Colorado State Researcher Finds Global Warming Unlikely Asset for Threatened Greenback Cutthroat Trout

Colorado native greenback cutthroat may actually benefit from increased temperatures attributed to global warming, according to recent research findings at Colorado State University.

Scott Cooney, fishery and wildlife research assistant at Colorado State, examined how increased water temperatures due to climate change might impact greenback population distributions. Cooney’s research suggests that more rapid snowmelt earlier in the year and increased water temperatures may make existing and surrounding habitats more viable for the greenback in certain locations.

"Due to competitive dominance of non-native trout, the greenback cutthroat trout have been limited to areas where they can exist in isolation," Cooney said. "Those habitats are not necessarily ideal in terms of temperature, flow regimes, habitat size and availability of spawning habitat."

Greenbacks, which are federally listed as endangered, tend to prefer cooler water, but the colder temperatures cause hatchlings to have fewer days to accumulate fat stores because they spawn in the spring. The time of year in which they spawn allows other species of trout to overtake their habitats. Competition with other trout species has driven greenbacks to smaller, inadequate habitats with colder water temperatures, limiting their distributions.

Cooney emphasizes the complexity of global warming and potential impacts on the environment caused by climate change. He points out that restoration plans for the greenbacks must consider how climate change may either enhance or degrade high-elevation habitats. While increased weather temperatures may provide the fish with warmer waters, there are other effects that may be detrimental.

Whirling disease, a parasitic infection that affects salmon and trout, creates another hurdle for greenbacks. The parasite becomes more virulent in warmer waters, which could pose a problem if temperatures increase in some habitats. Many major Colorado drainages contain the parasite, and scientists predict that all U.S. streams will be infected within the next 60 years.

"Global warming has the potential to lengthen the growing seasons in some of these (habitats)," Cooney said. "Consequently, these streams may support higher populations than they do currently, if all else stays the same. However, it is unknown at this point what effects, if any, global warming will have on the flow regime, frequency of floods or droughts and other potentially negative factors associated with the greenback cutthroat trout."

Approximately 20 stable greenback populations exist in Colorado’s high-elevation streams, lakes and other habitats that do not contain competitive non-native species. Natural barriers such as waterfalls protect these habitats, and the chance for non-native species invasion is unlikely unless humans intentionally introduce them.

In 1969, Robert Behnke, professor of fishery and wildlife biology, and his associates discovered a small population of greenbacks in a creek west of Boulder, Colo. Until this discovery, the fish was believed to be extinct for the past 30 years. Scientists now say the greenback populations are secure but fragile. The state and federal government allow the greenback to be fished on a catch-and-release basis only.

For more information about the greenback cutthroat research and global warming, contact Cooney, at (970) 491-7297, (970) 223-0958 or via e-mail at