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Tiny, Critically Endangered and Controversial Nevada Fish Experiences Dramatic Population Increase


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moapa daceFirst the good news: The world’s only population of the critically endangered Moapa dace (Moapa coriacea), a tiny fish endemic to the hot springs along a small stretch of Nevada’s Muddy River, has boomed this year. After a strange and still unexplained die-off in 2007 lowered the species’ population from 1,200 to 473 fish, its numbers have climbed nearly 150 percent to 1,181 today, according to the most recent count by the U.S. Fish and Wildlife Service (FWS). Most of that increase, which comes close to recovering the species to pre-2007 levels, has taken place in the past year. It’s a welcome success story for a fish that also nearly lost its sole habitat to fire in 2010.

Now the bad news: The Moapa dace population still needs to increase by another 4,819 individuals before the species can be considered recovered and taken off the endangered species list. Meanwhile, the fish remains unpopular with nearby residents, who complain that protecting the species limits agricultural and community water usage, keeps people from enjoying some of the area hot springs, costs too much and is taking too long—all for a fish that isn’t eaten by humans and doesn’t serve as food for any other native species.

The fish—which grows to a maximum of nine centimeters and only thrives in water temperatures of at least 30.5 degrees Celsius—could be found in 10 local hot springs in the 1930s. Today it can only be found in three springs along a three-kilometer stretch of the river. The dace became a federally protected species in 1967, as a result of development and groundwater pumping that tapped too much of the Muddy River, causing some streams to run dry and dramatically reducing the water flow in others, allowing them to become overgrown with vegetation.

The FWS and other agencies have spent years working to restore the Moapa dace’s habitat. Not only have they restored sections of streams that had gone dry or been clogged by plant life, they have also worked to eliminate invasive species such as shortfin mollies (Poecilia mexicana) and tilapia. Introduced to the river in 1963, the mollies ate the dace larvae. The tilapia, which showed up in the 1990s, ate the dace and its food. Jon Sjoberg, supervising fisheries biologist for the Nevada Department of Wildlife, told the Las Vegas Review–Journal that the agency suspects that the tilapia were finally removed from the river last year. If the invaders really are gone, the Moapa dace population could truly start to boom.

Several threats remain, however: Proposed groundwater developments could reduce the amount of water available for the dace, and the area remains at risk of wildfires like the one that struck in 2010 as well as an earlier conflagration in 1994 that killed half of the dace population that year. Last year the Southern Nevada Water Authority, which owns much of the land around the dace habitat, removed at least 900 palm trees that had encroached on the dace’s habitat because they could have fed fires—an act that local residents decried but which is proactive and has been going on for decades. The Review–Journal covered the controversy.

The Moapa dace is one of those endangered species that attract a lot of criticism because of the time and expense required to restore its habitat and population (the total interagency budget for protecting the dace hasn’t been disclosed, but it’s definitely in the millions). Detractors also point out that the dace’s numbers have dropped precipitously several times while it was under protection. But saving a species from extinction after decades of habitat loss is not a quick process, and it’s not easy. I think it’s time to applaud the efforts that have borne fruit in recent years and to look forward to what comes next.

Previously in Extinction Countdown:

Photo: U.S. Fish and Wildlife Service, Pacific Southwest Region

John R. Platt About the Author: Twice a week, John Platt shines a light on endangered species from all over the globe, exploring not just why they are dying out but also what's being done to rescue them from oblivion. Follow on Twitter @johnrplatt.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Greenberet 7:39 am 09/21/2012

    Despite the controversy about protecting Moapa dace, I am happy to see the growth of its population. I do not consider much economical value of protection, instead I hope we will be able to find the living ones of a specie rather than the paper ones.
    And I wonder: Moapa dace is neither human being’s food nor any other species that live in the same habitat. Is this phenomenon also a factor of population drop several years ago?

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  2. 2. Postman1 5:20 pm 09/21/2012

    From here, it sounds like another case of the EPA gone wild. Probably millions of our tax dollars to preserve a fish that nothing eats, by removing a fish which humans love to eat. (so what if it is non-native, it was thriving) At least, when the economy totally collapses, the locals could have eaten tilapia.

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  3. 3. bucketofsquid 2:39 pm 09/26/2012

    So people were wasting so much water that others down stream from them were facing shortages. Good thing the EPA stepped in and cut down on the greedy water wasters. I care nothing for a boring, useless fish but water is a wholly different matter.

    Not a big fan of tilapia either since it is a scavenger fish. Watched a show where tilapia were used to eat poo as part of a water treatment plan and then sold as food. I’ll pass on the poo fish, thanks anyway.

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  4. 4. John R. Platt in reply to John R. Platt 3:28 pm 09/26/2012

    And how long would it take to recognize that the water was disappearing if someone didn’t notice what was happening to the environment that the water supported?

    Link to this

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