Fish Facts: Colorado River Cutthroat Trout (Oncorhyncus clarkii pleuriticus)


Written by: Phil Monahan

This Colorado River cutthroat, from southern Utah, displays dark, rich colors.
Photo by Mike Hadley

Considered one of the more beautiful trout in North America, the Colorado River cutthroat trout (Oncorhyncus clarkii pleuriticus) once inhabited the high-elevation streams and lakes of the Green and Colorado River basins in parts of five states. As was the case with many cutthroat subspecies, however, the arrival of European settlers in the West led to massive declines in CRCT populations. Where the fish are still found, anglers prize CRCT for their willingness to eat flies, the beauty of their high-country habitat, and their spectacular colors. The cutthroat-slam programs of both Wyoming and Utah require anglers to land a Colorado River cutthroat to complete the collection of native fish species.

Range and Species History
The Colorado River cutthroat is considered by most experts to have evolved from the Yellowstone cutthroat based on geographical isolation. The original range of the CRCT was an inverted U shape, comprising the drainages of the Colorado and Snake River and included large sections of Colorado, Wyoming, Utah, and New Mexico, along with a small sliver in northeastern Arizona. The native subspecies was at home in high-country lakes and cool mountain streams, and many populations were “fluvial,” which means that they traveled within the river system as part of their life history—living in the main river but heading up small tributaries and the headwaters of the main stem to spawn.


The CRCT is native to parts of Utah, Wyoming, Colorado, and New Mexico.
Map via westerntrout.org

Historical accounts discuss CRCT as large as seven pounds inhabiting the larger rivers of the Upper Colorado system, but the majority of these lacustrine and fluvial populations were extirpated because of dams, overfishing, interbreeding, and habitat loss. In their place are often-isolated resident populations in high-country streams, many above 8,000 feet above sea level. An important fluvial population survives in the Little Snake River drainage, where the fish swim up into tributaries as soon as runoff subsides. After spawning, these fish drop back down to the main river, where they spend the rest of the year.

Like all members of the Oncorhyncus genus, CRCT are spring spawners, although low water temperatures at altitude can push spawning back as late a July. About a month and a half after the spawn, fry emerge from the gravel streambed and head for slow-moving water at the margins of streams. They are opportunistic feeders, focusing mostly on aquatic and terrestrial insects, although larger specimens will eat smaller fish. One of the reasons that anglers prize cutthroats is that they often eat in the middle of the day, and CRCT are no exception. The relative scarcity of food at high altitudes means that they aren’t all that choosy, as well.

Like many subspecies that now inhabit geographically isolated waters, CRCT can vary widely in coloration and spotting, and lake residents often look different from stream fish.


Efforts to reintroduce CRCT to their native waters have been gaining in momentum
Photo by Fred Hays

Conservation
Depending on which source you’re consulting, Colorado River Cutthroat trout now inhabit somewhere between 11% and 16% of their original range. Settlers to the region in the late 1800s found the fish to be a valuable food source, which resulted in overfishing that decimated fish populations. To compound the problem, men replaced the dwindling numbers of CRCT with other species, such as brook, brown, and rainbow trout, which outcompeted the natives, driving the CRCT from much of its range. Habitat loss and overgrazing continued the decline through the early 20th century. In the 1990s, the USFWS considered listing CRCT as “endangered,” but this would have created restrictive protections in states where the species remained. To forestall listing, Colorado, Utah and Wyoming entered a three-state agreement to lead an aggressive reintroduction program.

Reintroduction
The upper reaches of Hermosa Creek—north of Durango, Colorado—serve as a good case study of a CRCT recovery program. In the early 1990s, as more fisheries biologists and anglers became focused on bringing back native species, Colorado Parks and Wildlife used rotenone to remove all nonnative species above a waterfall on the creek’s east fork. They then stocked genetically pure CRCT in native habitat, without the threat of competition. One the project is completed this year, 23 miles of river will have been returned to the natives, and fish counts are strong—up to 600 fish per mile. Similar programs have been underway in Wyoming and Utah, as well, with Utah expending the most resources and restoring hundreds of stream miles. Although this is good news, the subspecies still inhabits less than a fifth of its original range.


The CRCT is at home in lakes and rivers, but loss of habitat has reduced their range.
Photo by Aaron Smith

Tactics and Flies
Because they live mostly at high altitudes, where the growing season is short, CRCT often don’t grow very large, and a twelve incher is a trophy. In lower-lying rivers and lakes, however, the trout can grow to several pounds. Like all cutthroats, they feed on aquatic and terrestrial insects and often aren’t particularly wary or selective—which makes them a favorite of anglers. CRCT seem especially fond of terrestrial patterns, perhaps because high-altitude streams often lack abundant food sources. If you’re heading out for CRCT, bring a box loaded with ants, beetle, and grasshoppers, as well as traditional mayfly and caddisfly patterns. Standard nymphs—such as Hare’s Ears, Pheasant Tails, and Copper Johns—will usually get the job done, as well.

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