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

Westwater Canyon to Price-Stubb Dam) reaches of the Colorado River was conducted
in 1998, 1999, and 2000 (personal communication, Doug Osmundson). The length
frequency of Colorado pikeminnow captured with trammel nets from the upper reach
during each of these three years was compared to the length frequency of
pikeminnow captured in the Redlands fish trap during the same years (Appendix;
Figure E.2.). There were only two years, 1997 and 1998, when there were
sufficient pikeminnow that used the passageway that a histogram could be
generated to provide comparison. Because population sampling for pikeminnow was
not conducted during 1996 or 1997, only one year, 1998, is available when
significant numbers of pikeminnow were captured both in the Redlands fish trap
and from river catches during the population study to allow a direct, within year
length-frequency comparison between the two.
This comparison showed the mean size of pikeminnow that was collected in
the fish trap of the Redlands passageway in each of the five years (516-566 mm)
was about 75-100 mm smaller than pikeminnow captured in both the Colorado and
Lower Gunnison River population downstream of Redlands Dam during 1998-2000 (607-
626 mm; personal communication, Doug Osmundson). The mean size of pikeminnow
captured by Osmundson steadily increased during his study: 1998 (607 mm), 1999
(612 mm), and 2000 (626 mm).
During this study, telemetry data indicated that six of the radio-tagged
pikeminnow (mean=812 mm; four were larger than 700 mm, two were between 660 and
700 mm) returned to the Lower Gunnison River and specifically occupied the plunge
pool below Redlands Dam during July and August of 1996, 1997, and 1998.
Telemetered pikeminnow were larger than the pikeminnow that used the passageway
during the same period, July and August 1996-2000 (pooled mean=529 mm). However,
none of the pikeminnow radiotagged in 1996 (mean length=733 mm), 1997 (mean
1 ength=688 mm) , or 1998 (mean 1 ength=691 mm) were found i n the fi sh trap nor were
any of these fish detected by antennas located at three different locations
within the passageway.
Although large (700 mm and greater) pikeminnow are present in the Upper
Colorado and Gunnison rivers (Appendix; Figure E.2.), why, then, have only a
small number of large pikeminnow used the Redlands fishway to date? The reason
that smaller pikeminnow tended to use the passageway, although larger pikeminnow
existed in both the Lower Gunnison and Colorado river is unknown, but one can
postulate as to why. One possible reason is that larger pikeminnow may have been
less likely to migrate up the Gunnison River following spawning because they had
already established home ranges in the Colorado River reaches of the Grand
Valley. All the pikeminnow that moved through the passageway did so during post-
runoff which was associated with the period immediately following spawning.
These smaller pikeminnow might have been migrating upstream in response to
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