7785

• UCREFRP Catalog Number: 7785
• Author: Thompson, J. M.
• Title: The Role of Size, Condition, and Lipid Content in the Overwinter Survival of Age-0 Colorado Squawfish.
• USFW Year: 1989.
• USFW - Doc Type: Colorado State University,
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

7

Research on the Colorado squawfish intensified after
the fish was listed as an endangered species in 1973. It
has focused largely on life history and ecology (Seethaler
1978; Tyus 1986), spawning behavior (Hamman 1981; Lamarra et
ale 1985; Tyus et ale 1981; Tyus 1985), habitat requirements
(Tyus and McAda 1984), preferred and optimal temperatures
(Black and Bulkley 1985a, 1985b), and food habits (McAda and
Tyus 1984; Pimentel et ale 1985). Studies of overwinter
survival of age-O Colorado squawfish are conspicuously
lacking. Osmundson (1987) found no evidence of size~
selective overwinter mortality among hatchery-reared
Colorado squawfish stocked into ponds near Grand Junction,
Colorado. However, the smallest fish at the onset of winter
in Osmundson's experiment were already 54 mm total length
(TL) , which is significantly larger than the mean length of
wild Colorado squawfish at the same time of year (Tables 1
and 2). As part of an investigation preliminary to the
present study, I held 331 hatchery-reared age-O Colorado
squawfish 39 to 87 mm TL, at simulated winter temperatures
from 22 January 1988 to 8 July 1988 (Appendix H). Fish were
fed pelleted trout food twice weekly at 2% of the total fish
biomass in each aquarium. survival rate was 100% for all
sizes of fish during the 150-day winter period. The
majority of the fish used in this preliminary effort,
however, were too large to be representative of the sizes of
age-O Colorado squawfish in nature (Tables 1 and 2). In