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Morphological variation and status.of Owens speckled dace, Rhinichthys osculus Donald W. Sada Bishop, California Morphology of Owens basin Rhinichthvs osculus collections made since the 1930's is examined and compared with a population from the adjacent Lahontan basin. Differences between all populations were statistically significant for many mensural and meristic characteristics, indicating that Owens basin speckled dace are distinct from R. o. robustus of the Lahontan basin. This also suggests that isolated populations in the Owens basin are subspecifically distinct. However, differences between many mensural and meristic characters of individual collections from a population were also statistically significant. This temporal variation and principle component analysis show the morphology of Owens basin populations is highly variable, and that these data cannot accurately describe taxonomic differences between populations. Other methods such as genetic analysis are required to determine the distinctiveness of isolated populations. The widespread historical distribution of speckled dace throughout the Owens Valley is indicated by museum collections. A field survey of 166 sites in the Owens basin from 1988-1990 found the species extirpated from most early localities, and existing at three sites not represented in early collections. The species is most widespread in the northern Owens Valley where five, low density demes persist in habitats that are distantly segregated by predatory fish populations. Two isolated populations in Long Valley, Mono County, and one population near Benton, Mono County, each occupy small springs and less than 1 km of stream. The species is extinct at Little Lake. The species has declined from its historic abundance and distribution because of the introduction of non-native fishes and habitat deterioration caused by diversion. Extant populations must be protected to prevent additional extinction of Owens speckled dace. 7