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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33

than a specific length; nonetheless, the change in the slope
of the curve in this threshold area may be quite sharp.
Several studies have demonstrated that age-O largemouth bass
that grow large enough to feed on fish grow more quickly
than those that are too small and must feed on invertebrate
foods (Aggus and Elliott 1975; Davies et ale 1982; Gutreuter
and Anderson 1985). Fast-growing members of an age-O cohort
that make the early transition to piscivory become the
recruitment class for the population (Gutreuter and Anderson
1985). Perhaps once Colorado squawfish exceed this
threshold length, their time to starvation becomes
effectively infinite.
The overwinter survival hypotheses represented by A, C,
and D in Figure 5 could be tested in field studies. The
curves presented in Figure 5 provide a range of possible
length-overwinter survival scenarios that may be occurring
in the wild. I believe the most likely relationship between
fish size and overwinter survival operating in wild
populations is curve D.
The actual shape and location of the length versus
overwinter survival relationship for age-O Colorado
squawfish probably varies with the latitude in which each
particular fish population occurs. Age-O fish in the
comparatively warmer Green and Lower Colorado Rivers are
generally larger than age-O fish in the Upper Colorado
River. Thus, Green and Lower Colorado River fish may