After being devastated by whirling disease in the 1990s, Colorado’s rainbow trout populations are recovering in most major rivers, Colorado Parks and Wildlife officials said.
“It’s been a long road, but bringing back populations of fish that were essentially extirpated from Colorado can only be called a huge success,” said George Schisler, a Fort Collins-based Parks and Wildlife scientist. The agency released a statement last week trumpeting the rainbow trout’s recovery.
Yet in the Animas River, trout are having a “tough time” because of reduced runoff in recent years and water-quality issues, said Joe Lewandowski, a Parks and Wildlife spokesman in Durango.
“The Animas, it still is challenging for fish,” Lewandowski said.
Reduced runoff has added to other concerns, such as water being drawn out of the Animas for Lake Nighthorse, harmful metals in the water and runoff from housing developments and agriculture. Lewandowski said. Scientists are seeing little natural reproduction in the Animas’ fish population.
“That’s kind of a signal the water quality is not as good as it could be, obviously,” Lewandowski said.
The agency is stocking the river with Hofer rainbow trout, which trace their lineage to a German hatchery and have proved resistant to the whirling disease parasite. It’s far too early to tell if the stocking effort will be successful, Lewandowski said. The stocking effort has boosted rainbow trout populations in other waterways.
“It’ll probably be several years until we can say how they’re doing,” he said.
Statewide, the picture is somewhat better. Since last summer, Fish and Wildlife said, anglers have reported they are catching good-sized rainbow trout in the upper Colorado, Rio Grande, upper Gunnison, Poudre, East, Taylor, Arkansas and Yampa rivers, among others.
Whirling disease devastated Colorado trout fisheries beginning in 1986. By the mid-90s, rivers in Colorado thoroughly were infected, Parks and Wildlife said.
Whirling disease is caused by a spore that infects the spine of very young fish. The infection deforms the spine causing the fish to swim in a whirling pattern. Trout die shortly after becoming infected.