Monday, October 18, 2004
Copyright © Las Vegas Review-Journal

Pupfish hang on with a little help from biologists

Since 1972, tank near Hoover Dam ensures rare species' survival

Fisheries biologist Jim Heinrich looks through a snorkel mask Wednesday to count Devil's Hole pupfish in a concrete tank near Hoover Dam. Photo by John Gurzinski. Measuring up to an inch long, the Devil's Hole pupfish is a unique breed. Unlike other species, it doesn't have pelvic fins. Photo by Tom Baugh/Special to Review-Journal. Click image for enlargement. Graphic by Mike Johnson.

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 less than 400.

The structure at Hoover Dam was built in 1972 under an agreement between state and federal wildlife agencies to serve as an insurance policy in case the pupfish population at Devil's Hole ever fell victim to a human-caused or natural 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 becoming extinct.

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 in circles and other times pausing to nibble on algae and the microscopic organisms and smaller life-forms that thrive on it as well.

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 if transplants coming from the Hoover Dam tank would survive their new digs.

As it turns out, the Hoover Dam population, because of an adequate food supply, are lunkers compared to their smaller cousins at Devil's Hole. In fact, 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 mimics more closely the actual conditions of water temperature, oxygen content, sunlight and algae in Devil's Hole.

Jim Deacon, a zoologist who founded the environmental studies program at UNLV, recalls that the Hoover Dam tank was designed as a holding pen.

Its purpose was to keep some fish alive in case the Devil's Hole population went extinct before the Supreme Court could decide a case that pitted conservationists against developers over pumping groundwater that affected surface level of Devil's Hole.

The high court in 1976 decided that the federally protected pupfish prevailed and that, to ensure their survival, water at Devil's Hole should not dip below a certain level.

In essence, Deacon said, the natural evolutionary process should determine if a species goes extinct, not a human-caused process such as groundwater pumping.

Preventing the demise of species from pollution and loss of habitat is important, he said, "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 in an interview last week.

"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."

In tracing the origin of the pupfish, Deacon believes their ancestors started in the Mediterranean area.

About 135 million years ago, as the supercontinent drifted apart, they existed on what is now the coast line of North America. Eventually, they were dispersed in the Rio Grande and Colorado rivers into Death Valley about 3 million years ago. But after that, scientists are unsure.

"The geologic evidence just doesn't exist that we can explain how they got into Devil's Hole from Ash Meadows a half mile away," Deacon said.

What also puzzles scientists is the plumbing of Devil's Hole. No divers have found the bottom, but it is believed to reach 450 feet deep.

Deacon has documented that a 1978 earthquake in Mexico shook Devil's Hole so much it disturbed algae on the shelf.

Now Deacon wonders if plans by the Southern Nevada Water Authority to pump groundwater from rural Nevada will put the Devil's Hole pupfish back in the same dilemma it faced in 1967, when it was listed as endangered.

"How much lag time is there before you see an effect?" he said. "Then, by the time your pin it down, is it already too late?"

A water authority spokesman, J.C. Davis, said his agency is obligated to follow the findings of a Bureau of Land Management environmental assessment to ensure pumping, though far removed from Ash Meadows, won't affect the water quality or level of Devil's Hole.

As part of the Ash Meadows recovery team, the authority conducts field studies and its biologists collect data about the habitat.

"We're very interested in making sure the pupfish are protected," he said.