Rhinichthys osculus subspecies

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General Information
Common Name: 
Owens speckled dace
FID: 
CRO04
Status: 

Conservation Status in California: Class 1, Endangered (Moyle et al. 2011).
The Owens speckled dace has been extirpated from a majority of its historic range in recent years due to habitat alteration, competition and predation from alien species, and water withdrawal. Only a handful of populations remain, mostly isolated from one another, in the East Fork of the Owens River near Benton and in irrigation ditches near Bishop. It is clearly in danger of extinction within the next 50 -100 years.

Life History: 

Life History: Particular life-history adaptations of speckled dace from the Owens Basin have yet to be determined. In general, speckled dace feed on small aquatic insects and algae (Moyle 1976). They typically live three years and attain a maximum size of 80 mm SL in inland basins (Moyle 1976). Owens speckled dace, however, rarely exceed 50 mm SL in length.
For a general life-history of speckled dace, see the Santa Ana speckled dace account in this report.

Habitat Requirements: 

Habitat Requirements: Speckled dace from the Owens Basin are known to occupy a variety of habitats ranging from small coldwater streams and hot-spring systems, although they are rarely found in water exceeding 29°C. They also have been found in irrigation ditches near Bishop. Despite the large variety of habitats apparently suitable to speckled dace of the Owens Basin, their disappearance from numerous localities since the 1930s and 1940s suggests their vulnerability to habitat modifications and to invasion by exotic fishes.
For a more general account of the habitat requirements of speckled dace please see the Santa Ana speckled dace account in this report.

Distribution: 

Distribution: California Department of Fish and Game (CDFG) files and museum records from the University of Michigan Museum of Zoology and the California Academy of Sciences, dating back to the 1930s, indicate that speckled dace historically occupied most small streams and springs in the Owens Valley. In the most comprehensive survey of Owens Basin aquatic habitat to date (166 survey sites), dace were found to have been extirpated from 8 of the 17 sites for which they had been historically recorded. Dace were also discovered at two new locations both of which have since been extirpated (Sada 1989, S. Parmenter, CDFG, pers. comm. 2009). Today, the nine sites in the Owens Basin where dace occur represent 7 populations. The population in Long Valley at Whitmore Hot Springs in now recognized as a separate taxon, which means 6 Owens speckled dace populations remain. Five of these populations are in the northern Owens Valley (North McNally Ditch, North Fork Bishop Creek, irrigation ditch in north Bishop, Lower Horton Creek, and Lower Pine and Rock creeks) and a single small population remains in the East Fork Owens River drainage at Lower Marble Creek near Benton.
Speckled dace no longer occupy the Hot Creek system, springs near Benton Crossing in Long Valley (Mono Co.), Fish Slough, irrigation ditches between Bishop and Big Pine or Little Lake (Inyo Co.). Dace were not found in Warm Springs, where CDFG biologists had planted 75 speckled dace in 1983 (Sada 1989).

Abundance Trends: 

Trends in Abundance: There is little data available on the historic abundance of this dace. Given its greatly diminished range due to extirpation of many populations, it is undoubtedly much less numerous than it once was. Even in the streams and irrigation ditches around Bishop, where they are widespread, speckled dace now occur at low densities (Sada 1989).

Description: 

Description: Owens speckled dace are highly variable. A morphometric comparison of all extant populations in the Owens basin found that although populations differ significantly for many characteristics there is also high morphological overlap among populations. The frenum was well developed only in the now extirpated Little Lake population. Maxillary barbels occurred in most populations but were poorly developed in Long Valley populations and absent from Walker River fish. Speckled dace in the northern Owens Valley have maxillary barbels on at least one side, a high lateral line scale count, a moderate lateral line pore count, and moderately sized fins. Benton Valley populations have low lateral line scale and pore counts, maxillary barbels on at least one side, and a comparatively long pelvic fin.
The following ranges in mean counts are for four populations in the Owens River drainage and one in the Walker River drainage: lateral line scales 59.3-70.7; lateral line pores 11.6-61.7; dorsal rays 7.8-8.0; anal rays 7.0-7.1; pectoral rays 12.0-13.9; pelvic rays 7.0-7.6; total vertebrae 36.9-38.1.
For a general and more in depth description of speckled dace please see the Santa Ana speckled dace account.