9660

• UCREFRP Catalog Number: 9660
• Author: U.S. Fish and Wildlife Service.
• Title: Colorado Squawfish Revised Recovery Plan - Draft.
• USFW Year: 1990.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

DRAFT
river channel, which may be controlled more by ambient air temperatures and
solar radiation. In laboratory experimentation, Marsh (1985) found that
optimal temperatures for embryo development and hatching of Colorado squawfish
was near 200C (68oF). Percentage hatch was highest and incidence of
abnormalities lowest at that temperature.
Temperature preferences have been determined in the laboratory for Colorado
squawfish reared at Willow Beach National Fish Hatchery in Arizona. Juvenile
Colorado squawfish acclimated to 200C (68oF) selected a higher temperature
(26.60C [800F]) than those acclimated to either 26oC (180F) or 140C (570F);
fish acclimated at 26oC (780F) selected 23.70C (750F); and those acclimated at
140C (570F) selected 21.90C (710F). Adults selected temperatures ranging from
21.50 (710F) to 25.70C (780F), with a final temperature preference of 25.40C
(780F) {Bulkley et al. 1982). Maximum growth of 45-100 mm (1.7-4 in.) TL
Colorado squawfish in a laboratory study occurred at 250C {770F), while growth
at 200C (68oF) and 300C (860F) was about 50 percent of the maximum (Black and
Bulkley 1985).
Table 1. Temperatures associated with Colorado squawfish migration and
spawning periods in the Yampa River, 1981-88 [adapted from Tyus and Karp
(1989)].
Type
Water
Year Year
1981 Low
Migration Saawnin4
Period Temp.(mean) Period Temp.(median)
Dates C0 F0 Dates C° F°-
5-12 to 6-20 13.80 570 _ 6-19 to 7-20 21.80 710
1982 Average 6-10 to 6-20 12. 70 550 7-4 to 8-8 22. 00 720
1983 High 6-10 to 7-10 13. 40 560 7-12 to 8-18 22. 50 730
1984 High --
1985 High --
1986- High --
1981 Low --
1988 Average 6-8 to 6-30
7-10 to 8-17 22.00 720
6-21 to 7;25 20.00 680
6-27 to 8-5
20.80 690
6-3 to 7-16
20.50 690
16.90 620 6-20 to 7-24 21.50 710.
Reproduction and Migration
-Wild, male Colorado squawfish do not mature until they reach or exceed 400 mm
(15.7 in.) TL and attain an age of at least 6 years; females mature a year
later {Seethaler 1978). Tyus et al. (1987) found that ripe males averaged

7