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

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Mean Clf -Daylight Seining LC 2 LC 3 LC 4 C 4
Little Colorado River Confluence
FtcuxE 7.-Relationships between mean catch rates by~ Flcuxe 8.-t1~leaaz catch rates for age-0 and juvenile
seine during darkness (2-14 seine hauls per mean; aver- humpback chubs collected by minnow traps and seines
age 6.9) and during d¢ylight (Z-18; 9.8) far age-0 and during darkness from reaches LC 2, 3, and d of the Little
juvenile humpback daubs in the Little Colorado River,
confluence, and Colorado River, 1980-181. Each data Colorado River and from tFee confluence of this tributary
point gives the mean catch rates for the 2-day collection wath the Colorado River, 1980-1981. Numbers desig-
nate multiple observations.
effort at a sampling site; efforts that yielded no humpback
chubs in both diet periods are not included. Seven data
paints are included in the aggregation near the origin.
humpback chubs avoid the clear, shallow water
swept by our seines during daylight, a hypoth-
esis supported by the occurrence of humpback
chubs in these same littoral areas when the water
is turbid.
Mean C/f for age-0 humpback chubs collect-
ed byminnow trap and by seine during darkness
from the Little Colorado (data largely from
1981) increased with proximity to the conflu-
ence (Fig. 8). Although this relationship sug-
gests that downstream reaches were most im-
portant for humpback chub reproduction in
1981, downstream drift or movement of small
fish could account for this distribution. Data on
seining during daylight for the postspawning
period in 1980 and 1981 are more detailed than
are the data for seining during darkness, and
they provide evidence of differences in hump-
back chub reproductive success between years.
Mean C/f for age-0 humpback chubs was ap-
preciably higher in 1980 than in 1981; density
was greatest at LC 2, where no age-0 humpback
chubs were collected in 1981 (Table 4). Sea-
sonalrunoff coincident with spawning could sig-
nificantly enhance humpback chub reproduc-
tive success in the Little Colorado, particularly
in upstream regions. Seasonal runoff occurred
during the spawning season in 1980 but not in
1981. Humpback chubs that spawned in hatch-
ery raceways laid eggs that adhered to rock sub-
strate where they were deposited (Hammon
1982). Runoff of the Little Colorado removes
fine travertine sediments that could suffocate
developing humpback chub embryos. Runoff
also dilutes chemically concentrated spring
waters, which otherwise might be harmful to
embryos and larvae.
Adults
Of 504 humpback chubs averaging 2'78 ± 54
(SD) mm long collected in trammel nets, 93%
were classified as adults. Higher catch rates dur-
ing sunset and darkness than during daylight
suggested that activity of the fish increased as
light diminished, although avoidance of nets
during daylight cannot be discounted. Many of