The Swan River, its hundreds of miles of tributary streams, large interconnected lakes and steady groundwater supply provide outstanding habitat for native fish. Shaped extensively by glaciers during the last ice-age, the Swan watershed collects snowmelt in tributary streams originating in roadless public land, including two federally designated wilderness areas. The network of lakes, streams and mainstem river are home to a host of native species including mountain whitefish, bull trout, westslope cutthroat trout, suckers, sculpin, and northern pikeminnow. Beginning as early as the late 1800’s, legal and illegal introductions of non-native fish to the Swan have added many other species including rainbow, brook, lake, golden and Yellowstone cutthroat trout, kokanee, northern pike and, as of 2015, walleye.
For a variety of reasons, range-wide declines in bull trout led to federal listing under the Endangered Species Act, but the situation with westslope cutthroat trout is less clear.
Our data suggests that pure westslope cutthroat trout today are thriving in about 20% of their historic stream habitat in the Swan River watershed, mirroring declines range-wide. The survivors live in small, fragmented populations in headwater streams and are no longer presumed to be one large, interconnected "metapopulation." Approximately 51% of historic cutthroat habitat in the Swan is occupied by hybrids. Westslope cutthroats are now a federal "species of special concern" and periodically have been considered for listing for protection under the Endangered Species Act.
A collaborative group of partners from Swan Valley Connections, Montana FWP, US Geological Survey, Montana DNRC, US Forest Service, the University of Montana, MPG Ranch, and private citizens, the Native Fish Subcommittee works to inform the conservation strategy which will best protect and restore westslope cutthroat in the Swan basin. To fill in knowledge gaps about the distribution, abundance, and genetic status of cutthroat in the Swan, SVC has worked over the past 6 years to survey tributary streams from Lion Creek south to the head of the Swan River. We will continue to monitor known populations and collect samples for genetic study in future years. Results to date about the status of each of the Swan’s known conservation populations can be found here.
To capture a snapshot of species distribution in the mainstem Swan River, SVC partnered with the Flathead National Forest over the past two years to conduct the first known systematic inventory of Swan River's fisheries resource via snorkel surveys. While we recorded every species identified, we were particularly interested in whether we would find large-bodied cutthroat trout that may indicate the presence of a migratory life history. Results from this preliminary study can be found here.
Monitoring of Tributary Streams in the Swan River Basin: Findings from 1997-2015 (PDF)
Beth Gardner, Flathead National Forest, Swan Lake Ranger District
IMAGE: Top - U.S. Geological Survey/photo by Johnny Armstrong