7145

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

containing optimum temperatures earlier in the season. Spawning migrations
and gonadal maturation of razorback suckers may largely be initiated by
photoperiod, with warm temperatures hastening final gonad maturation. In
the Grand Valley, sexual ripeness of razorbacks coincides with the period
of peak runoff (Fig. 13). Only during high flow conditions can razorbacks
of the upper basin find their optimum spawning temperatures in spring, but
they must leave the main channel to do so. The main channel during peak
flow averages 13.0 C (USGS gage data at Cameo; Appendix Table V). Razor-
back suckers can find water warmed to 20 C in off-channel habitats when
high spring flows flood low-lying areas adjacent to the river. These
still-water sites are warmed by direct sunlight and ambient air tempera-
tures and are generally much warmer than the main channel. Water tempera-
MAY 05-09
MAY 10-14
MAY 15-19
MAY 20-24
MAY 25-29
MAY 30-03
JUN 04-08
JUN 09-13
JUN 14-18
JUN 19-23
JUN 24-23
JUN 29-03
JUL 04-08
0 5 10 15 20 25 30 35
FREQUENCY M
Figure 13. Frequency of Colorado River peak flow dates during 1907-1989
(N = 83 years) and capture dates during 1975-1988 of razorback suckers (N
42 fish) in spawning condition (expressible sex products present) in the
Grand Valley, Colorado. Two ripe razorback suckers captured in early April
1975 are not represented. Data from McAda and Wydoski (1980), Valdez et
al. (1982), USFWS (unpublished), and Osmundson and Kaeding (1989).
40