Greenback cutthroat
trout (Oncorhynchus clarki stomias)
Historic Range:
Similar in appearance to the Colorado River cutthroat trout, the Greenback
cutthroat trout is intensely colored with large and pronounced spots
concentrated towards the rear of the caudal peduncle (the narrow region
forward of the tail). Their backs are not particularly "green." Greenbacks
are native to the Arkansas and South Platte River basins in Colorado's
Front Range mountains and a few South Platte tributaries in extreme
southeastern Wyoming. Greenback likely inhabited most coolwater habitats
from the foothills upstream to high altitude lakes and streams. Scientists
estimate the subspecies occupied up to 3890 miles of habitat in the
Arkansas River basin and 4312 miles in the Platte River basin.
Habitat requirements:
Like most members of the trout family, greenback cutthroat trout require
clear, cold water, naturally fluctuating flows, low levels of fine sediment
in channel bottoms, well-distributed pools, stable stream banks and
abundant stream cover.
Current population status:
Despite a 25-year formal Endangered Species Act-mandated recovery program,
these trout are extremely imperiled. Prior to September 2001, the Recovery
Team claimed to have 17 populations that were secure, stable and genetically
pure. Conservation populations with high genetic purity are estimated
to occupy less than one percent of this trout's historic range. As documented
in the Western Native Trout Campaign's report, Imperiled Western Trout
and the Importance of Roadless Areas, about 75% of the remaining populations
are associated with unroaded areas. Tragically, biologists recently
discovered that several of the Greenback populations were genetically
contaminated by as much as 33 percent with Yellowstone cutthroat trout.
Since those historic populations were used to create brood stocks for
restoration populations, the entire recovery program will need to be
retested for genetics. Only pure greenback cutthroat trout can be counted
as recovery populations under the recovery plan.
Threats to continued persistence:
Greenback cutthroat trout populations were decimated by the late 1800
by mining pollution, stream dewatering for agriculture, and over harvest.
The introduction of non-native trout species drove remaining populations
into the highest reaches of alpine stream systems, often to marginal
habitat. The average stream length for recovery populations is 2.5 miles
with population averages of 200 adults. Except for Rocky Mountain National
Park, the habitats for recovery populations are widely spaced, with
little opportunity for genetic exchange or refuge. Scientists have recently
cited the small population sizes and small isolated habitats as making
these populations vulnerable to droughts, fires, floods and other environmental
events. Genetic health concerns are also an issue with populations this
small. Displacement, competition, or predation by nonnative brook trout
(and possibly other species) continues to be the current major threat
to remaining greenback populations, with sedimentation from grazing
and roads being the current habitat threat. The problems with the genetic
purity of brood stocks are also a grave threat.
Listing status as of 6/15/02:
The greenback cutthroat trout was listed as endangered under the ESA
in 1973, and a recovery plan was initiated in 1978. At that time the
subspecies was downlisted to threatened in order to permit some sportfishing
and gain public support. The Recovery Plan was most recently revised
in 1998. The Western Native trout Campaign and Trout Unlimited have
asked that the recovery plan be revised again in 2003 to reflect the
best available science on minimum population numbers, size and habitat
to assure long-term persistence.
