Montana Fish, Wildlife and Parks is now more than three-quarters finished with a 10-year project aimed at treating alpine lakes above the South Fork Flathead River drainage to purge the presence of non-native trout.
A crew of 10 people, with support from the Backcountry Horsemen group, recently completed a toxin treatment of Lena Lake in the Big Salmon drainage. The week-long effort involved using Rotenone in the lake as well as two downstream tributaries to kill off hybrid fish. As with previous lakes involved in the project, Lena Lake will be promptly re-stocked with genetically pure westslope cutthroat trout in three age classes, ranging up to 12 inches in length.
“It went well,” said Matt Boyer, a fisheries biologist and project coordinator. “To me, the exciting part is the fisheries we’ve restored that are there for anglers to catch.”
Since the project was implemented in 2007, funded by the Bonneville Power Administration, 18 of 21 lakes have been treated, 12 of them with Rotenone and the remaining six with genetic swamping. Swamping involves overwhelming any hybrid populations with heavy stocks of westslope cutthroat. Three more lakes will be treated and the project is on schedule to conclude in 2016.
Boyer said he is impressed with how well all of the restored fisheries have bounced back. Within just a couple years after Blackfoot Lake was treated in the Jewel Basin, Boyer was catching 17-inch westslope cutthroats.
“The growth rates are phenomenal” because the newly planted fish have pristine environments with no competition, Boyer said. “They’ve got all the room in the world to grow and they do.”
Catch rates reported by anglers have been high, too.
“People have gone up there and had 20 to 30-fish days,” he said.
The stocked fish have been coming from the relatively new Sekokini Springs conservation hatchery near Blankenship Bridge, which has been raising fish derived from wild fish collected most recently from Danaher and Youngs creeks in the South Fork basin.
“Sekokini is playing a huge role in this project right now,” Boyer said.
The work at Lena Lake, which is in the Bob Marshall Wilderness, involved the use of 10 pack horses that had to make multiple trips to get gear in place. Chemicals were flown in by helicopter for safety reasons, Boyer said.
Treating the lake required the use of rafts and drip stations, positioned at carefully calculated intervals, were used to treat about six miles of downstream tributaries. A neutralizing chemical was used above a downstream barrier falls to ensure that Rotenone would not continue to travel downstream.
Because of the tributary work, it was the biggest effort undertaken so far in the overall project, Boyer said.
Next year, Koessler Lake is scheduled for treatment, followed by Handkerchief Lake in 2015 and finally, Sunburst Lake in 2016.
The South Fork drainage is considered a stronghold for westslope cutthroat trout, and the purpose of the project has been to prevent an eventual proliferation of trout with hybrid rainbow or Yellowstone cuttroat genetics. The largest concentrations of hybrids were detected in the alpine lakes that would “leak” fish into outlet tributaries that feed the South Fork Flathead River and eventually Hungry Horse Reservoir.