9410

• UCREFRP Catalog Number: 9410
• Author: Wydoski, R. S. and E. J. Wick.
• Title: Ecological Value of Floodplain Habitats to Razorback Suckers in the Upper Colorado River Basin.
• USFW Year: 1998.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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captive propagation because these elements are closely interconnected.

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II. FACTORS LIMITING ABUNDANCE OF SOME ENDEMIC FISHES

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The Colorado River and its tributaries flow through 2,317 km (1,440 miles) of
arid land (Carlson and Muth 1989) and serves over 15 million people with water
for various uses including municipal use, irrigated agriculture, industry, and
mining (Utah Water Research Laboratory 1975; Bishop 1971). Bishop emphasizes
that these various uses of water have resulted in conflicts. This river flows
through arid or semi-arid land that is supplied by only about 2.9 hectare-
meters per square kilometer (60 acre-feet of water per square mile) of surface
water annually which is less than any other major river in the United States
(Utah Water Research Laboratory 1975) .

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During the past century, water development in the Upper Colorado River Basin
to serve agricultural, domestic, industrial, and mining activities altered the
natural river ecosystem (Carlson and Muth 1989; Maddux et al. 1982; Miller et
al. 1982; Wydoski 1980; U.S. Fish and Wildlife Service 1990a,b, 1991). Dam
construction and water storage to serve human needs changed the natural
hydrograph through dam operations that released water for irrigated
agriculture (seasonal) or for generating power during peak use periods
(daily). Historic spring peaks in the hydrograph in the Green River (Vanicek
1967) and in the Colorado and Gunnison rivers (McAda and Kaeding 1991) were
decreased and streamflows were increased when the rivers would become
naturally low after the spring runoff. Changes in the hydrograph have, in
turn, altered aquatic habitats, particularly backwater and floodplain habitats
that are considered vital to survival during the early life stages of some
native fishes. Coldwater releases from dams reduced water temperatures of the
natural and historic warmwater aquatic ecosystem. Water depletions from the
system increased through irrigated agriculture. Nonnative fish species were
introduced in the rivers and manmade reservoirs, both intentionally and
accidentally, that changed the species composition of the fish community.
While native fishes in the Colorado River system have apparently been on the
decline since the 1800's (Miller 1961), they declined more rapidly in the
Upper Basin since the 1960's from habitat alterations of the river and
colonization by nonnative fishes (Miller et al. 1982; Carlson and Muth 1989) .

Although native Americans along the Colorado River constructed canals to
divert water for irrigating crops around 1000 A.D. (Graf 1985; Powell 1961),
irrigated agriculture via small diversions was not renewed until the middle to
late 1800's (Fradkin 1983) and did not become extensive until the 1920's (Hunt
and Huser 1988). Broad river valleys in the Upper Basin were colonized by
people who began to construct levees for flood control (Fradkin 1983). As
dams were constructed in the Upper Colorado River Basin -- particularly after
the completion of Flaming Gorge Dam on the Green River in 1963 and the Wayne
Aspinall Storage Unit on the Gunnison River in 1978 (Carlson and Muth 1989),
the historic peak spring streamflows decreased that allowed people to
construct levees that more easily controlled overbank flooding. Marshes and
floodplain habitats disappeared as levees were built to control the river from
regularly flooding agricultural lands. The connectivity of the river with
floodplains was severely reduced and dramatically disrupted the natural
function of the river/floodplain ecosystem that depended upon floodplains for
productivity. Many large, highly productive, floodplain areas in broad,
alluvial valleys along the Upper Colorado River Basin rivers are no longer
connected with the river.

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The geologic isolation of the Colorado River and its
watersheds resulted in a fish fauna where 64% of the
endemic to the Colorado River system (Miller 1961) .
unique, the fish fauna of the Colorado River Basin is
compared with other North American river basins. The
Colorado River system were adapted to dynamic natural

tributaries from other
native species are
In addition to being
very depauperate when
native fishes of the
aquatic conditions that

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