7996

• UCREFRP Catalog Number: 7996
• Author: Wydoski, R. S. and E. D. Wick.
• Title: Ecological Value of Flooded Bottomland Habitats to Endangered Fishes in the Upper Colorado River Basin.
• USFW Year: 1996.
• USFW - Doc Type: \
• Copyright Material: NO

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upstream, and particularly in downstream reaches of the main channels, where
razorback sucker larvae drift as the flooded areas from high streamflows recede.
If adequate control of nonnative fishes cannot be achieved, human intervention
may be required to rear razorback suckers in predator-free off-channel habitats
so that their populations can be maintained through augmentation stocking.

II. INTRODUCTION

Many riverine fish species exhibit seasonal movements into inundated floodplain
habitats for spawning, rearing, and foraging (Finger and Stewart 1987; Lambou
1963; Ross and Baker 1983). Seasonal flooding of bottomlands are important in
sustaining various fish species that are characteristic of river channels (Baker
and Killgore 1994). Baker and Killgore emphasize that the pattern of flooding
appears to be of paramount importance in structuring wetland fish communities and
that fish may spread over large areas of the floodplain during high streamflows.
The 1 atera 1 movement of fi sh on the fl oodp 1 a in decreases exponent i all y with
reductions in streamflow (Kwak 1988) and recruitment may not occur if water
levels remain low (Starrett 1951). A higher riverine fish standing stock was
associated with high spring floods in the Atchafalaya floodplain in the lower
Mississippi River whereas the standing stock was lower following low spring
floods (Bryan and Sabins 1979). Osmundson and Kaeding (1989a, 1989b) and Tyus
and Karp (1989) suggested that floodplain habitats were historically used as
nursery sites by native fish species in the Upper Colorado River Basin. During
high spring runoff, adult razorback suckers congregate in large eddies at the
mouths of ri vers, flooded bottoml ands, and off-channel ponds that have a
connection to the rivers (Tyus and Karp 1990). Ripe female razorback suckers
were collected from a large embayment on the Walter Walker Wildlife Area off the
Colorado River near Grand Junction, Colorado, indicating that spawning by this
species is not restricted to the riverine environment (McAda and Wydoski 1980).
Ripe razorback suckers were also collected at the outlet to Clifton Ponds along
the Colorado River near Cl ifton, Colorado (E. Wick, 1994, Personal
Communication). Several razorback suckers that became trapped in a gravel pit
known as Etter Pond along the Colorado River near DeBeque, Colorado, during the
high streamflows of 1983 and 1984 spawned successfully (F. Pfeifer, 1994,
Personal Communication) and captive razorback suckers spawned naturally and
successfully in earthen ponds at the Dexter National Fish Hatchery in New Mexico
(B. Jensen, 1994, Personal Communication).

It is hypothesized by some biologists in the Upper Colorado River Basin that the
food requirements of larval razorback suckers (Xvrauchen texanus), during the
critical period (Papilious and Minckley 1990) was met by the high productivity
of floodplain habitats in broad valleys of the Upper Colorado River Basin (Mabey
and Schiozawa 1993; Cooper and Severn 1994 a,b,c,d,e). The major reason for the
dec 1 i ne of endangered Colorado Ri ver fi shes is correlated with the 1 ack of
successful recruitment to maintain self-sustaining populations (U.S. Fish and
Wildlife Service 1987, 1990a, 1990b, 1991). In the Lower Colorado River Basin,
studies have demonstrated that predation by non-native fishes and the lack of
food limit the survival of larval and juvenile razorback suckers (Marsh and
Langhorst 1988; Papoulias and Minckley 1990, Papoulias and Minckley 1992). The

same factors appear to limit recruitment of the endangered Colorado River fishes
in the upper basin (Miller et al. 1982; Maddux et al. 1993).

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