On a hot day last summer, biologists from Montana Fish, Wildlife and Parks ventured to Danaher Creek, deep in the Bob Marshall Wilderness, and caught hundreds of young purebred westslope cutthroat trout.

The fish made the 24-mile journey out of the wilderness on the backs of mules, packed in water-filled coolers fed with bottled oxygen. Once out of the wilderness, they were transported to their new home at the Sekokini Springs hatchery in Coram.

“We had 100 percent survival,” FWP biologist Matt Boyer told interested anglers last week.

Many of those fish and their offspring will have a new home in the Necklace Chain of Lakes in 2012 as part of an ongoing effort to preserve westslope cutthroats in the South Fork.

Since 2007, the Westslope Cutthroat Trout Conservation Project has slowly, but surely, been replacing non-native fish and hybrids in lakes in the South Fork drainage in an effort to preserve some of the last remaining purebred strains of westslope cutthroats in the nation.

This year, the effort will continue in the Necklace Chain of Lakes in the Bob Marshall Wilderness. In late August, FWP biologists and technicians will treat the small lakes and a portion of the outlet stream with rotenone, a chemical that kills fish.

Rotenone is not hazardous to humans, but it prevents the absorption of oxygen across a fish’s gills. Death comes quickly. Rotenone was first used by South American and Asian natives to catch fish. It was originally derived from the roots of the derris plant, a pea species from Asia, and the lonchocarpus plant, from South America.

Rotenone will be hauled in by mules and applied to the Necklace Chain of Lakes. Biologists will cut the bladders of dead fish that rise to the top to prevent attracting bears and other birds.

The treatment can linger up to three months, biologists note. A chemical that neutralizes rotenone will be applied downstream from the outlets of the lakes to prevent harm to fish further downstream.

All told, the treatment will take a few days. The following spring, the effects of the rotenone will have dispersed, and the lakes can be re-stocked with purebred westslope cutthroat trout.

Prior to treatment, lakes in the conservation project were rife with non-native fish, including rainbow trout, rainbow-cutthroat crosses and yellowstone cutthroat crosses. The worry among biologists is that the continued hybridization of westslope trout with non-native fish eventually will wipe out the purebred cutts in the South Fork.

To date, Black, Blackfoot, Big Hawk, Clayton and Wildcat lakes have been treated and re-stocked. Many of the lakes are fishing well already, Boyer said, and some lakes already have natural fish reproduction just a year after being re-stocked.

Several other lakes are being treated through an effort known as “swamping,” where hundreds of purebred westslope cutthroat trout are added to a lake that contains hybrid fish. As the fish breed overtime, it’s hoped that the hybrid genetics will be squeezed out of the population.

All told, the entire project will cover 21 lakes in the Bob Marshall and Jewel Basin area. Biologists have also teamed up with the Backcountry Horsemen of the Flathead for packing services.

There are challenging waters ahead. Handkerchief Lake poses challenges because the outlet stream, Graves Creek, is short and flows into the Hungry Horse Reservoir. Biologists will have to be careful not to kill trout in the reservoir itself.

One the of the last lakes to be treated will be Sunburst, a large lake in the Bob Marshall that will need thousands of pounds of rotenone for treatment

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A state hatchery in Coram recently received the final funding it needs to complete its construction. The Sekokini Springs Westslope Cutthroat Isolation Facility, located off the North Fork of the Flathead River near Blankenship Bridge, is one of two hatcheries in Montana where wild, genetically pure strains of trout are accepted.

The Northwest Power and Conservation Council recently approved about $1.8 million in funding for the state-run hatchery that’s been operating as an advanced conservation hatchery for more than a decade. The funding will be used over the next few years to finish the hatchery’s master plan, which calls for an outdoor pond and stream habitat to complement the indoor isolation facility.

While other hatcheries rely on the state’s only westslope cutthroat brood stock at the Washoe Park Trout Hatchery in Anaconda, Sekokini Springs will serve as a diversity resource for Montana waters that have lost genetically pure strains of westslope cutthroat trout over the years, said Fish, Wildlife and Parks biologist Brian Marotz, who helped manage the Sekokini hatchery since it was acquired by the state in 1998.

Sekokini Springs operated as a private rainbow trout farm for about 40 years on land leased from the Flathead National Forest. The state acquired the improvements, including a 60-by-40-foot building with concrete raceways, for about $70,000. The building was insulated to prevent condensation, damaged siding was replaced, and the artesian springs that supply the facility were capped and piping was installed to secure the water supply from airborne contaminants.

Sekokini Springs is used to quarantine juvenile cutthroat collected from wild sources. The fish are held in raceways, tested for disease and genetic purity, and eventually certified for use as a hatchery resource. FWP has identified about 50 genetically pure strains in the wild to draw from, mostly in South Fork drainages. Cutthroats in other drainages have been exposed to hybridization with rainbow and Yellowstone cutthroat trout strains.

Ironically, Sekokini Springs may have been a primary source for rainbow hybridization in the lower Flathead River system. The hatchery likely “leaked” fish over the years into the North Fork Flathead River, Marotz said. The hatchery now is entirely contained, and its waste water is disposed of through a special drainfield.

With the new funding, the building will be expanded, and two large, still-functioning ponds will be restored and converted into four ponds. Another pond will be created to grow wild feed. Grasshoppers and meal worms already are being cultivated at the hatchery.