Genetics the key to developing pure westslope

Replacing non-native fish species found in backcountry lakes with genetically pure native westslope cutthroat trout takes time and a little scientific ingenuity.

Fish, Wildlife and Parks data suggests that westslope cutthroat are currently at 10 percent of their historic population. The Flathead Valley and its surrounding area has one of the last pure westslope populations in Montana.

Westslope cutthroat have been recommended for the endangered species list twice in the last decade.

FWP fisheries biologist for Region One, Matt Boyer, said one of their missions is to maintain and grow the range and population of the fish. Boyer and his crew have tackled the issue in the Swan Range’s lakes since 2007. He gave a project update at a FWP public meeting last Thursday.

“It’s kind of cutting edge stuff,” Boyer said. “It incorporates new technology, in terms of new genetics technology.”

New genetics technology comes into play once the non-native rainbow and Yellowstone cutthroat trout are eliminated. Elimination often comes in the form of chemically treating a lake to kill off all the fish.

The introduction of rainbow trout and Yellowstone cutthroat that happened in the 1920s is a big reason for westslope cutthroat’s population decline.

It’s not just the fight for food sources either, it’s also a hybridization between the fish species that has caused the decline in genetically pure westslope. While native westslope cutthroat have adapted to western Montana’s special breed of winter for thousands of years, the newer hybrid breeds of fish don’t necessarily have the same coping mechanisms.

At one point, genetically speaking, westslope cutthroat were considered westslope cutthroat. But that is no longer the case.

“Native populations can differ from area to area in terms of genetics,” Boyer said.

Compare westslope from the North Fork of the Flathead River with those from the South Fork, and each will have its own set of genetics. Boyer said the genetic variation is slight, but it has developed over time to help the westslope survive in each specific ecosystem.

Rather than restocking the Swan Range’s lakes with farmed fish, FWP is pulling juvenile fish from Danaher Creek in the Bob Marshall Wilderness, raising them to maturity at Anaconda’s Washoe Park hatchery, and restocking lakes with the offspring.

The goal of the project is to get as close to a genetically “correct” population into a lake as possible.

Westslope cutthroat are now the surviving species in 16 of the 21 lakes proposed for the project. Some of the lakes include Lena, Koessler, Sunburst and Clayton.

This May FWP will stock the Necklace Chain of Lakes with Dannaher Creek westslope. Last September they chemically treated the lakes with Rotenone.

Rotenone kills the fish by preventing the gills from absorbing oxygen. It is applied in one part per million to the lake and breaks down quickly in the sunlight.

While some amphibians and aquatic insects show a decrease in numbers after Rotenone treatment, Boyer said within two years both species and numbers are back to pre-treatment numbers. The chemical has no affect on mammals or birds.

“We don’t restock the lake until we get that negative reading with the chemical,” Boyer said.

For all the lakes FWP has applied Rotenone to thus far, they chemically treated the lake in the fall and were able to successfully plant westslope the following spring. Boyer has spoken with fisherman who fish the lakes after treatment and heard no complaints.

“Conservation programs like this are a step toward keeping them off the (endangered species) list,” Boyer said. “And keeping recreational fishing opportunities open.”