To the uninitiated angler, plucking a 12-inch brown trout from the Kootenai River might not seem like cause for alarm, let alone the sort of threat that could topple an entire trophy fishery.
But for biologists with Montana Fish, Wildlife and Parks, the appearance of a brown trout on the hook of an angler plying the Kootenai’s upper reaches marks the first confirmed sighting of a brownie in this stretch of river, which could spell trouble for local populations of native rainbow and bull trout.
The catch was reported in March and prompted FWP to propose a new management action requiring anglers to kill and report any brown trout they catch on the Kootenai River below Libby Dam and above Kootenai Falls, a mandate the Fish and Wildlife Commission unanimously approved April 19 at its meeting in Helena.
“This regulation and management action is intended to remove any brown trout before they become established, which could affect bull trout populations and rainbows,” Eileen Ryce, FWP’s fisheries division administrator, told the commission. “They could attain trophy size due to the abundant kokanee present there as a forage fish.”
Indeed, Montana’s record rainbow was caught on the Kootenai in 1997, measuring 33.1 pounds and 38.6 inches long. Since then, however, FWP has been tracking a decline in trophy rainbows, and biologists worry that if the Kootenai becomes a stronghold for brown trout, the species could outcompete the native populations by feeding on fry and fingerling.
“If brown trout become established and persist, it is quite likely this long-lived voracious predator will negatively impact both rainbow and bull trout populations, especially at fry and fingerling stages,” FWP Fisheries Biologist Mike Hensler said prior to the commission’s April 19 vote. “The proposed regulation in addition to active removal during FWP fisheries survey work will be used to hopefully remove brown trout before they become established.”
The detection of a brown trout also brings up another point of concern — bucket biology, meaning someone likely deposited the trout intentionally, either in the main river or a tributary. The only other explanation is the fish negotiated the raging Kootenai Falls without assistance, a scenario that made Hensler skeptical.
FWP Fisheries Biologist Leo Rosenthal said that while this marks the first time the agency has taken this sort of action on a trout introduction — FWP previously mandated a kill-and-report order for non-native, illegally introduced walleye in Swan Lake — it is consistent with FWP’s mission.
“I do think that for the sake of consistency we are treating this brown trout as we should on this stretch of water,” Rosenthal said. “I sometimes get accused of being pro-trout and anti-walleye, but I am simply anti-illegal introductions. It shouldn’t be something that is done with a bucket.”
Nick Gevock of the Montana Wildlife Federation said his organization supported the action.
“We are doing this because it is the right thing to do,” he said. “We don’t want to establish an incentive for unlawful introductions.”
Lucky Sultz, of the Flathead Valley Chapter of Trout Unlimited, said the local chapter supports the regulation.
“With all the other problems on the Kootenai River, the last thing we need is another non-native predator that will damage our native fisheries,” he said.
FWP’s Ryce said the agency is requiring anglers who hook into a brown trout to turn in the fish so biologists can remove its tiny inner ear bone, or otolith, which reveals a history of its growth and also contains a record of its migration pathways, like a geochemical diary of its life and its natal waters.
Once the otolith is removed, Ryce said the angler may keep the brown trout for supper.