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Warmer Waters Threaten Montana’s Prized Westslope Cutthroat Trout

The native westslope cutthroat trout has drawn generations of fly-fishers to the remote Flathead River system in western Montana. Trout fishing contributes tens of millions of dollars to Montana’s economy each year, and the westslope cutthroat is one of the most highly prized fishes. Yet the freshwater ecosystems on which they depend are changing, threatening the longevity of this species.


Rising temperatures are translating into earlier spring snow melt and run-off, lower summer flows, and warmer waters. Native fish, such as the westslope cutthroat trout, are losing habitat and invasive species – such as the rainbow trout – are expanding their range. The mountain streams that cutthroat prefer were once too cold for rainbow trout. But warming water temperatures have allowed rainbow trout to expand into cutthroat territory. Cutthroat and rainbow trout are now mating, decreasing the number of genetically pure westslope cutthroats, and spelling trouble for the long-term viability of this iconic species.


Results show that projected rising temperatures and reduced spring precipitation could increase hybridization between trout species and reduce the availability of cold water habitats for cutthroat, leading to further population declines. By mid-century, the decline in native trout in the Flathead River could cost Montana an estimated $5 million per year.


Understanding how changing conditions might alter the habitat of Montana’s native trout species is critical for their effective management and recovery. The results of this work will aid managers in identifying high-value conservation areas that can maximize returns on conservation investments and improve native trout populations – which will ultimately benefit Montana’s sport fishing industry.


Project Lead: Northwest Climate Adaptation Science Center
Partners: USGS Northern Rocky Mountain Science Center | The University of Montana | NOAA Fisheries
Stakeholders: Columbia River Inter-Tribal Fish Commission | Confederated Salish and Kootenai Tribes | Montana Fish, Wildlife & Parks | U.S. Fish and Wildlife Service | NOAA | National Park Service | Alberta Environment and Parks

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