Biologists in Montana are sounding alarms over the discovery of nonnative brown trout in the Flathead River in the northwestern part of the state. Montana Fish, Wildlife and Parks published a press release on July 14 warning of the detection, which occurred near the Pressentine Fishing Access Site near Evergreen, Montana, immediately northeast of Kalispell.
The Flathead River is one of the few water bodies in the state that lacks the predatory species, and fisheries managers would prefer to keep it that way. Brown trout were first introduced to Montana in the late 19th century and have since outcompeted more sensitive species like cutthroat, bull, and rainbow trout—all of which have native ranges in portions of Montana. Not only do brown trout dominate food and habitat resources of other native trout species, but they also prey on juvenile fish.
Brown trout also tend to be more tolerant of degraded environmental conditions and disturbances than other species, according to the Montana Field Guide, an ecological database maintained by the state. Mature browns can easily reach 20 inches in length, and they spawn in the fall. This means they’re less susceptible to the strain on water resources that irrigation can put on other trout species that spawn in the springtime.
FWP will use environmental DNA sampling technology to sniff out further evidence of brown trout presence in the Flathead. While there was no direct mention in the press release that the fish was illegally introduced to the drainage, FWP is reminding the public that moving live fish from one waterbody to another is illegal.
“Protecting our native trout populations is a priority,” said FWP Regional Fisheries Manager Mike Hensler. “Brown trout pose a threat to native species in the Flathead drainage, and we need the public’s help to manage this invasive species.”
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FWP requests that any angler who catches a brown trout in the Flathead River or any of its tributaries kill it immediately and report the catch to FWP’s Region 1 office. The agency also asks that anglers be prepared to hand the fish over to officials and provide the date and location of the catch, as well. The Region 1 office can be reached at 406-752-5501.
