9432 ‎(2)‎

• UCREFRP Catalog Number: 9432
• Author: Modde, T. and M. Fuller.
• Title: Feasibility of Channel Catfish Reduction in the Lower Yampa River.
• USFW Year: 2002.
• USFW - Doc Type: Vernal.
• Copyright Material: NO

seek new food sources (i. e., sub-adult pikeminnow made upstream
movements due to an inadequate supply of food in the lower reach), 2)
an innate physiological mechanism to move upstream, and 3) the urge to
spawn.
The population abundance of sub-adult and adult Colorado pikeminnow in
the Gunnison River upstream of the Redlands Diversion Dam was
estimated at N=13 (95% CI=9-31)(Appendix; Table L.1.). Between 1998
and 2000, the population abundance in the Upper Colorado (Green River
confluence to Price-Stubb Dam) was estimated at about 664 fish
(Osmundson 2000). The number of fish that used the Redlands fishway
between 1996 and 2000 (51) was about 390% of the estimated population
abundance in the Gunnison River and about 8% of the current estimated
population abundance of pikeminnow in the Upper Colorado River.
Several pikeminnow that passed upstream of Redlands Dam later fell
back over the dam. The fallback rate for pikeminnow was estimated at
31% (3 out of every 10 pikeminnow). Thirteen (25%) of the 51 Colorado
pikeminnow that passed through the passageway eventually fell back
over the Redlands Dam. In addition, five of the eight radio-tagged
pikeminnow that were released upstream of the dam subsequently fell
back over the dam. The low number (2) of pikeminnow that were
recaptured upstream of the dam after they had passed through the
fishway suggests that the fallback rate may be even higher.
Therefore, while the fishway provides the opportunity for pikeminnow
to pass upstream, many may not remain upstream and become long-term
residents because of their desire to return downstream to the Colorado
River. Other pikeminnow, though, that pass through the fishway may
remain and establish longer residency, similar to other pikeminnow
that have remained for several years upstream after being translocated
from the Lower Gunnison River.
2. The size of the pikeminnow population upstream of the dam will
probably be expected to increase over the years as more pikeminnow
pass through the fishway. The increase is expected to be only gradual
because the fishway use rate appears to be slightly higher than the
fallback rate.
3. Razorback sucker have yet to use the passageway.
4. Pikeminnow usage of the passageway to date has occurred almost
exclusively during the post-runoff months of July and August (98% or
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