Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
MOAPA VALLEY NWR: A Desert Oasis for the Endangered Moapa Dace
California-Nevada Offices , September 30, 2013
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The endangered Moapa dace. Listed in 1967, the Moapa dace is endemic to the upper reaches of the spring-fed Muddy River in southern Nevada.
The endangered Moapa dace. Listed in 1967, the Moapa dace is endemic to the upper reaches of the spring-fed Muddy River in southern Nevada. - Photo Credit: USFWS

By Cindy Sandoval

The Moapa Valley National Wildlife Refuge in the southern Nevada desert seems an unlikely place for an endangered fish to make a comeback, but the Moapa dace (Moapa coriacea) population is on the rise.

Twice a year the U.S. Fish and Wildlife Service (Service) conducts population surveys of the endangered fish, and the dace experienced a baby boom of sorts during the past 12 months. The February 2013 population survey, done by snorkeling the river and physically counting fish, found 1,226 dace in the system. These 1,226 dace were nearly double the 654 found in February 2012. The second 2013 population survey was completed in early August and the number of dace grew to 1,727, a 46 percent increase from August 2012.

The increase in the Moapa dace population is a result of habitat restoration efforts in the headwaters of its native Muddy River. These efforts have been ongoing since 2006. A number of warm springs and their outflow streams comprise less than 10 miles of the upper Muddy River and is the only known habitat for the small fish, as well as several other aquatic species.

"The Service and its federal, state, local, and industry partners are working together to reverse alterations to the dace's habitat," says senior biologist Lee Simons of the Service's Nevada Fish and Wildlife Office. "The work includes restoring spring outflow streams to their historically fast-flowing levels the dace need for foraging."

Extensive habitat modifications for irrigation and recreation, along with the introduction of the nonnative shortfin molly (Poecilia mexicana) and mosquitofish (Gambusia affinis), led to the dace's decline and listing as an endangered species in 1967.

In the mid-1990s, Moapa dace numbers collapsed when nonnative tilapia (Oreochromis aureus) showed up in the river. Tilapia are known to prey on the dace, and have eliminated the fish from several reaches of the Muddy River.

"Removing tilapia from the upper reaches of the Muddy River system has been a long-term effort," says Moapa Valley National Wildlife Refuge manager, Amy LaVoie. "Rotenone treatments removed the invasive fish from refuge waters initially in the late 1990s, and have recently pushed the tilapia further downstream.

The next step is to return adult Moapa dace to this historical habitat to grow larger, reproduce more successfully, and live longer.

The Service will continue to protect the Moapa dace, with the ultimate goal of restoring the fish population near its historical numbers. In order to be considered fully recovered and removed from Endangered Species Act protection, a dace population of at least 6,000 individuals must be sustained for five consecutive years.

Cindy Sandoval is an intern with the External Affairs Program in the Service's Pacific Southwest Regional Office.

Contact Info: Cynthia Sandoval, 916-978-6159, cynthia_d_sandoval@fws.gov
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