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DISTRIBDTION AND LIFE HISTORY OF MAJOR FISHES Colorado squawfish Distribution and Abundance Colorado squawfish, while not abundant anywhere, were captured consistently throughout a major portion of the study area. Adult squawfish were especially widespread in their distribution, probably a reflection of their predatory nature and the prevalence of suitable habitats throughout the river system. Juvenile and young-of-the-year ' (YOY) squawfish exhibited a much more localized distribution which was attributed to an affinity for habitats that were much more restricted in distribution. Investigations over the past two years have demonstrated that adult squawfish are inhabiting some 360 mi of the mainstem Green River and that their range of occupation extends 134 mi up the White River and 108 mi up the Yampa. On the mainstem Colorado above Lake Powell, Colorado squawfish were collected in the lower 200 mi of river and from the lower 30 mi of the Gunnison River. Collections were variable throughout the sampling period, but 87~ of the adult squawfish collected from the main Colorado were from a 50 mi reach between river mile (RM) 125 and 175, the section of river between Grand Junction downstream to the head of Westwater Canyon. In the Green River and its tributaries, adult Colorado squawfish were more prevalent in those reaches having a moderate gradient and less incised channel. Reaches located between Split Mountain Gorge (RM 320) and the head of Desolation Canyon (RM 212) and from the lower end of Gray Canyon (RM I32) to the confluence of the Green and Colorado Rivers produced 63x of the adult Colorado squawfish catch (Table 1). As spawning season approached during the spring of 1980 and 1981, mature radio tagged squawfish exhibited a heightened level of activity and migrated considerable distances. In 1981, seven of these tagged fish traveled to a common reach of the lower Yampa River. This congregation of fish lasted only a short time, approximately 10 daps, and then they dispersed back to the vicinity of their original capture. Juvenile squawfish were conspicuous in their scarcity in most collections, probably to some degree an artifact of gear selectivity. General trends in juvenile distribution showed them to be more prevalent in the lower 100 mi of the main Colorado River (Figure 2) and the reach of the Green River between the White River's confluence and Desolation Canyon (Figure 3). Considerable effort has been expended over the past 2~ years collecting larvae and YOY squawfish as a means of gaining insights into spawning areas and reproductive success. Some very solid information has developed from this work. c