July 6, 2023

The Misidentification of Cutthroat Trout in North America

The Misidentification of Cutthroat Trout in North America

Being a fly fisherman born and raised in Boulder, Colorado, I have always enjoyed the privilege of several wild trout species in my local water. Typically, I know which species I will find in which system, and I set out to specific creeks or rivers, expecting to see particular species at the end of my line. In Boulder Creek, I know that the further upstream I go, the more variety I will encounter: in town, predominantly brown trout. In the canyon before Boulder Falls, I'll find some rainbows in the mix. Past the falls and closer to the dam, the altitude-loving brook trout start to make rare but welcome appearances. The point is that knowing what I will find is part of the pursuit. I can be more accurate in my technique if I know what species are likely to be in the pocket in front of me, and I can understand more about my local ecosystems and what protections they're given based on the trout I find.

I targeted a different species: the Colorado greenback cutthroat trout a few years back. The greenback is the state fish of Colorado, and they're native to the high alpine streams and lakes of the Rockies. They are also threatened under the Endangered Species Act and were once considered entirely extinct until a few tiny populations were discovered within the South Platte and Arkansas River basins. I had heard that the streams and lakes in Rocky Mountain National Park were just lousy with these greenbacks, and I couldn't get out the door fast enough.

It sounded ideal. These highly endangered trout were living happily in one of the most well-protected designations of land, and the National Park Service was dedicating funds and resources to ensure the rejuvenation of the population. I chose my path and set out. Sure enough, after about six miles of some stunning trail, I had a cutthroat trout in my net. He was gorgeous, all colored up for the spawning season, with a bright red throat, belly, and a speckled green back. Pay dirt. I was so excited to have checked a bucket list species off my list. I told my friends, my family, and the pros at the local fly shop, proud is an understatement.

Actual Photo of the Above Mentioned Fish

A year or so passed, and I started hearing little whispers of information in the fly fishing scene in Boulder. The cutthroats in Rocky Mountain National Park are not greenback cutthroats, more likely Colorado River cutthroats. Now I was confused, bummed, and embarrassed that I had touted my successful hunt for one of North America's most coveted trout species. I headed back to the drawing board. If the greenbacks aren't in the Park, where are they? Are they extinct after all? This news also meant that they weren't under the expert stewardship of the National Park Service and that wherever the greenbacks were, they were likely not benefiting from a conservation plan. As I researched the issue further, I found that the misidentification of cutthroat trout in the American West is an issue that spreads far beyond the alpine streams and lakes of my corner of Colorado and that many endangered species have been incorrectly identified and are benefiting from protections that are needed elsewhere for other trout populations.

Photo from Trout's Fly Fishing in Denver, Colorado

The conservation of endangered species is a crucial task for scientists and conservationists worldwide. Identification is essential in tracking and protecting these species, which has proven complex and challenging. One significant issue is the misidentification of populations due to genetic similarities and incomplete understanding of their distribution. In a recent study by Metcalf et al. (2021), researchers used genetic forensics to analyze samples from historical and current populations of endangered cutthroat trout. This study revealed the misidentification of specific populations and emphasized the importance of genetic analysis in conservation efforts.

Cutthroat trout are native to western North America and inhabit cold, clear waters such as mountain streams and lakes. They are a culturally and ecologically important species, and their conservation is essential for maintaining the health and biodiversity of aquatic ecosystems. Identifying cutthroat trout populations can be challenging. They exhibit a high degree of genetic similarity across their range. This similarity can make it difficult to distinguish between native and non-native populations, leading to the misidentification of populations and the failure to prioritize conservation efforts.

Researchers used genetic analysis to examine samples from historical and current cutthroat trout populations across their range in the study. They used a variety of genetic markers to assess the genetic similarity of populations and to determine the origin of certain populations. The analysis revealed that some populations thought to be native were actually introduced, and vice versa. Specifically, the researchers found that populations in the Jarbidge River in Nevada, previously considered a unique native population, were introduced from another drainage. Conversely, once thought to be introduced, populations in the Humboldt River in Nevada were actually native to the area (Metcalf et al., 2021). The misidentification of these populations has significant implications for conservation efforts. It may fail to protect the most vulnerable and endangered populations.

The study noted above underscores the importance of genetic analysis in conservation efforts. Accurately identifying populations is crucial for effective conservation, as it directs resources toward the most vulnerable and endangered populations. Genetic analysis can also provide insights into species' historical distribution and movements, which can help inform conservation strategies. The study highlights the need for continued genetic monitoring and analysis of endangered species to ensure accurate identification and protection.

In addition to the implications for conservation efforts, this study has broader implications for using genetic forensics in ecological research. Using genetic markers to determine the origin and movements of populations can provide valuable insights into the ecology and evolution of species. This approach has been used to study a wide range of species, from plants to mammals, and has helped uncover previously unknown distribution and movement patterns. The study by Metcalf et al. (2021) demonstrates the power and versatility of genetic analysis in ecological research and highlights the need for continued research in this area.

Overall, this study provides a valuable contribution to the ongoing efforts to protect endangered species and emphasizes the critical role of genetic forensics in conservation efforts. The misidentification of populations can have significant implications for conservation efforts, and genetic analysis can help ensure that resources are directed toward the most vulnerable and endangered populations. The study by Metcalf et al. (2021) also underscores the broader implications of genetic analysis for ecological research and highlights the need for continued research in this area.

Photo from Colorado Trout Unlimited


It turned out that the only alleged population of the Colorado greenback cutthroat trout is in a small creek west of Denver in the foothills of the Rockies, well outside the jurisdiction of the National Park Service. They live in this system with several other species of trout, some of which are predatory and can decimate the greenback population. The greenbacks enjoy little to no protections here other than the threat of a fine if an angler is caught having killed one. For the sake of the fish, I will omit the name of the creek, but if you find yourself looking at a beautiful little fish with a green back, dark spots, and a red slash on its throat, count yourself lucky, keep it wet, and send it home.


Metcalf, J. L., Pritchard, V. L., Silvestri, S. M., Jenkins, J. B., Wood, J. S., Cowley, D. E., Evans, R. P., Shiozawa, D. K., and Martin, A. P. (2012). Across the great divide: Genetic forensics reveals misidentification of endangered cutthroat trout populations. Molecular Ecology, 21(17), 4179-4191. **https://doi.org/10.1111/j.1365-294X**