Westslope Cutthroat Trout Restoration On The Upper Missouri River

Diane Tipton, Montana Fish, Wildlife & Parks Statewide Information Officer

Restoration of westslope cutthroat trout to their traditional habitat in north central Montana is becoming a reality as a result of a partnership between Montana Fish, Wildlife & Parks and U.S. Forest Service biologists.

The westslope cutthroat trout is one of two subspecies of cutthroat trout found in Montana—the other is the Yellowstone cutthroat trout. The cutthroat trout is the Montana state fish, and a state species of special concern. The cutthroat trout is thought to be a survivor from the last ice age or even earlier.

Today genetically pure westslope cutthroat trout populations occupy only three percent of their historic range in the Upper Missouri River drainage, and only eight percent of their total historic range, including Idaho, Washington, Oregon and Wyoming.  

The sub-species suffered a drastic decline in the past century when non-native trout were stocked. These non-native fish colonized much of the state’s cold-water fish habitat. Rainbow trout cross-bred with westslope cutthroat trout, creating hybrid trout, while brook trout out-competed the native trout for space and food.

"Genetically pure westslope are an important part of Montanan’s heritage and a link with the ancient past. They are also likely to have unique genetic adaptations to local habitat conditions that may help them survive over the long term and that we have yet to fully appreciate," said David Moser, FWP Region 4 fisheries biologist. Hybrid fish have been shown to have reduced survival and growth when compared to those produced by genetically pure parent fish.

When FWP and the USFS considered how to best protect westslope cutthroat trout on the Upper Missouri River, they thought of the South Fork Judith River in the Little Belt Mountains of Lewis and Clark National Forest. It was a prime location, offering about seven small populations of mostly pure westslope cutthroat trout established in headwater tributaries. Just three miles downstream rainbow trout dominate the water—threatening the genetics of the remaining westslope cutthroat trout.

"Without some form of protection or barrier, the native fish would have become increasingly hybridized with the rainbow trout, and the brook trout were likely to displace them," said Moser.

The solution, an environmental barrier, took time to plan, design, obtain funding for and to complete the joint environmental assessment by FWP and USFS biologists.

The Future Fisheries Enhancement Program, administered by FWP, contributed nearly $75,000 to the project. Other supporters included the USFS, Montana Chapter of American Fisheries Society, Montana Trout Foundation, and the National Fish and Wildlife Foundation.

In 2006, the long-awaited barrier was constructed on the South Fork Judith River near the river’s confluence with Bluff Mountain Creek.

"With the barrier in place, rainbow trout and other non-native fish numbers must be reduced in a 16-mile stretch of protected water using electrofishing equipment," Moser said. With this step completed in summer 2007, a total of about 25 miles of pristine habitat for westslope cutthroat trout will exist.

"Large-scale projects such as this one take time, but they are one of the few ways to ensure the survival of westslope over the long-term by providing adequate habitat ," Moser said.

The majority of remaining pure westslope cutthroat trout populations east of the Continental Divide are isolated in the headwaters of major drainages in sections of stream under three miles in length. Their isolation and relative small size puts these populations at potential risk from drought, catastrophic fire, or genetic problems associated with limited breeding stock.