Moapa dace (Moapa coriacea) live in just a few warm springs in Nevada. For more than 40 years, this tiny fish have been protected under the Endangered Species Act. But despite efforts by the staff at the 106-acre Moapa Valley National Wildlife Refuge, moapa dace populations have been on a roller coaster for the past few years. Now the Center for Biological Diversity (CBD), headquartered in Arizona, is warning the U.S. Fish and Wildlife Service and Bureau of Land Management that it plans to sue them for allegedly failing to protect the moapa dace's habitat as required by law.

The moapa dace population plummeted from nearly 1,200 in 2007 to just 460 a year later, marking the first time its numbers dipped below 900 since they've been monitored. No clear reason for the decline has been identified. The FWS recovery plan (PDF) for moapa dace, published in 1983 and revised in 1996, states that a population of 6,000 fish would be required for long-term survival of the species.

"That precipitous decline in one year threw up red flags," says Rob Mrowka, the Center for Biological Diversity's conservation advocate for the state of Nevada, noting that new development nearby threatens to diminish the population even more – perhaps to the point of no return.

The Associated Press reports that new communities being developed around the Reserve could bring 150,000 new families into the area. This will require groundwater projects that could, according to the CBD's lawsuit, threaten the moapa dace. Mrowka points out that "the dace has a very narrow habitat range, in terms of water temperature, chemistry and flow," making it very vulnerable to changes in its environment. Moapa dace require waters that range in temp from 87 to 93 degrees Fahrenheit (30 to 32 degrees Celsius). "Groundwater withdrawals will affect water levels, temperature and chemistry," Mrowka says. The CBD fears that these changes could prove fatal to the fish.

Federal officials disagree. "There are certainly competing interests," says Cynthia Martinez, manager of the Desert National Wildlife Refuge complex at Moapa Valley National Wildlife Refuge (which is run by the Fish and Wildlife Service). "But that doesn't mean we can't work together to find solutions. We're doing what we can to protect these systems, working with the water authority and state engineer's office to monitor wells and the stress on the system before they authorize more water rights. As federal agencies, we're part of the process."

Martinez says a lot of work is ongoing to boost moapa dace habitats and population levels. "We just dug a new channel and diverted some new water to create a new habitat for moapa dace," she says. The Refuge has successfully used fish barriers to remove invasive tilapia, which competed with moapa dace for river vegetation, from two tributaries. The Refuge also recently purchased an additional warm spring area and turned it into a wildlife refuge where public swimming is no longer allowed, therefore extending the habitat for the fish.

Fish and Wildlife Service surveys last month found that the moapa dace population was holding steady at around 460, according to a report in the Las Vegas Review-Journal.

Image: U.S. Fish & Wildlife Service