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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demonstrated for yellow perch Perca flavescens (Toneys and
Coble 1979), smallmouth bass Microoterus dolomieui (Oliver
et ale 1979; Isely 1981), and sand smelt Atherina boveri
(Henderson et ale 1988). Thus, the larger members of an
age-O cohort are more likely to survive their first winter
and recruit to the adult stock (Gutreuter and Anderson 1985;
Henderson et ale 1988). Kaeding and Osmundson (1988)
speculated that the occurrence of comparatively larger age-O
Colorado squawfish in the Green River than in the Colorado
River may be the reason that adult Colorado squawfish are
more abundant in the Green River (Tables 1 and 2).
Colorado squawfish stop growing when water temperatures
fall below about 130 C (Kaeding and Osmundson 1988). The
130 C "growth threshold" is usually reached in october in
the Upper Colorado River Basin. In years of large,
prolonged seasonal-runoff flows that delay seasonal warming
of the river, age-O Colorado squawfish may have only 2
months to grow and accumulate fat reserves before the onset
of winter. Although Shuter and Post (1989) noted that many
warmwater and coolwater temperate-zone fishes severely
restrict their feeding during periods of low water
temperature, whether age-O Colorado squawfish cease or
restrict feeding activity during winter has yet to be
determined. If age-O Colorado squawfish do not feed during
winter, the smaller fish would exhaust their energy reserves
more quickly.