7225

• UCREFRP Catalog Number: 7225
• Author: Kaeding, L. R., D. B. Osmundson and C. R. Berry.
• Title: Temperature as a Resource Limiting Colorado Squawfish in the Upper Colorado River Basin.
• USFW Year: 1985.
• USFW - Doc Type: \
• Copyright Material: YES

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~-, 800
~ 700
~~
W 500
J
Q 400
F-
0 300
Q 200
W
~ 100

Northern pike
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I ,.
r
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Largemouth bass/.~
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Colorado squawfish
(River)
.~ Colorado squawfish
(Pond)
1 2 3 4 5 6 7 8 9 10 1i
YEAR OF LIFE
Figure 6. Comparison of the growth rate of Colorado squawfish in a pond near
Grand Junction, Colorado (Osmundson, 1985), with those of Colorado
squawfish in the upper Colorado River (Seethaler 1978), northern
pike and largemouth bass (bars are the median 50 percent of the
values provided for these species by Carlander 1969, 1977). The
dashed line on the curve for pond fish is projected growth.
Effects of Slow Growth on Colorado Squawfish
The temperature-controlled slow growth and late age of first reproduction
of Colorado squawfish in the upper river may have important implications on
the Colorado squawfish population of the upper basin today, and on efforts
that may be planned to maintain and increase this population.
Perhaps the most important effect of reduced growth rate of fish is to
delay maturity. The immature fish are therefore exposed to the causes of
mortality for a longer period and fewer of them reach maturity (Nikolsky 1963,
Weat.herley 1972). There are no definitive data on survival of Colorado
squawfish in the upper basin. However, it is possible to demonstrate the
effect of growth r-at.e on survival for° simulated populations of slow and fast-
growing Colorado squawfish. We assumed that fish in the."slow" population
grew at the rate of those in the upper Colorado Hiver (5eethaler 1978),
whereas those in the "fast" population grew at the rate of fish in the
Osmundson (1985) study (Figure 6). We further assumed that maturity in both
populations occurred at 410 mm TL (6 years of age for "slow" fish and 3 for
"fast"), and that mortality was related t.o fish size. Thus the important
difference between our simulated populations was the length of time fish
resided in each length class, which was controlled by growth rate. Several
simulations were made, each with different rates of mortality in the smallest
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