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

newly created habitat, and for zooplankton blooms to occur (see Cooper and Severn
1994b). A minimum duration of inundation that assures time for these two processes to
occur as well as provide time for larvae to feed and grow may be 3-4 weeks.
Within-channel Productivity
Assuming that reproduction and survival of young can be enhanced for Colorado
River populations of razorback sucker and Colorado pikeminnow, carrying capacity of their
environment will become the next factor that limits population size. Providing the
maximum amount of preferred mesohabitats partially addresses this constraint. In addition
to limitations imposed by physical habitat are the limitations of food availability. Habitats
containing abundant food will support more fish than those that do not. To provide more
food for the endangered fish, primary and secondary productivity should be maximized.
Algae and detritus form the base of the riverine food web, directly supporting invertebrates
and some fish. Adult razorback suckers feed on benthic and drifting invertebrates, algae,
and detritus (Bestgen 1990), as do sympatric bluehead suckers Catostomus discobolus and
flannelmouth suckers C. latipinnis (Osmundson 1999). Periphyton and terrestrial inputs of
organic debris are the source of detritus. Most terrestrial organic debris enters the river
during spring when high flows flood the banks and entrain shoreline and bottomland
accumulations of branches and leaf litter. For periphyton production, clean rock surfaces
for attachment sites are required as well as sufficient water clarity to allow light penetration
to the river bed. Invertebrates feed on algae attached to rock surfaces and on detritus both
in the drift and in the interstitial spaces among coarse substrate particles. In addition to
food, invertebrates, like fish, require certain physical habitats: these include rock surfaces
for attachment sites and interstitial spaces for shelter (Waters 1995). Fish that subsist on
algae, detritus and invertebrates in turn provide forage for the piscivorous Colorado
pikeminnow (Osmundson et al. 1998, Osmundson 1999).
To promote within-channel productivity, high spring flows are needed to clean
gravel-cobble substrates (Osmundson et al. 2001). In the absence of flows of sufficient
magnitude fine sediment (silt and sand) accumulates in the river bed filling the spaces
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