The critically-endangered Devils Hole pupfish faced a population crisis, dropping to just 20 individuals. Scientists have introduced captive-bred pupfish back into their natural habitat in Death Valley National Park to bolster their numbers.
Key points
Devils Hole pupfish are critically endangered
Population dropped to just 20 fish
Captive-bred fish were introduced into the wild
Release occurred in Death Valley National Park
Conservation efforts are ongoing
Mentioned in this story
Death Valley National ParkU.S. Fish and Wildlife Service
Devils Hole pupfish
A Devils Hole pupfish is pictured at the Ash Meadows Fish Conservation Facility in Nevada. Scientists recently took captive-bred pupfish from this facility and introduced them into the species' natural habitat in Death Valley National Park.
A Devils Hole pupfish is pictured at the Ash Meadows Fish Conservation Facility in Nevada. Scientists recently took captive-bred pupfish from this facility and introduced them into the species' natural habitat in Death Valley National Park.
Olin Feuerbacher/U.S. Fish and Wildlife Service
Olin Feuerbacher/U.S. Fish and Wildlife Service
The Devils Hole pupfish, a critically-endangered species and an icon of conservation, ekes out a precarious existence in Death Valley National Park. There, in the scorching desert, guarded by fences and video surveillance, this fish swims around in a sunken fishbowl made of rock that's been its only natural home for millennia.
About a year ago, the population abruptly dropped to just 20 fish. Wildlife managers were so alarmed that, for the first time ever, they decided to release some pupfish that they'd been breeding in a huge tank for over a decade as a kind of insurance policy. They started by putting 19 captive-bred fish into Devils Hole, and later added about 50 more.
This spring, biologists saw 77 fish swimming around in the hole. "We're breathing a lot easier at 77 than 20," says Olin Feuerbacher, a biologist with the U. S. Fish and Wildlife Service who manages the backup fish population in captivity.
But the move to augment the population in the wild happened so quickly — in part because of uncertainty about massive federal layoffs and a looming government shutdown — that the lab didn't take genetic samples from the first batch of captive-raised pupfish released into Devils Hole.
For millennia, the rare Devils Hole pupfish has survived in a single deep pool of hot water at the bottom of a cavern in Death Valley National Park. Last year, its population count fell perilously low.
For millennia, the rare Devils Hole pupfish has survived in a single deep pool of hot water at the bottom of a cavern in Death Valley National Park. Last year, its population count fell perilously low.
Olin Feuerbacher/U.S. Fish and Wildlife Service
Olin Feuerbacher/U.S. Fish and Wildlife Service
That means scientists now "cannot distinguish the introduced captive fish from wild fish. Nor can we track how these introduced captive fish will contribute to future wild generations," says Christopher Martin, a geneticist at the University of California, Berkeley who has studied this species.
"There's scientific questions we can't answer now, because there's just no genetic data on which fish were released," he says.
Martin says he believes this missed opportunity marked yet another scientific casualty of the political chaos at the time, and that the Devils Hole pupfish managers "made the best decision that they could under the extreme pressure of 'I'm going to be fired at any second.'"
Feuerbacher, who spoke with NPR and then answered additional questions by email, explains that the team had to make "choices between delaying action to do things perfectly, or doing the best we could within the perceived time constraints, and generally we decided that the benefits of rapid action outweighed the benefits of waiting."
"I think we saved the species," says Michael Schwemm, another biologist with the U.S. Fish and Wildlife Service.
"It was definitely whiplash"
The improbable life of the iridescent little Devils Hole pupfish, which somehow manages to persist in a single well of inhospitable water in the middle of a desert, has long fascinated scientists and the public.
U.S. Fish and Wildlife Service biologists Michael Schwemm (top) and Jenny Gumm (middle), with National Park Service biologist Jackson Glomb survey pupfish topside, while divers search below.
U.S. Fish and Wildlife Service biologists Michael Schwemm (top) and Jenny Gumm (middle), with National Park Service biologist Jackson Glomb survey pupfish topside, while divers search below.
Olin Feuerbacher/U.S. Fish and Wildlife Service
Olin Feuerbacher/U.S. Fish and Wildlife Service
"Devils Hole is considered probably the smallest known habitat for a vertebrate species," says Kevin Wilson, a supervisory biologist at Death Valley National Park, who says that the nutrient-and-oxygen-poor water in the cavern is 93 degrees Fahrenheit.
