7858

• UCREFRP Catalog Number: 7858
• Author: U.S. Fish and Wildlife Service.
• Title: Draft Greenback Cutthroat Trout Recovery Plan.
• USFW Year: 1995.
• USFW - Doc Type: \
• Copyright Material: NO

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Both populations began to spawn by 1990, with growth averaging only 20 mm for
Sandbeach from September 1989 to September 1991, and 16 mm for Pear from
September 1989 to July 1991.
Tag studies conducted on the Hunters Creek historic population, indicated that
growth for six greenbacks (178-252 mm in length), averaged only 6 g from June
1988 to June 1989 with no measurable change in length. Hunters Creek is 2,896
m in elevation, and has a large (118 kg/ha) stable fish population that is
used for egg collections and is closed to fishing.
Disease and Parasites
The first modern fish pathology work on wild greenbacks was conducted prior to
the transfer of 64 Como Creek greenbacks to the USFWS, Fish Technology Center
in 1977. Fecal material, ovarian fluid and seminal fluid from 78 Como Creek
pre-and post-spawning greenbacks failed to show any viral activity when
inoculated onto susceptible tissue cultures. one moribund greenback collected
from Como Creek on June 22, 1977, had numerous Gyrodactvlus BDp. and
Glossatella snu. covering the body, with Hexamita sDD. and Crevidostomum
farionis within the intestinal tract. Although bacteria were present within
the kidney, they were nonobligate to salmonids. Following the transfer of the
Como Creek greenbacks to the FTC, 11 greenbacks were lost within six months.
Examination of these fish revealed no viral activity, and no clinical
bacterial infection was found although Pseudomonas SDp. and Aeromonas
hvdrovhilia were isolated. Additional non-lethal fish disease samples (fecal,
seminal fluid, ovarian fluid) collected from Hunters Creek, Upper Hutcheson
Lake and South Fork of the Poudre River from 1983 to 1990, found no viral
activity and no obligate fish bacterial infections. Fish diagnostics work was
performed by the USFWS, Fish Disease Control Center, Fort Morgan, Colorado.
Due to the concern over the recent introduction of whirling disease (Mvxobolus
cerebralis) to Colorado, experiments were conducted on the response of
greenbacks to whirling disease at the USFWS, National Fieh Heath Research
Laboratory, in conjunction with the Colorado Division of Wildlife. The
experimental exposure of two to three month old greenbacks to a light exposure
of whirling disease (Mvxobolus cerebralis), indicated that greenbacks produced
7.5 times less M. cerebralis spores than rainbow trout after three months, and
15.6 times less spores than rainbows after six months. However, infected
greenbacks weighed about 45$ less than the infected rainbows, with greenback
mortalities 26$ to 32$, compared to 3 percent to 4 percent for infected
rainbows. These results indicate that although greenbacks showed no overt
signs of infections (skeletal deformities and tail chasing), mortalities for
infected greenbacks were higher than for infected rainbow trout. Mortalities
of unexposed controls were one percent for both species (Markiw 1990).
Seasitivity to nH
Research conducted by Woodward (1991), indicated that the threshold
concentration on greenbacks in the absence of aluminum was pH 5.0. However,
adverse effects were observed at pH 6.0 when 50 ug/1 of aluminum was present.
Greenback alevin and swim-up larva were found to be more sensitive to acidic
pH and elevated aluminum than eggs and embryos. However, growth of greenbacks
was not reduced at low pH, as was observed in Snake River and Yellowstone
cutthroats. Reduced pH ie a concern, because most of the historic greenback
populations and greenback restoration projects are located in alpine habitats
that are susceptible to acid precipitation.
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