FRISCO — Colorado’s native greenback cutthroat trout may be on their way to repopulating their historic habitat in the South Platte River Basin, thanks in part to a scientific sleuthing effort that helped trace the genetic roots of the colorful fish a couple of years ago.
About 1,200 greenback cutthroat fingerlings reared in federal and state hatcheries in Colorado were stocked into Zimmerman Lake, near Cameron Pass last week. An interagency recovery team hopes the stocking is a first milestone toward re-establishing populations of the state fish, which nearly vanished from Colorado’s rivers because of pollution, overfishing and stocking of native and non-native species of trout.
In 2012, scientists concluded that the only remaining genetically pure greenbacks were isolated in a small, single population — about 750 fish, all living in a four-mile reach of Bear Creek, a small Arkansas River tributary in the mountains west of Colorado Springs.
University of Colorado, Boulder researcher led the study that pinpointed the genetic history of the fish, clarifying the native diversity and distribution of several Colorado cutthroat trout strains. Tracking that history wasn’t easy. Historical records show that, between 1889 and 1925, more than 50 million cutthroat trout from the Gunnison and Yampa river basins were stocked in tributaries of all major drainages in the state, jumbling the picture of native cutthroat strains in Colorado through time and space.
“This is a conservation genetics success story,” said Metcalf. “We were able to use historical specimens to find out something quite novel about cutthroat trout biodiversity that has resulted in a management action. We are not just bringing a native species back to its historic range, but the greenback cutthroat trout, our Colorado state fish. I would have never imagined this outcome when we started our research in 2001.”
According to Doug Krieger, senior aquatic biologist for CPW and the Greenback Cutthroat Recovery Team leader, about 3,500 greenback cutthroat trout — offspring of fish taken from Bear Creek — have been raised at the Mt. Shavano State Rearing Unit and the Leadville National Fish Hatchery.
“We finally have the opportunity to bring these fish home,” Krieger said.
According to CU-Boulder Professor Andrew Martin, who spearheaded the 2012 study with Metcalf, researchers are trying to understand more about the characteristics of the greenback, including a collaborative effort to assess how the fish succeed in their new environment.
“Living in Zimmerman Lake in the Arapaho and Roosevelt National Forest at an elevation over 10,000 feet will be very different from living in Bear Creek at 6,100 feet or living the ‘cushy’ life in a hatchery,” Martin said, explaining that researchers will closely watch the newly stocked greenbacks in Zimmerman Lake.
“This is an extremely challenging situation,” said Martin of CU-Boulder’s ecology and evolutionary biology department. “But this recovery effort has been a joint project of many different people with different interests and backgrounds combining their energy toward one specific goal. We have a chance to bring a native species back from the brink, and I’m happy to be a part of it.”
Colorado’s greenbacks, along with 14 other recognized subspecies, all originated in the Pacific Ocean, evolving along different genetic lineages in river drainages across the West.
In Colorado, four lineages of cutthroats were previously identified: the greenback cutthroat, the Colorado River cutthroat, the Rio Grande cutthroat and the extinct yellowfin cutthroat. Work by the CU team also identified a previously undiscovered San Juan Basin cutthroat trout that is now extinct.
The study technique could pave the way for the gene sequencing of other wild creatures like reptiles and amphibians that were preserved in ethanol by early scientists, perhaps even helping researchers determine biodiversity levels in the late 1800s, said Metcalf,