GREENBACK CUTTHROAT TROUT

Species Description:  The greenback cutthroat trout (Oncorhynchus clarki stomias) is a member of the Salmonidae family, and is a subspecies of O. clarki.  Historically, greenback cutthroat trout typically weighs between one and two pounds, and does not exceed 12 inches in length.  Presently, size is dependant upon elevation and population size.  In small headwater habitats, the greenback can grow to 14 to 15 inches, where it is much smaller than most brook trout in similar habitat.  Depending upon population density, the growth of reproducing greenbacks at higher elevations can be much less.  They have dark, round spots on the sides and tail and two colorful blood-red stripes on each side of the throat under the jaw, hence the name "cutthroat."

Spawning occurs usually from late May to mid-July in higher elevations.  Male cutthroat spawn first at age two, and females mature a year later.  Females build an egg pit in gravel generally three to eight inches deep and one foot in diameter.  A 10-inch female will lay about 800 eggs.  Larger fish of about four to seven pounds will lay up to 6,000 eggs.

Location: Historically, the greenback is the only trout endemic to the headwaters of the South Platte and Arkansas River drainages.  Currently the greenback occurs in 61 sites.  At present, 20 populations (including both historic and restoration populations) are believed to be stable and self-sustaining.

These trout require clear, swift-flowing mountain streams with cover such as overhanging banks and vegetation.  Riffle areas are used for spawning.  Juveniles tend to shelter in shallow backwaters until large enough to fend for themselves in the mainstream.

Threats:  The greenback cutthroat trout is less tolerant of adverse conditions than are other trout such as brown trout or rainbow trout.  The decline of the greenback is attributed to habitat loss, modification, water diversion, water pollution, sedimentation, and the introduction of nonnative fish.  Land and water exploitation, mining, logging, and unregulated fishing all took their toll in reducing the numbers and habitat of endemic trout populations.  However, the major factor in the decline of the greenback cutthroat trout was the introduction of nonnative salmonid species (rainbow trout, brook trout, brown trout, and Yellowstone cutthroat trout), within the South Platte and Arkansas River drainages.  Greenback cutthroat trout readily hybridize with rainbow trout and other subspecies of cutthroat, and are outcompeted by brook and brown trout.  The greenback cutthroat trout has declined so severely that by the early 1900s the species was thought to be extinct.

Conservation Measures:  A cooperative recovery effort between the Colorado Division of Wildlife, U.S. Forest Service, Bureau of Land Management, Rocky Mountain National Park, and the Service was initiated for the greenback.  This recovery team, and university researchers and interested conservation groups, continue to conduct systematic searches for existing populations and suitable reintroduction sites.  The team also has initiated stream improvement projects and a hatchery-based restoration stocking program.  Adult and juvenile greenbacks have been stocked into alpine and montane lakes and streams in the South Platte and Arkansas River basins since the late 1960s.

Recent Actions:   Federal Register Notice - December 14, 2005 - Initiation of 5-Year Review of the Greenback Cutthroat Trout.
 

More information can be found on the Service's ECOS webpage

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