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. Comparison of River Flow Regimes and Relative Abundance . . Natives.- Correlation (Pearson r) among years between river flow parameters and abundance of larval speckled dace and flannelmouth sucker was examined. The association of Catch-per-unit-effort (CPUE) oflarval speckled dace and flannelmouth sucker with peak flow was significantly positive among years ( r = 0.92 and 0.94 respectively). This is consistent with other authors who have examined these associations (Muth and Nesler 1993; McAda and Kaeding 1989; Osmundson and Kaeding 1989, 1991; Valdez 1990). In the lower Yampa River, Muth and Nesler (1993) reported greater values ofCPUE for speckled dace, bluehead sucker, and flannelmouth sucker were associated with high discharge and lower values of CPUE for speckled dace, bluehead sucker, and flannelmouth sucker were associated with low-moderate discharge. In the Duchesne River, relative abundance of post-larval speckled dace remained high through the late summer of 1998 (Table 5). However, average relative abundance of post- larval flannelmouth sucker for all three reaches remained consistent among years. Correlation of CPUE for post-larval flannelmouth sucker with peak flows among years for each reach show a statistically significant (P ~ 0.10) negative association (r = -0.97) in the upper Myton reach and a strong positive association (r = 0.84) in the lower Ouray reach (Table 6). A reasonable explanation of this association is that flannelmouth sucker larvae in the Duchesne River are transported further down river from spawning areas during higher flow years resulting in lower densities of post-larval flannelmouth sucker in the higher gradient Myton reach and higher densities of post-larval flannelmouth in the nursery habitats of the lower gradient Ouray reach. Nonnatives.- Densities of several nonnative species decreased from 1997 to 1998 on the lower Duchesne River which may be a result of the high peak flows and sustained high base flows (Table 5). All statistically significant correlations among years between total discharge, peak flow and mean discharge and CPUE of nonnative fish indicate negative association with the exception of the correlation of peak flows and CPUE of green sunfish in the Myton reach which showed as strong-positive association (r = 0.78; Table 6). Statistically significant correlations for nonnative fish were inconsistent among reaches and flow parameters. Other authors have indicated high spring flows negatively impact some prolific nonnative fish species (McAda and Kaeding 1989; Osmundson and Kaeding 1991; Tyus and Saunders 1996; Muth and Nesler 1993); while production of native larvae (bluehead sucker and speckled dace) is believed to increase with increased peak flow. This negative impact was also apparent with smallmouth . . . . . . . 10 .