A large scale conservation project to restore genetically pure west slope cutthroat trout in northwest Montana nears the finish line. Three of 21 lakes remain for Fish, Wildlife and Parks to treat as part of the South Fork West Slope Cutthroat Trout Project.
Fisheries Biologist Matt Boyer said this September they’ll be working on Koessler Lake in the Bob Marshall Wilderness. This lake they’ll be treating with a poison called Rotenone and re-stocking with genetically pure West Slope Cutthroat Trout.
“The South Fork Flathead is a stronghold for West Slope Cutthroat Trout- Montana’s state fish. And it represents about half of what’s remaining in terms of genetically pure, interconnected populations for that species,” Boyer said.
This project started in 2007. Boyer said the list of 21-lakes they’ve been working through were all historically fish-less because they sit above barrier falls, and were stocked with fish like Rainbow Trout to create a recreational fishery.
“That was really during a time period or an era where there wasn’t the awareness for native fish conservation that there is today. Fish, Wildlife and Parks began sampling these lakes in the mid to late (19)80’s and genetic analysis of those lakes indicated that they were non-native trout, and hybridization was spreading downstream,” Boyer said.
“Downstream” is the west slope stronghold of the South Fork of the Flathead River. Boyer said in addition to Rotenone treatment they’ve also been “swamping” certain lakes with genetically pure west slope cutthroat trout, where hybridization gets reduced through successive reproduction with the influx of genetically pure trout. He said this project has broader implications for other conservation projects, particularly concerning the use of Rotenone.
“The pre-and-post treatment monitoring of the amphibians and the insects has indicated that those species are, they’re back, and, of course, if they weren’t that would be entirely counterproductive, because you’ve just damaged or had lasting effect on they prey-base; the source of food for the very species you’re trying to conserve,” Boyer said.
Boyer said 12 of the 21 lakes have been treated with Rotenone, and the final three lakes will be treated with Rotenone; Koessler and Sunburst Lakes in the Bob Marshall Wilderness, and Handkerchief Lake above Hungry Horse Reservoir.
The Project is slated to wrap up by 2016.
