth bass are not native to Montana, but they’re famously adaptable to new habitats. Their presence in the Bitterroot could be detrimental for the brown, rainbow, and cutthroat trout that call the river home, FWP said. As a result, the agency is proposing an emergency rule that would require anglers to keep, report, and turn in any smallmouth bass caught in the lower portions of the river—from the town of Florence downstream to Missoula. 

“The importance of this catch-and-kill mandate is that smallmouth bass—unlike the largemouth bass that have existed in the Bitterroot for years—are well-adapted to the main stem of the river. It’s really prime habitat for an invasive species to run roughshod over our native trout population,” longtime Bitterroot guide and Montana Wildlife Federation employee Jeff Lukas told Field & Stream. “It’s essential that we nip this in the bud, by making sure that all anglers know that these fish don’t have a place in our river—and that they should be killed and reported immediately.”

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Mandatory reporting has proven successful in other Montana fisheries. According to FWP, its implementation in the Bitterroot could help biologists determine the invasive bass’ distribution and abundance. The program could also help FWP understand how smallmouth showed up in the river in the first place and prevent others from spreading. The Montana Fish and Game Commission will decide whether or not to adopt the rule at their August 17 meeting.

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