7229

• UCREFRP Catalog Number: 7229
• Author: Kaeding, L. R. and M. A. Zimmerman
• Title: Life History and Ecology of the Humpback Chub in the Little Colorado and Colorado Rivers of the Grand Canyon
• USFW Year: 1983
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

BIOLOGY OF HUMPBACK CHUBS IN THE GRAND CANYON
ruary, 74% of 57 in April, and 17% of 23 in
May. Nuptial tubercles were observed on 50,
23, and 22% of the fish in these respective sam-
ples.
Observations on growth rate of humpback
chubs spawned and raised in a hatchery (Ham-
man 1982) indicated that fish 14-18 mm long
from the Little Colorado River part of the con-
fluence (C 4) in May 1981 (Fig. 3) probably
resulted from spawning 2 or 3 weeks earlier.
Humpback chubs from the Little Colorado,
Colorado, and the confluence exhibited post-
ovulatory characteristics of low gonadosomatic
indices in May, and some large residual ova.
Gonad-development stage appeared similar in
histological preparations from these concurrent
collections (Charlie Smitb, Fish Cultural De-
velopment Center, USFWS, Bozeman, Mon-
tana, personal communication). These data sug-
gest that female humpback chubs undergo
seasonal gonad development in the Colorado
and may spawn there. This observation was not
unexpected. Temperatures of the Colorado
during the period of rapid seasonal gonad de-
velopment are similar to those present before
Glen Canyon Dam was constructed (Fig. 2). We
found one male humpback chub with nuptial
tubercles and running milt among eight hump-
back chubs collected in an overnight set of a
trammel net in a Colorado River (C 3) back-
water in May 1981.
Although humpback chubs might spawn in
the Colorado, our data strongly suggest that
spawning there does not result in the produc-
tion of viable offspring and the recruitment of
young fish to the population. No humpback
chubs shorter than 145 mm were collected from
the Colorado upstream from the confluence,
even though mature fish were present in this
river reach (Fig. 3). This distribution suggests
that small humpback chubs in the Colorado re-
sulted from spawning in the Little Colorado.
This hypothesis is supported by results of recent
thermal tolerance tests that showed tempera-
tureslike those of the Colorado River study area
preclude appreciable reproduction of hump-
back chubs. Hamman (1982) found that at 12-
13 C, only 12% of fertilized humpback chub
eggs hatched after 340-475 hours of incubation
and only 15% of these reached the feeding-larva
stage in a controlled hatchery environment.
When water temperature was maintained at 16-
17 C, incubation time was about 167-266 hours;
585
TABLE 2.-Food arga~nisrns in the stomachs of humpba.ck~
chubs collected from the Little Colorado and Colorado
rivers. Data are mean percentages of the total number of
organisms per sample, and mean frequencies (percent of
stomachs) within saraptes for each food organism. A sam-
ple is the group of stomachs (including those that ruere
empty) collected during a season (quarter year). Ranges
for samples are in parentheses. T =trace (<0.5%).
Little
Colorado Colorado
Taxon or (4 samples; (2 samples;
measure 26 fish) 18 fish)
Number of organisms
per stomach 7 (3-14) 192 (49-336)
Chironomidae
% numbers 36 (6-92) 28 (T-55)
%frequency 37 (20-50) 50 (1 I-89)
Simuliidae
% numbers 22 (0-90) 71 (43-99)
% frequency 5 (0-20) 56 (33-78)
Other Dipterae
% numbers 12 (0-36) T (T)
%frequency 22 (0-50) 11 (Ll)
Trichoptera
% numbers 18 (0-67) T (T)
% frequency 16 (0-50) 6 (0-1 ] )
Neuroptera
% numbers 2 (0-10) 0
% frequency 7 (0-27) 0
Coleoptera
% numbers 2 (0-6) T (T)
%frequency 18(0-50) 11(11)
Gammarus
% numbers 0 1 (T-2)
%frequency 0 22 (I1-33)
Other°
% numbers 7 (0-17) T (T)
frequency 35 (0-100) 11 (11)
a Geratopogonidae, Hernerodromia, Ephydridae, Limno-
phora.
n Ephemeroptera, Orthoptera, Hymenoptera, Oligochae-
ta, Nematoda, Pirnephales firoraelas.
hatching success was 62%, and 91% of the em-
bryos that hatched became feeding larvae.
Humpback chub reproduction in the Colorado
is made more improbable by the frequent water-
level fluctuations (Fig. 2). A decline in water
level would expose fertilized eggs deposited in
shallow lentic areas-the only locations where
the water might be warm enough to otherwise
allow reproduction.
Stomach Contents
Stomach contents from humpback chubs were
numerically dominated by immature Chiro-