Moapa Dace

Moapa coriacea

Description

The Moapa dace, Moapa coriacea, measures 3 in (7.6 cm) in length. The back and sides are an iridescent gold or bronze, marked by a dark middorsal stripe. There is a distinctive black spot at the base of the caudal fin. It is similar in profile to both the roundtail chub (Gila robusta ) and the Moapa speckled dace (Rhinichthys osculus moapae ) but can be easily distinguished by its markings. The specific name, coriacea, refers to its decidedly leathery appearance.

Behavior

The Moapa dace feeds primarily on insects but also eats plant matter. Stomach contents have included beetles, moths, butterflies, true flies, leaf hoppers, true bugs, mayflies, dragonflies, worms, crustaceans, snails, algae, vascular plants, and detritus. It seems to feed primarily on drift items, but adults forage from the substrate as well. Larval dace feed on plankton. Moapa dace actively feed 24 hours a day, but peak feeding is at dawn and dusk.

Like other desert fishes that inhabit thermal springs, it spawns year-round with a peak in late spring or early summer. Moapa dace successfully breed in water temperatures of 86-89.6°F (30-32°C), and it must migrate upstream from the Muddy River into thermal tributaries to spawn successfully.

Habitat

The Moapa dace inhabits clear, warm, slow-flowing waters, fed by thermal springs. Spring pools and outflow streams may have sand, gravel, pebble, or mud bottoms. Algae in these waters is abundant, and overhanging vegetation includes mesquite, tamarist, and the only palm tree native to Nevada (Washingtonia filifera ).

Distribution

This species has probably always been restricted to the sources and headwaters of Nevada's Muddy (Moapa) River system. Before 1933, it was considered common in 25 springs and up to 10 mi (16 km) of outflow streams and river channel.

The Moapa dace occupies approximately 6 mi (9.5 km) of stream habitat in five thermal headwater spring systems and the main stem of the upper Muddy (Moapa) River in Clark County, Nevada. A range-wide survey documented 3,841 Moapa dace in August 1994.

Threats

During the 1950s and 1960s, most of the springs on the Desert Oasis Warm Springs Resort and the former 7-12 Resort were cemented, graveled, channeled, chlorinated, and otherwise cleared of vegetation, actions severely restricting Moapa dace habitat. In addition, studies indicate a strong correlation between the decline of the Moapa dace and the introduction of the predatory shortfin molly sometime around 1963.

Conservation and Recovery

In 1972, an unsuccessful attempt was made to transplant 20 Moapa dace to Shoshone Ponds near Ely, Nevada, a Bureau of Land Management facility for conserving endangered fishes. In 1979 the U.S. Fish and Wildlife Service (FWS) purchased the 7-12 Resort and established the Moapa National Wildlife Refuge to protect the dace. In 1988 the National Fisheries Research Center in Seattle completed a three-year study on the life history and habitat requirements for the Moapa dace so that suitable habitat can be provided at the refuge.

A serious fire (reportedly started by a cigarette or fireworks) in the Moapa Dace National Wildlife Refuge in late June 1994 may have wiped out a number of Moapa—prior to the fire, the refuge supported more than 500 Moapa dace. On July 5, 1994, however, only one could be found on the refuge. But the following month, a range-wide survey found nearly 3,850 adults. Intensive management will be needed to prevent the loss of this monotypic genus. Personnel from the Desert National Wildlife Refuge complex, the FWS Reno Office, and the Reno Field Office of the National Biological Survey (NBS) removed fire debris from the stream channels in an attempt to accelerate rehabilitation of Moapa dace habitat. NBS biologists will monitor habitat conditions and the populations of affected aquatic species.

In 1996, the FWS released the Recovery Plan for the Rare Aquatic Species of the Muddy River Ecosystem, which covers not only the Moapa dace but also seven aquatic species of concern (three fish, two snails and two insects.) The plan notes that the Moapa dace will be considered for downlisting (from Endangered to Threatened) when three major critieria are met. Existing stream flows and historical habitat in three of the five occupied spring systems and the upper Muddy River must be protected through conservation agreements, easements, or fee title acquisitions. In addition, 4,500 adult Moapa dace must be present among the five spring systems and upper Muddy River; and the Moapa dace population must be comprised of three or more age classes, with reproduction and recruitment documented from three spring systems.

After downlisting is achieved, the species will be considered for delisting (removal from the Endangered Species list altogether). For this to occur, 6,000 adult Moapa dace must be present among the spring systems and upper Muddy River for five consecutive years; 75% of the historical habitat of the five spring systems and upper Muddy River must provide Moapa dace spawning, nursery, cover and/or foraging habitat; and non-native fishes and parasites must no longer adversely affect the long-term survival of the Moapa dace. These recovery criteria are preliminary and may be revised on the basis of new information.

Reclassification of Moapa dace from Endangered to Threatened could be initiated in 2000, if recovery criteria for threatened status are met. Delisting could be initiated in 2009 if reclassification to Threatened status occurs as scheduled.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232
(503) 231-6118 http://pacific.fws.gov/

References

Cross, J. N. 1976. "Status of the Native Fish Fauna of the Moapa River, Clark County, Nevada." Transactions of the American Fisheries Society 105(4):503-508.

La Rivers, I. 1962. Fishes and Fisheries of Nevada. Nevada State Fish and Game Commission, Reno.

U.S. Fish and Wildlife Service. 1983. "The Moapa Dace Recovery Plan." U.S. Fish and Wildlife Service, Portland, Oregon.

U.S. Fish and Wildlife Service. 1996. "Recovery Plan for the Rare Aquatic Species of the Muddy River Ecosystem." U.S. Fish and Wildlife Service, Portland, Oregon.