The Greenback Cutthroat Trout: A Story of Survival and Scientific Discovery
The greenback cutthroat trout (*Oncorhynchus clarkii stomias*) holds a prestigious place in the American West, serving as the official state fish of Colorado since 1994. As the easternmost subspecies of cutthroat trout, this resilient fish has a history marked by dramatic declines, near extinction, and complex scientific mysteries that have taken decades to unravel.
Once a common sight in the river systems of Eastern Colorado and Southeast Wyoming, the greenback cutthroat now occupies less than 1% of its historical range. Today, it is a symbol of both the fragility of native ecosystems and the intensive conservation efforts required to protect them.
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Key Facts
- Status: Listed as threatened under the Endangered Species Act and critically imperiled by NatureServe.
- Range: Historically widespread in the Arkansas and South Platte River drainages; currently highly restricted.
- Distinguishing Features: Features the largest spots of all cutthroat subspecies and brilliant spawning colors.
- State Symbol: Adopted as the Colorado state fish on March 15, 1994.
- Pure Population: As of 2012, the only remaining genetically pure population was identified in a 4-mile stretch of Bear Creek.
Physical Characteristics and Description
The greenback cutthroat is a striking fish known for its unique aesthetic. While it shares the signature red coloration on the lower jaw and throat common to all cutthroat trout, it stands out due to its spawning coloration, which is reported to be exceptionally brilliant. Additionally, it possesses the largest spots among all cutthroat subspecies.
In terms of size, these trout typically reach a maximum length of 18 inches (46 cm), though historical records indicate they have been known to grow as large as 4.5 kilograms (9.9 lb).
Natural History and Evolution
Scientists believe the cutthroat trout lineage evolved over the last two million years from other Oncorhynchus species. These ancestors migrated through the Columbia and Snake River basins before moving into the Green and Yellowstone River basins. Approximately 20,000 years ago, during the last ice age, a population crossed the Continental Divide, eventually giving rise to the greenback subspecies.
The Decline of a Native Species
The decline of the greenback cutthroat began in the late 19th century alongside the arrival of settlers. Several human-driven factors contributed to their disappearance from much of their range:
- Mining Activities: Led to toxic runoff and increased sediment in native river basins.
- Water Diversion: Large-scale water use for agriculture altered natural habitats.
- Overfishing: Direct removal of fish from the wild.
- Non-native Species: The introduction of brook trout (*Salvelinus fontinalis*) and brown trout (*Salmo trutta*) created competition for resources. Furthermore, the introduction of rainbow trout (*O. mykiss*) led to hybridization, creating "cutbows" and diluting the genetic integrity of native populations.
A Complex Conservation History
The history of the greenback cutthroat is intertwined with scientific confusion. In 1857, Army surgeon William A. Hammond collected specimens and sent them to the Academy of Natural Sciences. However, his labels—noting the samples came from "the South Platte River at Fort Riley, Kansas"—caused significant confusion. Because the South Platte does not flow through Kansas, early researchers struggled to identify the origin of the fish.
It was not until later that ichthyologists like David Starr Jordan resolved these discrepancies, suggesting the samples were likely collected near Fort Bridger in Wyoming. Modern DNA testing eventually revealed that Hammond's original samples were actually Rio Grande cutthroat trout, likely collected in New Mexico, rather than greenbacks.
Recovery Efforts and Genetic Breakthroughs
After being considered extinct in the 1930s, a population was rediscovered in 1957 within the Big Thompson River, a tributary of the South Platte. This discovery led to the subspecies being listed as threatened under the 1973 Endangered Species Act.
Recovery efforts, supported by the U.S. Fish and Wildlife Service, Trout Unlimited, and the Bozeman National Fish Hatchery, faced a major setback when researchers realized that many fish being reintroduced were actually a different subspecies: the Colorado River cutthroat trout. A landmark 2012 genetic study clarified this, identifying that the only truly pure greenback population resided in Bear Creek, a tributary of the Arkansas River.
There is, however, reason for optimism. In 2022, Colorado Parks and Wildlife announced that greenback cutthroat trout have been found naturally reproducing in Herman Gulch following reintroduction efforts.
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Summary of Species Classification
| Rank | Taxonomy |
|---|---|
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Actinopterygii |
| Order | Salmoniformes |
| Family | Salmonidae |
| Genus | Oncorhynchus |
| Species | O. virginalis |
| Subspecies | O. v. stomias |
Frequently Asked Questions
What makes the greenback cutthroat trout unique?
They are distinguished by having the largest spots of all cutthroat subspecies and possessing particularly brilliant coloration during the spawning season.
Why did the greenback cutthroat population decline?
The decline was caused by a combination of mining runoff, water diversion for agriculture, overfishing, and competition or hybridization with introduced non-native species like rainbow and brook trout.
Is the greenback cutthroat trout endangered?
It is currently listed as threatened under the Endangered Species Act and is considered critically imperiled by NatureServe.
Can I fish for greenback cutthroat trout?
Yes, catch and release fishing for the greenback cutthroat is currently permitted in certain parts of the South Platte and Arkansas River basins.
What is a "cutbow"?
A cutbow is a hybrid fish created when native cutthroat trout breed with introduced rainbow trout.