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less water will be available for dilution of natural and <br />anthropogenic pollution sources. If increases in water use <br />outpace the process of pollution abatement within the Colorado <br />River Basin, frequency and magnitude of contaminant-induced toxic <br />effects will increase even if contaminant inputs remain constant. <br />Geographical distribution of Colorado squawfish has been greatly <br />reduced and reproducing populations currently inhabit less than <br />25% of the former range (Tyus 1991). There are no refugia for <br />Colorado squawfish if remaining habitat becomes unsuitable-for <br />any life-stage requirement. Given that many human-induced <br />catastrophic and cumulative changes responsible for decline of <br />Colorado squawfish are still present in the Colorado River Basin <br />(Behnke and Benson 1983; Carlson and Muth 1989; Tyus 1991), it is <br />important to prevent further anthropogenic degradation. Unlike <br />biological interactions like competition or predator-prey <br />dynamics, contaminant effects can be relatively easily quantified <br />by laboratory and field experiments, and effects on wild <br />populations can be predicted (Suter 1993). <br />Traditional toxicity testing procedures do not detect <br />behavioral changes that may affect predator avoidance, mating, <br />feeding in patchy environments, or homing and migration. <br />Although the temporal scale of these behaviors may be short, <br />(e.g., predator avoidance may occur over a period of seconds) <br />they facilitate intense interactions that may have extreme <br />outcomes (e.g., survival or death). Behavioral toxicity tests <br />bridge the gap between traditional laboratory toxicity tests and <br />21 <br />