Resurrecting the Greenback, Take Two

After a case of mistaken identity, scientists face an upstream swim to save a fabled fish.

It’s early October in northern Colorado, and aspen leaves are falling in droves onto the surface of West Creek, a small stream that flows through Rocky Mountain National Park’s southeast corner. Rain from the night before has cast a perfectly formed rainbow across the sky and is feeding an invigorated flow of water over the stream’s rocks. The backcountry scene is undisturbed aside from three men slowly plodding along the stream, their equipment emitting a rhythmic beeping over the sounds of the gurgling creek. 

Wading in the water is Chris Kennedy, a fish biologist with the U.S. Fish and Wildlife Service. He wears a sturdy gray box on his back, reminiscent of the “proton packs” from the movie Ghostbusters. With each beep, the pack flashes a red light and emits a pulse of electrical current, which Kennedy guides through the water using an electrode on a pole and a live wire. If done properly, the current will force trout in the stream to involuntarily swim closer to the current where they become stunned, giving Kennedy and his two volunteers a chance to scoop them up with nets.

“If you do it wrong, you get a fish fry,” Kennedy jokes. “If you have a hole in your waders it can be a long day.”

As they make their way upstream, the men fill a bucket with a species of trout that Kennedy’s team had painstakingly stocked in the stream in previous years. At the time, the trout were thought to be greenback cutthroat trout (Oncorhynchus clarkii stomias), a critically threatened native subspecies that is also Colorado’s state fish. West Creek was one of more than a dozen sites where non-native fish were poisoned and removed to make way for greenback stocking, part of a 30-year, multi-million-dollar effort to restore the fish to its native range. 

The greenback was well on its way to being removed from the endangered species list when new genetic research changed the game. It turns out, the fish in Kennedy’s bucket aren’t greenbacks but a closely related cousin, a fish that was never actually native in these waters—and is abundant elsewhere. Kennedy will test West Creek’s fish for disease and then clear them all out. They’ll be moved to another location and replaced with the true greenback. 

As the fish sit in the bucket recovering from their run-in with the electric shock, they are clearly oblivious to their precipitous fall from grace, and to the scientific and political upheaval their existence has caused. 

The greenback mix-up was first discovered in the lab of Dr. Andy Martin, an evolutionary biologist at the University of Colorado, Boulder. Known among students for his informal demeanor, Martin is frequently seen around campus wearing his trademark Hawaiian shirts and flip-flops. When we meet in his lab one afternoon, I find myself seated next to a plastic food container that holds the office pet, an axolotl, a purple salamander that looks like a tiny dragon.

“It’s a salamander that never grew up,” Martin says, referencing its gills, which it never loses as an adult. “It’s really cool, but they’re complete idiots. Even feeding them is hard.”

Much like his atypical taste in pets and fashion, Martin often eschews traditional conservation strategies for edgier ideas. His email signature proclaims, “a mind once stretched never returns to its original shape”—a statement now befitting the greenback conservation effort.

Martin and his research team first became involved with greenback cutthroat recovery in 2007 when one of his students, Jessica Metcalf, embarked on a gene-mapping project for her PhD thesis. To an aspiring scientist in Colorado, cutthroat trout seemed like the perfect subject for such a project.

The species had been in the region for 3 to 5 million years, carried from the Pacific coast through interconnected river systems and a series of glacial floods. Eons later, settlers moving west named the trout for the red streak under its jaw, which resembles a bloody gash. Naturalists eventually subdivided the cutthroat into 14 subspecies, including the greenback, which was native to Colorado’s South Platte River watershed. 

But by the time cutthroat subspecies were being sorted and named, some were already disappearing, falling victim to destructive practices such as mining, logging, and damming that impacted so many organisms and ecosystems as the West was being settled. The greenback occupied streams that ran through some of Colorado’s most populous regions east of the Rocky Mountains, and faced even greater human pressure than its backwoods cousins. It was officially declared extinct in 1937. 

