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Greenback cutthroat trout

The greenback cutthroat trout (Oncorhynchus clarki stomias) is endemic to the headwaters of the South Platte and Arkansas River drainages on the eastern slope of the Rocky Mountains (primarily in Colorado) [1]. It is estimated that the greenback cutthroat historically occupied up to 13,231 km of habitat (6,276 km in the Arkansas River Basin and 6,955 km in the South Platte River Basin) [2]. Although once abundant, the greenback cutthroat declined rapidly after the arrival of large numbers of immigrants to the Front Range of Colorado in the mid-to late 1800s [2].

Greenback declines were the result of mining pollution (sediment and toxic runoff exterminated numerous populations [3]), dewatering of streams for agriculture, and the harvest of greenbacks for commercial sale [2]. By the early 1900s, the greenback cutthroat was extirpated from most of its native range [1]. In addition, during the early 1900s nonnative trout were widely introduced into greenback habitat, likely eliminating greenback cutthroat from nearly all of their remaining habitat (cutthroat trout are often replaced by brook and brown trout and readily hybridize with rainbow trout and nonindigenous subspecies of cutthroat) [2, 3]. By the 1930s, the greenback cutthroat was thought to be extinct [1]. In 1973, however, two small populations (about 2,000 fish total) were confirmed in about 4.6 km of stream and the greenback cutthroat was listed as endangered [1].

Recovery efforts for the greenback cutthroat have focused on establishing new populations and locating additional historic populations [1]. Starting in 1977, captive broodstocks were established for reintroduction (typically following the removal on nonnative trout species) into streams and lakes [1]. By 1978, a third genetically pure population had been discovered and five translocation attempts had taken place [2]. This led to the 1978 downlisting of the greenback cutthroat to threatened (a status that allowed for sportfishing) [2]. To date, six additional historic populations have been discovered for a total of nine historic populations [1]. Greenback cutthroat trout have now been found or introduced in 68 waters with over 639,000 fish distributed between 1985 and 1996 [3]. Introduced fish were reared or produced primarily by three hatcheries: the Bellvue Fish Research Hatchery in Colorado, the Bozeman Fish Technology Center in Montana, and the Saratoga National Fish Hatchery in Wyoming [3]. At eight of the 68 sites, recovery efforts have been abandoned or greenback cutthroat populations extirpated because of invasion by nonnative salmonids, unsuitable habitat, or lack of reproduction by greenback cutthroat trout [3]. As of 1998, greenback cutthroat occurred in 61 sites totaling 166 ha of lake and 165 km of stream habitat (this includes the nine historic sites) [1]. Forty-seven of these sites were open to catch-and-release fishing [1].

In 1999, 21 greenback cutthroat populations were reported to be stable and self-sustaining (18 in the South Platte River basin and three in the Arkansas River basin) [2]. This was close to meeting the delisting goal of 20 stable populations with at least five populations in the Arkansas River basin, presented in the 1998 recovery plan [2]. The recovery plan proposed that the greenback be delisted when two additional stable populations were created in the Arkansas River basin and a long term monitoring plan was completed [1]. Concern has been expressed, however, about the adequacy of recovery criteria (specifically the thresholds set for minimum biomass, abundance, habitat size, and year-class success) for securing populations from demographic instability or loss of genetic variation [2]. Although the status of the greenback cutthroat has certainly improved, they still face significant threats due to their inhabiting waters that are small, isolated, unproductive, in close proximity, and at risk of extirpation by natural events [2]. In addition, eight of the 14 stable introduced populations are in high elevation lakes that are outside the native range of greenback cutthroat and where they cannot develop the highly mobile life histories that were historically common [2].

In 2005, Colorado Division of Wildlife reported that greenback cutthroat occur in 58 streams and lakes with 23 populations meeting the population criteria required by recovery goals [4].

[1] U.S. Fish and Wildlife Service. 1998. Greenback cutthroat trout recovery plan. Denver, Colorado.
[2] Young, M.K. and A.L. Harig. 2001. A Critique of the Recovery of Greenback Cutthroat Trout. Conservation Biology 15(6):1574-1584.
[3] Young, M.K., A.L. Harig, B. Rosenlund, and C. Kennedy. 2002. Recovery History of Greenback Cutthroat Trout: Population Characteristics, Hatchery Involvement, and Bibliography. General Technical Report RMRS-GTR-88WWW. USDA Forest Service, Rocky Mountain Research Station.
[4] Colorado Division of Wildlife. 2005. Greenback Cutthroat Trout Species Profile. Website <http://wildlife.state.co.us/WildlifeSpecies/Profiles/Fish/GreenbackCutthroat.htm> updated 12/2/2005 accessed April, 2006

Banner photo © Phillip Colla