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Inside the boots-in-the-water effort to preserve and restore Colorado’s iconic greenback cutthroat trout

In the only waterway where the state fish is known to reproduce naturally, aquatic biologists set up a mobile lab to strengthen the species’ genetics

Colorado Parks and Wildlife is working to expand the population of the threatened Greenback Cutthroat Trout in Colorado. CPW biologists, left to right, Cassidy English, Brianna Fett and Travis Sauder used a backpack electrofisher in Bear Creek June 7, 2022 to attract the fish and then mildly stun them to collect eggs and sperm. (Mark Reis, Special to The Colorado Sun)
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On a sunny morning just west of Colorado Springs, Cory Noble slowly makes his way upstream in Bear Creek, sloshing through the shallow flow beneath towering pines and bending back tangles of low brush heavy with the drenching residue of the previous night’s rain.

He’s looking for greenback cutthroat trout — a species more than once written off as extinct, but 10 years ago discovered populating this 3½-mile stretch of the creek. Although greenback cutthroats, Colorado’s native state fish, have been preserved and restored to certain waters through hatcheries, they are so far known to naturally reproduce only here, behind a locked gate restricting access to the dirt road that slices through the canyon.

And it’s the hope of providing a genetic boost for the state’s broodstock that has brought a team of Colorado Parks and Wildlife staff to these picturesque foothills to find the fish and extract their eggs and semen — all part of an on-site spawning project designed to strengthen the species that two years ago showed a concerning population dip. So this now twice-annual exercise (though CPW took a pass last year to reduce stress on the fish) has become a high priority for the state agency as the Bear Creek population looms critical for the greenback’s survival.

The U.S. Fish and Wildlife Service considers the greenback a threatened species. The status is scheduled for review, but it could take a year or more before the agency determines any possible change in status.

Colorado Parks and Wildlife is working to expand the population of the threatened Greenback Cutthroat Trout in Colorado. CPW fisheries technician Brianna Fett used a backpack electrofisher in Bear Creek June 7, 2022 to attract the fish and then mildly stun them to collect eggs and sperm (milt) from the fish. (Mark Reis, Special to The Colorado Sun)

Noble, a CPW aquatic biologist who hiked this steep canyon drainage since he was a kid growing up in Colorado Springs, feels a personal connection to the work. In chest-high waders, he navigates shin-high water on the gradual upstream ascent, laden with a 30-pound, fully charged backpack electrofisher.

In one hand, he grips a metal rod to probe the creek’s pools and hiding spots with an electrical charge that briefly incapacitates the fish. In the other, he wields a net. Following behind him, two more CPW biologists also carry nets to back him up, plus two buckets — one for captured males and the other for females. Farther downstream, an identical team, with aquatic biologist Brianna Fett handling the probe, works another section of the creek.

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A CPW pickup truck runs a constant relay along High Drive, retrieving plastic buckets with live fish from the teams, driving them to holding pens immersed in the creek at the operation’s base and then heading back toward the teams as they continue their slow progress upstream.

Already, the CPW workers have established a makeshift lab at a nearby trailhead. For two hours, the retrieval teams will work Bear Creek before reconvening beneath the lab’s shaded canopy. There, Noble will extract the reproductive material, fertilize a few dozen eggs (known as roe) in a small dish for transport to the state’s Mount Shavano Hatchery in Salida to become part of its broodstock, a relatively small population kept in optimal conditions for breeding. 

Then he’ll capture additional semen (called milt) in vials for use at the federal Leadville National Fish Hatchery, where it will fertilize more greenback eggs, which are then returned to the Salida hatchery. Eventually, young fish will be dispersed in state waterways, where their populations can be established with the goal of discovering that the species is once again reproducing in the wild.

“So coming here and bringing fish genetic material from this population helps us make it a more genetically diverse broodstock in the hatchery,” Noble says, “and ensure that we minimize any inbreeding that’s taking place in that population.”

Some of the greenbacks spawned at Leadville this fall will go into reclamation waters in the west fork of Clear Creek, as well as Dry Gulch and Herman Gulch near the Eisenhower tunnel, says Bryan Johnson, the hatchery manager in Salida.

“There’s very few on the landscape right now but the goal is to eventually have multiple conservation populations out there of native greenbacks in their native range,” Johnson says, “which is the South Platte drainage.”

