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.
N_
LL
~•
O
L
d
Z
4 years
.. r = 0.06
- r 0.18
•- - r 0.03
140 280 425 565
5 years
• ~ = 0.27
r 0.43
i
• r = 0.53
140 280 425 565
Discharge (rri~/sect
Status of Razorback Sucker 115
A
6 years
r = 0.01 • •
r = 0.01
I
• r = 0.01
140 280 425 56;
E
E
n
m
J
F
E
E
io
II
J
F

a
m
J
H
Figure 5. Comparison of the number of razorback suckers among the three smaller (A) and three Zarger (B) total
length intervals, with discharge occurring 4, 5, and 6years prior to capture in the middle Green River.
vals of 456-465 mm (Fl,lo = 5.98, p = 0.035) and 466- Discussion
475 mm (Fl,lo = 6.83, p = 0.026) 5 years following fish
capture (Fig. 5). Both tests indicated that the number of Growth of individual razorback suckers from the middle
smaller fish was positively related to increases in dis- Green River was slow during the study period and con-
charge 'five years preceding capture. Six of the remain- sistent with the low rates reported by Tyus (1987). Simi-
ing comparisons of small fish showed nonsignificant lar low estimates of growth were reported in the razor-
positive slopes. No significant relationships were ob- back sucker from Lake Mohave by Minckley (1983). The
served among larger fish, with seven of the nine compar- slow growth in body size of the razorback sucker makes
isons reflecting nonsignificant negative slopes. it difficult to determine population replacement using
Length-frequency data suggest that most small fish in length frequency. Even fish less than 500 mm showed
the population are male (Fig. 6). Therefore, the ob- growth of only several millimeters per year. Thus, not all
served relationship of recruitment to prior flow repre- small fish in the population were new recruits. Despite
Bents the relationship only to male appearance at the the slow growth rate, however, some shift in the length
spawning and post-spawning aggregation sites. Based on frequency over the 13-year study period should have oc-
length intervals only, it would be difficult to detect re- curred if there was no replacement to the population.
cruitment of females because their size overlaps with The absence of reduced numbers of fish smaller than
that of larger males. 480 mm throughout the study period and, particularly 5
Conservation Biology
Volume 10, No. 1, February 1996