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Colorado: Some cutthroat trout mysteries solved

What next for Colorado’s state fish?

A Rio Grande cutthroat trout. Photo courtesy Andrew Todd.

By Bob Berwyn

SUMMIT COUNTY — After some genetic sleuthing and intensive scrutiny of historic fish-stocking records, a team of federal, state and university biologists said they’ve pinned down Colorado’s greenback cutthroat trout to just a single population — about 750 fish, all living in a four-mile reach of Bear Creek, a small Arkansas River tributary in the mountains west of Colorado Springs.

Greenback cutthroats — the Colorado state fish — were originally native to the South Platte drainage, but now appear to survive only in that single population outside of the species’ native range.

Biologists say native cutthroats in Colorado declined because of  pollution, overfishing and stocking of native and non-native species of trout.

The Bear Creek strain may have been transplanted from the South Platte Basin in the 1880s by a hotelier who stocked the fish in a pond at the Bear Creek headwaters to help promote an early tourist route up Pikes Peak. They are the last remaining representatives of the federally protected greenback cutthroat trout.

The genetic study was led by CU-Boulder postdoctoral researcher Jessica Metcalf. It was based largely on DNA samples taken from cutthroat trout specimens preserved in ethanol in several U.S. museums around the country that were collected from around the state as far back as 150 years ago.

“It’s ironic that stocking nearly drove the greenback cutthroat trout to extinction, and a particularly early stocking event actually saved it from extinction,” she said.

DNA trail

For the study, Metcalf analyzed DNA from wild trout and from museum specimens from sites around Colorado and New Mexico as far back as 1857. The trout were collected by a number of early naturalists, including Swiss scientist and former Harvard Professor Louis Agassiz and internationally known fish expert and founding Stanford University President David Starr Jordan.

Based on the findings, biologists will have to fundamentally rethink their conservation strategy for Colorado’s state fish, which is also listed as threatened under the federal Endangered Species Act.

For one thing, it means that cutthroat trout on the West Slope, including several populations in Summit County, are not greenbacks; they come from various lineages of Colorado River cutthroats, said Colorado Parks and Wildlife biologist Kevin Rogers.

The study shows that each major drainage had fish that developed subtle differences, resulting in spread-out “patchwork of lineages,” Rogers said.

On top of that, massive trans-drainage and trans-basin stocking of fish occurred during the state’s settlement era, jumbling the distribution of the fish “through space and time,” according to the researchers.

“We’ve been doing conservation for a long time, preserving all the species … now we can set about deciding where we want them. All  these lineages are native to Colorado. These are our native fish, they’re just not in the streams where they evolved,” Rogers said.

Fish history 101

The new research helps untangle the history of those lineages.

“With the insight afforded by the historical data, we now know with a great deal of certainty what cutthroat trout strains were here in Colorado before greenbacks declined in the early 20th century,” said Andrew Martin, of CU’s ecology and evolutionary biology department. “And we finally know what a greenback cutthroat trout really is.”

“We’ve known for some time that the trout in Bear Creek were unique,” said Doug Krieger, senior aquatic biologist for Colorado Parks and Wildlife and the greenback cutthroat trout recovery team leader. “But we didn’t realize they were the only surviving greenback population.”

The new findings won’t immediately affect the current status of the greenback cutthroat trout, said U.S. Fish and Wildlife Service biologist Leslie Ellwood, adding that the agency will do a thorough review of the data before making any changes.

That process will include public input, with a workshop on cutthroat trout conservation tentatively scheduled for the spring of 2013. Basically, the USFWS will evaluate all identified cutthroats in Colorado and determine if a species, subspecies, or Distinct Population Segments warrants listing or a change in current listing status.

Epic stocking

During a conference call, the scientists said they were surprised at the magnitude of historic fish stocking by pioneers during the state’s settlement era. Between 1889 and 1925, more than 50 million cutthroat trout from the Gunnison and White River Basins were stocked across Colorado, including locations on the Front Range, in large part shaping the current distribution of cutthroat trout in Colorado.

The new study built on 2007 research also led by Metcalf and Martin, which found that several Front Range cutthroat populations previously thought to be greenbacks were actually West Slope fish that were transplanted to the East Slope.

Ongoing efforts to protect cutthroat trout and their habitat is still important, said Mike Thabault, USFWS assistant regional director for ecological services.

“We think it’s important to note that recovery efforts have preserved the genetic diversity of native cutthroats and their habitat throughout Colorado,” Thabault said.

Cutthroats are the state’s only native trout. The rainbow and brown trout so popular with anglers were all imported during the settlement era, but cutthroats originated in the Pacific Ocean and managed to spread to the interior West. They are considered to be one of the most diverse fish species in North America and a symbol of wildness in the American West.

For thousands of years, cutthroat trout evolved across the western U.S. into 14 recognized subspecies, including the giant yellowfin cutthroat, an Arkansas Basin strain that once grew to prodigious size in Twin Lakes near Leadville, the greenback cutthroat east of the Continental Divide, the Colorado River cutthroat from the western slope and the Rio Grande cutthroat in streams surrounding the San Luis Valley.

During their research, Metcalf and her colleagues also identified a previously undiscovered San Juan Basin cutthroat that is now extinct. Metcalf also looked for evidence that the yellowfin had survived to modern times, but concluded that it too was extinct.

Groundbreaking science

Colorado Parks and Wildlife aquatic research scientist Kevin Rogers said that the study gives biologists a better understanding of cutthroat biology and serves as a good reminder of how science works — even if the results are uncomfortable.

“The integrity of the scientific process depends on researchers who are willing to use new tools to explore difficult issues and challenge existing paradigms,” Rogers said. “Advances in technology have allowed us to analyze the DNA of fish collected during the early years of Colorado’s settlement. This study has opened an astonishing window into the past.”

A protected broodstock of Bear Creek cutthroats is being propagated in Colorado Parks and Wildlife’s hatchery system and at the Leadville National Fish Hatchery, run by the Fish and Wildlife Service. The offspring will be used to establish wild populations in the future.

Funding for the study was provided by agencies of the Greenback Cutthroat Trout Recovery Team, including the Fish and Wildlife Service, the U.S. Forest Service, the Bureau of Land Management, the National Park Service and Colorado Trout Unlimited.

A fact sheet on the recent research:

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2 Responses

  1. [...] biologists recently identified the Bear Creek population as the only remaining genetically pure strain of the greenback cutthroats. The settlement came a [...]

  2. [...] here in Colorado, we have finally figured out which fish is which (see paper here and this piece by Bob Berwyn) and there is a settlement agreement with CBD that stops motorcycles only from [...]

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