Biologists in the Flathead are about halfway through a high-mountain effort to bring back Westslope Cutthroat trout. The goal is to keep hybridized trout out of the system by poisoning the mountain lakes, and restocking them with genetically pure Westslope Cutthroat.
The area for the project includes the headwaters of the South Fork of the Flathead River “so the initial impetus for this project was that there was the potential threat for hybridization to spread further down into the river system,” said Matt Boyer, Fisheries Biologist with Fish, Wildlife and Parks.
FWP is targeting up to 21 high mountain lakes in the Jewel Basin and the Bob Marshall Wilderness. He says historically, the mountain lakes were stocked with Yellowstone Cutthroat and Rainbow Trout, the last planted sometime in the 19-50’s or 60’s. The first lakes were treated with the poison Rotenone in 2007 in the Jewel Basin, and restocked with genetically pure Westslope Cutthroat Trout from a hatchery in Anaconda.
Boyer says they’ve since treated 10-lakes, but have altered their planting methods. He says they’ve started collecting wild trout from other streams in the South Fork to use for restocking.
“When you look at the genetic structure of Westslope Cutthroat Trout across its range, you see pretty large genetic differences from one population to another,” Boyer said.
The project has drawn criticism as the mountain lakes constitute popular fishing destinations, with anglers catching large, hybrid trout. Rotenone has been used in the past to kill fish in a water body so managers could restock it with fish considered more recreational for anglers to catch. It has been used more recently to kill *non-native* fish in a water body in order to re-stock it with native fish.
When the issue first went out for public review people also raised concerns about this latest management effort with many concerned managers were doing more harm than good. 4-and-a-half-years in Boyer says they believe they’re seeing signs of success with natural reproduction occurring in the treated lakes, and good catch rates reported by anglers.
Boyer says after they treat a lake with Rotenone in the fall, the following summer they restock it with several age classes of Westslope Cutthroat trout, “including fish of a size that are catchable to anglers so we can restore that recreational fishery the first summer after treatment,” Boyer said, “and then stocking continues for generally three to four years after that, and you’ve filled in the age classes, and then that coupled with natural reproduction, at that point, we hope to walk away and have these lakes be self-sustaining.”
Boyer was among the speakers giving an update on fisheries management projects to the Flathead Chapter of Trout Unlimited recently. Those assembled were receptive to the efforts to restore the native trout. Some of the biggest concerns raised by the group focused on another non-native, historically introduced species on the valley floor, lake trout moving up the Flathead River. Currently, management efforts to curb and suppress the booming lake trout population are ongoing from Flathead Lake, up to water bodies in Glacier Park.