Research finds home of true greenback cutthroat trout
Using DNA extracted from samples as old as 150 years, two University of Colorado-Boulder scientists have located the last surviving wild population of the federally protected greenback cutthroat trout.
Researchers Jessica Metcalf and Andrew Martin analyzed DNA extracted from wild trout and from museum specimens collected from sites around Colorado and New Mexico as far back as 1857. Their research indicates the only population of pure greenback cutthroat trout survives today in a four-mile section of Bear Creek, a small stream near Colorado Springs.
The adult population is estimated at approximately 750 fish.
Further research suggested the greenbacks, the native cutthroat of the South Platte, likely were stocked in Bear Creek in the early 1880s.
“We’ve known for some time that the trout in Bear Creek were unique,” said Doug Krieger, senior aquatic biologist for Colorado Parks and Wildlife and the Greenback Cutthroat Trout Recovery Team leader. “But we didn’t realize they were the only surviving greenback population.”
The greenback was presumed extinct by 1937, but in 1969 a few remnant populations were found.
The fish was placed on the endangered-species list in 1973.
The recent findings will trigger a re-evaluation of the greenback recovery program by the U.S. Fish and Wildlife Service and the Greenback Trout Recovery Team, which have been overseeing the recovery of the fish.
Cutthroat trout originated in the Pacific Ocean and moved to the Intermountain West when climatic and geologic conditions changed.
After thousands of years, the trout evolved across the western U.S. into 14 recognized subspecies, including the now-extinct yellowfin cutthroat, an Arkansas River basin strain that once grew to prodigious size in Twin Lakes near Leadville.
In 2007, Metcalf and Martin discovered several Front Range cutthroat populations thought to be greenbacks were actually Western Slope Colorado River cutthroat trout stocked on the Front Range.
One of the surprising findings of the new research was the magnitude of those early fish-stocking efforts.
Fish and Wildlife Service fisheries biologist Chris Kennedy documented more than 50 million Colorado River cutthroat trout from the Gunnison River and White River basins were stocked across the state between 1889 and 1925.
Scientists previously identified four closely related lineages of native Colorado trout: the greenback cutthroat east of the Continental Divide; the Colorado River cutthroat from the Western Slope; the Rio Grande cutthroat in streams surrounding the San Luis Valley; and the extinct yellowfin.
Colorado Parks and Wildlife aquatic researcher Kevin Rogers said the study significantly improves scientists’ understanding of cutthroat biology and serves as a good reminder of how science works.
“The integrity of the scientific process depends on researchers who are willing to use new tools to explore difficult issues and challenge existing paradigms,” Rogers said. “Advances in technology have allowed us to analyze the DNA of fish collected during the early years of Colorado’s settlement. This study has opened an astonishing window into the past.”
A Fish and Wildlife Service spokesperson said no changes in the greenback’s endangered-species status will occur until the review has been completed.