Story and photos by Cody Olivas,
Reprinted from The Mountain Mail, February 26, 2020
For decades Colorado Parks and Wildlife has made efforts to restore rainbow trout populations, ever since whirling disease wiped out many of the fish in the 1990s.
“It (whirling disease) damages the cartilage of young and developing fish,” CPW aquatic biologist Mike Atwood said about the disease. “They don’t develop properly so they end up with crooked backs and are unable to swim effectively.”
He said their crooked backs make it harder for the fish to feed and also makes them more susceptible to predation. “Their mortality rate is really high,” Atwood said.
Hofer rainbow trout were found to be 100 times more resistant to the disease than various CPW rainbow strains. However, the German strain showed no flight response, which is needed to elude predators in the wild.
Researchers started crossing the Hofer rainbow trout with wild strains. Those fish were stocked in rivers around the state and some natural reproduction started. In the east portal of the Gunnison River, the rainbows have demonstrated a strong resistance to the disease.
“Thanks to advance genetic testing, we know these fish are maintaining their resistance to whirling disease,” said George Schisler, CPW’s aquatic research chief, in a press release. “Now they are surviving, reproducing and contributing to future generations of Gunnison River rainbows.”
On Tuesday, for the fourth consecutive year, volunteers from the Collegiate Peaks Chapter of Trout Unlimited helped the CPW prepare some of the Gunnison River Rainbows to be released into the wild.
About a dozen volunteers began clipping the adipose fin off of approximately 22,000 3-inch fish in the morning, helping the CPW identify the stocked fish once they’re in the wild.
“This wouldn’t happen without volunteers,” Atwood said. “It’s really nice to have their volunteer time.”
After this year, the CPW will have stocked roughly 75,000 of the clipped Gunnsion River Rainbows into the Arkansas River at Salida East.
Some of the rainbows that were stocked four years ago are now as big as 17 inches while a bunch are 15-16 inches long, Atwood said.
“These fish are doing well; they’re growing better in the Arkansas River than at the hatchery,” Atwood said, noting the brood stock fish are wild and more accustomed to a natural river environment.
Mike Perry, one of Tuesday’s volunteers, said he’s caught a few rainbow trout recently in the Arkansas, but noted there are still more brown trout than rainbows in the river.
“They’re already producing a good angling experience,” Atwood said, adding that most of them are located within a protected seven-mile stretch of the river that’s catch-and-release only.
Now, the next hurdle for the fish to clear is to start reproducing naturally in the Arkansas, which should begin now in the fourth year.
“Hopefully this fall we’ll see some evidence of naturally occurring rainbow trout,” Atwood said. “We’ll know that if we catch some small rainbows who haven’t had their adipose fin clipped off.”
Including the 22,000 Gunnison River Rainbows that the CPW and volunteers were working on this week, Atwood said they will stock approximately 100,000 fish in the Arkansas River this year, from Granite down to Parkdale. The rest of the fish, however, won’t have their adipose fin clipped off.
Atwood said the clipped fish will probably go into the river at the end of March. In October or November when they survey the river, he said they’ll see if the fish have started reproducing.
“I’m still optimistic,” Atwood said. “This being year four, now we should expect to see some natural reproduction. If natural reproduction is not happening, we know they’re still growing well and providing some good recreational opportunities.”