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Westslope Cutthroat Trout Species Information

The Westslope Cutthroat Trout is one of the two subspecies of cutthroat trout native to Montana, historically sharing the state’s water with the Yellowstone Cutthroat Trout. Identifiable by a speckled olive body that has a thin streak of vibrant red along the belly and along the jaw, westslope cutthroat are one of Montana’s most prized species. Known scientifically as Oncorhynchus clarkii lewisi, the westslope cutthroat trout was first included in the writings of western settlers when William Clark of the Lewis and Clark expedition described a westslope cutthroat caught in Montana’s Missouri River. “Clarkii,” in the scientific name, is in fact a tribute to William Clark. The common name derived from the fact that westslope cutthroat were found almost exclusively west of the Continental Divide. Westslope cutthroat are native to all of western Montana as well as the upper Columbia River system in northern Idaho and southern British Columbia. Today, westslope cutthroat can be found in almost all of Montana’s major rivers, from the Judith River to the Gallatin, and their tributaries. Westslopes are the only subspecies of cutthroat trout that live in each the Pacific, Atlantic and Arctic ocean drainages. Due to their expansion outside of their native region, today there are now several isolated populations of westslope cutthroat across the west, including in Washington and Oregon.

Size, Spawning Habits and Life Cycle

Although some individuals can grow larger than 18 inches, westslope cutthroats typically grow to between 8 and 12 inches in length. In Montana, west slopes exist in both fluvial and adfluvial form: this means that some fish will spend their entire lives in rivers, while others will live in lakes and travel to rivers or small streams just to spawn. The species can also be found in many of Montana’s high alpine lakes. Like rainbow trout and other subspecies of cutthroat, westslope cutthroat spawn in the spring, usually between March and early June, although the specific timing depends on the body of water and the year. Once the water temperature warms to the mid-40 degrees fahrenheit after winter, female westslope cutthroat trout will migrate to shallow and fast-flowing sections of rivers and streams. Here, they will beat their tails against the riverbed to create a patch of gravel known as a “redd” on which they deposit their eggs. Once this has been completed, a male will fertilize the eggs, which usually hatch within a few weeks, although some will take up to two months. West slopes will then live up to eight years, providing exciting fishing opportunities to anglers across the state of Montana.

Due to the introduction of non-native species and cross-mating, genetically pure strains of westslope cutthroat exist in only three percent of their native range in Montana. Both other species of cutthroat and rainbow trout are able to spawn with westslope cutthroat, so hybrid strains of cutthroat and cutbows (a rainbow and cutthroat trout hybrid) are common in Montana. This, alongside habitat degradation, has caused a significant decline in west slope populations in Montana. Thus, catch-and-release practices are advised when fishing for these fish, and anglers are asked to avoid fishing for west slopes during their spawning season. Despite this, anglers will find many exciting opportunities to fish for this wonder species in beautiful Montana waters.