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

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3

zone. Hamman (1981) stated that Colorado squawfish spawn
when water temperatures reach 20-220 C, which usually occurs
during July or August in the Upper Colorado River Basin
(Kaeding and Osmundson 1988). Haynes et ale (1984)
estimated that fish may have spawned as late as 26 August in
the Upper Colorado River in 1981. In the Lower Colorado
River Basin (below Glen Canyon Dam), where Colorado
squawfish were once abundant but are now extirpated, the
20-220 C spawning threshold was usually reached in early May
(Kaeding and Osmundson 1988). As a result of their
confinement to the northern portions of their historical
range, the remaining populations of Colorado squawfish spawn
relatively late in the year. This late spawning leaves
age-O fish only a brief period to grow and accumulate fat
reserves before entering their first winter.
During winter; most temperate-zone fishes undergo
physiological changes that result in declining condition and
depletion of energy reserves (Cunjak 1988). studies by
Oliver et ale (1979), Toneys and Coble (1979), and Henderson
et ale (1988) demonstrated that overwinter survival is
directly related to fish size. Because weight-specific
basal metabolism increases as fish size decreases, the
higher metabolic demands of small age-O fish result in their
eXhausting energy supplies more quickly during winter
(Shuter et ale 1980; Shuter and Post 1989). A positive
relation between body size and lipid content has been