Few mourned the fish’s loss. Colorado had already re-stocked most of its rivers with hardier non-native species, like brook and rainbow trout (Salvenlinus fontinalis and Oncorhynchus mykiss, respectively), and the region’s booming population had little regard for which specific brand of creature latched onto the ends of their lines and landed on their dinner plates. It wasn’t until the 1960s that new scientific knowledge and a surge of environmental awareness pushed scientists to show interest in preserving native trout. 

One of those scientists, Dr. Robert Behnke, had heard talk of an unusual-looking trout caught at the University of Colorado’s Mountain Research Station in Nederland, east of the Continental Divide. He took a team up to the secluded mountain cabin and took samples, and in 1968, he announced the rediscovery of the greenback cutthroat trout. Five years later, the fish landed on the very first endangered species list, and became the subject of a dedicated restoration effort that would last more than three decades. 

By the time Metcalf began her gene-mapping project, the greenback had rebounded enough that it was being considered for removal from the endangered species list. The restoration effort was considered a huge success, and Metcalf hoped to bring new insights to the evolutionary history of cutthroats using genetic technology.

“The only real expectation was that the fundamental tenants of biogeography would apply,” Metcalf says. “That you’d have genetically similar fish near each other.”

“What no one expected was that the stocking efforts had reached such remote areas, so extensively that they could have overwritten evolutionary history.”

— Jessica Metcalf, evolutionary biologist 

But when she crunched the data, Metcalf found that the cutthroats’ genes were scattered all over the place. Fish that had been genetically isolated for millions of years now occupied interconnected streams, while some closely related fish were found far apart. The cutthroats hadn’t been moved by slow shifts in geology, Metcalf concluded, they had been moved by people. 

“What no one expected,” Metcalf says, “was that the stocking efforts had reached such remote areas, so extensively that they could have overwritten evolutionary history.”

The study also showed that the fish so carefully restored throughout Colorado’s Front Range weren’t greenbacks at all. They were two genetically distinct lineages of the Colorado River cutthroat trout, another subspecies. To some on the greenback recovery team, the findings were devastating. Not only had they failed to bring back the greenback, they had spread yet another fish across a non-native territory, just as the stockers of the 19th Century had done.

“The greenback cutthroat trout recovery program was a 30- to 40-year effort; it was considered a huge success; it cost a ton of money, and people built careers on it,” says Sierra Love Stowell, one of Martin’s former PhD students who works with cutthroats. “So that was turned on its head.”

Among the disappointed was Robert Behnke, the scientist who “rediscovered” the greenback. He initially resisted the study’s findings and then proposed a surprising new hypothesis: that the fish he identified as the greenback must have come over the mountains on its own before its discovery in the South Platte in the 1800s, distributing its genes on both sides of the Divide. 

To determine the greenback’s true origins, Metcalf and a team went further back in history, comparing the genetics of historical fish samples from museums to living samples in the wild. Their testing immediately revealed one source of the greenback mix-up.  

The greenback type specimen—a preserved sample that’s considered the defining representative of a species—was actually a Rio Grande cutthroat trout (Oncorhynchus clarki virginalis). An army surgeon named William Hammond, who had collected specimens of the creatures during his missions, had preserved the original in the 1850s. Reviewing Hammond’s old letters, the team determined he had likely gotten his specimen from the Rio Grande River, not the South Platte as it was labeled.

Using other historical greenback specimens, Metcalf determined that the greenback had gone extinct in the South Platte in the early 1900s just as most people thought. But she also found a small population of cutthroats from a different watershed that could be the long-lost greenback.

The mystery fish were in Bear Creek, a small stream on the southern slope of Pike’s Peak, near Colorado Springs. For years, fish biologists had been mystified by this unusual trout and had nicknamed the stream “weird Bear Creek.” No one knew what type of trout it was or where it had come from until, on the heels of the Metcalf studies, Kennedy pored through old newspaper articles, books, records, and even old diaries and letters to piece together the fish’s journey. 

After more than five years of research, Kennedy concluded that Bear Creek was historically fishless. The greenbacks had been stocked sometime after 1874 by a man named Joseph C. Jones. Jones had come to Colorado as a prospector during the gold rush and later built an inn for the hordes of tourists that visited Pike’s Peak. There he built a series of fish ponds for guests, where it is believed he stocked the greenback far outside of its native range. 

