Hybrid trout removal promising

Efforts by the Montana Fish, Wildlife and Parks to eradicate hybrid trout from several lakes seems promising thus far.

Results from testing done at Black Lake and Blackfoot Lake show the lakes are recovering after being treated in 2007.

"By the second year we see comparable species diversity," said FWP fisheries biologist Matt Boyer.

The state is trying to eliminate hybrid trout by using a poison specific to fish. The lakes are treated, killing the fish and then restocked with pure westslope cutthroat trout.

Westslope cutthroats are the native trout of the Flathead drainage. Stocking of non-native species in lakes during the 1950s and 1960s began threats of hybridization by non-native Yellowstone cutthroat and rainbow trout.

FWP aims to reverse the trend and protect the hybrid trout from moving from lakes farther into the Flathead drainage. Several lakes are being treated with poison or by using genetic swamping, stocking a lake with a high number of native trout to create a pure population over time.

FWP began the poison treatment project in the fall of 2007. Black Lake and Blackfoot Lake were treated first. In 2008, Lower Big Hawk Lake was treated and then Margaret and Clayton lakes followed in 2009.

Amphibian and invertebrates species levels are monitored before and after treatment to ensure the lake recovers. Treatment takes place in the fall and stocking occurs the following year after the poison has broken down. Different age-class trout are introduced into the lake to quickly return the best recreation fishing to the lake.

Boyer said the biggest-size fish should return to the lake between four and eight years after treatment, depending on the lake.

The most data is available for Black and Blackfoot lakes so far.

"With the release of a bunch of nutrients because of the dead fish we get pretty good growth," Boyer said.

The idea is that after treatment the lakes will be stocked to keep recreation fishing available at the lakes based on historic trends.

"Ideally once they're stocked with different age classes we can leave them alone and they will take care of themselves," Jim Vashro, fisheries manager, said. "If we can keep the trout (genetically) pure we can keep them off the Endangered Species list and can keep them for recreation fishing."

Margaret Lake has been known as a trophy lake and will likely be returned to that, Boyer noted.

Seven lakes are planned for treatment through 2016.

This fall FWP will treat Wildcat Lake, which has historically been stocked with non-native rainbow and Yellowstone cutthroat trout. The lake will be closed for public safety during treatment.

The FWP Commission voted to lift harvest limits on the Wildcat Lake prior to treatment to allow increased public opportunity for harvest. Limits on George, Woodward, Pyramid and Pilgrim lakes, which are being treated with genetic swamping, have also been lifted. Daily and possession bag limits are removed now through Oct. 1.