Scientists Help Maintain Devil’s Hole Pupfish Population

November 1, 2004

Release from: Associated Press

LAS VEGAS — For three decades, they’ve swum in the 92-degree spring water that biologists channeled from a crevice in the rocks above Lake Mohave to a concrete tank near Hoover Dam.

Without much fanfare from the scientists behind this long-term project, the obscure, rectangular tank, smaller than a backyard swimming pool, has been holding a few handfuls of one of the rarest fish on Earth, the endangered Devil’s Hole pupfish.

The “refugium,” as its called, is a smaller version of the deep pool and algae-covered shelf at Devil’s Hole, a water-filled, limestone cave in the Mojave Desert, 90 miles northwest of Las Vegas.

Once known as a bathtub for miners, the pool is a fragile ecosystem that for 60,000 years has been home to the tiny fish that now number fewer than 400.

The structure at Hoover Dam was built in 1972 under an agreement between state and federal wildlife agencies as an insurance policy in case the pupfish population at Devil’s Hole ever fell victim to catastrophe. A flash flood, for example, could disrupt the shelf and change the material composition of the pool or its temperature.

Jim Heinrich, a fisheries biologist for the Nevada Department of Wildlife, has maintained the Hoover Dam tank since the early 1990s. He knows how fragile the Devil’s Hole system is.

“We hope we never have to use fish from this refugium, but you never know,” Heinrich said.

At last count, Devil’s Hole had 219 pupfish. It’s the only place on Earth they can be found except in captivity at the Hoover Dam tank and another structure at Ash Meadows National Wildlife Refuge.

Combined, there are 379 Devil’s Hole pupfish left on the planet, including 74 at Hoover Dam.

Biologists hope they can maintain those numbers to keep the endangered species from extinction.

Measuring up to an inch long, the Devil’s Hole pupfish is a unique breed. Unlike other species, it doesn’t have pelvic fins.

In clear spring water, the males at times have a neon blue appearance when sunlight pierces the water. They flit about from nooks and crannies, sometimes chasing females around and other times pausing to nibble on algae and organisms.

What fascinates scientists is how the Devil’s Hole pupfish has managed to maintain a viable gene pool with so few fish in the mix.

The Hoover Dam pupfish are the descendants of eight fish from the original transplant.

Living perhaps only a year or two, their offspring and generations later survived a breakdown in the plumbing system that caused a die-off in the mid-1980s, Heinrich said.

“These fish need 90-degree water or they die,” he said.

His colleague, Brian Hobbs at the Department of Wildlife’s Las Vegas office, said scientists are trying to comprehend mysteries surrounding the pupfish. How did they get there in the first place? How do they survive and propagate with so few fish in the population?

“We don’t understand how they’ve persisted in those systems without some serious, catastrophic bottlenecks,” Hobbs said.

Hobbs noted that if something should ever happen to the natural population at Devil’s Hole, no one’s really sure whether transplants coming from the Hoover Dam tank would survive their new digs.

The Hoover Dam population, because of an adequate food supply, are lunkers compared to their smaller cousins at Devil’s Hole. They might not be able to adapt to a less fertile place.

Hobbs said that’s why wildlife biologists are planning to build another refugium, one that better replicates the actual conditions of water temperature, oxygen content, sunlight and algae in Devil’s Hole.

Preventing the demise of species from pollution and loss of habitat is important, said Jim Deacon, a zoologist who founded the environmental studies program at the University of Nevada, Las Vegas, “not only for Devil’s Hole pupfish but all species on Earth.”

“Their natural time cycle gives us an index of the health of the planet. As we accelerate extinction of species, it’s like telling us the Earth is less and less capable of supporting life of various kinds,” Deacon said.

“The kicker is that we don’t know what kind of utility various species might have in the future. I believe we owe our children the opportunity of finding out if these things are useful.”