Westslope Cutthroat: Oncorhynchus clarki lewisi


Written by: Phil Monahan

The state fish of both Montana and Idaho, the westslope cutthroat is actually misnamed, for it occurs on both sides of the continental divide. The Latin name for the subspecies comes from the fact that the fish was first described in the journal of Capt. Meriwether Lewis, who headed the Corps of Discovery alongside William Clark:

These trout (caught in the falls) are from sixteen to twenty three inches in length, precisely resemble our mountain or speckled trout in form and position of their fins, but the specks on these are of a deep black instead of the red or gold color of those common to the U. States. These are furnished long sharp teeth on the pallet and tongue and have generally a small dash of red on each side behind the front ventral fins; the flesh is of a pale yellowish red, or when in good order, of a rose red. (June 13, 1805)

Westslopes once had a native range larger than that of any other cutthroat subspecies—stretching about 1,000 miles from central Idaho to the Canadian Rockies, and from central Montana’s Judith River west to the Cascades in Washington—but habitat loss, the introduction of non-native species, and hybridization with other subspecies of cutthroats caused a massive population decline.

Today, pure strains of westslope cutts are estimated to exist in just 2 to 4 percent of their historic stream distribution. The strongest populations are in the Flathead Basin and Glacier National Park in Montana, and fishable numbers thrive in Idaho’s St. Joe and Lochsa rivers. Several drainages in Alberta and British Columbia also hold good numbers of the subspecies. The remote northwestern corner of Yellowstone National Park holds Wyoming’s only westslopes, although that population is in danger of extinction through hybridization with the Yellowstone cutthroat.

Recent decades have witnessed a concerted conservation effort to save the westslope cutt and restore it to many waters from which it has disappeared. Orvis has taken part in the effort through its support of the Western Native Trout Initiative.

Illustration by Joseph Tomelleri, americanfishes.com.

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