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A Talk on the Wild Side.

That's One Big Leap for Such a Little Fish!

By Kendall Slee

For the Moapa dace - an endangered fish species found only in the thermal springs and streams feeding Nevada’s Muddy River - 2012 was a banner year.

Last August, a snorkeling survey of the Moapa dace habitat counted 1,181 fish - a 65 percent increase from 2011. The population jump indicates that Moapa Valley National Wildlife Refuge habitat restoration efforts are helping the species recover.

moapa_fishA snorkel survey last summer found a large increase in the species’ population. (Photo: Mark Hereford/USGS)

The minnow–size Moapa dace is adapted to thermal spring waters in the Mojave Desert that can reach 90 degrees and have low oxygen levels, but the species has been struggling for survival because of habitat destruction and non–native competitors.

The small refuge 60 miles northeast of Las Vegas was established in 1979 to secure critical habitat for the dace. Initially the refuge protected just one spring and stream, restored the habitat and re–introduced the dace. From 1996 through 2006, the refuge gradually expanded to 116 acres and three thermal spring sources that are the Muddy River’s headwaters.

The dace population declined as nearby springs and streams were converted into resort swimming pools and hot tubs, or degraded from ranching use. The population dropped from 3,400 in 1994 to below 500 in 2008. As the refuge acquired acreage, removed hot tubs and concrete channel liners, and re–vegetated/restored stream channels to their condition before development, the fish gradually reclaimed the waterways.

As with other refuge endangered species recovery efforts, partnerships are essential. In 2007 the Southern Nevada Water Authority purchased a 1,220–acre ranch adjacent to the refuge and protected it as the Warm Springs Natural Area. The U.S. Fish and Wildlife Service and other federal and state agencies offer technical and other assistance to restore the Muddy River tributaries on that property.

Restoration of streams flowing into and out of the refuge has allowed the Moapa dace to venture past refuge boundaries again. “The fish are now spreading out across all the available habitat,” says refuge manager Amy LaVoie. “In the past couple years they had been pushed up on the refuge.”

The Nevada Division of Wildlife (NDOW) has taken the lead in combating another challenging threat to the dace: blue tilapia.

That non–native fish entered the Muddy River system in the 1990s and ravaged native vegetation and fish with its voracious appetite. Tilapia has been eradicated from the refuge and other upper reaches of the system; NDOW is working to clear tilapia from the main stem of the Muddy River. This will lead to the next step in the dace recovery plan.

Once tilapia is eradicated, a fish barrier will be removed, allowing the dace to expand into the main stem river. “Only when the dace can swim from the springheads to the Muddy River will they be able to live their natural wandering lifestyle and grow large and fertile,” says Lee Simons, a biologist in the Service’s Nevada field office.

Habitat restoration also benefits other endemic species adapted to the Muddy River’s warm waters, including the Moapa White River springfish, the Moapa pebble snail and three insects. Stream restoration benefits other native southern Nevada invertebrates, as well as riparian–dependent birds, bats, amphibians and reptiles.

As the long task of riparian restoration continues, LaVoie is cautiously optimistic about the dace’s recovery.

“We have a long way to go in terms of the number of fish, age classes and how they’re distributed throughout the system,” she says. “We need to continue to restore the habitat and ensure other threats such as the tilapia remain at bay.”

Kendall Slee is a freelance writer based in Upstate New York

(This story was originally published in the January/Feburary 2013 issue of Refuge Update.)

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