It was human stocking—the same practice that had killed off or pushed out so many of Colorado’s native trout—that had accidentally preserved the greenback. With only 800 individuals left in the entire subspecies, it would be up to humans again to save it.

At the National Fish Hatchery in Leadville, a pair of true greenback cutthroats swim in twisting corkscrews in separate tanks of liquid anesthetic. At the sound of a timer, an apron-clad hatchery worker plucks the first fish from her soporific pool, gives her a firm squeeze on her abdomen and releases a spray of neon orange eggs into a plastic bin. The male in the tank next door gets the same rough squeeze, spreading his gametes over the eggs before two new fish are scooped into the tanks. 

 At the helm of this bizarre breeding ritual is Chris Kennedy, who stands against one of the concrete trout raceways, squinting at his laptop. Loni, a 10-month-old Australian shepherd, circles him excitedly as he calls out the tag numbers of the next fish needed in the tanks. Trout raised in hatcheries almost never breed on their own, so every summer wildlife conservationists and a few volunteers gather to manually “strip” the fish of their sperm and eggs and spawn the next generation. This procedure is common, but while most hatchery fish are randomly paired, the greenbacks get a personalized matchmaking experience known as gene matrixing. 

“This is the eHarmony for cutthroat trout,” Kennedy says. “We are trying to find the perfect match.”

Laid out on a simple spreadsheet on Kennedy’s computer, the cutthroat’s dating site lacks the graphics and swiping mechanism of Tinder, but it does have a killer algorithm. Based on the genetic information of each fish, the matrixing table indicates which individuals are the least closely related to each other. After more than a century of isolation, the Bear Creek greenbacks are deeply inbred. Many hatch with deformities like missing gill covers or beards on their chins, and the greenbacks have an incredibly low survival rate. Only about 20 percent of greenbacks bred in the hatchery make it to adulthood, compared to about 80 percent in most other cutthroat species. 

Breeding these relatively distantly related pairs should, in theory, yield fish with more genetic diversity and physiological fitness, but after three years of use, the matrixing hasn’t proven particularly successful. Five months after the latest artificial spawning routine, Kennedy returns to Leadville to take inventory of the new hatchlings. He surveys the tanks with a worried look on his face, recording the number of each fish on a small tablet computer. “Not a lot of fish,” he says looking into one of the tanks. After the inventory, matrixed fish are typically consolidated into larger tanks at the back of the hatchery. Kennedy had planned to use three tanks for this batch, but the surviving fish easily fit into one.

According to Kennedy, this particular breeding failure could be due to anything from the hatchery diet to the temperature of the water, but there is also another more frightening possibility: that the remaining greenbacks’ genes are too similar and flawed to produce healthy offspring. Some scientists, like Martin, believe this may be the case.

“It’s just a very derivative organism,” Martin says. “If it hadn’t lived in Bear Creek it wouldn’t have had a shot. It survived because there are no fish there other than it.”

The recovery team is banking on continued isolation as the key to the greenback’s survival. State agencies only stock new greenbacks in areas with impassible waterfalls or barriers that keep other fish out. Other fish never occupied most of these stretches of stream, but where fish are present, the recovery team uses Rotenal, an EPA-approved synthetic plant compound, to poison the stream and clear it out before stocking greenbacks. 

This isolation strategy is common with other native fish, but it’s time consuming and expensive. The U.S. Forest Service’s Longdraw Project is one of the largest greenback recovery projects now underway. It will require 15 to 20 years to implement and cost $1.2 million. The project will create 37 miles of interconnected greenback habitat in Rocky Mountain National Park and the Roosevelt National Forest, and it will all be isolated with manmade barriers.   

Instead of keeping the genetically crippled greenbacks in quarantine, Martin proposes trying to breed a better fish. Crossing the greenback with another cutthroat subspecies, he says, could purge the fish’s problematic genes.  But while Martin thinks hybridization is the greenback’s best shot at survival, others on the recovery team think it would be the fish’s final downfall. The creation of a hybrid fish wouldn’t be preservation, they argue, it would be human engineering in the wild. The native greenback, as it is, would cease to exist. 

