Westslope Cutthroat Trout

Westslope Cutthroat Trout, Jonny Armstrong-USGS PhotoWestslope Cutthroat Trout, NPS PhotoWestslope Cutthroat Trout, Clint Muhlfeld-USGS Photo

Westslope cutthroat trout (Oncorhynchus clarkii lewisi) is a native species found in the waters throughout the Crown of the Continent. Cutthroat have been in decline throughout their native range and have been petitioned for listing under the Endangered Species Act, but the listing has been declined. As a species that requires pure, cold, and connected aquatic systems to survive, and main stems as protection from nonnative fish, cutthroat trout is considered an indicator species for the health of the ecosystem that they inhabit.

High incidences of hybridization with nonnative fish, such as rainbow trout, create offspring with reduced survival and growth rates. Cutthroat trout’s high intolerance to disturbances and subsequent habitat loss, fishing pressure, and fragmentation are also factors in declining numbers. Non-hybridized populations of westslope cutthroat trout currently inhabit less than 10% of their historic range in the United States and around 20% in Canada.

Research in Glacier National Park is underway to map the distribution of westslope cutthroat trout populations and the extent of hybrid populations.