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

possible, Colorado pikeminnow may prevent this by selecting foraging sites with high rates
of energy return (food) for energy expended (foraging activity). Good conditions for
growth include suitable temperatures in combination with relatively high availability of
forage fish. The benefits of high forage density may be enhanced by a combination of
physical habitats and river features that facilitate efficient foraging, thereby promoting fish
growth and allowing more Colorado pikeminnow to occupy a given reach of river (i.e.,
forage availability as opposed to forage abundance). Supportive evidence for this includes:
(1) the dispersal of adults in the Colorado River to reaches upstream of Westwater Canyon
where native forage is most abundant (Osmundson et al. 1998), (2) the relatively high
density of adult Colorado pikeminnow in the 18-mile reach (downstream from the Gunnison
River confluence) where total area of specialized habitats (non-run habitats) is highest
(Osmundson et al. 2001), (3) the preference for river segments that contain a complex of
habitat types, as opposed to simple, single-thread, run-dominated segments (Osmundson
and Kaeding 1991), and (4) the preference for certain habitat types, such as pools, eddies,
etc. (previously discussed). Because habitat and food are so tightly interrelated, it is
difficult to separate selection for food from selection for habitats that allow efficient
foraging (Magnuson et al. 1979). Nevertheless, to promote growth of individual Colorado
pikeminnow and maximize carrying capacity of the river, abundant forage and a diversity of
habitats are important.
SEASONAL PARTITIONING OF THE YEAR
To provide favorable habitat for the endangered fish, flows must change in a
seasonal manner corresponding to season-specific habitat needs. Osmundson et al. (1995)
blocked months into seasons by analyzing habitat-use patterns of each species and
identifying changes in behavior that marked the beginning or end of seasons. Though
coexisting under the same conditions, the different behavioral patterns of razorback sucker
and Colorado pikeminnow result in a year that is partitioned somewhat differently (Fig. 3).
However, because only one flow regime can be recommended for the river, a third seasonal
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