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

4. Nonnative game fish species are distributed ubiquitously in the Colorado River study reach
at low relative abundance levels with sporadic concentrations in a few backwaters each
year.
5. Backwater populations of centrarchid fish species are comprised mostly of young-of-the-
year and juvenile fish and fewer adults; black bullhead are represented by more adult fish,
and channel catfish populations are comprised primarily of adult fish.
6. Adult Colorado pikeminnow and other native fish species share backwater habitat with
channel catfish and carp only in the spring and early summer, and vacate backwaters by
July.
7. Adult channel catfish in the Colorado River demonstrate a robust weight gain with
increasing length, though the length-weight relationship is less robust than that for channel
catfish in the Yampa River.

Objective 2: to determine the incidence of predation by non-native, non-salmonid gamef'lSh
species upon the endangered f'lShes.

1. Largemouth bass is the most piscivorous of the nonnative gamefish species present in
Colorado River backwaters compared to green sunfish, black bullhead, and channel
catfish. The diet of the latter three fish species was comprised largely of aquatic insect
larvae.
2. The fish prey base for nonnative gamefish in Colorado River backwaters is comprised
mostly of nonnative, small-bodied cyprinid species whose populations are composed
mostly of fish sizes that are vulnerable to predation by the most commonly occurring sizes
of gamefish species.
3. Fish prey selection by centrarchid gamefish species reflect the relative abundance of fish
prey species present in backwaters, and may be characterized as opportunistic rather than
species selective. ,
4. Predation effects of nonnative gamefish species on native fish species in Colorado River
backwaters are affected by low relative abundance (centrarchids), low frequency of fish
ingestion (icta1urids), and a relatively large alternative fish prey, base comprised of
nonnative cyprinids.
5. Potential negative impacts from red shiner and fathead minnow may be more significant
to the growth and survival of Colorado pikeminnow and razorback sucker young compared
to predation by nonnative gamefish species due to the large differences in relative
abundance.
6. The diet of channel catfish in the Colorado River is omnivorous and fish predation by this
species is not likely a source of food competition to the highly piscivorous Colorado
pikeminnow in the presence of a relatively large alternative fish prey base comprised of
nonnative cyprinids.
7. The abundance of adult channel catfish in Colorado River backwaters and their documented
predation on razorback sucker in other studies may pose survival and recruitment problems
in the recovery of that species.

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