6012

• UCREFRP Catalog Number: 6012
• Author: Miller, W. H., D. L. Archer, H. M. Tyus and K. C. Harper.
• Title: Colorado River Fishery Project
• USFW Year: 1982.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

velocities. They were found to frequently venture into backwaters and
other off-stream hab t is during early evening and morning. Beamsderfer
and Congleton ~l~~o~served northern squawfish in a wide range of
conditions but found them to prefer moderate de ~s an to -to moderate
velocities during daylight. They suggest tha~~eii e~r probably
changed during darkness because they were captured in nets in areas that
they rarely were seen in during daylight times. We suggest that these
captures probably were a result of a foraging activity during the period
of darkness and not an example of a change in preferred habitats fvr
resting periods or times of inactivity.
We generally concluded that adult squawfish are not especially
demanding in their habitat needs and that suitable habitats were quite
prevalent throughout much of unimpounded sections of the upper basin.
Limiting Factors

v
Temperature - Water temperature is a critical factor to ad It fish
for gonadal development, spawning and growth. Hamman (Appendix,' observed
that female Colorado squawfish require about 30 days at 20°C for ova
development and a temperature of 20-22°C for natural spawning to occur.
Spawning both inn th tchery and in the field occured between June 15
and July 15 ( ). Temperatures in the river usually are in
the low twenties at this time of year and apparently are conducive to
spawning. Spawning migrations have been documented by our field crews
using radiotelemetry. Responding to some triggering mechanism, several
fish at different locations initiated long migrations at similar times.
Rising temperatures, descending flows and photoperiod appear to be
important stimuli to the adult migration.
C-
Bulkley et al (Appendixa have shown that velocities at which adult L
Colorado squawfish could swim were lower at both 14°C and 26°C than at
20°C (Figure 4). The velocities (interpolated) at which they could swim
for one hour were 0.87 m/s at 14°C, 0.88 m/s at 26°C and 0.98 m/s at
20°C. In preference tests, temperature selected by adults varied from
21.5 to 25.7°C depending on acclimation temperature. The estimated
final preferendum for adults was 25.3°C.

Egg development, hatching success and larval development are affected
by temperature. At 13°C, egg mortality was 100X in a controlled test
(Appendix At 16-18°C, development is slightly retarded, but hatching `"
success and survival of larvae were higher. At 20-26°C, development and
survival through the larval stage were up to 95X.
Field studies found a similarity between juvenile ( 200 mm) and YOY
Colorado squawfish in behavior and habitat selection. They were most
often caught in backwaters and Biel movements between the backwaters and
the main river were observed. Apparently, the backwater provides cover,
food and warmer temperatures for, them during the day and through the
evening hours. However, in the early morning hours when the main channel
temperatures are equal to or are higher than those found in the back-
waters, the young fish move out into the main channel. Maintaining
themselves in the warmest water available promotes more rapid growth as
observed in the laboratory and hatchery.