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Against all odds, the rare Devils Hole pupfish keeps on swimming

Devils Hole pupfish gather on the precious rocky shelf that supports their entire fragile existence in the wild.
Olin Feuerbacher
Devils Hole pupfish gather on the precious rocky shelf that supports their entire fragile existence in the wild.

Have you ever felt stuck in a bad situation that you couldn't get out of, through no fault of your own, and all you could do is just make the best of it?

Such is the life of the Devils Hole pupfish.

This small, iridescent blue-or-green fish swims in the hot waters of an inhospitable fishbowl made of rock in a Nevada section of Death Valley National Park, where it somehow got trapped thousands of years ago.

The deep cavern that is this fish's only home is surrounded by a chain-link fence, razor wire, and other security measures designed to protect this incredibly rare endangered species.

In 2013, its population hit a low of only 35 fish. But over the last couple of years, the Devils Hole pupfish has bounced back, thrilling and somewhat baffling wildlife managers who still are trying to figure out how this tough little fish manages to make a go of it.

Devils Hole pupfish are about an inch long.
Olin Feuerbacher / NPS
Devils Hole pupfish are about an inch long.

Last year, in the spring, they counted 175 observable fish. This spring, the count was the same, which means that the population has been holding steady.

A wild population of just 175 fish doesn't sound like a lot. But this is the best the Devils Hole pupfish has been doing in about two decades.

"Times are good now with Devils Hole pupfish, compared to how they've been in the past," says Jenny Gumm, a fish biologist with the U. S. Fish and Wildlife Service.

Exactly how the pupfish have recovered to this point is a bit of a mystery.

"The question that I receive and my colleagues receive is, 'Why?' And you know, we're trying to answer that," says Kevin Wilson, an aquatic ecologist at the National Park Service.

A fish that's able to cope

Wilson first learned of this iconic fish as a kid back in the 1970s, when he tagged along with his geologist mom on a field trip that stopped by Devils Hole.

"I just remember as a young lad just laying down on this wooden observation deck, looking down into this immense hole in the ground and was fascinated," says Wilson.

At the bottom of the hole is the pool where the fish swim. No one knows how deep it is — scuba divers have explored to a depth of over 400 feet.

The pupfish, which are only about an inch long, have no natural predators. Without fear, they'll curiously swim up to inspect divers or anything else that enters their isolated world.

The fish tend to hang out near the top of the pool, swimming around in the shallow water that covers a rocky ledge. There, they feed on algae and spawn.

The water isn't exactly cozy. "It's 93 degrees fahrenheit all the time," says Wilson, and its oxygen levels are low.

Plus, for about four months in winter, the pool remains entirely in shadow, which is not good for the tiny plants that the fish eat.

This 2006 photo shows biologist Mike Bower, left, with the National Park Service, and Fish and Wildlife Service field supervisor Cynthia Martinez, as they peer down into Devils Hole.
This 2006 photo shows biologist Mike Bower, left, with the National Park Service, and Fish and Wildlife Service field supervisor Cynthia Martinez, as they peer down into Devils Hole.

"It's not a great place to live if you're a fish, that's for sure," says Gumm.

The reduced amount of food in winter is thought to be why spring counts of this fish have historically been lower than counts done in the fall. Last fall, researchers observed 263 fish. The next count will come in September.

"I'm hoping that we cross the threshold of 300," says Wilson.

Earthquakes and flash floods

Part of this fish's recent revival may be due to some dramatic events that have shaken up life in Devils Hole.

In July of 2021, a rare flash flood poured in an enormous amount of muddy water.

"The volume of water that went into the habitat was just so much," says Gumm, who worried the fish would die from a change in water chemistry — or even just the sheer violence of the flood and its churning debris.

It was the first time Gumm felt like these fish really might go extinct on her watch. She recalls going to the hole just after the flood.

"Walking into it, we just weren't sure what was going to be there," she recalls. "And the water looked like chocolate milk. You couldn't see any fish."