Officials have spent decades monitoring the fish closely, counting its fluctuating population every spring and fall. Since 2007, they've put supplemental food into the water, and in 2013 biologists also started breeding a backup population at Ash Meadows Fish Conservation Facility, which has a 100,000-gallon tank the size of a small building that's designed to be a faithful replica of Devils Hole.
The idea had always been that scientists might transfer captive-bred fish into Devils Hole in an emergency situation, but such reintroductions aren't done lightly. Captive populations are slightly different from wild ones, and releasing them into the wild could have unknown effects, such as introducing diseases.
"It's in our strategic plan as an option but it's one that nobody really wanted to talk about because we never thought that we would be in that position," says Feuerbacher.
After all, in recent years the wild population was booming, relatively speaking, given that it had gone as low as just 35 fish in 2013. By the fall of 2024, the cavern's pool contained 212 fish.
"We had had several years of great growth, great survival," Feuerbacher says, noting that the fish living in Devils Hole "had already exceeded the numbers that I had ever seen in my almost two decades of working with them. And so everybody was kind of flying high, that the population was looking great."
But in December of 2024, and then again in February of 2025, large, distant seismic events sent shockwaves rumbling through the Earth. These earthquakes roiled the seemingly-bottomless pool inside Devils Hole, creating mini-tsunamis. Water sloshed across a shallow, rocky shelf, sweeping away the sediments there, along with the algae that serves as the primary food source for this species.
Similar disruptions have happened before. But this time, because these back-to-back earthquakes occurred in winter, during the months when zero direct sunlight reaches the Devils Hole pool, the algae couldn't regrow.
This mini-tsunami at Devils Hole in Death Valley National Park was triggered by a far-off magnitude 7.6 earthquake in Mexico in September 2022. Such "desert tsunamis" can clear the rocks of algae that the Devils Hole pupfish rely on for food.
This mini-tsunami at Devils Hole in Death Valley National Park was triggered by a far-off magnitude 7.6 earthquake in Mexico in September 2022. Such "desert tsunamis" can clear the rocks of algae that the Devils Hole pupfish rely on for food.
Ambre Chaudoin/National Park Service
Ambre Chaudoin/National Park Service
By late February of 2025, the population had dropped by 90 percent. Twenty fish were left.
"We went from record-high numbers to the lowest that we've ever counted," Feuerbacher says. "It was definitely whiplash in everybody's heads, going from having just fantastically healthy fish in great numbers to wondering if the population is going to exist within a month or two."
Wilson, who has "vivid memories" of being a kid in the 1970s and peering down into Devils Hole during a trip he took with his mother, says he realized they were looking at a "real possibility of this species being extirpated from its only known habitat on the planet."
The pros and the cons
Meanwhile, the scientists were experiencing their own seismic shift: A new administration had just come into the White House, and its Department of Government Efficiency was axing research programs and starting drastic layoffs across multiple federal agencies. The widespread chaos in the world of science left everyone wondering what might be the next target for cuts.
"It was a time of, you know, a lot of stress and a lot of confusion for people," says Feuerbacher. They focused on the fish.
The team immediately decided to put more food into Devils Hole — that seemed like a no-brainer. The discussion of whether or not to add in captive-bred fish was more fraught.
"We took time. We looked at the pros and the cons," says Wilson. "We spent a long time discussing our options."
There were meetings of an interagency group called the Devils Hole pupfish Incident Command Team, which includes representatives of the U.S. Fish and Wildlife Service, the National Park Service, and the Nevada Department of Wildlife. This team makes management decisions for this species, and its strategic plan, written in 2022, has scenarios developed to help decision-makers think through the possibilities.
"Having that plan was a really important thing," says Schwemm, because it helped the group act quickly.
Feuerbacher recalls about two weeks of discussion until it was decided that putting captive-bred fish in the hole was the right thing to do.
"When we did make the decision to stock the fish, we were actually backing up against a government shutdown," he recalls. "We decided we have to move quickly. We have to get them in the water. And then, you know, once that occurs, we'll see who's available to actually monitor and see if it was successful."
On March 11, 2025, about a dozen workers went to the giant refuge tank with nets, to chase down some fish and scoop them out. The plan was to immediately transfer them to Devil's Hole that same day.
This underwater video shows pupfish raised at Ash Meadows Fish Conservation Facility being released into Devils Hole.
