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km upstream of its original location at the Moab bridge (RK 104.1), and to the opposite side of the river (Figure 1). It was approximately 80 km downstream from another suspected spawning site (Doug Osmundson, pers. comm.). The flows near the sites were measured by the nearest United States Geological Survey (LJSGS) gages. Flows for the Westwater sites were measured by the Stateline gage (LTSGS gage # 09163500) which was 2.4 km upstream from the Colorado/Utah State line (RK 215.4), and 12 km above the Westwater site. Flows at the Moab site were measured by the Cisco gage (USGS #09180500) which was 1.6 km below the confluence with the Dolores River (RK 156.1), and 50 km above the Moab site. The Westwater site had a higher current velocity relative to Moab. Substrates at Westwater were cobble, gravel and sand, while Moab substrates were comprised of mostly fine sands and silt. Drift samples were taken daily from the third week in June (flood stage allowing) to late August to bracket the entire drift period in most years. The nets were set for two hours, from 0600 to 0800. Collection time was reduced if debris volume was too great. In 1996, some additional samples were taken at the Moab site. After the standard two-hour dawn sets, the nets were set again from 900 to 1100 hours, during the weeks when pikeminnow catch rates were highest, beginning five days after the first pikeminnow was collected at Moab. At each site, three conical plankton drift nets were deployed. The nets were set adjacent to one another and perpendicular to the flow, in a near-shore area with shallow (< 0.5 m) fairly laminar flow over cobble or graveUsand substrate, and were moved as needed to remain submerged as flows declined. The nets used were 4 m long, with a mouth diameter of 0.5 m, set into a rectangular frame (0.3 x 0.46 m), tapering to 10 cm, and ending in a removable collection bucket. A mechanical General Oceanics flow meter was secured in the mouth of each net to determine water velocity, and thus the volume of water sampled (formulae given in Appendix A). Each day all debris collected in the nets was preserved in 95 to 100% ethanol. Preserved fish were separated from the debris, and were delivered to the Larval Fish Laboratory at Colorado State University to be identified to species, counted, and measured to the nearest 1 mm. The total volume of water filtered through the nets and the relative density of drifting larvae were estimated for catch-per-unit-effort (CPE) in #fish/1000 m3. However, this catch rate does not account for the differences in total river volume between years during the collection times. The same number of larvae, diluted by a larger water volume could result in an underestimated catch rate. Therefore, the catch rate was expanded to #fish/hour transported past the drift sites, corrected for the total river volume past the site (see Appendix A for formulae). However, this method depends heavily on the assumption that the larvae are distributed throughout the water column and that abundance is similar at these locations among years. Drift density has been observed to vary by time of day, and in response to changes in turbidity in the Green and Yampa Rivers (Bestgen et al. 1998). Bestgen et al. (1998) reported variable drift densities with higher catches at noon and midnight; the differences at least partly dependent on water clarity. This suggests some minimal ability of the larvae to enter and exit the current in response to environmental variables. However, dawn sampling was the most consistent for larval densities in the Green and Yampa Rivers. Valdez (1985) reported that near-shore, early morning sampling produced the highest catch rates in the Colorado River. Nesler (1987) and Bestgen et al (1998) conducted cross-channel sampling in the Yampa River. Both studies concluded that drifting larval Colorado pikeminnow were distributed throughout the water column. However, Bestgen et al (1998) added that diel and cross channel densities may vary 2