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8 Miller et al. (1982a) studied the lower 241 kID of the White River to its confluence with the Green River. Of 15 fishes collected, eight were nonnative. Red shiner was the most common and widely distributed of the introduced fishes. Miller et al. (1982a) observed that red shiner juveniles and adults had greatest abundance at lower sites and decreased in numbers at upper sites. Gila spp. abundance was the opposite, with greatest number at upper sites. They postulated this could indicate that either habitat was more suitable for natives in the upper strata or competition existed between Gila spp. and red shiner at lower strata, with Gila spp. apparently losing the battle. Relationship between abiotic parameters and abundance of nonnative fishes The literature surveyed often revealed apparent relationships between abiotic factors and the abundance of introduced fishes. The most common abiotic factors mentioned were habitat alteration and flow events. Several examples follow. In the San Rafael River, Utah, a tributary to the Green River, McAda et al. (1980) found native fishes only at upstream stations. Introduced fishes were found at downstream stations near the Green River. This was attnbuted to differences in habitat between the two sections. The lower section was dewatered, less diverse, and more uniform than the upper section. A similar pattern was noted by Deacon and Bradley (1972) in the Moapa River, Nevada. .. Lanigan and Berry (1979, 1981) studied the White River (106 km) in Utah from 1978-1979. Red shiner was the most commonly collected species (62%) of all fish collected. They cited a study by (Crosby 1975) in 1974-1975 that collected similar numbers of red shiner (52%). Lanigan and Berry (1979) noticed that introduced fishes had replaced endemic fishes in the lower White River and were becoming more numerous in upstream reaches. They also suggested that the fish fauna may have been influenced by habitat alterations because numbers of nonnative fish increased as habitat diversity decreased. In the Colorado River, Colorado, low spring flows apparently benefitted nonnative fishes that were adapted to stable environments (Osmundson and Kaeding 1991). High spring flows, however, flushed nonnatives from backwater habitats and into the main channel. Turbulent riverine conditions and delayed warming probably intedered with nonnative reproduction (V~dez 1990; Osmundson and Kaeding 1991). Abundance of, fathead minnow, sand shiner, and red shiner larvae decreased with increased peak flow in three Grand Valley, Colorado, reaches in the Colorado and Gunnison rivers (Osmundson and Kaedingl991). Numbers of other introduced fishes (mosquitofish, green sunfish, and largemouth bass) were also negatively correlated with peak flow, but correlations were not strong enough to be significant given the small sample size of years in which sampling was conducted