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Pulling Colorado's State Fish Back From The Brink

Mariah Lundgren
Platte Basin Timelapse, used w/ permission
A greenback cutthroat trout, Colorado's state fish, just pulled from Bear Creek.

Colorado's mountain streams are premier trout fishing destinations, but anglers aren't likely to reel in a greenback cutthroat trout. That's because until a few years ago, Colorado's state fish was on the brink of extinction.

"Last time we pretty much just focused on the pools, there wasn't much sitting in these faster areas," said biologist Josh Nehring as he wades up Bear Creek, a few miles outside Colorado Springs. "But it's just running so high this year."

Nehring is electrofishing: sending a current through the water to attract and stun the fish, making them easier to catch. Nehring hopes to find a few trout here to help establish many more elsewhere.

"Oh, saw one over here, where'd he go… he either went up or… there he is, nice job. You got him, you got him! Perfect. Just hold him in the water for a second," Nehring said, directing a co-worker with a net.

It's spawning season. After pulling the fish from the net, Nehring determines its sex and whether it's carrying eggs or sperm, called milt. Those that do are termed "ripe." They get lucky with the first pick, a ripe male.

Nehring and his coworkers continue moving upstream, catching trout. Many are too young or too small. But the "ripe" ones get put in a bucket. Nehring, who works for Colorado Parks and Wildlife, is pleased with the catch, because these are special fish: greenback cutthroat trout.

"It's the last remaining genetically pure greenback cutthroat strain that we have in the wild," Nehring said.

Colorado Parks and Wildlife is one of several state and federal agencies that has been working for decades to recover the greenback cutthroat trout — once thought extinct and now federally listed as an endangered species. A few years ago, new genetic research revealed that they'd been saving the wrong subspecies. Greenback are just one kind of Colorado's native trout.

"We have several different strains," Nehring said, "the Rio Grande cutthroat trout, the greenback cutthroat trout and then two different lineages of Colorado River cutthroat trout."

Researchers had spent years recovering a different cutthroat subspecies, likely one native to the Colorado River Basin. After comparing modern trout DNA with historic specimens collected by early explorers, researchers determined the fish swimming in Bear Creek were the only genetically pure greenback cutthroat trout left in the wild.

Credit Ariana Brocious / Platte Basin Timelapse, used w/ permission
Platte Basin Timelapse, used w/ permission
Josh Nehring (R) and Frank McGee (L) of Colorado Parks and Wildlife prepare to collect milt from the fish.

Nehring and others have collected milt from the fish spawning at Bear Creek to help rebuild the species.

"If there's only one stream in the world that has these fish, they're pretty important," Nehring said.

Back on the road, under a pop-up tent near the river, Nehring and his staff lay out an arsenal of tools, vials and coolers. Nehring explains milt is water-activated. Without any eggs around to fertilize, it's essential to keep it dry for now.

After drying it with a paper towel, he gently squeezes each fish over a glass dish to collect a drop or two of milky fluid. The first fish produces two drops of milt.

"Surprisingly, that is a fairly good male," Nehring said.

After Nehring collects milt, length measurements and fin clips from each fish (for genetic research), the vials go into a cooler then sent straight to the Leadville National Fish Hatchery.

These fish are resilient. But in much of Colorado, cutthroat trout have suffered from habitat loss and competition from introduced, nonnative fish species like rainbow and brown trout. So researchers still take great care to minimize their disturbance at Bear Creek as they work to save this fish.

"They're an important part of the ecosystem," Nehring said. "They've evolved here over a long period of time and fill a niche in the environment."

"...how sad would that be, [if] the state fish of Colorado is extinct?"

At the Leadville National Fish Hatchery, several fish biologists prepare for the day's work: to fertilize hatchery-raised eggs with the wild milt collected at Bear Creek, as well as milt from hatchery fish. In 2008, biologists collected an initial batch of greenbacks from Bear Creek to spawn in hatcheries in Salida and Leadville.

"This is a very hard to raise subspecies of cutthroat trout," Ed Stege said, manager of the Leadville hatchery and longtime employee of the U.S. Fish and Wildlife Service. "And so it has been difficult to keep alive in captivity."

Even with established populations at both hatcheries, Stege said the wild Bear Creek milt is critical to increase genetic diversity and hatch rates.

"The biggest challenges for the greenback cutthroat going forward I think is going to be the genetic diversity. You know being that there was only one population remaining... that's all the genetics we have to work with. We can't go out and get anymore," Stege said.

Researchers plan to soon begin a project to further increase genetic diversity.

Greenback cutthroat trout are actually native to the South Platte River Basin, further north. Biologists think homesteaders likely introduced greenbacks to the formerly empty streams in the Bear Creek area more than a century ago. That may have saved the species.

Now, because of the efforts of Colorado Parks and Wildlife, the U.S. Fish and Wildlife Service and others, Bear Creek is no longer the only place greenback cutthroat trout can be found in the wild. The first reintroduction of genetically pure greenback cutthroat trout took place in 2014 at Zimmerman Lake, west of Fort Collins. This is the ultimate goal of the recovery program, re-establishing new wild populations in the species' historic range of the South Platte River Basin.

"I'm not going to say we're successful until we've produced enough progeny out there and they've reclaimed enough streams to where we have a lot of self-sustaining viable populations out there," Stege said.

The Zimmerman Lake population is a wild brood stock where biologists can continue growing more greenback cutthroat trout. State agencies are working on removing non-native fish from a few other streams to provide additional places to reestablish the fish, Stege said.

"We have no idea how they might contribute to the overall welfare of the ecology or even humankind. But if we don't save the parts now, there won't be anything down the road for future generations to enjoy or to even witness," Stege said.

Other threats to the greenback cutthroat still remain: increased sediment and habitat loss from forest fires, warming waters from climate change, disease and hybridization with other fish. But in time, more anglers might find native greenback cutthroat trout back in the South Platte Basin.

"I mean it's the state fish," Stege said. "You know, how sad would that be, [if] the state fish of Colorado is extinct?"

This story comes from the Platte Basin Timelapse project, which is putting an entire watershed in motion.

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