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EXECUTIVE SUMMARY Colorado squawfish (Ptychocheilus lucius), a large piscivorous cyprinid endemic to warm- water reaches of the Colorado River system, is well known for its spawning migrations and long-distance drift of resulting larvae. However, little is known about the dispersal movements of juveniles recruiting to the adult population. Our objective was to describe these movements among Colorado squawfish in the upper Colorado River in an attempt to better understand the life history strategy of this endangered species. River-wide, capture-recapture data of PIT-tagged fish were used to document movements of subadult and adult Colorado squawfish. Capture and tagging efforts were made during spring runoff (mid-April to mid-June) from 1990 through 1995. Most captures were made by trammel-netting flooded backwaters, but data were also supplemented with electrofishing captures. Limited capture and tagging efforts were made in 1990 and only in the upper reach (upstream of Westwater Canyon). During 1991-1994, three passes through the upper reach were made each year to net Colorado squawfish; with each pass, every backwater was netted. Two such passes were made each year through the lower reach (downstream of Westwater Canyon), with only one pass made during 1991. Recapture data obtained during 1995 was from other electrofishing and netting studies conducted in both reaches. Longitudinal distribution of Colorado squawfish was described in terms of mean size of fish and mean number of adults captured per net in six river strata. Concentration areas of Colorado squawfish during the spring runoff period were also noted. Movements of fish captured one year and recaptured in a subsequent year were compared among size classes of fish and between those fish initially captured in the lower reach and those captured in the upper reach. Sizes of those fish moving from the lower reach to the upper reach were also noted. After hypothesizing that dispersal movements are a response to food resource gradients, we compared relative body condition of similar-sized adults from the lower and upper reaches and compared relative abundance of native forage fish among river strata. Average length of Colorado squawfish progressively increased upstream and was most pronounced during the first years of the study. During 1991-1992, most adults (> 500 mm TL) were concentrated in the upper reach and very few adults were found in the lower reach. As the study progressed, demographics changed as 2-3 consecutive strong year classes, hatched during the mid-1980's, grew and dispersed as they recruited to the adult population. As a result, average length increased in lower-reach strata and decreased in upper-reach strata. By 1993, there was a five-fold increase in catch rates of adults in the lower reach. Lower-reach sites where subadults and adults were most concentrated during runoff included the mouths of Indian and Kane Springs creeks in Stratum 1, and Cisco and Sagar's washes in Stratum 3. Concentration sites for adults in the upper reach during runoff included B-v