Rhinichthys osculus subspecies

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General Information
Common Name: 
Long Valley speckled dace
FID: 
CRO05
Status: 

Conservation Status in California: Class 1, Endangered (Moyle et al. 2011).
Long Valley speckled dace are highly vulnerable to extinction in their native range within the next 50 years because they exist in a single spring complex fed by the chlorinated outflow of a public swimming pool. This sole habitat is also under threat from invasion by predatory non-native tiger salamanders.

Life History: 

Life History: Particular life-history adaptations of speckled dace from Long Valley have yet to be determined. In general, speckled dace feed on small aquatic insects and algae (Moyle 2002). For a general account of speckled dace life-history see the Santa Anna speckled dace account in this report.

Dispersal Capability: Only capable of natural colonization via hydrologic stream connection. Currently confined to one small marsh habitat. Dispersal unlikely.

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. After morphometric analysis of both extant and museum specimens Sada (1989) theorized that Long Valley speckled dace were a deep bodied form adapted to spring habitats. Despite the large variety of habitats apparently suitable to speckled dace in the Owens Basin, their disappearance from numerous localities suggests that they are quite vulnerable to habitat modifications and to invasion by alien fishes.
For a more general account of the habitat requirements of speckled dace see the Santa Ana speckled dace account in this report.

Distribution: 

Distribution: The entire native range of this dace lies within the 700-thousand-year-old Long Valley volcanic caldera, just east of Mammoth, Mono County, including Hot Creek and various isolated springs and ponds. The formation of the caldera likely led to their isolation long before the other populations of the northern Owens Basin where cut off from each other. Long Valley Speckled Dace have been extirpated from all but one of their historic collection sites. The sole population within the native range is in Whitmore Hot Springs (Sada 1989). Whitmore Hot Springs have been developed and are operated as a swimming pool by Mono County. Lightly chlorinated discharge from the swimming pool (approximately 2 cfs) feeds an alkali marsh approximately 1 acre in area. In 1989, dace occupied 250 yards of stream and two large shallow ponds that did not exceed half a meter in depth. These dace population here appears to be heavily parasitized (Sada 1989, S. Parmenter, CDFG, pers. comm. 2009). Surveys in 2002 and 2009 by CDFG found this population to be relatively stable (S. Parmenter, CDFG, pers. comm. 2009).
Long Valley speckled dace were translocated from Whitmore Hot Springs to an undisclosed location near Bishop (S. Parmenter, CDFG, pers. comm. 2009). On average, six additional fish from the Whitmore Springs population are translocated to the refuge population annually in an effort to minimize genetic drift.
In 1988, Sada discovered a population in an unnamed spring at Little Alkali Lake but this population was subsequently extirpated. Dace occupied an estimated 600 meters of stream between the spring source and the lake. Fish were not believed to occupy the spring source where water temperatures exceeded 28°C or Little Alkali Lake itself. When last surveyed, large numbers of western mosquitofish (Gambusia affinis) were observed, but no speckled dace (S. Parmenter pers. comm. 2009). Speckled dace were last sampled in Hot Creek in 1962 but were likely extirpated from this habitat due to alterations to the system by the creation and operation of Hot Creek Hatchery (Sada 1989).

Abundance Trends: 

Trends in Abundance: There are little data available on the historic abundance of this dace. However, the extirpation of all but one of the historically identified populations means that it is undoubtedly much less numerous than it once was. According to the US Fish and Wildlife Service (1998), it is continuing to decline.

Description: 

Description: The following is a general description of speckled dace which is followed by specifics for the undescribed Long Valley subspecies. Speckled dace are small cyprinids, usually measuring less than 8 mm but occasionally reaching 11 cm SL (Moyle 2002). Although physically variable, they are characterized by a wide caudal peduncle, small scales (47-89 along lateral line), and pointed snout with a small subterminal mouth. At maturity the dorsal fin usually has 8 rays and originates well behind the origin of the pelvic fins (Moyle 2002). The anal fin has 6-8 rays. Pharyngeal teeth (1,4-4,1 or 2,4-4,2) are significantly curved with a minor grinding surface. The maxilla usually has a small barbel at each end. The snout is connected to the upper lip (premaxilla) by a small bridge of skin (frenum). As their common name indicates, most fish larger than 3 cm have distinctive dark speckles on the upper and sides of the body, although some fish from highly turbid waters may lack speckles. Dark blotches present on the side can merge creating what looks like a dark lateral band. A stripe on the head, below the eye, extends to the snout, and there is black a spot on the caudal peduncle. The rest of the body is dusky yellow to olive, with the belly being a paler color. Breeding adults of both sexes have fins tipped by orange or red, while males also have red snouts and lips, and tubercles on the head and pectoral fins.
Long Valley speckled dace are distinguished by high pectoral fin and pelvic fin ray counts, high lateral line scale count, low lateral line pore count, and the absence of maxillary barbels (Sada et al. 1995). This population was the only one examined with a fixed allelic difference (at the D allele of the PEPA locus) (Sada et al. 1995).
The following mean counts (standard error) are from Long Valley speckled dace collected in Whitmore Hot Springs and at an unnamed spring at Little Alkali Lake (Sada 1989): lateral line scales 61.7 (1.4); lateral line pores 19.0 (5.0); dorsal rays 8.0 (0.0); anal rays 7.0 (0.0); pectoral rays 13.0 (0.4); pelvic rays 7.4 (0.2).