But the prelude to the science lab begins with the teams dropping off High Drive, working to maintain their footing through the snarl of brush on loose, wet ground, and beginning their march upstream. Progress proves slow and a couple of times is interrupted as Noble and his team scramble back to the road when the underbrush proves impassible. Then they find another path back to the creek and resume the taxing work of collecting the greenbacks — what one CPW staffer calls “boots in the water conservation.” 

“It’s a mixture of art, science and sport,” Noble says, explaining the arduous and exacting form of electrofishing. “It is definitely a skill.”

Colorado Parks and Wildlife is working to expand the population of the threatened greenback cutthroat trout in Colorado. A team of CPW biologists used backpack electrofishers in Bear Creek June 7, 2022 to attract the fish and then mildly stun them to collect eggs and sperm (milt). Pictured, left to right, are Brianna Fett, Travis Sauder and Cassidy English. (Mark Reis, Special to The Colorado Sun)

Attention to detail

Preparation for this operation pays close attention to detail — particularly with regard to avoiding any contamination that could prove harmful. As the biologists stage near the trailhead, they shed the boots they wore to the site and pull on disinfected waders to avoid transmitting any potentially damaging organisms or chemicals to the habitat. 

Even observers who have come along to watch are cautioned not to set foot in the water, or even dip an object, such as an underwater camera, into the flow.

The project itself has been confined to a stretch of Bear Creek downstream from the staging area. Everything upstream is left alone and allowed to proceed with natural reproduction, Noble says. That provides another layer of protection for the greenbacks.

“There’s always some risk that we could introduce a disease or something here so if that happened then we’d still have the stuff upstream protected,” he explains after gearing up in his waders. “So we just stick here for our spawning purposes. We do have a fairly abundant population down here so it’s been a pretty good place to spawn in recent times.” 

After a short hike down High Drive, Noble and his two helpers veer off to begin scouring the creek. Knee deep in the water and ready to begin, Noble has one of his colleagues adjust the settings on his backpack to send a mild electric current to the rod. A length of cord trails in the water behind him, like a tail, completing the electrical circuit.

After several minutes of fruitless probing, a rustle of activity.

“We got one,” Noble announces. “Male.”

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After plopping the fish into one of the buckets, he pulls a small notebook from a pocket on the chest of his waders and begins his tally. Noble not only tracks gender, but also examines the fishes’ bellies to determine whether the females appear ripe to spawn — meaning they have eggs that can be harvested — or are “spent,” meaning that their seasonal time has passed.

The timing is delicate. Already, late spring snow and diving temperatures caused CPW to delay their effort for a week amid fear that the weather may have skewed the spawning cycle. After this foray into the creek, CPW plans another collection next week to bracket a likely window of spawning opportunity.

Since discovering the greenback population here a decade ago, the agency also has directed work on Bear Creek to shift it away from sediment eroding from the steep canyon walls and enabled other enhancements to make it more hospitable to the trout population.

Colorado Parks and Wildlife aquatic biologist Cory Noble stores semen (milt) collected from a greenback cutthroat trout taken from Bear Creek in Colorado Springs, Colo Tuesday, June7, 2022. A small amount of semen from one male fish can fertilize thousands of eggs. (Mark Reis, Special to The Colorado Sun)

After all, the greenback cutthroats’ very presence in these trickling waters seems a minor conservation miracle. Nearly a century ago, the species was all but written off as a casualty of natural competition from other types of trout, fishing and mining pollutants. 

The subspecies, native to Colorado’s northeastern stretches of the South Platte River, had a brief — but ultimately illusory — resurgence. Discovery of populations in the Arkansas and South Platte rivers in the 1950s raised hopes that the greenbacks had resurfaced — and even triggered breeding efforts. But in a 2012 study, University of Colorado researchers found, by comparing the genetic makeup of what were thought to be greenback cutthroats to museum samples from a century earlier, that the supposed native greenbacks actually originated elsewhere.

Improbably, Bear Creek offered hope. Here, the original South Platte genetics matched, and CPW confirmed the CU study’s findings. But how could that be, since the creek doesn’t even run in the South Platte drainage? One plausible explanation credits a 19th-century innkeeper named Joseph Jones for introducing greenbacks into a couple of ponds he created and stocked along Bear Creek for his guests’ entertainment.

Although the ponds, constructed in an area now called Jones Park, have long since dried up, the greenbacks may have migrated into the creek and established themselves.

“So the fish in this creek most likely were brought here over 100 years ago, probably the 1870s or 1880s,” Noble says. “And they’ve survived and reproduced. And just as a matter of dumb luck, this ended up being the only surviving population of greenback cutthroat trout.” 

