Colorado River Cutthroat

Oncorhynchus clarki pleuriticus

Native Trout Fly Fishing

Colorado River cutthroat from a small stream in Rocky Mountain National Park.

Introduction

The Colorado River cutthroat is another minor subspecies of cutthroat and is believed to have derived from the Yellowstone cutthroat. These fish are native to streams and lakes in the Colorado River drainage in Colorado, Wyoming, Utah, New Mexico and a small part of Arizona. In the Colorado Rockies, these beautiful trout have been stocked into a number of formerly fishless alpine lakes, where they provide a popular fishery. Like many subspecies of cutthroat these fish have suffer great declines across much of their native range

Life History Information

The Colorado River cutthroat's native range is typified by numerous high mountain lakes and cool mountain streams and as such these fish exhibit lacustrine, fluvial and stream resident life histories. The Colorado River cutthroat has been rapidly displaced across much of it's native range over the last century and most populations have been pushed back into isolated headwater streams, often above 8,000 feet in elevation. Due to this the stream resident form may now be the dominant life history strategy exhibited by these trout. As with all other cutthroat trout the Colorado River cutthroat are spring spawners. However in the high altitude streams that they a found in water temperatures are typically not warm enough for spawning until late May or even mid July (Trotter 2008). Fry emerge from the gravel in late July through early September, about a month and a half after spawning occurred. According to Bozek and Rahel (1991) juvenile Colorado River cutthroat preferred slow moving water along the margins of streams. In these high elevations streams the growing season is short and the trout feed opportunistically on a variety of aquatic and terrestrial insects. As such the typical adult Colorado River cutthroat is five to eight inches long, although some populations do produce much larger fish.

Historically fluvial and lacustrine populations were widespread across the native range of these fish, but today these life history forms are much less common and the fluvial form has been all but eliminated. Accounts from the 1800's indicate that fluvial cutthroat were found in all of the larger rivers of the Upper Colorado basin and that some of these fish reached sizes of 5 to 7 pounds at an age of 6 to 8 years. One fluvial population that remains today is in the Little Snake River drainage for Wyoming and these fish spawn mainly in tributaries as soon as flows subside in the spring, than drop back down to the river (Young 1995). Young et al. (1997) showed that fish from this population also fed primarily during the day and that terrestrial insects made up a substantial portion of their diet.

While native lacustrine populations are much less numerous today, some have remained into modern times and as such much more is known about these fish than those from fluvial populations. The best understood lacustrine population of these fish occurred in Trapper's Lake, Colorado. However in the 1970's rainbow trout made their way into the lake and these cutthroat became hybridized shortly after (Behnke 2002). These trout migrated up the lake's tributaries to spawn during June and July and typically remained in the streams for about three weeks after spawning, before dropping back down into the lake (Snyder and Tanner 1960). According to Snyder and Tanner (1960) up to 16% of a given spawning run in Trapper's Lake was made up of repeat spawners. Fry would being emerging in July and would almost immediately migrate down to the lake to feed. This migration occurred at night and generally peaked during August (Drummond and McKinney 1965). Once in the lake these fish fed primary on aquatic and terrestrial insects, but historic accounts from other lakes indicate that some populations became piscivorous (Trotter 2008). The Trapper's Lake fish reached a maximum size of about 15" at an age of five years, but fish from Grand Lake were reported to reach sizes up to 20 pounds.

Status

The Colorado River cutthroat has suffered extensive declines across it's native range due to over-harvest, habitat degradation and the introduction of non-native fish. Today the Colorado River cutthroat consists of about 100 pure populations that are mostly isolated in small streams above barriers (Behnke 2002). In light of their drastic decline, in 2000 the Colorado River cutthroat were petitioned to be listed the under the endangered species act, however the US Fish and Wildlife denied this petition in 2007 due to restoration efforts that are currently underway. Fish and Wildlife crews continue to work to establish new populations of these fish, while also securing remaining populations and it appears that the prospects for this trout are finally beginning to improve.

Habitat degradation was a major factor leading to the decline of these fish and continues to be a problem in some drainages. The impacts of anthropogenic alterations can be seen when comparing the status of populations that fall inside wilderness areas with those that don't. Kershner et al. (1997) showed that the lengths and weights of Colorado River cutthroat within wilderness areas were significantly higher than those of fish in nonwilderness areas. They also showed that habitat quality tended to be much higher in wilderness areas, when compared with nonwilderness areas. Mining practices have been one particularly harmful source contributing to the degradation of the Colorado River cutthroat's environment. During the 1800's mining camps popped across the range of these trout and poor mining practices caused wiped many populations out. Although mining is not nearly as pervasive today, the effects of past mining practices are still being felt. According to Oberholtzer (1987) toxic effluents from an abandoned copper mine in the Haggerty Creek drainage of Wyoming have eliminated almost all of the fish that once occurred downstream. Currently mining related issues are known to be impacting at least ten of the populations of these fish and limit restoration efforts in some streams (USFWS 2000). While habitat destruction has contributed to the decline of these fish, the real kicker for the Colorado River cutthroat has been the introduction of non-native trout.

Case after case show that once non-native trout are introduced into a stream containing Colorado River cutthroat, within a few generations are cutthroat had been completely replaced by the invaders. Whether by hybridization or competition this susceptibility for replacement comes from the Colorado River cutthroat's long isolation from other salmonids. In one case a single introduction of brook trout into a high mountain lake in the 1950's eliminated the entire population of Colorado River cutthroat in Battle Creek, Wyoming (Young 1995). Even large lake populations aren't safe from these introductions as Colorado River cutthroat quickly vanished from Grand Lake in Colorado and Fremont Lake in Wyoming after non-native trout were introduced. While the fish of Trapper's Lake persisted in a relatively pure form until the 1970's introductions of Yellowstone cutthroat and rainbow trout have resulted in the hybridization of at least half of the population (Rogers and Wangnild 2004). As if hybridization didn't provide a big enough problem for this population brook trout were introduced in the 1980's and by the 1990's the now hybridized cutthroat population showed great declines. However not all is lost for this population as in 1931 fish from Trapper's Lake were transplanted into Williamson Lake in the Sierras of California, prior to the introduction of any non-native trout. Restoration efforts are now under way and by using a combination of seining for brook trout and restocking the lake with fish from Williamson Lake it is hoped that some day Trapper's Lake will again be noted for its lacustrine population of Colorado River cutthroat.  

Description

The Colorado River cutthroat is one of the most brilliantly colored of the subspecies of cutthroat trout. Their coloration varies from population to population, but they typically have greenish-brassy colored backs, which transition to a orangish-yellow or bronze-gold color along the sides. Some individuals exhibit a pale band of pink or red along their lateral line and an orangish-red color on their gill plates. The bellies on some fish, especially sexually mature males may be a bright orange or red color. Like the coloration the spotting pattern on these fish is highly variable, with populations from the Upper Green River drainage having small to moderate size spots. On the opposite end of the spectrum, Colorado River cutthroat from the Little Snake River in the Yampa drainage may have spots that are nearly as large as those on the greenback cutthroat. The spots on these fish tend to be concentrated above the lateral line and towards the caudal peduncle.

Stream Resident Form - Colorado River Drainage

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Stream Resident Form - Upper Green River Drainage

 

Native Range

Native Trout Fly Fishing

A map of the original native range of the Colorado River Cutthroat trout. Data Source: Behnke (2002) and Trotter (2008).