From the Loveland Reporter-Herald (Pamela Johnson):
Anglers have been reporting catches that they haven’t seen in Colorado rivers in many years — good size rainbow trout — due to an effort from scientists to restore populations of the fish that were devastated by whirling disease.
Colorado Parks and Wildlife scientists have been breeding whirling disease resistant fish in hatcheries across the state and stocking them in waters around Colorado since 2006, including in the Poudre River west of Fort Collins.
“We are seeing an increase in the rainbow trout population,” said Eric Fetherman, aquatic research scientist. “We haven’t seen them reproduce in the (Poudre) River. We’re not to that point yet.
“We are starting to the see natural populations coming back in other parts of the state. In the Gunnison River, the natural population there is enough to consider not restocking.”
On the Poudre, the fish are stocked above the narrows near Rustic but have made their way downstream and onto the hooks of happy fishermen and women all along the river.
“We’ve had reports of people catching them at Picnic Rock and even all the way through town,” said Fetherman…
In 1986, a private hatchery unknowingly imported infected rainbow trout from Idaho and stocked them in 40 different waters. The disease -— which infects the spine of young fish, causes then to swim in a whirling pattern and ultimately die — spread throughout the state and essentially ended natural reproduction of rainbow trout in most Colorado rivers.
Brown trout, which are not susceptible, took over as the dominant fish.
Then in 2002, at a national conference in Denver, researchers learned about a family named Hofer in Germany who was raising rainbow trout that were resistant to the parasite that causes whirling disease, according to Colorado Parks and Wildlife.
Colorado researchers imported eggs from the Hofer hatchery and began to study them.
Sure enough, research showed that the Hofer trout were resistant to whirling disease, and some were stocked in reservoirs west of Berthoud.
However, because these fish had been in domestic hatcheries for generations, researchers knew they would have little chance of survival in creeks and rivers because they did not possess the instinct to avoid predators and to survive in fluctuating water.
So, the research team, led by George Schisler, an aquatic scientist based in Fort Collins, began cross-breeding the Hofers with wild trout. After three years, they stocked the first Hofer-cross rainbow trout, but the first fish did not survive.
Again in 2010, biologists stocked fingerlings in the Colorado River, and just over a year later, they found good numbers of 15-inch rainbow trout and evidence that the young fish were hatching in the wild, according to Colorado Parks and Wildlife.
Since then, the fish have been stocked in many rivers including the Poudre, East, Taylor, Gunnison, Rio Grande and Yampa. Biologists vary the time of year, size and location to optimize survival of the rainbow trout.
This year, 6 million Hofer crosses will be raised across all the Colorado Parks and Wildlife hatcheries and released into water statewide. At the Bellvue fishery right now, 150,000 Hofer crossed with Colorado River rainbow are growing in troughs to be released into the Poudre and St. Vain Rivers in late August and early September.