Montana Field Guide

The Rocky Mountain Cutthroat Trout ( formally Yellowstone Cutthroat Trout) is one of two species of native cutthroat found in the state. Together they have been designated Montana's state fish, the Blackspotted Cutthroat Trout. They have a golden coloration and larger spots more widely distributed on their sides than the Westslope Cutthroat Trout. The Rocky Mountain Cutthroat Trout, is native to the Yellowstone River drainage of southwest and south-central Montana. Originally their range was as far downstream as the Tongue River, but today pure, unhybridized populations are limited to some headwaters streams and Yellowstone National Park. Rocky Mountain Cutthroat Trout are a Montana Fish of Special Concern. Much of their spawning habitat in tributaries of the upper Yellowstone River has been lost to irrigation withdrawals which dewater the streams before spawning and egg-incubation are completed in July and August. The Big Timber hatchery of the Montana Department of Fish, Wildlife, and Parks maintains a pure Rocky Mountain Cutthroat Trout broodstock. Rocky Mountain Cutthroat Trout are used extensively for mountain lake stocking on the east slope of the Rocky Mountains and in the Absaroka-Beartooth Wilderness where they can grow to sizes up to 15 pounds. In general, Rocky Mountain Cutthroat Trout are larger than Westslope Cutthroat Trout and more prone to eat fish as part of their diet.

For a comprehensive review of the ecology, conservation status, threats, and management of this and other Montana fish species of concern, please see Montana Chapter of the American Fisheries Society Species of Concern Status Reviews.

The Rocky Mountain Cutthroat Trout is visually distinguished from other trout species by its two prominent red slashes on the lower jaw, and from other cutthroat trout subspecies by its medium-large, black spots that tend to be concentrated posteriorly, and its drab brownish, yellowish, or silvery coloration, with brighter colors generally absent even in mature fish (Behnke 1992, Baxter and Stone 1995, Montana AFS Species Status Account).

Tiny teeth are usually present on the floor of the mouth behind the tongue. These are embedded in tissue and difficult to see but may be felt if brushed with the side of a needle. Red on the side of the head and gill cover becomes intense in the breeding male.

Rocky Mountain Cutthroat Trout inhabit relatively clear, cold streams, rivers, and lakes. Optimal temperatures have been reported to be from 4 to 15 degrees C., with occupied waters ranging from 0 to 27 degrees C. (Gresswell 1995, Montana AFS Species Status Account).

Rocky Mountain Cutthroat Trout may live as long as 11 years (Gresswell 1995, Montana AFS Species Status Account).

There are three primary life history patterns: resident, fluvial, and adfluvial (Gresswell 1995). Resident fish occupy home ranges entirely within relatively short reaches of streams. Fluvial fish migrate as adults from larger streams or rivers to smaller streams to reproduce. Adfluvial fish exhibit a similar pattern, but migrate, sometimes many kilometers, as mature adults from lakes to inlet or outlet streams to spawn (role of stream ice on fall and winter movements and habitat use by Bull Trout and cutthroat trout in Montana headwater streams).

Movement in Rocky Mountain Cutthroat Trout may also be associated with temporal habitat changes. At low water temperatures in winter, fry (and probably juvenile) Rocky Mountain Cutthroat Trout entered spaces in the stream bottom during the day, and emerged from them at night (Griffith and Smith 1993). Larger Rocky Mountain Cutthroat Trout may also shift habitats from fall to winter as water temperature declines and anchor and shelf ice develop (Brown and Mackay 1995, Jakober et al. 1998). Rocky Mountain Cutthroat Trout probably undergo localized movements associated with changes in habitat or food availability in other seasons (Young 1996, Young et al. 1997, 1998, Montana AFS Species Status Account).

Rocky Mountain Cutthroat Trout typically spawn in spring and early summer after flows have declined from their seasonal peak and tend to select sites with suitable substrate (gravel less than 85 mm in diameter), water depth (9 to 30 cm), and water velocity (16 to 60 cm per second) (Varley and Gresswell 1988, Byorth 1990, Thurow and King 1994). Water temperature determines the time of hatching and emergence of fry. After emergence, fry immediately begin feeding, typically in nearby stream margin habitats, but they may also undertake migrations to other waters (Gresswell 1995). Juvenile fish require three or more years to mature. Spawning fish tend to be from 200 to over 600 mm long and weigh from 0.1 to 5 kilograms (Thurow et al. 1988, Montana AFS Species Status Account).

To maintain healthy populations of Rocky Mountain Cutthroat Trout and to ensure the wide-ranging persistence of this subspecies in Montana and elsewhere, a number of tactics have been proposed in recent status assessments (Yellowstone Cutthroat Trout Working Group 1994, Gresswell 1995, May 1996, May et al. 1998, Dufek et al. 1999, Wyoming Game and Fish Department 2000). These include field surveys, harvest management, habitat protection and improvement, non-native species control, and broodstock management (Montana AFS Species Status Account).

Gresswell (1995) and Kruse et al. (2000) considered nonnative fish species the greatest threat to the persistence of Yellowstone cutthroat trout. Because Rocky Mountain Cutthroat Trout and Rainbow Trout readily hybridize and produce fertile offspring, sympatric populations often form hybrid swarms (Allendorf and Leary 1988; Henderson et al. 2000). Introductions or invasions of Brown Trout (Salmo trutta), Brook Trout (Salvelinus fontinalis) and Lake Trout (Yellowstone Lake) have led to displacement of cutthroat trout throughout the western U.S.