The restoration of the Animas River has begun.
Colorado Parks and Wildlife on Thursday stocked 1,500 rainbow trout in the Animas River at a few locations from the 32nd Street Bridge to the High Bridge on South Camino del Rio, a 5-mile stretch of river that runs through Durango.
It marked the first significant restocking of fish in the Animas since mudslides and floods from the 416 Fire burn scar this summer caused a near complete die-off in the waterway.
“One thing we’d like to see is how well these guys survive,” said Jim White, an aquatic biologist for CPW in Durango. “Because it’s going to take a while to rebuild the fishery.”
The first reported fish kills as a result of runoff from the 416 Fire burn scar occurred in mid-July. A massive storm that caused heavy flooding around July 17 is thought to have killed most of the fish in the Animas.
It’s a lingering problem that burn scars pose throughout the West. When rain hits an area that has experienced wildfire, a deluge of dirt and ash into a river can cut off oxygen and suffocate fish and other aquatic life.
In the wake of the fish kill, however, the absence of any substantial fish populations have created a sort of blank slate for wildlife managers in restocking the Animas River.
Thursday’s stocking of 1,500 rainbow trout is the first step in what’s expected to be a years-long effort.
“It’s not a lot of fish,” said Joe Lewandowski, spokesman for CPW. “But … given they’ll have little competition in the river, there’s a good chance they’ll make it through the winter.”
The rainbows released into the Animas are spawn of wild rainbow trout from the Gunnison River that inexplicably developed a natural resistance to whirling disease, which is caused by a parasite that leaves fish deformed.
As a result, infected fish are unable to reproduce. The deformities cause them to swim in circles and die in large numbers, either from starvation or by predators.
Making its way first from Europe to the United States’ East Coast, whirling disease was discovered in Colorado in the late 1980s. Just a decade later, rainbow trout had all but vanished from the state because of the ailment.
In response, the state launched a robust effort to clean up infected hatcheries and start breeding in captivity strains of rainbows resistant to whirling disease. The effort met relative success, said Eric Fetherman, an aquatic research scientist with CPW.
“We have been stocking those fish pretty widely throughout the state,” Fetherman said. “And we’re starting to see rainbows coming back in a bunch of rivers – the Colorado, the Yampa.”
But a major breakthrough in the rainbow trout’s recovery occurred when researchers found wild populations in a remote part of the Gunnison River that had developed a natural immunity to whirling disease.
Ever since, CPW has been trapping and breeding the fish, and spreading them throughout the state. Mike Atwood, an aquatic biologist for CPW in Salida, did not return calls seeking comment.
But Atwood told The Mountain Mail last week that these Gunnison River rainbow trout were thriving after being introduced in the Arkansas River.
“The Gunnison River rainbows actually thrive and grow faster in the river than they do in the hatchery under controlled conditions, a hopeful indicator of how well-suited they are to the Arkansas River,” he said.
This same hope is being held for the fish released into the Animas, White said.
Fish in the Animas River, historically, have been unable to reproduce on their own, and populations in the waterway have relied on CPW’s stocking.
Whirling disease is present in the Animas River and contributes to the inability of fish to reproduce, but White said a number of other factors – pollution from legacy mining in Silverton, low water, higher water temperatures – all contribute to the issue.
It’s not expected the 1,500 rainbows released will reproduce this year, White said, but the fish are marked, which will allow researchers to see if they survive when another fish count is conducted next fall.
CPW typically stocks 20,000 brown trout and 20,000 rainbow trout fingerlings after spring runoff in a 7-mile stretch of the Animas through town. White said CPW is planning to monitor the river before taking any actions.
Angling companies in Durango, too, are waiting to see how the fish fare in the Animas before taking out guided trips.
Statewide, CPW spends about $3.8 million annually to stock lakes and streams. And according to a 2017 CPW economic report, fishing provides a $2.4 billion economic jolt statewide and $120 million in Southwest Colorado.
In the meantime, the Gunnison River rainbow transplants, at 10 to 12 inches, will provide immediate fishing opportunities.
“It’s going to take a little time for it to recover,” said Tom Knopick, co-owner of Duranglers. “But at the same time, the Durango area offers so many fishing opportunities, it’s not just restricted to the Animas.”