9404

• UCREFRP Catalog Number: 9404
• Author: Douglas, M. E. and P. C. Marsh.
• Title: Ecology and Conservation Biology of Humpback Chub ‎(Gila cypha)‎ in the Little Colorado River.
• USFW Year: 1996.
• USFW - Doc Type: Tempe.
• Copyright Material: NO

p--_.ticularly summer through winter. At confluence, 17% (n = 33)
C_ ]Mdividuals tagged in spring were subsequently retaken there
sur.. -?r t? rough winter, while 76% (n = 54) of chub tagged in
sump,..- were recaptured in that same reach summer through winter.
Similarly, 77% (n = 10) of chub tagged at confluence in autumn
were retaken there autumn/winter. At Powell, 23% (n = 45) of
individuals tagged in spring were again recaptured there summer
through winter, 78% (n = 80) of those tagged during summer were
recaptured summer through winter. In addition, 91% (n = 20) of
those tagged in autumn were recaptured in that same reach
autumn/winter. A similar situation occurred at Salt, where 53% (n
= 109) of individuals tagged during spring were recaptured there
summer through winter, while 93% (n = 159) tagged during summer
were recaptured summer through winter. In autumn, 89% (n = 24)
tagged at Salt were recaptured there autumn/winter. Overall, 70%
of recorded movements in 1992 was static (i.e., within-reach).
Evidence is minimal for movement of G. cypha between reaches
during collecting periods (Table 1--4). In 1991, 13 out of 3272
fish were recaptured during the same trip in a reach upstream
from their initial capture, while 23 of 3272 were recaptured
downstream from their initial capture reach (i.e., N = 36; 0.01%
of total; Table 1--4). In 1992, only 1 of 4030 fishes was
recaptured during the same trip in a reach upstream from their
initial capture, while none was recaptured in downstream reaches
(i.e., N = 1; 0.0003% of total; Table 1--4).
DISCUSSION
The Colorado River as habitat.---During historic times,
temperature and flow regimes of the Colorado River fluctuated
greatly; seasonal flooding transported heavy sediment loads while
low waters carried vast amounts of dissolved salts to the Sea of
Cortez (Carlson and Muth, 1989). In flood, the Colorado was a
wild, swift, turbulent river, the result of extreme flow, a
channel constrained for most of its length by steep cliffs, and a
3700 m drop in altitude from headwaters to sea (Fradkin, 1984).
Dams and Impoundments.---Dam construction and chronic dewatering
for agriculture and urban development precipitated major changes
in the Colorado River ecosystem. Temperature and flow regimes as
well as salt and sediment loads of the river are now greatly
ameliorated. The 2400 km of riverine habitat suitable for
large-river fishes has been reduced to 965 km (Miller, 1982).
Those sections of the Colorado River that were converted
into lakes Mead and Mohave (following closure of Hoover and Davis
dams in 1935 and 1954, respectively), clearly possessed the
river's unique fish fauna, including G. cypha (Miller, 1955).
These fishes (except for relictual bonytail chub (Gila elegans)
and razorback sucker (Xyrauchen texanus)] are now extirpated (see
7