She mentally prepared for the worst. But then she saw a few fish, and then a few more the next day.

It turns out that the flood may ultimately have helped the species, by bringing new nutrients into their environment.

And a couple of days after that flood, the fish got hit by another unusual whammy.

A biologist with the U.S. Fish and Wildlife Service observes captive Devils Hole pupfish.
Ryan Hagerty / USFWS
A biologist with the U.S. Fish and Wildlife Service observes captive Devils Hole pupfish.

A magnitude 8.2 earthquake struck Alaska. Even though the epicenter was more than 2,000 miles away, it created a mini-tsunami inside Devils Hole.

Video cameras caught the water sloshing around. All that sloshing may have helpfully redistributed materials brought in by the flooding.

Another mini-tsunami happened last year, when a magnitude 7.6 earthquake in Mexico caused 4-foot waves inside Devils Hole.

Wilson says that these kinds of disturbance events can clean off the precious rocky shelf that the fish depend on, benefiting the fish by basically hitting the reset button for the whole system.

Video from one earthquake shows pupfish streaming past the camera, as if the fish knew what was happening and where to go to be safe, says Gumm.

"They've been living here for a lot longer than we really comprehend," she says, with the best estimates suggesting they've been in the hole for about ten thousand years.

"They are used to it. And they know what to do."

'It's had a huge impact'

The fish have gotten some help from humans. Wilson says they're now fed supplemental food, since at one point they looked emaciated.

"It was somewhat controversial to start feeding the fish," says Wilson.

The pupfish also enjoy the extra shelter of some plant material that wildlife managers attached to their rocky ledge, to give them increased shade and more options for hiding — because the older fish aren't above eating the young'uns.

"I think society has a duty to protect species that humankind has negatively impacted," says Wilson. He points out that groundwater pumping lowered the water level in Devils Hole, and the top of the pool is about six or eight inches below the historical pre-pumping level.

The Devils Hole pupfish is famous in conservation circles. It was one of the first species to be listed as endangered under the Endangered Species Act. After nearby development threatened to siphon water away from its lonely refuge, lawsuits aimed at saving it went all the way to the U. S. Supreme Court.

"It's had a huge impact on water conservation and water rights throughout the western United States," says Steve Beissinger, a conservation biologist with the University of California, Berkeley.

Over the decades, several efforts have been made to set up a captive population of these fish in a separate tank, as a back-up insurance policy in case the wild fish met an untimely end. Past attempts all failed for various reasons, such as mechanical issues.

"The approach that we take now for the refuge population is a much larger scale," says Gumm, who manages a fish conservation facility located near Devils Hole. There, its unique ecosystem has essentially been recreated in a 100,000-gallon tank.

"Most of it is actually underground, simulating that cave environment of Devils Hole," she says.

The fish's all-important rocky shelf was faithfully copied by the tank's designers. "They actually went out and 3-D scanned the shallow shelf of Devils Hole and carved it out of styrofoam," she says. "It is an exact replica of the habitat at Devils Hole."

The refuge tank has a population of about 300, created from eggs taken from the wild. An additional 100 or so fish live in smaller tanks that are kept for breeding.

Climate change could make Devils Hole even hotter, and that's a concern for the future. Still, Beissinger thinks the fish could keep on keeping on, as long as they continue to get help.

"You can never relax with a small population like that," he says.

Not everyone thinks that so much time and money should go into safeguarding these fish. Once someone told Wilson that "they should just drown those fish."

Drown the fish?

"I had to shake my head," he recalls. "You know, it's tough, and it's about water."

But love them or hate them, Beissinger thinks everyone should at least respect the tenacity of these beleaguered fish.

"It's certainly, in many ways, an inspiring story of survival," says Beissinger. "You've got to admire that, something that can cling on and adapt to such a difficult environment — with nowhere to go."

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Nell Greenfieldboyce is a NPR science correspondent.