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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J F M A M J J A S O N D
. MONTH
Figure 4. Comparison of temperature regimes (average mean-monthly
temperatures) of the historic lower (near Yuma, Arizona, 1917-1924,
from Dill 1944) and middle Colorado River (near Grand Canyon,
Arizona, 1943-1947, 195?), and of the present. upper Colorado River
(near Colorado-Utah border, 1972-1978). Horizontal lines are
temperature thresholds for growth (14 C) and the onset of spawning
(20 Cj of Colorado squawfish. Numbers in parentheses are the
relative availability of temperatures suitable for Colorado
squawfish growth provided by each temperature regime {see text).
Temperatures from middle and upper river are from the United States
Geological Survey. See Figure 1 for sites of temperature-data
collection.
suitability indices to temperatures in the growth--rate vs. temperature
relation according to the percentage of optimum growth that they provided
(Figure 5). Thus 25 C had a suitability index of 1.0, 20 and 30 C had
suitability of 0.5, and temperatures of 14 C and cooler had suitability of
zero. Indi.ees for intervening temperatures were calculated by interpolation.
Mean-monthly temperatures were multiplied by their respective suitability
indices, and resulting values were summed aver the year for each of the
Colorado River temperature regimes (Figure 4).
Temperature regimes of the historic lower and middle--river reaches would
have allowed greater annual growth of Colorado squawfish than would that of
the upper river. This conclusion is based on our estimates of the relative
availability of temperatures suitable for growth as well as nn the length of
the growing seasons provided by the temperature. regimes (Figure 4). The
growing season of the upper river is less than five months, whereas those of
the middle and lower river were about six and eight months, respectively. How
rapid growth in the lower river might have been is unknown, however. There is
no information on Colorado squawfish growth in nature under conditions
(including temperatures) that are more nearly optimal. Pivnicka (1983)
reported that seven fish species, including four cyprinids, were able to
increase their growth rate 12 fold in optimum conditions. Colorado squawfish
might therefore be capable of appreciable annual growth under conditions like
those of the historic lower river. Data that support this conclusion has
recently been gathered by Osmundson (1985). In October, 1983, Osmundson
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