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1 1 1 1 1 survival and recovery of Colorado squawfish. Data describing aspects of the ecology of Colorado squawfish life stages have been collected for over 15 yeazs, but causal mechanisms that affect recruitment have not been identified and efforts to synthesize individual studies have been limited by lack of integrative approaches. A primary goal of this reseazch was to quantitatively integrate existing knowledge of biotic and abiotic factors that influence recruitment of Colorado squawfish eazly life stages. This was accomplished by constructing a conceptual life-history model, and a mechanistic computer simulation model that estimates relative survival and growth of age-0 Colorado squawfish during their first summer. The mechanistic model presented in this report estimates the response of age-0 Colorado squawfish to a variety of environmental conditions including (a) interactions with a potentially predacious and abundant nonnative species, the red shiner Cyprinella lutrensis, (b) temperature regime, (c) water clazity, and (d) availability of alternate prey for red shiner. To illustrate how the mechanistic model can be used to evaluate the relative effects of environmental factors and potential management actions on Colorado squawfish populations, we implemented the model using different water-temperature regimes, larval growth rates, predator densities, and date of colonization of nursery habitat. The effect of each environmental factor was assessed by analyzing survival and growth of Colorado squawfish during each simulation. The Conceptual Life History Model Model Development We constructed a conceptual life history model for Colorado squawfish that links recruitment to successive developmental stages with important biotic and abiotic controlling 3