They traveled in buckets, passed hand to hand from truck bed to lakeshore, before being carefully upended just above the surface by proud biologists. With each splash, another batch of young greenback cutthroat trout slid into the glassy waters of Zimmerman Lake – back into their native range high in Colorado’s South Platte River Basin.
“It’s been a journey,” said Doug Krieger, senior aquatic biologist for Colorado Parks and Wildlife (CPW) and Greenback Cutthroat Trout Recovery Team leader. Since the native trout subspecies—once thought to be extinct—was rediscovered in the 1950s, state and federal agencies have worked tirelessly to bring Colorado’s state fish back to streams and lakes. Its listing as endangered under the Endangered Species Act in 1973 (later changed to threatened) further spurred those efforts.
Zimmerman Lake has been used in the past for cutthroat trout recovery, as CPW Senior Aquatic Biologist Ken Kehmeier noted while pouring out his bucket of fish.
“Three’s a charm,” Kehmeier said, “This is actually the third time I’ve put cutthroats in this lake…I think we got it right this time.” Prior efforts to recover greenback cutthroat trout assumed different subspecies were native to their respective river basins around the state.
Then, in 2007, new genetic research revealed that might not be the case.
“It was a shock wave,” said Leslie Ellwood of the U.S. Fish and Wildlife Service. Finding out “all these fish on the eastern slope that we’ve been carefully protecting all these years as greenbacks aren’t greenbacks or may not be greenbacks…that really upset the bucket.”
University of Colorado Boulder Professor Andrew Martin and Senior Research Associate Jessica Metcalf published that 2007 report. They surveyed cutthroat trout subspecies in different drainages around the state and found that while distinct genetic lineages did exist, they were all mixed together. Research by Chris Kennedy of the U.S. Fish and Wildlife Service into decades of stocking records supported the theory that the mixing was likely a result of humans stocking fish in lakes and streams in the late 1800s, rather than evolution.
Following her 2007 research, Metcalf used ancient DNA dating techniques to analyze preserved trout specimens from museum collections dating back to the mid-1800s. Her research showed all the museum specimens in the South Platte Basin had a unique genetic fingerprint.
“And the exciting thing was that we still had one of these populations left, albeit outside its native range,” said CPW Research Scientist Kevin Rogers.
Rogers canvassed current cutthroat trout populations across the state to support Metcalf’s data. Together, they determined that the only pure strain of greenback cutthroat trout existed in a single stream in the Arkansas River drainage named Bear Creek.
“So our goal is then to replicate that population so we don’t lose any of that diversity that’s out there,” said Rogers. With the release of 1,200 hatchery fish reared from ones taken out of Bear Creek, said Rogers, “today is the first step in that process.” Because preserving greenback genetic purity is so critical, biologists cleared the lake of any other fish prior to stocking to remove the risk of competition or hybridizing.
Rogers and his team held 200 fish back a little longer before releasing them to record baseline data in this first brood. Because the initial genetic pool was a mere 65 fish, many of these greenback cutthroat trout developed genetic defects from inbreeding. Crouched on the edge of lake, the team measured, weighed, fin clipped and photographed the fingerlings as Rogers called out traits like “double chin” to be recorded. During the next few years the team and university researchers will track these traits in the release population to determine which ones succeed in the wild.
On a hot August day, the lakeshore buzzed with excited land managers and biologists as bucket after bucket of the rare fish slipped back into their historic home waters.
Face shaded by his navy CPW hat, Doug Krieger expressed relief that Bear Creek is no longer the only population of greenback in the wild. “One stream, four miles of habitat…it makes you nervous when you have all of your eggs in one basket,” he said, particularly given recent years of drought and fire in the Arkansas Basin. This new brood will go a long way to help ensure security of the species.
But successfully establishing a second batch of wild greenback cutthroat trout is just the beginning, Krieger said. “From here we’re going to start moving more fish into the South Platte Basin. We’ve got some candidate waters already lined up.” Those other lakes and streams will be stocked with fish from this new wild population once they spawn.
All parties involved in the restoration hope that this first major reintroduction will go a long way toward helping reestablish the greenback cutthroat population. The U.S. Fish and Wildlife Service is reviewing the greenback’s endangered species status in light of the new genetic research, said agency spokesman Theo Stein.
Standing by the lake’s edge, Krieger answered an often-asked question: why do we care so much about one subspecies of fish? Beyond the scientific and historical value, Krieger said, we owe it to subsequent generations to preserve our heritage. That value can be hard to quantify, but Krieger likens it fine art. If one species winks out, he said, it’s like losing a masterpiece by Monet or Van Gogh. “You still have others, but there’s a piece there that’s missing,” he said. “That’s a piece we’re trying to maintain.”