The Brief

Good news for one of nature’s rarest and unlikeliest species: The critically endangered Devils Hole pupfish has been making a resurgence after a very close brush with extinction last decade.

The fish — whose full natural habitat consists of a hole in Death Valley National Park with a surface area of about 10 feet by 60 feet, little oxygen and very warm water — has been central for conservationists and biologists interested in how the species managed to develop in such extreme conditions.

So it was with guarded optimism that officials announced a few weeks ago that the spring pupfish census had counted 191 of the silvery fish, which measure little more than an inch long. That's a far cry from the 35 counted in 2013, when the species was at its closest to the brink since being studied.

Back from the brink

Before the population started declining a few decades ago, roughly 200 to 250 specimens were counted each spring by scuba divers. Typically, the population roughly doubles for the fall count, Death Valley National Park aquatic ecologist Kevin Wilson said, because sunlight starts to reach the water in the hole in the late spring and summer. That allows for algae to grow as a food source.

However, the species has faced a series of challenges. First, development in the 1960s threatened the fish’s habitat, which is connected to an underground aquifer that started being tapped in the desert for agricultural purposes. And even after protections were put in place to save the endangered fish, the population started declining in the mid-1990s before reaching its low point in 2013.

Although the population’s been on the rise for a few seasons, officials said they wanted to be cautious before publicizing the upswing since the count is prone to major swings, with fall typically having much higher numbers than spring.

This pupfish’s unique habitat

Devils Hole is located within Death Valley National Park, though it’s easy for visitors to miss since it’s located in an exclave of the park across the Nevada border, about 10 miles from Death Valley Junction. The hole itself is at least hundreds of feet deep — its bottom has never been mapped.

“It's not a flowing spring. It's not a bubbling spring. It's just kind of this geological fault that opened up this cave, and you're looking at the aquifer,” Wilson said. “It's kind of a strange term for folks, but you're just looking at water that's underground and we just have a window to see it.”

It’s in this unlikeliest of spots that the Devils Hole pupfish managed to take root, eventually evolving into a separate species from other local pupfishes, with a tolerance for extreme conditions and no pelvic fins.

“There's a lot of species that we don't expect to survive because humans have manipulated the environment to the extent that we have driven them to extinction,” said Michael Schwemm, senior fish biologist with the Fish and Wildlife Service. “What's unique about this one is the isolation. The fish managed to get [to Devils Hole] during times of high water and evolve independently and go on their own trajectory.”

Devils Hole as pictured from above.

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Courtesy National Park Service/Kim Stringfellow

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Other than the isolation and unique evolutionary developments, Devils Hole pupfish are remarkable for another reason: Wilson said they live in the smallest habitat for any known vertebrate species.

You can actually see the pupfish for yourself: Just keep in mind that the hole is fenced off to protect the fish, so you may need to bring binoculars.

A conservationist flashpoint

The Devils Hole pupfish isn’t just notable from a biological perspective, it was also at the center of a debate over water use and conservation in the late 1960s and 1970s.

“A local landowner put a well in right on the boundary of National Park Service land, turned it on, and the water level went down right away and the pupfish population declined,” Wilson said.

The debate got contentious enough that bumper stickers that read “kill the pupfish” or “save the pupfish” were popular.

The battle made it all the way to the Supreme Court in 1976, when the court decided in Cappaert v. United States that the federal government could restrict pumping of the aquifer that feeds Devils Hole in order to preserve the pupfish population. This set the precedent for the federal government to claim the rights to not just water sources on federal lands, but also adjacent aquifers in order to protect endangered species.

The future of the Devils Hole pupfish

Conservation biologists have been working to restore the pupfish population since the decline started, which Schwemm called one of the “smallest population sizes that a population has ever rebounded back from in a completely natural setting.”

Scientists routinely monitor the pupfish in Devils Hole.

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Kurt Moses

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National Park Service

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Though scientists want to keep the Devils Hole pupfish in its natural environment, they’ve had a little intervention: Owing to the population decline and scarce food sources, scientists started to feed the fish in 2007, and the population numbers have been monitored via diving expeditions for decades.

According to Schwemm, the fish is of great interest to researchers as they work to understand how the fish evolved to survive in high-temperature water with low levels of oxygen and food.

But even if the species’ natural habitat changes and becomes unviable for the fish in the years to come – which is possible with climate change – scientists have instituted a stopgap measure. A nearby tank mimicking the natural conditions of Devils Hole, including a 93-degree water temperature and very low oxygen, has managed to sustain a separate pupfish population.

And since pupfish populations appear to be stable or growing in both the natural and artificial habitats, officials are looking forward to being able to study the fish without devoting most of their energy to survival.

“It really opens up the door for future research,” Schwemm said. “We were really limited on our ability to do research before, and I think that's going to really help us.”