8234

• UCREFRP Catalog Number: 8234
• Author: Marsh, P. C. and M. E. Douglas
• Title: Predation by Introduced Fishes on Endangered Humpback Chub and Other Native Species in the Little Colorado River, Arizona
• USFW Year: 1997
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

NOTES
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TABLE 2.-Frequency of occurrence of food items as percentage of total stomachs examined for each of five species
of predatory introduced fishes collected in the Little Colorado River, Arizona, July 1991-June 1995.
Food item
or statistic
Rainbow trout
Brown trout Predator
Channel catfish
Black bullhead
Yellow bullhead
Detritus 0 0 3 8 10
Vegetation 9 0 5 0 0
Algaea 47 0 10 0 0
Gammarus 12 0 2 0 0
Corydalidae 1 0 2 0 0
Simuliidae 19 0 4 0 0
Chironomidae 14 0 1 0 0
Gastropoda 1 0 0 0 0
Oligochaeta 0 0 1 0 0
Odonata 0 0 1 0 10
Tipulidae 0 0 1 8 0
Coleoptera 3 0 1 0 0
Ceratopogonidae 0 0 1 8 0
Trichoptera 1 0 0 0 0
Aquatic insectsb 1 0 9 0 0
Terrestrialsb•c 3 20 4 0 0
Humpback chub 2 0 4 17 0
Speckled dace 1 10 2 0 0
Common carp 1 0 1 0 0
Bluehead sucker 1 0 2 0 0
Flannelmouth sucker 1 0 1 0 0
Fathead minnow 1 0 1 0 0
Fishb 9 10 1 0 20
Fish eggs 1 10 1 0 0
Number of stomachs 174 10 202 12 10
(number with food) (114) (3) (91) (7) (4)
Mean TL (mm) 354 397 286 158 166
(Range) (210-491) (296-566) (37-796) (70-228) (75-212)
a Primarily Cladophora.
b Taxa not determined.
Terrestrial invertebrates
and terrestrial invertebrates. Brown trout con-
tained terrestrial insects and fish (20% each) and
fish eggs (10%); black bullheads ate detritus (8%),
aquatic insects (16%), and fish (17%); and yellow
bullheads contained detritus and odonate naiads
(10% each) and fish (20%). Proportion of empty
stomachs varied among species from 34% to 70%
(Table 2).
Food habits of potential piscivores were unre-
markable. The relatively low diversity of food
items probably reflected a paucity of food in the
Little Colorado River. Diets of individual species
were qualitatively consistent with other reports
from the Colorado River basin (Minckley 1973,
1982; Marsh 1981; AZGFD 1987; Tyus and Nikirk
1990) and elsewhere (Calhoun 1966). All studies
concluded that channel catfish were opportunistic
omnivores and that fish were a small part of their
diet.
Predatory fishes represent a threat to humpback
chub in the Little Colorado River and may exert
a major negative effect on the population there.
Our data indicate that on average about 3% of
rainbow trout and channel catfish ate an average
of 2.3 humpback chubs. If our estimated average
meal of 2.3 prey is taken once a week, a predator
population of 1,000 would annually consume
3,588 humpback chub. Predatory fishes probably
number in the thousands. Recent population esti-
mates generated under five different models for
adult (> 150 mm TL) humpback chub in the Little
Colorado River were 4,508-10,444 (Douglas and
Marsh 1996). Although most humpback chub in
predator stomachs were juveniles, channel catfish
ate humpback chub as large as 200 mm TL and
other fish up to 250 mm (Table 2). Thus, predation
may not only limit recruitment by removing ju-
veniles from the population, but it might also in-
crease total adult mortality. Although some
streams like the Little Colorado River retain a nat-
ural character (particularly hydrologic features)
thought to favor native over introduced fishes
(Minckley and Meffe 1987), predation impacts
may limit native species populations.