MOAPA VALLEY NATIONAL WILDLIFE REFUGE
MOAPA VALLEY NATIONAL WILDLIFE REFUGE
ncr 38. Box 700
Las Vegas, Nevada 89124
The Moapa Valley Refuge was established on September 10, 1979, to secure habitat for the endangered Moapa dace. This small fish, the sole member of the genus Moapa, is endemic to the Muddy River system. Dace populations have declined due to habitat destruction and the introduction of nonnative fish species.
This modest refuge--106 acres--located in Clark County, Nevada, 60 miles north of Las Vegas, is critical to prevent extinction of the Moapa dace. Dace habitat on the refuge consists of stream channels supported by six thermal springs emerging near the center of the refuge. Moapa Refuge is a unit of the Desert National Wildlife Refuge Complex.
The refuge is comprised of three adjacent, but visually distinct units. The Pedersen Unit, to the west, was acquired in 1979 and is 30 acres in size. The Plummer Unit, to the east, was acquired in 1997 and is 28 acres in size. The Apcar Unit was acquired in 2000 and is 48 acres in size. Each unit has a separate stream system supported by the steady and uninterrupted flow of several springs that come to the surface at various places throughout the refuge. The total combined flow of the Pedersen Stream is about 3.6 cubic feet per second and the total combined flow of the Plummer Stream is about 3.1 cubic feet per second. These springs and streams eventually flow into the Muddy River. The springs are thermal in nature and have an average annual water temperature of 90 degrees Farenheit at the point of discharge. Water quality is good, although high in calcium carbonate.
Moapa Valley NWR was established to secure habitat for the Moapa dace (Moapa coriacea), a federally listed endangered species of fish, making it the first refuge within the National Wildlife Refuge System to be created for an endangered fish. The Moapa dace is unique because it is the only representative of its genus and it is found nowhere else in the world. It is a small fish once found throughout the headwaters of the Muddy River system and it is dependent upon this warm spring habitat for reproduction. Attempts to transplant this species into waters of two other habitats failed. Threats to its survival include modification, degradation, and loss of habitat; construction of impoundments; use of harmful chemicals; and introduction of non-native fishes and parasites. Currently over 95% of the dace produced in the valley come from the refuge springs and occur in the area below. The remainder of the system is unavailable to the dace due to an invasion of tilapia (Oreochromis aurea), a non-native fish, and other habitat modifications.
Until 1994, the dominant vegetation feature of the Pedersen Unit was a dense stand of non-native palm trees (Washingtonia filifera and Phoenix dactylifera). Their root masses were encroaching into Moapa dace spawning, nursery, and adult foraging habitats and constricting spring outflow channels. Following a wildfire in that year, about 200 of these trees were removed to prevent future catastrophic fires, to improve stream and pool habitats, and to open the canopy to allow sunlight to reach the water to increase primary production within the stream system. Aquatic plants such as Chara and other algae, spike rush (Eleocharis spp.), water nymph (Najas spp.), watercress (Nasturtium spp.), and pondweed (Potamogetonspp.) are now abundant in the spring pools and other slack water areas. With a ground cover of salt grass (Distichlis spicata), native riparian species have begun to return, including ash trees (Fraxinus velutina), honey mesquite (Prosopis glandulosa), and screw bean mesquite (P. pubescens). Plant species on the drier, upland areas of the refuge are fourwing saltbush (Atriplex canescens) and creosote bush (Larrea tridentata). Removal of non-native species, such as Canadian thistle (Cirsium arvense) and salt cedar (Tamarix spp.) is an on-going task.
The Plummer Unit continues to bear the scars of the 1994 wildfire and is still dominated by a dense stand of palm trees. The spring pools and stream are inhabited by non-native mosquitofish (Gambusia affinis) and shortfin mollies (Poecilia mexicana) and portions are choked with non-native eel grass (Vallisneria spp.). However, efforts are continuing to create and improve habitat in both the Pedersen and Plummer stream systems for all three life stages of Moapa dace (larval, juvenile, and adult). This involves strategically placing substrates, logs, and boulders to provide the optimum arrangement of pools, riffle, and run habitats.