“If you blend them all together, you lose the significant pieces of what comprises a species,” says Kevin Rogers, an aquatic biologist with Colorado Parks and Wildlife. “That’s really the key tenant of conservation—preserving the pieces that you have.”

Despite his misgivings about a hybrid fish in the wild, Rogers was interested to find out if additional genetic diversity could help the greenback, and teamed up with Martin and Sierra Love Stowell to conduct a hybridization experiment. The researchers took a pure Bear Creek greenback and crossed it with a closely related cutthroat. As Martin suspected, the introduction of genetic diversity doubled the survival and growth rates of the hybrid greenbacks. 

The super greenbacks were crossed again with both pure greenbacks and other cutthroats to spawn a second generation. These new combinations will help Rogers and his team isolate which specific greenback genes are problematic. But once that research is done, the fish will likely be killed.

If greenback recovery fails, hybridization may be put back on the table, but for now it’s on hold, and Martin and Love Stowell see the experiment’s termination as a missed opportunity. Martin would like to see subsequent generations of hybrids bred only with Bear Creek fish, creating an almost pure greenback with some light genetic patch-ups. The hybrids won’t restore the past, he and other proponents say, but they will allow the fish to face a human-dominated future.

The hybrids represent a version of the wild created not by Mother Nature, but by humans. To hardcore conservationists, this is an unacceptable solution. But to some, that manmade future is already a reality. 

“We are making a value judgement about seeing natives in their native range,” Love Stowell says. “How much do we balance our own desires of what we want to see in the environment against ecological integrity?”

Brian Johnson was born and raised in Eagle County, in the heart of the Colorado Rockies, and started fly fishing with his father in the early 1990s when he was just 10 years old. He grew up in the midst of a fly-fishing wave set off by the 1992 movie A River Runs Through It. The movie’s portrayal of idyllic Montana rivers inspired Johnson to head into the backcountry in search of rare species of fish, an aspect of fishing less appreciated by early pioneers whose primary objective was putting food on the table.

“Part of it is the hunt; part of it is the scenery,” Johnson says. “I’m looking at the bugs; I’m looking at the water; I’m looking at the bushes. I’m out there to be out there.”

A century of plenty has shifted attitudes about nature and by the 1990s many anglers had become less interested in dominating the wild and more interested in being part of it. Nothing embodied this cultural shift better than the restoration of the greenback cutthroat. In 1994, the greenback replaced the non-native rainbow trout as Colorado’s state fish, and it became a wilderness icon. Tiny greenbacks were sewn onto fishing vests and drawn into outdoor outfitter’s logos, and the fish still grace a number of craft beer labels today. 

Now 39, Johnson has come to terms with the fact that the greenback he painstakingly pursued as a young man was the wrong fish. He’s joined efforts to try to restore the real one as a member of “The Greenbacks,” a group of young professionals within the fish conservation organization Trout Unlimited. The group raises money and works on stocking and habitat restoration for the greenback. Among these anglers, the fish has become a legend, a symbol of the restoration of western wilderness so longed for. But through this work, Johnson says he’s started to see just how managed the “untamed” wilderness really is.

The greenback can’t simply be put back into its native range. Much of the fish’s historic area is contaminated with wastewater, agricultural pollutants, and diseases introduced by non-native fish.  Other patches of river run dry every year, their water flows diverted to irrigate crops and water lawns along Colorado’s Front Range. Every drop of river water in the state is accounted for and appropriated. Before the greenback can be stocked, it has to be granted a legal right to the water it needs to survive.

