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RESULTS AND DISCUSSION Speckled Dace (Rhinichthys osculus) Speckled dace were collected from 20 of the 27 sites sampled and a total of 96 haplotypes were identified among the populations (Table 4). The number ofhaplotypes per population ranged from a low of two (Groundhog Creek- site # 21) to a high of 16 (White River below Kenney Reservoir - site #6), with an average of 7.5 haplotypes per population. Given the high number of haplotypes found in the survey, unique patterns were expected, and these ranged from no unique haplotypes in Groundhog Creek of the Dolores River system (site 21) to a high of eight unique haplotypes in the San Juan River (site 27). The populations averaged 3.6 unique haplotypes each. The overall distribution and frequencies ofhaplotypes among populations are shown in Table 5. The haplotypes are numbered from 1 through 96. The 20 stations containing speckled dace are the columns, ordered by drainage basin. Only haplotype 1 shows a wide distribution, being present in samples from the Yampa, White, Colorado and Dolores rivers. It is most frequent in the Colorado and Dolores Rivers. Haplotype 12 occurs in both the Colorado River and the Dolores River subbasins. Four haplotypes, numbers 52, 54, 58, and 64, were shared between the White and Yampa subbasins. The remaining haplotypes occur either within single populations or between populations within a river subbasin. This pattern indicates that a strong tendency exists for speckled dace to be unique within drainages. The least separation between river subbasins occurs between the White and Yampa rivers. A more formal examination of the degree of genetic differentiation between populations and river systems is obtained with fixation indices (F statistics). The sampled populations were grouped by major river subbasin, resulting in five groups, the Yampa River, the White River, the Colorado River (including the Gunnison River), the Dolores River, and the San Juan River. Speckled dace were only collected from 20 of the 27 stations, but the original site numbering (Figure 1) was retained on the matrices. The Fst values for speckled dace are given in Table 6. In general, values less than 0.05 indicate little genetic divergence. Populations within this range are similar enough to be considered to be identical. Fst values between 0.05 and 0.15 are considered indicative of moderate differentiation and those with values from 0.15 and 0.25 are highly differentiated. Any value over 0.25 indicates great genetic divergence (Hartl and Clark 1997). Further, Arlequin (Schneider et al. 1997) generates a list of those Fst values that can be considered statistically significant, based on sample size and the degree of genetic differentiation. These are highlighted in bold type in table 6. None of the populations within the same river subbasin have significantly different Fst values. That is, within each of the major river systems, the Yampa, White, Colorado, Gunnison, Dolores, and San Juan rivers, little differentiation can be directly detected with the Fst index, despite the presence of a number of unique haplotypes in many of the populations. Populations from the two systems that share the most haplotypes (Table 5), the Yampa and White rivers, are moderately to highly divergent from one another with the exception of Station 9 which is not significant in its differences from two of the four Yampa River sites. Station 9 is the downstream-most sampling station on the White River system. Both the Yampa and White 27