8272

• UCREFRP Catalog Number: 8272
• Author: Wydoski, R. S. and E. J. Wick.
• Title: Flooding and Aquatic Ecosytems.
• USFW Year: 2000.
• USFW - Doc Type: 238-268, Chapter 9
• Copyright Material: YES

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252

Flooding and Aquatic Ecosystems

Figure 9.2. Instantaneous peak
discharge in the Green River,
upper Colorado River basin, just
below Flaming Gorge Dam at
Greendale, Utah. (U.S.
Geological Survey data: pre-dam
period 1951-62; post-dam period
1963-95)

20

18 ...._._.__.....n_m........

16 .._00.......
W
~ 14 m."nn"",
~ 12 ...-....-..-
~ 10 .......-.
-I
U. 8 ----
::s::::
i1i 6 ..--...-
a... 4 ......_

2.--
o

1951-1995

YEAR

1995

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I'

r

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(Ptychocheilus ludus), and humpback chub (Gila cypha) are now listed as
endangered under the Endangered Species Act (16 U.S.C. [United States
Congress] 1531-1544). Other native fish species (e.g., flanneImouth sucker,
Catostomus latipinnis; bIuehead sucker, Catostomus discobolus) are still
able to maintain self-sustaining populations, despite the drastically altered
condition of the historic river environment. In less-altered river reaches,
native fish species still dominate the fish fauna (Anderson, 1997; Burdick,
1995), whereas, in more altered reaches, nonnative fish species are more
abundant. This suggests that nonnative species are b~tter suited to the
altered ecosystem and can quickly dominate and alter an established native
fish community (Li and Moyle, 1993; Meffe, 1985; Stanford et aI., 1996).

Importance of Floodplain Habitats to Recovery of Endangered
Colorado River Fishes

Although the endangered Colorado River fishes are often considered river-
ine species, they evolved in a system where lacustrine habitats were part of
the natural system. For example, Hamblin (1990) described the formation
of natural dams from lava flows in the Grand Canyon. In the Upper Basin,
lakes and other lowland areas were regularly flooded. Historically, these
off-channel habitats were common in the Upper Basin.before dams were
constructed and levees built to control the rivers from flooding agricultural
lands. Therefore, the endemic Colorado River fishes evolved in a dynamic
river system of lotic and Ientic aquatic habitats.
The declining numbers of the endangered Colorado River fishes are at-
tributed to the lack of recruitment. For example, the long-lived adult ra-
zorback sucker can spawn successfullY and produce larvae during some
years, but high mortality during the early life stages limits recruitment. In
an earlier section, it was emphasized that larval fish must initiate feeding
during the critical period after swimup or they will reach a point of irre-
versible starvation that results in high mortality (Miller et aI., 1988). The