Fish Species Survives in 9... 5... 1 Stream?

Greenback Cutthroat Trout; courtesy USGS.

The greenback cutthroat trout (Oncorhynchus clarki somias) was designated as Colorado's state fish in 1994.  In the years since, this endangered native fish has come to symbolize some of the major struggles inherent in the conservation of various fish species throughout the Colorado River basin.  The greenback cutthroat trout, a relatively small fish that grows to be an average of 38 centimeters long, is assumed to have originated in "all mountain and foothill habitats of the South Platte and Arkansas river drainage systems."  Today, there is a complicated debate over where it actually still exists that brings into question both scientific information and human values.

On September 25, 2012, the New York Times ran an article entitled, "Rare Trout Survives in Just One Stream, DNA Reveals."  Based on a study by post-doctoral researcher Jessica Metcalf that was published in Molecular Ecology, the article explained how after "analyzing DNA sampled from cutthroat trout specimens pickled in ethanol for 150 years, comparing it with the genes of today’s cutthroat populations, and cross-referencing more than 40,000 historic stocking records," researchers discovered that there was only one wild population of greenback cutthroat left.  This research is being replicated by a second group to verify the results.

Courtesy Rocky Mountain Field Institute.

This remaining population of greenback cutthroat trout lives in Bear Creek, an alpine stream running from the eastern slope of Pikes Peak near Colorado Springs, CO.  Somewhat ironically, researchers believe that this specific population may have "descended from fish stocked at the Bear Creek headwaters in the 1880’s by a hotelier seeking to promote a tourist route up Pikes Peak."  If this is truly the case, the only existing population of this species was not saved by conservationists at all, but rather by citizens seeking to derive economic benefits.


Aside from the shock of discovering that only a single population of an endangered species exists, the findings were particularly surprising in light of the controversy surrounding recent conservation efforts of the species.  While the fish was thought to have gone extinct in 1937, researchers in the 1950's claimed that "remnant populations were found in tributaries."  After the fish was added to the endangered species list in the 1969, biologists used these populations to breed additional greenback cutthroat trout in hatcheries and propagate them into new waters.

However, in 2007, a three-year study done in part by University of Colorado researchers claimed that "out of nine fish populations believed to be descendants of original greenbacks, five were actually Colorado River cutthroat trout."  This second species of cutthroat trout is extremely similar to the greenback cutthroat, both to the naked eye and to early scientific tests, but actually has a distinct genetic line.  The Colorado River cutthroat trout, native to streams West of the Continental Divide, that were stocked into habitats with the greenback cutthroat trout may have actually out-competed the fish that researchers were attempting to save.

Courtesy New York Times.

In fact, there are fourteen subspecies of cutthroat trout, four of which have been found in Colorado.  However, it appears that humans have been stocking these different trout populations into various streams since the mid-1880's.  Although species have been transplanted outside of their native range, many have thrived and contributed to functional ecosystems.  Now, the population from Bear Creek is being bred and stocked in other locations.  In addition, just a few days before the newest study was released, the Center for Biological Diversity filed a Suit to Protect Rare Greenback Cutthroat Trout from the pollution and other habitat destruction caused by the use of off-road vehicles near Bear Creek.  Issues including "sedimentation and erosion impacts from 3.9 miles of the Pike National Forest system trail #667 which runs adjacent to upper Bear Creek" are already being managed to improve the trout's habitat.  Obviously, this new flood of information has raised the stakes of the suit.

Greenback Cutthroat Native Habitat Map; Courtesy USGS.

Jessica Metcalf, lead researcher on the newest study, acknowledges the irony of the situation:  “It’s ironic that stocking nearly drove the greenback cutthroat trout to extinction, and a particularly early stocking event actually saved it from extinction."  This issue seems to symbolize some major conservation conflicts and questions, especially for the unique Colorado River region:  should species be stocked into habitats where they are likely to thrive, even if those habitats are outside of their native range?  What unintended consequences--or in this case, benefits--may come from this type of management? The answers to these questions require a deeper exploration of the complex values and continuously evolving science surrounding the issues at hand.