The decline in Bear Creek’s greenback cutthroat population that emerged in 2020 caused immediate concern. The data, which represent extrapolation from estimates taken from smaller stretches of the creek, worked out to 47.5 adult fish per mile of the 5-mile habitat — a steep drop from the 2017 density estimate of 344.5 adult fish per mile. 

While concerning, Noble allows that it’s not clear whether that should be cause for alarm. Some species, he notes, see their populations expand and contract in cycles. And since CPW didn’t start intensely sampling the Bear Creek population until 2011, it’s hard to determine whether the numbers indicate a troubling trend.

“We don’t have that long-term, decadeslong data set to really understand what the population dynamics would look like in terms of the expansion and contraction,” Noble says. “We are hopeful that we’ll see them rebounding well, but we don’t know how much that’s just natural ebb and flow in terms of their populations.”

Colorado Parks and Wildlife aquatic biologist Cory Noble uses a goose feather to mix in sperm (milt) with eggs collected from female greenback cutthroat trout taken from Bear Creek in Colorado Springs, Colo Tuesday, June7, 2022. (Mark Reis, Special to The Colorado Sun)

Trailhead science lab

And so the spawning work continues. The two-hour slosh up the creek yields two females and about 10 males, ranging in size from about about 4 to 8 inches. Noble settles onto a stool before a portable table beneath the canopy — shade is essential for what he’s about to do next — and begins the process designed to reinforce the greenback cutthroat population.

He begins with the females, identifiable by bellies full with eggs that appear bulbous, sometimes slightly protruding, around the vent where the eggs are expelled. Additionally, males usually feature a longer jaw and reddish orange or crimson coloring on their bellies, which appear more slender and keel shaped around its vent.

Noble scoops one female from its bucket, dries it on a paper towel, and proceeds to firmly squeeze its eggs into a small dish before returning it to another bucket. Only three eggs — spent. But when he repeats the process with the second female, she yields dozens of eggs, a mass that’s gratefully received, underscoring the value of the reproductive material.

Setting aside the roe, he turns to the males. Noble extracts the milt from three males, squeezing them in a manner similar to the way he handled the females, and mixes it with a stabilizing solution. A quill-sized goose feather serves as his tool for filtering out any natural debris, like dirt or feces, that might carry fungus or bacteria.

“So I’m being super careful with that,” he says.

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He mixes the milt with the roe to ensure good fertilization and genetic diversity. He adds water, stirs for 30 seconds to keep the eggs from clumping. The eggs must be fertilized quickly so they don’t go bad. He adds more filtered water and checks the temperature of the mixture so that hatchery workers can match it upon arrival. He texts the Mount Shavano Hatchery in Salida with the data and places the fertilized roe in a cooler for transport.

All told, the Salida hatchery will receive 86 fertilized eggs. Of those, maybe 10% will survive, hatchery manager Johnson estimates. The numbers may seem underwhelming, but their impact is significant, he points out. Simply continuing to develop a hatchery broodstock would essentially domesticate the species.

Colorado Parks and Wildlife aquatic biologist Cory Noble collects eggs from a female Greenback Cutthroat Trout taken from Bear Creek in Colorado Springs, Colo Tuesday, June7, 2022. Teams of biologists used backpack electrofishers which send an electric charge into the creek which attracts fish and then mildly stuns them so they can be collected. (Mark Reis, Special to The Colorado Sun)

“And so going back into the source population and taking basically the wild genetics and infusing those back into the hatchery broodstock is super important to represent the entire population,” Johnson says. “The thing is, any numbers of these greenbacks are important because Bear Creek is the only naturally reproducing population in the world.”

Finally, Noble focuses on the remaining males. As he extracts the milt, he adds a preservative solution before transferring it to vials. A colleague injects the vial with a burst of pure oxygen from a nearby tank for the trip to the hatchery. The milt will be enough to fertilize thousands of eggs at the Leadville facility.

Eventually, the greenbacks captured and contributing to the process will be released back into their habitat — probably more stressed than when they began the day, but also unwitting accomplices in the effort to sustain and grow their numbers. For the aquatic biologists, an exhausting exercise in the field, to be repeated again in a few days, promises incremental impact on one of Colorado’s signature subspecies.

“Today went well,” Noble says. “Really well. We’ll definitely do a lot of good in the hatchery.” 



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