7354

• UCREFRP Catalog Number: 7354
• Author: Wydoski, R. S.
• Title: Biological Review of Endangered or Imperiled Fish in the Upper Colorado River Basin.
• USFW Year: 1985.
• USFW - Doc Type: Washington, D. C.
• Copyright Material: NO

fish is very high based upon information on the abundance and
distribution of their young. A limiting factor for survival
of the young rare fish may be the quantity (abundance) and
quality (size) of potential food organisms that are available
and can be eaten by the various early stages. Finally, there
is still confusion on the taxonomy of the Gila complex in the
UCRB that should be resolved to determine the significance of
forms with overlapping characteristics.
Consideration - The basic consideration for the rare
0 orado ever fish is that few fish appear to be recruited
into the populations. Therefore, information on the life
history is needed so that the stocks can be managed to
prevent their extinction. The biology and habitat
requirements are of particular importance for spawning and
early life stages. In addition, information on the basic
life history and movement of these species is needed to
understand what factors might be limiting their numbers.
Basic life history information can be obtained from fish that
are collected in doing other studies such as movement that
would be best determined through the use of radiotelemetry.
Habitat utilization can be determined by making measurements
of the habitat where the fish are collected.
o Study the responses of rare fish and survival of young through experimental
releases from Flaming Gorge Dam as a potential management tool to enhance
wild stocks.
Rationale - Suitable water temperatures that are closely
associated ed with streamflow are important for spawning,
growth, and survival of the rare Colorado River fish.
Flaming Gorge Dam can provide a natural outdoor laboratory to
study the responses of rare fish to controlled water releases
and to determine if experimental releases can be used as a
management tool to increase survival of young that would
enhance wild stocks.
Considerations - The abundance and growth expressed as the
mean total length of larval Colorado squawfish in the Green
River during August and September have been directly
correlated with discharge. Correlation coefficients of
-0.894 for abundance-discharge and -0.873 for growth-
discharge have demonstrated that high discharge in the Green.
River at that time adversely affects young Colorado
squawfish. Experimental releases from Flaming Gorge Dam
could be used at critical times in the early life of the
squawfish to determine if controlled releases would be
beneficial to the species.
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