7960

• UCREFRP Catalog Number: 7960
• Author: Modde, T., K. P. Burnham and E. J. Wick
• Title: Population Status of the Razorback Sucker in the Middle Green River ‎(U.S.A.)‎
• USFW Year: 1996
• USFW - Doc Type: Conservation Biology
• Copyright Material: YES

Modde et al Status of Razorback Sucker 113
McCarthy and Minckley (1987), the angle of inclination
in the growth rate of male razorback sucker from the
lower Colorado River Basin occurred between the fourth
and sixth growing seasons. This estimate of maturation
is supported by the growth rates observed among wild
subadults collected from the middle Green River in 1994
(U.S. Fish and Wildlife Service, unpublished data). The
relationship of flow preceding fish capture to the num-
ber of small individuals was determined by simple linear
regression of the mean monthly flows of May and June
during the 4, 5, and 6 years following fish capture. Only
years with similar collecting effort were used for analysis
(data from 1975, 1978, 1979, and 1983, which included
five or less collecting dates, were excluded). For each
temporal comparison the number of fish from the three
smaller-decimeter length intervals were regressed (446-
455 mm, 446-465 mm, 446-475 mm) with the monthly
discharge average for the months of May and June. To
distinguish the appearance of nonrecruitment related re-
lationships, the numbers of fish in the three larger deci-
meter length intervals (556-565 mm, 556-575 mm, and
556-585 mm) were also regressed with discharge dur-
ing the same time periods. The number of fish in each
length interval included cumulative totals (fish in the
446-475 mm length interval included fish from the pre-
vious two length intervals). The number of fish in the
three larger intervals did not include fish from smaller
intervals (less than 556 mm). Discharge data for the
Green River was collected at the U.S. Geological Survey
gage station in Jensen, Utah. We used total fish numbers
rather than data on catch per unit effort because of the
relatively small number of fish in the population and be-
cause most fish were taken from a few general locations
that were sampled most years (during the study approxi-
mately one third of the fish captured were recaptured).
20 . 1980 - 1982
16
12
8
4
6 _
20 ~ 1983 -1985
16
12 -
A 8
v 4
H 0 ~-t
3 30 1986 -1988
d 2a
1i 1g
12
6
0 -
40
30 ~ 1989 -1992
20
10
6
440 460 480 500 520 540 560 580
Total length in mm
Figure 2. Length frequency (total length) of razorback
suckers collected from the middle Green River between
1980 and 1992.
u~,
30
20
E
E 10
d
m a
~_
~ -10
-20
-30
Figure 3. Absolute growth of razorback suckers, be-
tween initial capture and last recapture, collected
from the middle Green River between 1975 and 1992.
Results
Individual Growth Characteristics
The data base used in this analysis included 687 observa-
tions of 461 individual fish collected between 1975 and
1992, although all but 10 observations took place be-
tween 1980 and 1992. Among these fish 156 individuals
were recaptured and 213 were reproductively mature
(primary or secondary sexual characteristics present), al-
lowing sex determination. Razorback suckers were col-
lected between RKM 80 and 560, with only 13 observa-
tions below RKM 368.
630
610
590
~ 570
6
550 3
Z
~ ~6

~ 530 j
[
yR„ 510 I

F-
490 r
470 k
~~
59
77
3
68
36 17 62 36 3q
87
51

Figure 4. Comparison of mean length (± SD) of ra-
zorback suckers collected from the Green River be-
tween 1980 and 1992.
Conservation Biology
Volume 10, No. 1, February 1986
Days between captures