6012

• UCREFRP Catalog Number: 6012
• Author: Miller, W. H., D. L. Archer, H. M. Tyus and K. C. Harper.
• Title: Colorado River Fishery Project
• USFW Year: 1982.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

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stage where the species was experiencing the mast damaging problem, 3)
What flow condition or flow related conditian was impacting the critical
life stage, 4) What changes in flows had occurred at the critical areas
from past pre-development times to the present and 5) What flows are
needed and at what time at the critical areas to assure survival of the
target species?
The above determinations were made based upon findings from the
field, laboratory, hatchery and contracted studies under this project.
Analysis of present, past and needed flow levels were made using
the USGS flow records, 1960-1980, and the CRSS model developed by BR
which predicted virgin flow conditions and developed flow conditions
{see Appendix B for details of flow partitioning). Weighted Useable
Area (WUA) for squawfish YOY and humpback adults were related to flow at
key areas to assist in analysis of present, past and future flow needs
of the target species.
What we have determined from this study is that for Colorado
squawfish and humpback chub there are a number of critical areas in the
Upper Colorado River system (Table 2). For Colorado squawfish the
critical life stage is the actual spawning area including egg survival,
and YOY rearing areas. For humpback chub the critical life stage is the
actual spawning period. We could not identify what the critical life
stage of the bonytail chub was, but believe it may be more than one
stage. The razorback sucker was experiencing recruitment problems with
survival of larvae believed to be the primary area of impact.
In analyzing the needs and problems of Colorado squawfish, we had
to consider large sections of river and deal with a highly mobil fish
species. In contrast, when we evaluated humpback chub needs, we only
had to consider small isolated habitats where all Life stages were
occurring. Razorback suckers also seemed to be somewhat conf fined and
only a few areas are probably important for su rvival. Not enough information
has been acquired on the bonytail chub to determine how broad or narrow
the area of consideration should be for this species. Right now we are
proceeding with a hatchery propagation program to prevent the species
from becoming extinct.
Basic flow recommendations are made for average monthly flows and
are presented in Table 2. Minimum instantaneous flows should at no time
drop below the minimum recommended for the designated period of time and
the overall monthly average 'should at least fall in the range presented.
For humpback chub in Black Rocks and Westwater Canyons, an evaluation
of hybridization needs to be conducted. By WUA and 1981 field data, we
can show that spawning took place and adult habitat is available at
2,000-3,000 cfs. There is a possible need for spawning separation of
roundtail and humpback chub and with low flows in the spring this
hybridization problem may be aggravated. Temperature is believed to be
a possible factor in separation of the spawning time of roundtail and
humpback chub and when the river warms to Quickly in the spring spawning