Overview
Colorado’s state fish nearly disappeared without anyone noticing. The greenback cutthroat trout is native to the South Platte and Arkansas river drainages on the eastern slope of the Colorado Rockies — streams that flow through some of the most populated and recreated land in the state, where hatchery trout stocking began in the late 1800s and has continued at scale ever since. By the time anyone looked carefully, most of what people thought were greenback cutthroat were something else.
The 2012 taxonomic revision that reshuffled the identity of Colorado’s native cutthroats is one of the more humbling chapters in the state’s conservation history. For decades, fish managers believed multiple populations of greenback cutthroat existed across the South Platte and Arkansas drainages. Genetic analysis revealed that most of those “greenback” populations were actually Rio Grande cutthroat, Colorado River cutthroat, or hybrids. The fish in Bear Creek and Como Creek in Rocky Mountain National Park were confirmed as genetically pure greenback cutthroat. Those two populations, plus a few stream segments in the South Platte drainage, constitute the entire pure genetic legacy of Colorado’s state fish.
Recovery from that near-extinction has been real. Approximately 75 stream segments now contain pure or nearly pure greenback cutthroat, stocked from hatchery fish derived from the Bear Creek and Como Creek lineage. The population trend is increasing. The story is not finished.
Natural History
The greenback cutthroat trout (Oncorhynchus clarkii stomias) is recognized by its large, irregularly shaped black spots concentrated toward the tail, a greenish hue along the back, and the vivid red or orange slash marks beneath the jaw that give all cutthroat trout their name. Adults in mountain streams are typically 20–35 centimeters; fish in lakes can grow larger.
The subspecies is adapted to cold, well-oxygenated mountain streams and lakes at elevations from approximately 1,800 to 3,500 meters — the streams that drain the high Front Range peaks into the South Platte and Arkansas systems. These are not big rivers; they are small headwater systems, often in narrow drainages above most human settlement, where the fish evolved in relative isolation over thousands of years following the last glaciation.
Greenback cutthroat are opportunistic feeders, taking terrestrial and aquatic invertebrates, small fish, and in lakes, zooplankton. Spawning occurs in spring as water temperatures rise. They are relatively short-lived — most individuals in wild populations are three to five years old — and populations can recover quickly from disturbance if suitable habitat and pure genetic stock are available.
Habitat in Colorado
Rocky Mountain National Park is the conservation anchor for this subspecies. Bear Creek and Como Creek, where the genetically confirmed pure populations were found, are protected within the park. CPW and RMNP have worked cooperatively to expand the number of stream segments holding pure greenback populations, primarily through nonnative trout removal, fish barrier installation to prevent upstream recolonization by nonnative species, and stocking of fish from the confirmed pure Bear Creek and Como Creek lineages.
The South Platte drainage holds additional recovery streams — headwater segments where nonnative trout have been removed and greenback populations established. The Jefferson County foothills streams and South Park headwaters are recovery focus areas.
Critical habitat has been designated in stream segments across the recovery range, providing consultation requirements for federal agency actions that might affect occupied reaches.
Threats
Hybridization with introduced rainbow, brown, and other nonnative trout is the primary threat that drove the greenback to near-extinction in the first place. Once hybridization begins in a stream segment, it proceeds to genetic absorption quickly — within a few generations, the genetic integrity of the native population is lost. The only reliable defense is physical separation using fish barriers, either natural falls or artificial barriers below pure populations.
Nonnative trout competition and predation reduces greenback recruitment even without hybridization. Rainbow, brook, and brown trout, all introduced to Colorado waters, are well-established competitors that can displace native cutthroat from occupied reaches.
Whirling disease, caused by the parasite Myxobolus cerebralis, is present in many Colorado streams and selectively affects salmonids, potentially including greenback cutthroat in occupied and recovery stream segments.
Climate change threatens to reduce the extent of cold-water habitat at the upper end of the greenbacks’ elevational range and increase the frequency of drought events that reduce flow and raise water temperatures in occupied streams.
Recovery & Conservation
The greenback cutthroat trout was listed as endangered in 1973; downlisted to threatened in 1978 as recovery progressed. Recovery has relied on an integrated approach: confirming genetically pure source populations, raising pure fish at the Leadville National Fish Hatchery, removing nonnative trout from target stream segments, installing barriers, and stocking pure greenbacks.
The 2012 taxonomic revision, while deflating, redirected recovery resources toward the correct target. Recovery streams that had been stocked with fish believed to be greenbacks but now known to be other subspecies were identified and corrected. The program is now working from an accurate genetic baseline.
Progress is real. The number of stream segments with established greenback populations has grown substantially since the 2012 revision, and the overall population trend is positive.
What You Can Do
- Report trout observations from headwater streams in Rocky Mountain National Park and the South Platte drainage to eBird, iNaturalist, and CPW. Unusual trout, or trout in streams not typically stocked, are worth reporting.
- Follow all fishing regulations for greenback cutthroat stream segments, including catch-and-release requirements and barbless hook requirements where applicable. Check CPW fishing regulations for the specific stream you are fishing.
- Avoid transferring equipment between watersheds without thoroughly drying and cleaning fishing gear to prevent the spread of whirling disease and aquatic invasive species.
- Stay out of streams in Rocky Mountain National Park’s greenback recovery areas during the spring spawning season when posted.
Sources
Species status, population data, and natural history drawn from:
- USFWS Species Profile: Greenback Cutthroat Trout (primary source for listing status)
- Recovery Plan for the Greenback Cutthroat Trout, USFWS
- NatureServe Explorer: Oncorhynchus clarkii stomias (G4T1)
- Colorado Parks and Wildlife: Greenback Cutthroat Trout Recovery Program
- Metcalf et al. (2012): Taxonomic revision of native cutthroat trout in Colorado
Last reviewed: January 2024