The westslope cutthroat trout is the official Montana state fish and one of two native cutthroat trout types found in the state. The westslope is native to western Montana and is also found in the Missouri River drainage on the east side of the Continental Divide. Westslope cutthroats probably swam over the Divide during the last period of glaciers in Montana, about 10,000 years ago. As the glaciers moved south, they dammed up some of the major rivers in western Montana and created huge reservoirs that sometimes backed up all the way to the Divide, spilling water (and cutthroat trout) into rivers and streams on the East side of the Continental Divide. Montana was very different back then!
The other native cutthroat trout in Montana is the Yellowstone cutthroat trout, which is found only in the Yellowstone River drainage. Apparently, the westslope and Yellowstone varieties did not mix because the Missouri and Yellowstone rivers are far apart and are separated by lots of warm murky water that is not suitable for trout. Hence the two unique strains stayed separate. They look similar, except for differences in spotting patterns and color differences during spawning season.
We estimate that westslope cutthroat trout were present in about 365 miles of rivers and streams in the Sun River and its tributaries downstream from Diversion Dam prior to the arrival of the settlers. However, it appears there are no genetically pure native populations left in the Sun drainage. Biologists have only found about five remaining westslope cutthroat populations in the Sun drainage, but they are slightly hybridized and inhabit a total of less than 10 miles of creek.
The status of westslope cutthroat in the Sun is a commonly repeated story in the Missouri River drainage. Originally, westslopes were probably found in about 10,000 miles of rivers and streams in the Missouri River drainage. Now, genetically pure native cutthroat are found in only about 600 miles of Missouri River tributaries, meaning they have disappeared from about 94% of their range on the east side of the Continental Divide. Nowadays, the only remaining genetically pure westslopes in the Missouri River drainage are almost all found in areas above natural barriers (waterfalls, dry sections of creeks) that non-native brook trout and rainbow trout have been unable to invade.
The Montana Department of Fish, Wildlife and Parks and the U.S. Forest Service have been putting extra effort in recent years to restore westslope cutthroat to make sure this beautiful Montana native does not disappear from its native range. Fish surveys and genetic testing have been done on about seven suspect populations in the Sun drainage since 1991. Surveys were also conducted to find “fishless” areas in small creeks above natural waterfalls that might provide good reintroduction sites for native cutthroat.
One such site was found in Petty Creek, a tributary to Smith Creek, which eventually flows to Elk Creek, which joins the Sun River near the town of Augusta. In this case, about 1.5 miles of suitable habitat with no fish was found above a waterfall. In 2002, 122 pure westslope cutthroat were transferred by helicopter 70 air miles from Deep Creek in the Smith River drainage to the empty habitat in Petty Creek. An additional 200 fish were transferred in 2003. The native cutthroats from Deep Creek were tested for diseases before the transfer to make sure no new fish diseases would be moved to a new drainage. Also, stream insects and amphibians (frogs and salamanders) were inventoried in Petty Creek to be sure there would be no harmful effects of introducing fish. Biologists will closely monitor this new population over the next few years to determine if the fish establish themselves and reproduce successfully. There is some concern that water temperatures may be too cold in some of these headwater streams for successful cutthroat reproduction.
Another 1.5 miles of suitable fishless habitat was found in the headwaters of Ford Creek (another tributary to Smith Creek) in the Sun River drainage. Approximately 100 genetically pure native cutthroat trout (5-7 inches long) were airlifted 160 miles from the Spring Creek drainage near Lewistown and introduced into their new home in the Sun River drainage in August, 2004. Biologists hope to transfer more fish in 2005 and will also closely monitor the results of the introduction.
