Desert dace

Eremichthys acros

SPECIES CODE: E03C V01

STATUS:

Listed Threatened with Critical Habitat (50 FR 50304 50309, March 11, 1967). Recovery plan completed on May 27, 1997.

SPECIES DESCRIPTION:

Desert dace is the only member of the genus Eremichthys of the Cyprinidae family. It can grow to a maximum length of about 60mm (2.4 inches) (Hubbs and Miller 1948), and their life span is likely 1 to 3 years (Ono et al. 1983, Sigler and Sigler 1987).

Desert dace are omnivorous, feeding primarily on filamentous algae, diatoms, aquatic vegetation, zooplankton, snails, and aquatic insect larvae (Nyquist 1963, Ono et al. 1983).

REPRODUCTION AND DEVELOPMENT:

Ovaries of sexually mature desert dace contain ripe eggs throughout the year, and reproduction in the wild has been documented in March, May, and November, and in April under laboratory conditions (Nyquist 1963). Size at sexual maturity has not been reported in the literature; however, specimens reared in the laboratory spawned at 13 months of age (Nyquist 1963).

Desert dace eggs are probably unattended and adhesive (Sigler and Sigler 1987). Incubation period is unknown, but is likely relatively short (2wks or less) because of the high water temperature (Vinyard, pers.comm.1994). Larval and juvenile desert dace likely inhabit shallow, shoreline areas of the outflow streams, sheltering among aquatic and emergent vegetation (Vinyard, pers. Com.. 1994). In one impounded outflow stream, larval dace have been observed among emergent vegetation in still water less than 5 centimeters deep.

RANGE AND POPULATION LEVEL:

This species currently inhabits eight major thermal springs and about 5km of outflow creeks in Humboldt County, Nevada. There is no recent population estimate available, however in 1977 the population was estimate at 50, 000-100,000 individuals (Mr. V.G. Stickley in litt. 1977, as cited in USFWS 1984).

HABITAT:

Springs and outflow streams are contained within an area of approximately 1,550 hectares (3,830 acres). Desert dace occupy a variety of habitats in Soldier Meadows including spring pools up to 15 meters in diameter and 3.4 meter deep; outflow streams typically less than 0.3 meter deep; alkali marsh areas with overland flow among cattails (Typha domingensis), hardstem bulrush (Scirpus acutus), and other herbaceous plants; artificial impoundments; and earthen irrigation ditches. Substrate composition in the spring pools and outflow streams is variable and includes silt, sand, pebbles, and rocks.

Desert dace have the highest temperature tolerance of any minnow in western North America (Nyquits 1963) and occupy habitats varying in temperature from 18-40.5°C (64-104°F). Water temperature is a determining factor in desert dace distribution within a spring system. Cooler habitats (23-29°C, 73-84°F) downstream of springheads generally have the highest fish densities. Within the outflow streams, desert dace occur predominantly in upstream sites with higher velocities, but also occupy lower velocity reaches where water temperatures are relatively high (Vinyard 1988). Distribution apparently shifts seasonally according to water temperature. In the summer, springhead pool temperatures may exceed desert dace tolerance limits and the fish move downstream. As stream temperatures decrease in winter, the species’ range contracts upstream.

PAST THREATS:

Modification to spring systems in Soldier Meadows for agricultural purposes started over 100 years ago. Some spring outflow streams were permanently dewatered when flows were diverted into earthen ditches or pipes for irrigation purposes, or to leach minerals from the soil. Desert dace were left stranded in dry channels when the natural outflow streams were permanently or seasonally dewatered, and dace entering the diversions were stranded in the irrigated fields. (USFWS 1997)

Thermal springs and their outflow creeks inhabited by the desert dace occur on private lands. The local landowner has modified much of the species’ habitat for livestock grazing, and diverting water away from natural channels into manmade ditches for stock watering. This is especially detrimental in spring systems were the headpool temperature exceeds 100°F and the species can only occupy the outflow creeks. Grazing also posses the threat of trampling and overgrazing.

CURRENT THREATS:

Past threats remain.

Recreational uses of the thermal springs have resulted in rock dams and excavated spring outflows to create deep pools with silt and sand substrates for bathing. The rock dams may prevent migration; the impoundments are less suitable habitat; and frequent, long-term use of the pools may disrupt normal behavioral patterns of desert dace in the immediate vicinity and downstream. Also, bathers may crush individuals; their habitat may be silted over; soaps and shampoos may have potential toxic effects on fish, and decrease water quality; and the practice of using dry chlorine to control parasitic flukes has the potential to eliminate most aquatic life in these spring systems.

Predation by exotic fishes, and parasitism by anchor worm copepods (Lernaea spp.) are also threats to the desert dace.

CONSERVATION MEASURES:

LITERATURE CITED:

Nyquist, D. 1963. The ecology of Eremichthys across, an endemic thermal species of cyprinid fish from northwestern Nevada. M.S. Thesis. University of Nevada, Reno. 247 pp.

Ono, R.D., J.D. Williams, and A. Wagner. 1983. Vanishing fishes of North America. Stone Wall Press, Washington, D.C. 257pp.

Sigler, W.F. and J.W. Sigler. 1987. Fishes of the Great Basin: A natural history. University of Nevada Press, Reno. 425pp.

Stickley, V.G. 1977. Letter to F.C. Kobetich, U.S. Fish and Wildlife Service, dated December 14, 1977.

U.S. Fish & Wildlife Service. 1997. Recovery Plan for the Rare Species of Soldier Meadows. Portland, Oregon. 50pp.