7206

• UCREFRP Catalog Number: 7206
• Author: Lanigan, S. H. and H. M. Tyus
• Title: Population Size and Status of the Razorback Sucker in the Green River Basin, Utah and Colorado
• USFW Year: 1989
• USFW - Doc Type: North American Journal of Fisheries Management
• Copyright Material: YES

70
LANIGAN AND TYUS
40
20
0
20
0
20
0
U
Z 20
w
m 0
w
? 20
E-
Z o
w
U 20
tY
w
CL o
20
0
20
0
20
0
1988
n-60
1987
n-62
1986
n-79
1985
n-19
1984
n-86
1983
n-3
1982
n-34
1981
n-66
1980
n-18
42 44 46 48 60 52 64 66 58 60 62
TOTAL LENGTH (cm)
FIGURE 2.-Size-classes of razorback sucker caught in the Green River basin, 1980-1988.
only 1.8 and 33%, respectively, of the catches of
the federally endangered Colorado squawfish.
Population estimates are meaningful only if
population characteristics meet the assumptions
of geographic and demographic closure; i.e., the
population is confined to a discrete area, and re-
cruitment and mortality do not occur during the
experiment (White et al. 1982). Population esti-
mation in a large geographic area, over a long time
period, is normally ill-advised because the as-
sumptions of closure are usually violated. How-
ever, we believe the unique distribution and life
history of the razorback sucker in the Green River
basin meets the closure requirement and that our
population estimate is valid. Our reasoning fol-
lows.
A review of available data indicated no razor-
back sucker movement occurred between the up-
per and lower portions of the Green River, nor
between the lower Green and Colorado rivers.
Substantial rapids in Gray and lower Desolation
canyons (km 211-282) appear to form a barrier
between the upper and lower Green River, and a
diversion dam at km 206 presents a further barrier
to fish movement. The confluence of the Green
River with the Colorado River forms the lower
boundary of the lower Green River; no razorback
suckers tagged in the Green River were later caught
in the Colorado River. Only one individual (col-
lected at km 29 of the White River in 1987) was
found more than 2.4 km upstream of the mouth
of tributaries entering the Green River (electro-