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

Osmundson, unpublished data). During this same period, the whole river
population increased from.465 to 664 (43%). One reason for this increase in
population could be that a strong year-class of pikeminnow was produced in the
early 1990's. There are other possible reasons for this increase, but they are
also only speculative. If food sources and supply were inadequate in the lower
reach, and the number of sub-adult and adult pikeminnow had exceeded the carrying
capacity for the reach during this period, then a greater number of sub-adult
pikeminnow may have moved upstream to the upper reach during the mid-1990's in
search of new food sources. Or, possibly an innate physiological mechanism
compelled sub-adult pikeminnow to disperse upstream (e. g., seek new home range).
If this is so, this may explain why pikeminnow river net catch rate in the upper
reach peaked in 1998 and why the numbers of pikeminnow that used the Redlands
passageway were also the highest in both 1997 and 1998. If this is true,
conversely one might suspect that the number of pi kemi nnow that moved through the
passageway during 1997 and 1998 was aberrantly high compared to the number of
pikeminnow that passed through during 1999 and 2000.
Fallback
Some of the native fish that had passed through the passageway fell back
over the Redlands Dam following their release upstream of the dam. Evidence for
this was provided by marking three of the non-endangered native species
(flannelmouth sucker, bluehead sucker, and roundtail chub) and nonnative fishes
that were captured in the fish trap in 1996. Marked native and nonnative fish
that had reascended the passageway and were later recaptured in the fish trap
provided data on numbers of fish that did fall back over the dam and that fish
could survive such an event. Colorado pikeminnow captured in the fish trap that
were either PIT- or radio-tagged and subsequently recaptured either in the fish
trap or in reaches of the Lower Gunnison and Upper Colorado rivers downstream of
the diversion dam provided additional evidence that fish had successfully
negotiated the fall over the diversion dam.
In 1996, 7,187 flannelmouth sucker, bluehead sucker, and roundtail chub
found in the fish trap were marked. Of these, 143 (2.0%) reascended the
passageway and were recaptured in the fish trap. Of 370 nonnative fishes marked,
34 (9.2X) reascended the passageway and were again found in the fish trap.
Nonnative fish recaptured included white sucker (31), green sunfish (2), and carp
(1). Of 100 hybrid suckers marked, 5 (5%) were recaptured in the fish trap.
As described earlier, seven different PIT-tagged Colorado pikeminnow
reascended the passageway and were recaptured in the fish trap. Six other
pikeminnow that ascended the fish passageway and were released immediately
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