8192

• UCREFRP Catalog Number: 8192
• Author: Wydoski, D.
• Title: Review of Report Regarding Evaluation of Gravel-Pit Ponds.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

INTRODUCTION

General

Historically. upper Colorado River basin floodpl ains were inundated
annually by flows during spring runoff. but today floodplains are not regularly
connected to the river because of channelization by levees. dikes. or rip-rap
near population centers and in agricultural areas. Introduced salt cedar or
tamarisk (Tamarix spp.) has become establ ished along the shorel ine of major
rivers resulting in sediment deposition and stabilized banks that further reduce
the connectivity of the river with historic flooded bottomlands (Graf 1978). The
periodicity of out.of.channel flooding in the upper Colorado River has
dramatically decreased following the onset of transmountain water diversions.
irrigation diversions, and the construction of mainstem dams (Osmundson and
Kaeding 1991). The construction of dikes coupled with the reduction of high
spring flows has altered the natural hydrograph and ei ther reduced or e 1 i mi nated
regular flooding of bottomlands. It is believed that flooded bottomlands may
have served as nursery areas for the razorback suckerl (McAda 1977: Osmundson and
Kaedi ng 1991). In addi t ion, Osmundson and Kaedi ng suggested that oxbow 1 akes and
flooded pastures in the Grand Valley near Grand Junction. Colorado, were
historically the primary spawning habitats of the razorback sucker. They also
suggested that low velocity. off-channel habitats were used by adult Colorado
squawfish during high streamflows.

Numerous studies (Grawboski and Hiebert 1989; Tyus and Karp 1989; Wydoski
and Wick 1994) have suggested the importance of seasonal flooding to river
product i vi ty . Other studi es have suggested that flooded bottom 1 ands were
important to adult razorback sucker for feeding prior to and after spawning and
for the rearing of their young (Tyus and Karp 1989). Adult fish may have used
these off. channel habitats for "velocity shelters" to escape the high water
velocities from the spring runoff.

The turbid rivers in the upper basin are not very productive for
zooplankton that are essential for survival during the early life s~ages of the
razorback sucker. When compared to the riverine environment! and river
backwaters, inundated bottomlands produce the highest densities of [zooplankton
(Grabowski and Hiebert 1989: Mabey and Shiozawa 1993). Although pnedation has
been documented to be a limiting factor in survival of larval razo~back sucker
in the lower basin (Minckley et al. 1991). starvation may also li~it survival
(Marsh and Langhorst 1988; Papoul ias and Minckley 1990). It is hypot~esized that
the loss of these productive flooded bottomland habitats appears tojbe limiting
the recruitment of the razorback sucker in the upper Colorado River b~sin because
of the lack of the right sizes of food organisms at the right time and in
sufficient quantity (Wydoski and Wick 1994).

Flooded bottoml and habi tats occur in broad vall eys along l!ow grad; ent
stream reaches. Bottomlands are off. or out-of-channel habitats that include

1 Scientific names and two-letter codes of all fishes mentioned in this report are give~ in Appendix A:
Table A.I. Only common names for these fishes are used in the text. '