These degraded ecosystems impact more than just the greenback. Many native fish species in Colorado are no longer able to procreate on their own. Most wild fish populations are kept afloat through Colorado Parks and Wildlife’s robust stocking program. The agency stocks around 91 million fish each year, 2 million of which are trout of catchable size. Some fish wind up in manmade reservoirs and easily accessible lakes and rivers, but the agency doesn’t shy away from remote wilderness. At incredible risk, pilots in specially equipped planes fly up into the Rocky Mountains every year to drop fish into 250 high-altitude lakes. Johnson has visited some of these spots on his backcountry trips. Before his work with Trout Unlimited, he had no idea that so many of the fish he caught in remote areas had been hatchery raised.

“It’s pretty amazing what they have to do to keep fish out there,” He says. “Knowing that they stock everything, even in the backcountry, yeah it did change [my experience], but it is what it is.”

Back at the Leadville hatchery, a small museum sits just steps away from the tanks where the greenback cutthroats swim. The walls have a few plaques dedicated to the life cycle of trout, but the vast majority of the displays detail the history of the Bureau of Fisheries—the precursor to the U.S. Fish and Wildlife Service. From 1903 to 1940, Bureau officials from Leadville stocked fish throughout the entire Mountain West, replenishing the region’s lakes and rivers with non-native fish. 

The old photos show men in suits and ties wading in rivers while holding buckets of fish or loading milk jugs full of fingerlings onto trains. “Bureau of Fisheries employees were considered an elite group,” one plaque says. The job was considered an honor, and the fish-stocking program was regarded as a great triumph. Today, the Bureau of Fisheries is described in fewer glowing terms. 

“The hatcheries then were the Johnny Appleseeds of the fish world,” Ed Stege, the hatchery manager, tells me during a tour of the museum. “They stocked fish everywhere without much thought.”

For Stege, his forebears’ drive to change, to meddle, and to conquer can also be seen in the hatchery building. Built in 1889, the hatchery was once considered the “most magnificent building in western Colorado,” with a wraparound Victorian porch, vaulted wood ceilings, and fish tanks made of redwood imported from California. Then, starting in the 1970s, hatchery managers developed a distaste for the building’s dated, Victorian style. They tore down the porch and swapped its hand-carved window frames for chunky glass blocks. The wood ceiling was covered to make an attic, and a large bat colony now lives upstairs.

“They did everything to make it as ugly as possible,” says Stege. “For a long time people didn’t care about the historical look; they wanted something modern.”

During his tenure as manager, Stege has done whatever he can to restore the building. He’s helped recreate the old porch, and this year, he plans to replace the glass blocks with replica windows and French doors. But Stege says that some parts of the building are so altered they can’t be restored. The building will always bear the marks of the hatchery’s past administrations, just as the state’s rivers will.

Much of the Fish and Wildlife Service’s work now, at least as far as Colorado trout are concerned, is geared toward undoing the actions of the Bureau of Fisheries, removing non-native fish and replacing them with the originals. There has been some success in this. In at least one stocking site, Colorado Parks and Wildlife has seen greenbacks survive a winter, and by all accounts—even Martin’s—the greenback will likely swim the streams of Colorado’s Front Range once again. But no matter how much time or money is spent on the project, the greenback and its landscape will always reflect an altered past.

For Stege and most of the recovery team, the fact that some things can’t be undone is what makes hybridization unthinkable. “Man has altered the environment enough,” says Stege. “The whole mindset is different now.”

But mindsets are continually changing. So are environments, and the world isn’t getting any less hostile for native fish. The greenback, and all species, face a growing set of problems from continued habitat loss and degradation due to climate change. Future generations of humans may decide that meddling with wildlife genes is the most ethical solution.

Whether the future form of Colorado’s state fish is a genetically hobbled version of its past self or a manipulated super greenback, it will need to weather changes both to its environment and to the whims of the people who safeguard it. To truly survive, the greenback will have to adapt on its own. 

“You can’t stop evolution,” Martin says. “It’s just happening all the time.”

Lindsay Fendt

Lindsay Fendt is a freelance reporter and photographer who works frequently in Latin America. She primarily covers the environment and human rights, and is a 2017-18 Scripps Fellow for Environmental Journalism at the University of Colorado Boulder.

bioGraphic is powered by the California Academy of Sciences, a renowned scientific and educational institution dedicated to regenerating the natural world through science, learning, and collaboration.