9413

• UCREFRP Catalog Number: 9413
• Author: Osmundson, D. B.
• Title: Flow Regimes for Restoration and Maintenance of Sufficient Habitat to Recover Endangered Razorback Sucker and Colorado Pikeminnow in the Upper Colorado River.
• USFW Year: 2001.
• USFW - Doc Type: Grand Junction.
• Copyright Material: NO

Trammel and Chart (1999b) concluded that scour-channel backwaters comprised the
majority of backwater area and are preferred by YOY Colorado pikeminnow. The authors
suggested this preference may be due to the greater depth and persistence of this backwater
type compared to the more numerous, smaller backwaters created by migrating sand waves.
High flows do not increase backwater number or area in the year they occur, but they are
critical for the continued persistence of backwaters of sufficient size and quality. Periodic
large floods are necessary to rebuild bar topography and channel relief. Moderate peaks in
years following large floods rearrange the deposits which later become mid-channel bars at
base flow (Rakowski and Schmidt 1997). Because bar topography changes annually, there
is no single discharge that maximizes backwater number or area during base flows; the base
flow that maximizes backwater availability in fall depends on antecedent flows. However,
McAda (2001) reported that backwater number and area in the lower Colorado River
declines when base flows exceed 4,000 cfs.
It is difficult to arrive at specific base flows in the Palisade-to-Rifle reach that will
provide optimum flows for nursery habitat downstream near Moab. Clearly, very high
spring flows are periodically needed to rebuild eroded sand bars in the lower river and high
base flows should be avoided so that flows near Moab do not exceed 4,000 cfs.
Flooded Bottomlands for Razorback Sucker
Spring flows high enough to inundate bottomlands adjacent to the river channel are
periodically needed to benefit razorback sucker reproduction and survival of young
(Wydoski and Wick 1998). Larval razorback suckers initially feed on diatoms, rotifers,
algae, and detritus (Bestgen 1990, Papoulias and Minckley 1992); soon afterward, they
select larger zooplankton, primarily cladocerans and copepods (Marsh and Langhorst
1988). To survive the critical first phase of life (the transition from endogenous to
exogenous nutrition), razorback sucker larvae require 30-60 food organisms per day
(Papoulias and Minckley 1992). Such zooplankton densities were found in floodplain
habitats of the Green River, rarely found in backwaters, and never found in the main channel
of upper basin rivers (Cooper and Severn 1994a, 1994b, 1994c, 1994d, Grabowski and
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