7772

• UCREFRP Catalog Number: 7772
• Author: Bestgen, K. R. and M. A. Williams.
• Title: Effects of Fluctuating and Constant Temperatures on Early Development and Survival of Colorado Squawfish.
• USFW Year: 1994.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

Colorado squawfish apparently have complex adaptive strategies for reproduction in
historically fluctuating riverine habitats of the Colorado River basin and may use discharge
level and variation, and water temperature, as primary environmental cues to initiate
reproduction (Kesler et al. 1988; Tyus 1990). In its unregulated state, flow and temperature
regimes in the Colorado River basin varied dramatically across seasons and years. Given
such variability, eurythermicity of embryos and early larvae is -not surprising.
Reduced summer water temperature is thought to be partially responsible for extirpation
of Colorado squawfish in river reaches immediately downstream from dams (Holden 1979;
Behnke and Benson 1983; Marsh 1985). Reestablishment of self-sustaining populations of
Colorado squawfish in reaches affected by dams may require restoration of temperatures
that more closely approximate historical regimes (Tyus and Karp 1989). Effects of a
diverse and abundant nonnative fish community on Colorado squawfish should also be
considered. Integrated laboratory and field research is needed to better determine the role
of temperature and other factors that control migration, spawning, early development, and
survival of Colorado squawfish in the Colorado River basin.
Acknowledgments
Funding for this project was provided by the U. S. Bureau of Reclamation, Salt Lake
City, Utah under Cooperative agreement 8-FC-40-06460 with the Larval Fish Laboratory,
Colorado State University, and by the Recovery Implementation Program of the Upper
Colorado River Basin. Project administration was facilitated by R. Williams, L. Crist, and
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