Bringing native greenback cutthroats back from the brink of extinction

Seated high in the Rocky Mountains west of Fort Collins, Zimmerman Lake was abuzz last week, and not just from the swarms of pesky mosquitos that had a heyday dive-bombing visitors.

Instead, scientists and students from the University of Colorado Boulder and fisheries biologists and managers from state and federal natural resource agencies were focused on the inhabitants of a water tank in the back of a Colorado Parks and Wildlife fish-stocking truck. Inside were hundreds of colorful trout known as greenback cutthroats, about to be released into their native river drainage after vanishing for decades.

The event was a conservation management milestone, a result of a novel 2012 genetic sleuthing study led by CU-Boulder Senior Research Associate Jessica Metcalf of the BioFrontiers Institute that helped to clarify the native diversity and distribution of several Colorado cutthroat trout strains. The study was largely based on DNA samples taken from specimens collected in Colorado as far back as 150 years ago that were compared with DNA of modern-day cutthroat trout.

The biggest surprise in 2012 was that the cutthroat trout strain native to the South Platte River drainage survived only in a single population—a small stream known as Bear Creek that actually is in the nearby Arkansas River drainage. The trout living in Bear Creek most likely were collected from the South Platte River drainage in the 1880s and stocked into Bear Creek.

“This is a real win for conservation genetics,” says 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.”

The members of the Greenback Cutthroat Trout Recovery Team, involving CU-Boulder and state and federal agencies, hope the milestone is the first step in reintroducing the federally protected fish into selected waters in the South Platte basin, which the CU-Boulder research team inferred to be its historical haunt.

According to Doug Krieger, senior aquatic biologist for Colorado Parks and Wildlife 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,” he says.

CU-Boulder Professor Andrew Martin, who spearheaded the 2012 study with Metcalf, says researchers are trying to understand more about the characteristics of the greenback, including how well the fish succeed in their new environment. “Living in Zimmerman Lake 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,” he explains.

Data from a random sample of fingerlings being released at Zimmerman Lake included DNA collection as well as physical measures of trout appearance. In the next several years Martin and his colleagues, including CU-Boulder students, will revisit the lake to follow the fate of 200 individual, marked cutthroats as a way to assess the success of the initial stocking effort and whether natural selection is playing a role in determining the success and failure of different individuals.

“This is an extremely challenging situation,” says 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.”

CU-Boulder senior Peter Omasta, who is majoring in ecology and evolutionary biology and is funded to do summer research by the National Science Foundation’s Research Experiences for Undergraduates program, says the stocking event may have been a once-in-a-lifetime opportunity. “So often we hear about what’s wrong with the environment, and how biodiversity is disappearing,” he explains. “But I had the opportunity to be part of an historical conservation experience—introducing a native species back into its own environment.”

The museum specimens used in the study came from the California Academy of Sciences, the Smithsonian Museum of Natural History in Washington, D.C., the Academy of Natural Sciences in Philadelphia and the Harvard University Museum of Comparative Zoology. Metcalf and her colleagues first collected multiple samples of tissue and bone from each of the ethanol-pickled trout specimens, obtaining fragments of DNA that were amplified and then pieced together like a high-tech jigsaw puzzle to reveal two telltale genes of the individual specimens.

The decline of native cutthroat trout in Colorado occurred because of a combination of pollution, overfishing and stocking of native and non-native species of trout, says Metcalf. “It’s ironic that stocking nearly drove the greenback cutthroat trout to extinction, but a particularly early stocking event actually saved it from extinction.”