7142

• UCREFRP Catalog Number: 7142
• Author: Joseph, T. W., et al.
• Title: Evaluation of the Status, Life History, and Habitat Requirements of Endangered and Threatened Fishes of the Upper Colorado River System.
• USFW Year: 1977.
• USFW - Doc Type: \
• Copyright Material: NO

with strikingly altered temperatures in main channels downstream. In
addition to the downstream impact, the accumulation of sediment in the
reservoirs creates a definite problem regarding their life expectancy.
The native fishes of the Colorado River basin evolved in, and are
ideally suited to, the great flows and high turbidities of the system.
Originally there were no large lakes in the basin; so the native fishes
lack lacustrine adaptations. The appearance of large reservoirs and
associated temperature alterations and reductions in flow and turbidity
represented a severe negative impact to native fishes, while at the same
time giving some introduced species a competitive advantage. To complete
the picture, it is necessary to mention that the sediment load reaching
the Gulf of California has been considerably reduced, resulting in
dramatic changes in marine life and the loss of valuable fishery re-
sources that were formerly dependent on the natural flows of the Colorado
River into the Gulf of California.
Land along the many rivers and tributary streams was extensively
grazed as early as the mid-1800's. Extensive mining and prospecting
with little or no consideration given to environmental effects also
began at this time and have continued to the present. Additional
impacts such as unsound forestry practices, channelization of streams
for road construction and irrigation, water diversion out of the basin,
coupled with the construction of large dams, have caused dramatic
changes in the upper Colorado River basin habitat and have resulted in a
decline in native fish populations. In addition, the introduction of
exotic (non-native) fish species resulted in severe competition with the
endemic species and has become a serious challenge to the continued
survival of the endemic species.
This report is an evaluation of the status, life history, and
habitat requirements of the endangered and threatened fishes of the
upper Colorado River system. It is essential that a picture of total
system be reviewed if one expects to understand or appreciate the
significance of the few species which are the focus of this report.
In discussing the fishes of any river basin, we refer to resident
species as being native, endemic, exotic, and threatened or endangered.
Presently there are 13 native, 7 endemic, at least 27 exotic and 6
threatened or endangered species in the upper Colorado River system.
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