7355

• UCREFRP Catalog Number: 7355
• Author: Wydoski, R. S.
• Title: Assessment of Introduced Sport Fishes As Potential Competitors with or Predators upon the Rare Colorado River Fishes with Reference to Fishery Management in Kenney Reservoir.
• USFW Year: 1987.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

Like many fish, largemouth bass are selective when choices are available
(Epinosa and Deacon 1973; Holton 1977; Lewis et al. 1961; Lewis and Helms
1964; Snow 1961) but may become opportunistic when one prey is more abundant
and can be captured easier.
Vulnerability of forage fish to largemouth bass depended upon how conspicuous
the prey was to the predator and the mobility of the prey (Lewis and Helms
1964) as well as the physical fitness of the forage fish (Herting and Witt
1967; Mossman 1955). Parasitism and disease lowers physical fitness and
increases vulnerability of prey to predators (Coble 1970).
The percentage of stomachs of largemouth bass from two backwaters along the
lower Colorado River that contained fish ranged from 27 to 83% for samples of
18 to 62 bass for four seasons during two years (Singer 1973). Singer noted
that use was directly correlated with food availability.
Size of the prey is also important to feeding because largemouth bass are
restricted to swallowing fish with a maximum depth equal to the mouth width of
the bass (Lawrence 1957).
Vulnerability of the prey can also be affected by the type of feeding behavior
that the largemouth bass exhibits. Vanderhurst (1967) described two main
types of feeding behavior in the largemouth bass: (1) a reflex-like response
where the bass instantly "strikes" and captures the prey, and (2) a
preparatory behavior prior to feeding in which the bass goes through a series
of body movements. Forage fish are very vulnerable to the first type of
behavior but show a marked escape response to the second type of feeding
behavior since they have time to react before the bass attempts to consume
them.
c?
Obviously, water temperature plays an important role in feeding rates (Markus
1932). Below 10 C, the largemouth bass show little natural feeding reaction
(Johnson and Charlton 1960) and the feeding rate increases until temperatures
reach 27 C. Feeding declines above 27 C (Niimi 1973) and fish may remain
quiet in shaded areas with empty stomachs at higher temperatures (Denyes and
Joseph 1956). _
Discussion Related to Potential Competition/Predation
Fingerling largemouth bass and juvenile Colorado squawfish feed on
zooplankton, feed more intensely at warmer water temperature, and occupy the
same quiet habitats with similiar water temperatures so that the potential for
competion is high.
,However, the greater threat from largemouth bass in establishing Colorado
squawfish populations in Kenney Reservoir would be predation. The bass is an
,effective predator that can can reduce the numbers of native fish (Rivero
1936; Curtis 1942).
Longhorst and Marsh (1986) reported that abundant razorback sucker larvae in a
predator-free Lake Mohave backwater disappeared within 4 weeks after invasion
Eby largemouth bass, green sunfish, bluegill, and some other warmwater fishes.
However, these authors pointed out that predation rates and the impact of
predation on razorback sucker recruitment are unknown.
F