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SUCKER WETLAND USE Regulated Flows 1,000 ---- Unregulated Flows 800.1 1996 600 u s? N = 174 400 zer' ^ , 200 1 mE 600 W 0 400 lY Q 200 U a 1 uut. J 600 Z¢ 600 u? 400 200 1 1994 N = 1,217 10 1101 5 15 25 5 15 25 5 15 25 5 15 25 April May June July FIGURE 4.-Comparison of the periods when larval razorback suckers were collected in the Green River from 1993 to 1996 (rectangular boxes located at a flow of 575 m3/s) with those of flows in the presence (regulated) and absence (unregulated) of Flaming Gorge Dam. The filled area of each rectangle represents the period when the first 50% of the larvae were collected. The arrow on the descending limb of the discharge line represents the flow magnitude at which most main-channel backwaters appear under regulated flows (Pucherelli et al. 1988). itats, Mabey (1993) reported only 1.3 and 0.3 zoo- plankters/L in July and August, respectively. In a laboratory study, Papoulias and Minckley (1990) recorded significant starvation mortality of larval razorback suckers when the densities of Artemia sp, were less than 50 zooplankters/L. In experi- mental ponds, no differences in the survival of razorback sucker larvae occurred when prey den- sities varied from 13 to 43 organisms/L; however, there were significant differences in fish growth between prey densities (Papoulias and Minckley 1992). Thus, riverine floodplain habitats that offer refuge from velocity, nearly optimal temperatures, and high prey numbers provide an opportunistic bioenergetic environment for larval fishes. Given optimal growing conditions, razorback suckers grow more rapidly than most fishes (Minckley et al. 1991; Osmundson and Kaeding 1989), which can reduce the impacts of predation by nonnative fishes. Age-0 offspring of wild ra-