Biologists on Monday will start second-phase treatment in the Hermosa Creek watershed to create a home for native Colorado River cutthroat trout.
Colorado Parks and Wildlife and U.S. Forest Service personnel will apply Rotenone to kill non-native fish, specifically brook trout.
Rotenone, derived from the root of a tropical plant, is registered by the Environmental Protection Agency as a pesticide. It degrades quickly, leaves no residue and is no threat to humans or other wildlife.
We did the first treatment last summer, Joe Lewandowski, a parks and wildlife spokesman, said Thursday. Then in June they went back to electroshock, which found fish that can live in little water.
The Rotenone applied this week will catch all survivors, Lewandowski said.
In late summer or in the fall, native Colorado River cutthroat will be stocked in that section of the stream, Lewandowski said.
Native cutthroat today inhabit only 14 percent of their historic habitat. Wanton consumption, the introduction of non-native fish starting in the 1850s and degradation of water quality nearly wiped out the native cutthroat.
Concerned biologists used remnant populations to create brood stock that now sustains stocking. Habitat protection also is an important protective practice, Lewandowski said.
Next year, the Forest Service is scheduled to install two fish barriers one on the East Fork of Hermosa Creek, the other below the confluence of Hermosa Creek main stem and the East Fork.
A barrier already exists on Hermosa Creek at Hotel Draw.
Barriers prevent nonnative fish from migrating into areas designated for native cutthroat.
The Forest Service work will be funded in part by a $56,000 grant from the National Fish and Wildlife Foundation.
The Forest Service also is rehabilitating 1,000 feet of eroded Hermosa Creek stream bank, installing 16 in-stream rock structures to create deep pools for fish.
Trout Unlimited is helping fund reseeding of stream banks.
Anglers need not despair, Lewandowski said.
The project to expand the range of the native cutthroat will interrupt fishing for a time on Hermosa Creek and the East Fork. But the main stem of Hermosa Creek below Hotel Draw to the Animas River will be open to fishing, Lewandowski said. The stretch covers some 20 miles.
Three trout subspecies, including the Colorado River cutthroat, were isolated in what is now Colorado by glacial movement eons ago.