7065

• UCREFRP Catalog Number: 7065
• Author: Behnke, R. J. and D. E. Benson.
• Title: Endangered and Threatened Fishes of the Upper Colorado River Basin.
• USFW Year: 1983.
• USFW - Doc Type: Bulletin 503A,
• Copyright Material: NO

The environmental alterations resulting from
large dams converted a turbulent river of great ex-
tremes of flow, temperature, and turbidity into a
series of great ponds from which cold, clear water
is released below the dams at a relatively constant
flow and temperature, year round. The native fishes
were ill-adapted for these new conditions and were
placed at a great disadvantage in competition with
the non-native fishes.
The large dams and reservoirs, however, cannot
be wholly blamed for the present rare status of the
native fishes. Man's influence on the land and the
watersheds from logging, livestock grazing, agricul-
ture, and irrigation removed the natural vegetation,
caused accelerated erosion, and greatly increased the
amplitudes of flood peaks. These watershed altera-
tions, in turn, caused great changes in the size and
shape of river channels and reduced the amount of
lagoon or quiet backwater habitat so important as
nursery areas for the native fishes. Thus, squaw-
fish and several other native fish species disappeared
from the Gila River of Arizona and were replaced by
non-native fishes. Three major interacting factors
explain the present status of the native fishes of
the Colorado River basin: 1) Reservoirs; 2) land
and water use; and 3) the environmental changes
resulting from 1 and 2 which give a competitive
advantage to non-native fishes.
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