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spawning during spring and eazly-mid summer for each yeaz of the study. 4. Determine relations among observed trends, over the course of the study, in distribution and abundance of Colorado pikeminnow, razorback sucker, other native fishes, and nonnative fishes in the lower 34.5 miles of the Duchesne River. Methods Study Area and Sampling Sites The study azea consists of the lower 34.5 miles of the Duchesne River, from Lake Fork Diversion neaz Myton, Utah, downstream to the confluence with the Green River. The river is divided into three reaches (Figure 1). The upper reach extends from Lake Fork Diversion (RM 34.5) downstream to the Ouray School Diversion (RM 23.1), the middle reach extends from Ouray School Diversion downstream to the confluence of the Uinta River (RM 14.5), and the lower reach from the Uinta River to the confluence with the Green River (RM 0.0). Three specific study sites were selected to provide a standardized, representative overview of the river. The Myton site (RM 29.0-27.0) represents the upper, higher gradient habitat with many cobble riffle azeas. The Uinta site (13.7-11.7) represents the intermediate gradient with meanders and split channels, and island complexes, and the Ouray site (RM 3.0-0.0) represents the low gradient, delta habitat, with steep banks stabilized by dense stands of tamarisk and Russian olive. Adult Sampling Adult fish were sampled throughout the study area (RM 34.5-0.0) in 1997 and 1998 during pre-peak, peak, and post-peak flows using an electrofishing boat or raft (4-kilowatt generator and Coffelt WP-15, spherical anodes, and direct current not exceeding 300 volts and 8 amps. In addition, in the Ouray reach fyke and trammel nets were fished in the main channel and in an adjacent floodplain habitat at the confluence of the Green River. During base flows in August and September, the Myton, Uinta, and Ouray sites were sampled by electrofishing (wading when flows were low or rafting when flows were high). Apre-winter sampling between RM 34.5 and 0.0 was completed 17-20 November 1997. The dates and types of adult sampling are given in Table 1 and the dates and corresponding flows are given in Figure 2. All native fish were weighed and measured; all nonnative fish were counted and a sample (usually >50%j was weighed and measured. Larval Sampling Light Traps. The light traps were floating quatrefoil units (commercially manufactured as the Edlite by Southern Concepts, Birmingham, Alabama; modified after the original design of Floyd et al. 1984) with 4-mm wide entry slits. Light traps were deployed overnight and picked up just prior to sunrise. Six light traps were set overnight twice each week in slack~water habitats during the 8