The lab didn't take DNA samples from each fish, which can be done by clipping off a tiny bit of one fin. Feuerbacher says the clipped fish would need a week of antibiotics, then even more time after that to recover fully. Because more of the wild fish in Devils Hole could die off at any moment, the team didn't want to wait.
What's more, "the uncertainty about potential government shutdowns and staffing changes also loomed and added to the urgency — we wanted to make sure we had all the resources we needed to maximize chance of success," Feuerbacher explains. They did try an untested technique for genetic sampling, which was saving some water that each individual fish had been in with the hope of later being able to extract DNA.
But Martin, the fish genetics expert, doesn't see the need for giving antibiotics after what he calls a simple fin clip. In response to a follow-up email after speaking with NPR, he says he's fin-clipped around 6,000 fish of various species and none have died.
"I think that when you have hundreds of fish in a refuge tank," opines Martin, "you can risk fin-clipping a handful before introducing them to the wild population."
Big, beefy fish
Feuerbacher saw the captive-bred fish as being sensitive and vulnerable, and worried that they might go belly-up when they hit the water inside Devils Hole.
After all, these fish had always lived in the relatively cushy, human-controlled tank where the water was slightly cooler and more oxygen-rich. This population had been essentially isolated there since 2013, when biologists removed some eggs to create the lifeboat population, although a small number of additional eggs from the wild have been collected over the years to try to maintain the genetic connection.
A baby Devils Hole pupfish developing in an egg in Ash Meadows Fish Conservation Facility.
A baby Devils Hole pupfish developing in an egg in Ash Meadows Fish Conservation Facility. Olin Feuerbacher/U.S. Fish and Wildlife Service
Olin Feuerbacher/U.S. Fish and Wildlife Service
Just hours after fish had been removed from the refuge tank, Feuerbacher and Wilson were down in Devils Hole with a transparent plastic tub full of captive-bred fish. Feuerbacher remembers slowly adding water from the natural pool into this tub, to try to help the fish acclimate a bit before they were released.
"It very much was surreal," says Feuerbacher. He looked up and saw, on the rocks above, about twenty people watching. "Every single one of them had their phone up recording us."
Schwemm remembers the scene being "eerily quiet. Because we were like, 'Oh God, I hope this works.'"
When the tub got tipped into the water, so that the fish could swim free, they immediately began exploring their new home.
Wilson says that leading up to that moment he was "really stressed" but once it was done, "it was like a weight was lifted off my shoulders. We made a decision. We did it. We can't go back."
Not only did the captive-bred fish survive in the hole, for a while they were easy to spot. Compared to their nearly-starved wild relatives, they looked like "big, beefy fish," says Feuerbacher. Eventually, though, all the fish in the hole started to look the same.
Martin, the geneticist, says it's likely that the tank-raised fish started taking over — although without knowing the genetic make-up of every fish added, that's impossible to track.
He says fish that grew up fat and happy in the refuge could potentially out-compete the wild fish, and bigger males could monopolize mating opportunities.
"Those refuge pupfish are probably mostly contributing to the next generation of pupfish in the wild, even though they've actually never experienced the selective pressures of this extreme environment of Devils Hole," says Martin. "Essentially what this will do, probably already has done, is to reduce the genetic diversity in the wild by about half."
He says this could affect the ability of this species to withstand future threats.
That could be a concern, agrees Steven Beissinger, a conservation biologist at the University of California, Berkeley who has researched the use of captive populations in managing wild, endangered ones. Still, he says, "sometimes you have that emergency, dire moment where you've got to do the best you can."
"If you're down to 20 individuals, that they were just seeing there, they needed to act," says Beissinger.
He points out that when an endangered species reaches that kind of turning point, there's often no backup population available, or the backup animals are kept in conditions that don't mimic life in the wild — unlike the Devils Hole refuge tank, which the government created to be prepared.
The Devils Hole pupfish Incident Command Team is currently working on a genetics management plan, according to Wilson. And with the time pressure removed after the first release of fish, the refuge is now collecting DNA from all fish that go in.
When biologists went to Devils Hole this spring to do the official count, they found lots of baby and juvenile fish, suggesting that the fish are now reproducing well and that the population is headed in the right direction. "I don't remember seeing this many young fish in Devils Hole any time that I've been working there," says Feuerbacher.
Transfers of fish from the captive population to the wild have been getting increasingly simple and smooth "for both the staff and fish," he notes.
The most recent took place in February of this year, and from his point of view it went so well, "the fish seemed to barely notice that they were someplace new."
