7145

• UCREFRP Catalog Number: 7145
• Author: Inslee, T. D.
• Title: Spawning of Razorback Suckers
• USFW Year: 1981.
• Copyright Material: NO

adults probably spawn, no young have been reported in the upper Colorado
River in the past 27 years and captures of adults in the Grand Valley have
decreased dramatically in the last 17 years (Fig. 12 and Appendix Table
IV). Our evaluation of existing information leads us to believe that the
decline of this fish is linked to the reduction in spring flows.
Razorback suckers spawn in spring. It is not known whether gonadal matura-
tion and degree of ripeness is primarily controlled by photoperiod or
water temperature. Bulkley and Pimentel (1983) found that the preferred
temperature of adults is between 22.9 and 24.8 C. Hamman (1985) suggested
that egg incubation temperature was a critical factor in the reproductive
cycle of the razorback sucker; his work and that of Inslee (1982) indicat-
ed that optimum temperatures for reproduction were 20-22 C. Marsh (1985)
250
200
CC 150
W
m
100
Z
50
0
74 75 76 79 80 81 82 85 86 87 88
YEAR
Figure 12. Razorback sucker captures from the Colorado River between Loma
and Palisade, Colorado (RM 152.8-185.1), 1974-1990. Effort among years was
not constant. Individuals captured upstream or downstream of the Grand
Valley are not included. Missing years are due to either no effort expend-
ed (1977-1978), or no fish caught despite minimal effort (1983 and 1989)
or extensive effort (1984 and 1990). Data from Appendix Table IV.
38