7311

• UCREFRP Catalog Number: 7311
• Author: McCarthy, M. S. and W. L. Minckley
• Title: Age Estimation for Razorback Sucker ‎(Pisces
• USFW Year: 1987
• USFW - Doc Type: Catostomidae)‎ from Lake Mohave, Arizona and Nevada
• Copyright Material: YES

IOURNAL OF THE ARIZONA-NEVADA ACADEMY OF SCIENCE VOL. 21
Table 2. Size variation in razorback sucker hatched in
February of various years at DNFH. Different data for
combined sexes in 1981 reflect variation in 2 separate
ponds. Limits of SL in mm; means t one standard error
in parentheses.
Year Class Month Sex n SL
of life
1981 7 combined 50 95-139
(113±1)
1981 7 combined 50 76-125
(91 ± 1)
1981 28 male 15 251-341
(306 ± 91
1981 28 female 36 263-357
(316-4-4)
1982 7 combined 50 74-121
(95 ± 2)
1982 15 combined 50 129-226
(186±6)
[n = 81 and 298:t 10 mm SL [161). This pattern could
indicate growth enhancement by lentic conditions. The
species has a protrusible, almost-terminal mouth and
closely-spaced, "fuzzy" gill rakers indicating facultative
planktivory (Hubbs and Miller 1953). Adults in Lake
Mohave feed mostly on zooplankton (Marsh 1987). Rapid
growth in a filling reservoir could reflect response to
increased availability of planktonic foods. The species may
well be more adapted for feeding in backwater and oxbow
habitats of the unmodified Colorado River than for the river
channel.
Maximum natural longevity of razorback sucker is
unknown. The largest specimens from Lake Mohave have
been an unweighed female 57.6 cm SL (73.6 cm TL) and an
unmeasured 4.99 kg female (Minckley 1983; unpubl. data).
Individual weights of 12 to 14, and occasionally 16 pounds
(5.45, 6.35, and 7.26 kg, respectively) were reported on the
basis of local testimony by Hubbs and Miller (1953) from
Saguaro Lake, central Arizona. Miller (1955) reported
lengths "over 30 inches long" (ca. 60 cm SL) on the basis
of the same testimony. Actual specimens were not seen,
so these records are suspect (R. R. Miller, University of
Michigan Museum of Zoology, pers. comm.). Lengths and
weights of largest fish represented in archaeological remains
in Catclaw Cave, Arizona, were estimated at "2-3 feet (ca.
48-72 cm SL] and 10-12 pounds [4.54-5.45 kg]" on the basis
of proportional sizes of bones (Miller 1955). This site, now
inundated by Lake Mohave, was about 24 km downstream
from Hoover Dam. A vertebra from Quiburi, an 18th
Century Indian site on the San Pedro River, Arizona, was
from a razorback sucker "perhaps nearly 3 feet long [ca. 72
cm SL]" (Miller 1955).
0
a
0
H
W
Q
Q
z
w
u
w
a
Figure 7. Percentage of growth to SL at capture achieved
by male (above) and female (below) razorback sucker caught
from Lake Mohave, Arizona and Nevada, at various, back-
calculated ages. Horizontal lines are means, boxes indicate
t one standard error of the mean, and vertical lines con-
nect limits.
Minckley (1983) documented a pattern of disappearance
of razorback sucker from Colorado River basin reservoirs
40 to 50 years after initial impoundment, and predicted the
same for Lake Mohave. Our data corroborate his conten-
tion that no detectable recruitment has occurred in Lake
Mohave since 1958, and little since 1954. Unless this trend
is reversed, population extirpation may be expected before
the year 2000.
ACKNOWLEDGEMENTS
This paper was revised from a thesis submitted by
McCarthy in partial fulfillment of requirements for a Master
of Science in Zoology at ASU. Research was supported in
part by ASU and U. S. Fish and Wildlife Service (USFWS),
Office of Endangered Species, Albuquerque, New Mexico.
We thank personnel of WBNFH, DNFH, AZGFD, and
CADFG for providing specimens. Numerous others assisted
in specimen acquisition and preparation, and we acknow-
ledge them all. Comments of Drs. f. E. Deacon (University
of Nevada, Las Vegasj, P. C. Marsh (ASU), B. D. Taubert
(AZGFD), and H. M. Tyus (USFWS) improved the manu-
script.
YEARS OF LIFE