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information is available. The life cycle of the Colorado pikeminnow is relatively complex, including spatial separation of life stages and energetically-costly migratory behavior (Tyus 1986, 1990). These components are part of the life strategy and tactics ~ that have maximized fitness of the Colorado pikeminnow over millions of years. The foregoing review has been assembled ftom many sources, each reporting on a small facet of life history. There is a lot of "noise° in the compilation of facts, because it is based in part on actions of individual fish and their response to environmental factors. Consequently, this collection of facts lacks cohesiveness. The following narrative seeks ~ coherence and cohesiveness for the most important features of the life history,-but the cost of simplifying complex phenomena is the loss of detail. In general, adult Colorado pikeminnow spend most of the baseflow period (Sep-Apr) in upper river reaches that extend as far as the downstream edge of Coldwater trout habitat. Each fish occupies a relatively stable home range located in areas that have ~ high densities of native suckers and chubs. Physical habitat conditions are variable, and habitat selection is probably related to prey abundance. Adults exhibit considerable tolerance to cold and remain active throughout the winter. Adults become very active in spring when snowmelt cause the rivers to rise. Rising ~ flow, increasing temperatures, and other environmental influences stimulate gonadal development and reproductive behavior. During peak runoff, usually in May, adults begin migrating to spawning areas. Homing, guided presumably by olfactory cues, takes the adults to the same spawning site from which they emerged as sac-fry; pefiaps more than a decade before. Spawning activity occurs over a 3-4 week period ~ when flows are declining after peak runoff, and when water temperatures are in the range of 22-25°C. Adult females may use overbank areas for staging, and the higher temperature in these habitats may hasten the maturation of ova. The adhesive eggs are deposited on cobble bars and develop for 7-10 days before ~ hatching. The newly emerged sac-fry drift downstream and soon reach suitable nursery habitat about 100 km of the spawning area. The young fish may continue to move downstream another 20 km, or more, during the next few months. Backwater nursery habitat is created by the declining flows that follow peak runoff. If peak flows are low, few backwaters are formed. If flows remain high, potential backwaters are inundated. However, past studies have demonstrated that a simplistic flow/backwater area relationship does not occur; instead, the duration, timing, and magnitude of flows and sediment inputs seem to be implicated. In the nursery area, the larvae and postlarvae feed on zooplankton and benthos. As they grow in size, they begin to consume fish as well. Postlarvae continue to feed actively throughout the ~ winter, but can withstand extended periods of starvation, if food is unavailable. The juvenile fish (60-200 mm) occupy backwater areas in the spring of their first year, but are difficult to find after spring runoff, apparently because they begin using other habitats. 18