9591

• UCREFRP Catalog Number: 9591
• Author: Nesler, T. P.
• Title: Interactions Between Endangered Fishes and Introduced Gamefishs in the Colorado River, Colorado, 1986-1991.
• USFW Year: 2002.
• USFW - Doc Type: 91-29,
• Copyright Material: NO

occurrence data for largemouth bass and green sunfish suggest this degree of selectivity in the field
is not happening. In backwaters where centrarchids might be concentrated, predation would be
greater on all prey species present, and could result in local depletion of Colorado pikeminnow
young and juveniles or stocked razorback sucker and bonytail juveniles.

Adult channel catfish shared spring backwater habitat with adult Colorado pikeminnow,
but comPetition for food resources does not appear likely given the observed low percentage of
fish ingested by channel catfish and the availability of fish prey for both species. In contrast to
the omnivory of channel catfish, Colorado pikeminnow are quite piscivorous (Vanicek and Kramer
1969). Certainly, the opportunity exists for channel catfish to engage in piscivory in summer
backwaters containing abundant cyprinid prey. The high proportion of "Other" food items,
composed mostly of insect taxa, and low proportion of fish prey for channel catfish in the
Colorado River was similar to that observed for the species in the Yampa River (Nesler 1995).
This suggests insectivory is an important foraging strategy for channel catfish in these rivers. A
low level of piscivory and high use of macroinvertebrates and plant material was also observed
for channel catfish in the San Juan River (Brooks et aI. 2000). Brooks et al. suggested, however,
that even with a low level of piscivory, an abundant channel catfish population may still exert a
negative effect on recruitment of native fishes. Consumption of fish prey by both channel catfish
and black bullhead apPeared infrequent in this study. The presence of mostly fish remains and
unidentifiable fish prey may be a result of omnivorous scavenging of dead or injured fish or a
sampling bias due to nighttime ingestion coupled with daytime stomach sampling. Predation by
small catfish upon drifting Colorado pikeminnow was not observed in Yampa Canyon (Ruppert
et aI. 1993). Evidence from Muth and Beyers (cited in Lentsch et aI. 1996) indicated young
catfish fed on fish prey, but only at night.

No razorback sucker young or adults were collected in backwater habitat during spring,
summer, or fall seasons in this investigation. The predatory and competitive influence of
abundant red shiner, fathead minnow, channel catfish and carp in backwater habitat in the
Colorado River may have contributed to the decline and current absence of razorback sucker in
mainchannel habitat of the Colorado River (Bestgen 1990). The potential for channel catfish to
act as predators on razorback sucker under certain circumstances has been clearly documented by
Marsh and Brooks (1989) and Johnson and Hines (1999). The stocking of smaller size classes of
hatchery-reared razorback sucker in restoration efforts has illustrated that vulnerability. Johnson
et aI. (1993) found razorback sucker larvae to be less adept in avoiding predation compared to
another sucker species adapted to the predator-rich environment of the Mississippi River fish
community. While stocking plans for the reintroduction of razorback sucker (Ryden 2000, Nesler
2001, Hudson et aI. 2001) attempt to circumvent this vulnerability by releasing fish >300 mm
in length, it remains to be seen if channel catfish predation (among other nonnative fish
interactions) impact naturally-reproduced cohorts of razorback sucker sufficiently to inhibit
recruitment to adult populations. Juvenile razorback sucker resulting from natural reproduction
in the middle Green River have been captured from an inundated floodplain habitat that also
supported an abundance of common carp, fathead minnow, green sunfish, channel catfish, black
bullhead, red shiner, and black crappie (Modde 1996). The inference from this study was smvival.

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