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ABSTRACT OF DISSERTATION <br />EFFECTS OF PHYSICAL AND BIOLOGICAL FACTORS ON <br />RECRUITMENT OF AGE-O COLORADO SQUAWFISH <br />Recruitment is central to population ecology because the abundance of young <br />individuals often drives dynamics of subsequent life stages. However, understanding <br />mechanisms that regulate recruitment is challenging because it integrates numerous life- <br />history processes including timing and success of reproduction, and growth and dispersal <br />of young. Recruitment processes are particularly difficult to understand in riverine <br />ecosystems that are physically disturbed by the presence and operations of impoundments <br />and biologically altered by numerous non-native species. I used a combination of <br />laboratory and field investigations to evaluate the importance of physical and biological <br />factors that may affect recruitment of early life stages of endangered Colorado squawfish <br />Ptychocheilus lucius in the Green River, a regulated river of the Colorado River basin. <br />Colorado squawfish embryos reared in three constant (18, 22, 26°C) and three <br />fluctuating temperatures (18, 22, and 26°C; diel fluctuation ~ 2.5°C) had relatively high <br />hatch rates of 54-79%, whereas hatching success was only 38% at constant 30°C. There <br />was no significant difference in hatch between constant and fluctuating temperatures. <br />Survival of larvae to 7-d was 52-88% in water temperatures ranging from 18-26°C but <br />was only 13% at constant 30°C. Survival of larvae was 10-31% higher in fluctuating than <br />in constant temperatures. Incidence of abnormalities was 2-22% at 18-26°C and 100% at <br />30°C. Differences in abnormality rates were not detectable between constant and <br />fluctuating temperatures. Time to initiation of hatch, swim bladder inflation, and <br />iii <br />