7724

• UCREFRP Catalog Number: 7724
• Author: Snyder, D. E.
• Title: Contributions to a Guide to the Cypriniform Fish Larvae of the Upper Colorado River System in Colorado.
• USFW Year: 1981.
• USFW - Doc Type: \
• Copyright Material: NO

mighty Colorado River System no longer flows, as
it had for eons, into the Gulf of California.
Man's reservoirs, diversions, and agricultural
practices (including overgrazing and removal of
natural riparian vegetation) have resulted in
considerable reduction of habitat suitable for the
long-term survival of many native species. This
loss of habitat may be dramatically accelerated in
the near future as streams are further modified with
still more dams and reservoirs for water storage and
hydroelectric production, and with massive water
withdrawals to support the exploitation of vast coal
and oil shale energy resources within the Upper
Colorado River System.

Only a little over a century ago, the fish
fauna of the Upper Colorado River System consisted
of only 13 species; all but four of these native
fishes are cypriniforms (Table 1). Due to the long
and effective isolation of the Colorado River System,
SlX of these species are unique forms endemic to
only this river system, i ,e., they are found nowher~
else in the world. In addition two subspecific
forms of more wide-spread species are also recog-
ni~ed as being endemic to the upper portion of the
svstem, but one is not represented in the state of
Colorado (Rhinichthys oscuZus thermaZis is known
only in the outflow ofkendall Warm Springs in
Wyomi ng) .

Compared with the fish communities in river
systems to the east, the original fish communities
in the rivers of western Colorado, in fact, the

RIVER SYSTEM AND ITS FISHES 3

entire Colorado River System, were indeed depauper-
ate with respect to the number of species represented.
Without much consideration of long-term impacts.
man set about to quiCkly rectify this .rIa"? of natllr'e
by the introduction of other fishes, usually with
the intention of establishing a fishery of ~xmiZ:~p
game fishes. In recent years, at least 46 species,
33 of which are non-native and exotic, have been
reported in Colorado's portion of the river system.

The modification and loss of suitable habitat
as well as competition with non-native and exotic
fishes has resulted in a general decline in the
populations of most, perhaps all, native fishes.
Of the seven endemic fishes present or formerly
found in Colorado's portion of the system, five
are considered in danger of extinction: the
Colorado squawfish (Ptychocheilus lucius, largest
cyprinid in North America), the bony tail chub
(GiZa eZegans), the humpback chub (Gila cypha) ,
the razorback sucker (Xyrauchen texanus), and the
Colorado cutthroat trout (SaZmo clarki pleuriticus)
(Deacon et a1. 1979). Behnke and Benson (1980),
as well as Joseph et al. (1977), summarized much
of what is known about the habitat, behavior,
distribution, and causes for decline of the
threatened or endangered species in the Upper
Colorado River System. The status of Cottus
beldingi and Catostomus platyrhynchus in Colorado
is still in need of study. Considering their
apparent distribution and abundance, they should
probably be considered for addition to the state
list of threatened or endangered species.