Las Vegas Sun

December 7, 2021

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Scientists have a devil of a time with pupfish

So far scientists have been stymied by an inch-long fish.

For the last decade the population of an endangered pupfish, which lives only in Devils Hole, a deep, water-filled limestone cavern about 80 miles northwest of Las Vegas, has dwindled.

And efforts to revive the population, which was tallied by divers last month at 84, have so far failed.

Jim Deacon, a UNLV biologist who has studied the pupfish and participated in a conference on the issue last week, said the adult population was the same as the February count.

"The expected increase this fall did not happen," Deacon said. "All through last summer there was egg-laying and babies produced, but not enough to increase the adult population, so we're still at very dangerous levels."

As much as half of the remaining wild population was wiped out late last summer, dying in traps after flash floods unexpectedly pushed scientific equipment into the isolated cave. In what observers called a tragic irony, the scientific equipment was part of research efforts designed to preserve the endangered species.

Scientists and officials from the National Park Service, U.S. Fish and Wildlife Service and the Nevada Wildlife Department have been working since then to restore the cave to a state suitable for pupfish reproduction.

The work included removing about 60 cubic feet of debris that washed into the cave in last year's flooding. Scientists had hoped that the removal would provide a good habitat for spawning and help the fish recover.

Cynthia Martinez, Fish and Wildlife assistant field supervisor, said the agency representatives and scientists have reached a consensus that a small population of the pupfish artificially maintained in a refuge near the base of Hoover Dam may need to be increased.

About two dozen of the fish live in the refuge, and increasing the its population would maintain the genetic diversity of the species, Martinez said.

Observers are increasingly worried that whatever they do, the species may be on a slide to extinction.

"I'm hopeful we are going to be able to make a difference, but it's not a sure thing at this point," said John Wullschleger, a National Park Service fish biologist.

In the meantime, the scientists are looking for whatever clues they can find to explain the gradual decline of the population. One possibility is that climate change is affecting the pupfish's habitat.

"A very small shift in temperature could be a factor," Wullschleger said. "I wish we knew more on which to base our decisions."

Deacon said that although last year's incident is well understood, understanding the gradual decline is more difficult for scientists.

"It doesn't look like there was a change in the ecological relationships," Deacon said. "One easy cop out is to say there is a genetic bottleneck, but I think that's too easy. They've been there for 10,000 or 60,000 years, somewhere in that neighborhood, so why would they blink out now?"

Martinez said the goal of all the observers is to bring the pupfish population back to viability, but she admits it will be difficult.

Deacon and Martinez said geneticists who specialize in working with small populations are involved in the efforts to preserve the species.

Other steps that are being considered include a little mood lighting -- actually changing the light conditions inside the cave to encourage growth of the algae that the pupfish eat, Deacon said.

He said the researchers and government officials, for now anyway, have more questions than answers.

"We've done a lot of research out there, and there is no good hypothesis that seems to fit what is going on."

Launce Rake can be reached at 259-4127 or at [email protected]