GENERAL31841

• Permit No: M1999002
• IBM Index Class Name: General Documents
• Doc Date: 7/22/1999
• Doc Name: FINAL ENVIRONMENTAL IMPACT STATEMENT VOLUME 2 APPENDIX L
• Media Type: D
• Archive: No

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in these downstream reaches and maturing Colorado pikeminnow begin to
move up and down the river seeking better feeding grounds.
Eventually, adult Colorado pikeminnow discover the abundant supplies
of native fish, primarily bluehead and flannelmouth sucker, in the
upper river including the 15-mile reach and remain in these upper
reaches for the remainder of their lives. Forage fish are generally
more abundant in these upper reaches because food for these fishes,
algae and aquatic insects, is more abundant (Lamarra 1999). Algae,
phytoplankton (free-floating algae) and periphyton (algae that grows
on rock surfaces), is more abundant because the higher water clarity
allows deeper light penetration necessary for its growth. Aquatic
insects are more abundant because the swifter currents resulting from
generally higher gradients flush gravel and cobble substrates
providing silt-free crevices required by many aquatic insects.
Because of the increasing abundance of forage fish as one moves up
river, the average size of Colorado pikeminnow increases as one moves
up river with the 15-mile reach containing the greatest proportion of
large adult Colorado pikeminnow.
The 15-mile reach appears to provide the optimum balance between
temperature and food abundance for adult Colorado pikeminnow
(OSmundson et al. 1998, Osmundson 1999).
Razorback suckers also are found in the 15-mile reach and use the
reach as a spawning area (OSmundaon and Kaeding 1989, 1991). The
complete life cycle of the razorback sucker, in terms of its entire
river habitat use pattern, is largely unknown but may be similar to
that of Colorado pikeminnow because adults are generally concentrated
in upstream reaches of the Colorado and Green Rivers and larvae from
spawning sites in the upper Green River have been found to drift long
distances down river. Other evidence suggests that bottomlands in
both upstream and downstream reaches historically served as nursery
areas for larvae when these habitats flooded during the historically
higher spring runoff period.
The 15-mile reach also is important for the survival and recovery of
Colorado pikeminnow and razorback sucker because it provides a refuge
for the Colorado River Basin populations should a catastrophic event
such as an oil spill or chemical spill affect the Gunnison River or
the Colorado River below the Gunnison River confluence.
In summary, the 15-mile reach is important for several reasons:
1. The 15-mile reach provides valuable spawning habitat for
Colorado pikeminnow and razorback sucker.
2. The 15-mile reach provides an optimum balance between
temperature and food availability for adult Colorado pikeminnow in
the Colorado River.