Ash Meadows Speckled Dace

Rhinichthys osculus nevadensis

Description

The Rhinichthys osculus nevadensis (Ash Meadows speckled dace) is a small silvery slender minnow about 3 in (7 cm) long. It is plain except for its poorly defined blotches and speckles on the sides. It has small eyes, small, irregularly place scales, and a small subterminal mouth with a barbel at each corner. All fish in the genus have a double row of teeth in the pharynx. Body coloration varies widely within a population. Generally, the dorsum is olive-gray blending ventrally to golden. Black spots frequently cover the body and there may be one or two distinct, black lateral strips. It reaches a maximum length of approximately 3.9 in (10 cm) and may live as long as four years.

This fish was first described in 1893 as a full species, Rhinichthys nevadensis. However, in 1948, it was determined to be a subspecies of Rhinichthys osculus.

Behavior

The Ash Meadows speckled dace reaches maturity in the second summer. It spawns once in early spring and again in late summer. It feeds on a variety of small aquatic animals that inhabit the thermal springs.

Speckled dace generally prefer flowing streams where they feed on drifting insects. Spawning occurs primarily during the spring and summer over stream riffles where eggs are broadcast by females and fertilized as they drift to the substrate.

Habitat

The Ash Meadows speckled dace occurs in spring systems and aquatic habitats formed by the spring waters. It is known to occur in headwater spring pools, spring outflow creeks, and marshes formed by the spring flows. It also occurs in irrigation ditches and canals that utilize the spring flows for irrigation. The seeps and springs comprising Ash Meadows formerly flowed into an extensive marsh that was drained in the mid-1960s. Thunderstorms occasionally cause flood waters to discharge from Ash Meadows into the Amargosa River.

Distribution

The Ash Meadows speckled dace has not been found outside of Ash Meadows. It formerly inhabited much of the interconnected surface warm springs and outflows.

Dace populations and suitable habitat have been severely reduced by agricultural and residential development and groundwater pumping. Manipulation of springs and their outflows reduced the number of populations so that speckled dace are presently found only in the Bradford Springs, Big Spring, Tubbs Springs, and Jackrabbit Spring. The population in Jackrabbit Spring was estimated at zero and 11 in 1982 and 1983, respectively, and the population in Big Spring was estimated at 15 and 13 in these same two respective years. Speckled dace populations continued downstream some distance from both of these springs when these estimates were made, however, no estimate of population size in these streams was attempted. Tubbs Spring spring pool population was estimated at 35. No population estimates have been made in Bradford Springs. The total population size of Ash Meadows speckled dace is estimated at 500. The habitats occupied by dace, and 164 ft (50 m) on both sides of the aquatic environment, are designated critical habitat for the speckled dace. Much of this area is also critical habitat for the Ash Meadows Amargosa pupfish and spring-loving centaury. Critical habitat for the speckled dace includes approximately 36 acres (14 hectares).

Threats

A number of exotic fish species, such as the mosquitofish and black molly have been introduced to Ash Meadows where they compete with and prey on native fishes. The Ash Meadows killifish (Empetrichthys merriami ), now extinct, was eliminated by predation from introduced species.

Conservation and Recovery

The critical habitat of the Ash Meadows speckled dace is now owned by the Fish and Wildlife Service and is protected against development. However, non-native fish should be eliminated from its habitat. The populations of the Ash Meadows speckled dace should be monitored, and research undertaken into its biology and habitat needs. A captive-breeding population should be establishes, and consideration given to reestablishing extirpated populations where the habitat is suitable.

Contact

U.S. Fish and Wildlife Service Regional Office
Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

U.S. Fish and Wildlife Service
Nevada Fish and Wildlife Office
1340 Financial Boulevard, Suite 234
Reno, Nevada, 89502-7147
Telephone: (775) 861-6300

References

Gilbert, C. H. 1983. "Report on the Fishes of the Death Valley Expedition Collected in Southern California and Nevada in 1891 with Descriptions of New Species." North American Fauna 7:220-234.

Soltz, D. L., and R. J. Naiman, eds. 1978. "The Natural History of Native Fishes in the Death Valley System" Natural History Museum of Los Angeles County, Science Series 30:17.

U.S. Fish and Wildlife Service. 1983. "Determination of Endangered Status and Critical Habitat for Two Fish Species in Ash Meadows, Nevada," Federal Register 48(172): 40178-40186.

Williams, J. E. and D. W. Sada. 1985. "Status of Two Endangered Fishes from Two Springs in Ash Meadows, Nevada." Southwestern Naturalist 30(4): 475-484.