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

800
700
~ soo
LZLJ 500
J
Q 400
H
~ 300
Q zoo
W
~ ioo
Northern pike
Largemouth bass f
I ~~
~/
I
I ~ Colorado squawfish
I .~
I / MATURE AGES
I j
~ Colorado squawfish
Northern pike and Largemouth bass
1 n n
' ~ w o b / 8 9 10 11
YEAR OF LIFE
Figure 3. Comparison of growth rate and mature ages of Colorado squawfish
from the upper Colorado River (Seethaler 1978) with these
characters for northern pikes and largemouth bass (vert.ical bars are
the median 50 percent of the values provided for these latter
species by Carlander 1969, 1977; data on mature ages are also from
these references).
suitable prey species are abundant (Tyus et al. 1982). Many are introduced
cYprinids, which laboratory studies have shown are readily eaten by Colorado
squawfish (C. Berry, unpublished data). A .t imitation of temperature seemed a
more likely explanation for this slow growth. We summarized water-temperature
data for three, widely separated Colorado River locations within the historic.
and present range of Colorado squawfish {Figure 4). Middle and lower-river
data were taken prior to modification of temperature regimes by upstream dams.
There was a progressive, downstream increase in temperature throughout the
year. Mesa-monthly summer temperatures in the historic lower river neared 30
C, whereas those of the upper river only rear_h about 22 C.
Black and Bulkley (1985a) studied the relation between temperature and
body growth with excess food for small (45-100 mm TL) Colorado squawfish.
They found that. optimum growth occurred at 25 G, whereas growth at 20 and 30 C
was 50 percent of optimum. We performed a least-squares regression of the
growth--rate vs. temperature data provided in Table .l of Alack and Bulkley
(1985a) to estimate the threshold temperature for growth (that below which no
growth will occur regardless of food availability) as about 14 C. Preferred
temperature is generally considered the optimum for many physiological
processes, including growth (see for example Magnuson et a1. 1.979). Results
of temperature-preference investigations (Black and Bulkley 19$5b, Bulkley et
al. 1981) supported thel5-C optimum for growth reported by Rlack and Bulkley
(1985a)', and also indicated its applicability to adult fish. The growth-rate
vs. temperature relation of Colorado squawfish is somewhat intermediate t.o
those of representative cool and warm-water species (Figure 5). We assigned
150
i