Refuge Habitat

USFWS Photo

Moapa Valley National Wildlife Refuge (NWR) is located in the Warm Springs area of the upper Moapa Valley in northeastern Clark County in southern Nevada. It lies just south of State Highway 168 and the Muddy River, between Interstate 15 on the east and U.S. Highway 93 on the west. The refuge is bounded on the North by Warm Springs Road, on the south by Battleship Wash, and on the east and west by private property. It is approximately 60 miles northeast of the city of Las Vegas and 9 miles west of the town of Glendale.

The refuge is comprised of four 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. The Pederson #2 Unit was acquired in 2006 and is 11 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.

Prior to acquisition, both the Pedersen and Plummer Units had been developed and operated as resorts, with swimming pools, bath houses, snack bars, and recreational vehicle hook-ups. The primary management objectives of the refuge are to restore these units to as near a natural condition as possible and to optimize available stream habitatx for recovery and delisting of Moapa dace. In 2002, restoration efforts took place on the Pedersen Unit, where all non-native fish and most artificial structures have been removed. Significant habitat restoration has occurred on the Plummer Unit since 2006. However, these streams are inhabited by non-native mosquitofish ( Gambusia affinis ) and shortfin mollies (Poecilia mexicana), and efforts are ongoing to reduce these populations from the system. Additional 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.

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.