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

INTRODUCTION
This study represents an evaluation of the present state of knowl-
edge concerning the aquatic flora and fauna of the upper Colorado River
basin. Relative detail of treatment varies according to the quantity
and quality of available information, and all the information that would
be desirable is not available for any particular subject area. Emphasis
of the report is placed on the endangered and threatened fishes, their
status, habitat requirements, and overall ecology.
The upper Colorado basin comprises an area of approximately 109,580
square miles, encompassing all of the Colorado River drainage above
Lee's Ferry, Arizona. Streams in this basin begin as clear, cold,
first-order streams draining the mountains of Wyoming, Utah, and Colo-
rado. They join to form larger streams that flow into the desert areas
of southeastern Utah, western Colorado, and northern Arizona and New
Mexico. In these regions they are large third- to fourth-order rivers
that flow through some of the world's most spectacular canyons.
The river system of the upper basin is geologically old and has
taken millions of years to carve its way through thousands of feet of
rock. Headwater streams typically flow over igneous and metamorphic
rocks. Sedimentary rocks predominate in and below areas of second- or
third-order streams and in some headwater regions. The aquatic fauna of
this system are also very old, for they evolved in accord with the
geological changes that took place in the basin. The indigenous native
fish species of the system have been-isolated from other drainages
nearly as long as the present Colorado drainage has existed, and have
largely evolved independently of fishes of other regions. This has
resulted in a high degree of endemism in Colorado River fish species.
Other aquatic flora and fauna have terrestrial dispersion mechanisms
which have prevented the development of a high degree of endemism.
The Colorado River basin has historically been a river of great
fluctuations in flow, turbidities, and temperature. However, man-
induced changes have dramatically influenced these regimes. Man's
activities within the basin have increased sediment load and total
dissolved solids (TDS). Man-made reservoirs in turn precipitate out
this load, resulting in drastically reduced turbidities and flow, along
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