To Reintroduce Colorado’s State Fish, Wildlife Officials Must Remove Their Non-Native Predators — Other Trout

August 25, 2021
Greenback Cutthroat Trout from the south prong of Hayden CreekGreenback Cutthroat Trout from the south prong of Hayden CreekCredit Josh Nehring/Colorado Parks and Wildlife
Greenback Cutthroat Trout from the south prong of Hayden Creek

The greenback cutthroat trout is Colorado’s official state fish, but it’s been listed as “Threatened” under the Endangered Species Act  since 1978. Once thought to be completely extinct, wildlife biologists have been working for decades to help the species rebound. 

But last year, CPW reported an 80 percent decline in adult trout populations over a three year period, a troubling regression after years of progress. 

In an attempt to rehabilitate the population, Colorado Parks and Wildlife officials began what it calls “aggressive recovery efforts” in 2014. That effort is now continuing, with work underway along two creeks in the Roosevelt National Forest in Larimer County. 

Greenback trout were previously introduced to George Creek and its tributary stream Cornelius Stream in the early 1980s. However, the state fish’s non-native predators — the brook trout and brown trout — have since re-invaded the streams and killed off greenback populations.

Jason Clay, a public information officer for CPW, said the two non-native species have a long history in the state.

“They were brought back many decades ago, really for angling opportunities,” Clay said. “They started from European beginnings way back when and populated out in the east as both a food source and an opportunity for anglers, as the west was getting developed.”

Both the brook trout and brown trout are extremely abundant in Colorado, thanks to high spawn rates and their tendency to out-compete other fish. These trout also prey on smaller fish, like the greenback cutthroat, pushing them out of their habitats. They are also more resistant to the parasite that causes whirling disease, which can kill or massively deform young trout.

The CPW closed the area around the two creeks for three days on Monday as it worked to kill all the brown and brook trout in the streams using a common population control compound called rotenone. The streams must  be left fishless for several years in order for whirling disease parasites to die off. Once tests show an absence of parasites, greenback trout will be reintroduced to the creeks.

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