From the North Forty News (Cherry Sokoloski):
In August, the DOW and volunteers removed 1,400 brown trout, or 90 percent of the estimated population, from a 0.6-mile section of the Poudre River downstream of the Poudre Unit hatchery, then moved the browns to a different location. At the same time, the agency planted thousands of rainbows in the section where browns were removed and in a control section where browns were not removed. Special antennae at either end of each section have tracked movement of fish by reading tags implanted in the stocked rainbows. The relocated browns were also tagged, and Fetherman discovered that some of them made it back to the removal area.
The DOW planted 4,000 rainbows using strains that are resistant to whirling disease, which wiped out wild rainbows in the Poudre in the 1990s. Half the ‘bows were Hofer-Harrison crosses, and the rest were Hofer-Colorado River Rainbow hybrids.
In late October, Fetherman and others did a fish count in both the removal area and the control area, to check on populations of browns and rainbows. The results were significant. “In the short term, the removal was successful,” a smiling Fetherman said. In the control area, where browns were not removed, only 503 rainbows remained – 26 percent of the planted fish. In the removal area, however, the DOW counted 1,185 rainbows, or 60 percent of those planted.
This initial success suggests that, as hoped, stocked rainbows can succeed when competition from browns is removed. Fetherman thinks it’s likely that removal of the browns gave the rainbows a toehold in the territory before competing browns moved back in…
In addition, Fetherman found evidence that browns do prey upon the rainbows. Nine browns that were captured in October had rainbow tags in their stomachs.
More restoration coverage here.