A Fish Out of Water 
Illustration by Andrew Recher
By Scott Kirkwood
What type of fish lives in the desert? Sounds like a child’s riddle, but in this case, the answer isn’t a pun, it’s a pupfish—the Devil’s Hole pupfish, to be precise. Named after the isolated body of water it calls home, the fish’s presence was a key reason the satellite unit was added to nearby Death Valley National Park in 1952. But more than 50 years later, scientists still aren’t sure how the pupfish got itself in such hot water.
“Like many freshwater fish, pupfish invaded from salt water, arriving during the Miocene epoch, then making their way to the large Pleistocene lakes, and eventually becoming isolated in these various systems as the water receded,” says John Wullschleger, a fisheries biologist with the park service. “We’re not talking about a bunch of fish picking up and moving over the course of a year, but over thousands and thousands of years, gradually expanding into new habitats as they become available.” Once those bodies of water began to dry up and become isolated from one another, each species evolved independently, yielding various sorts of pupfish adapted to its own conditions. But here’s the mysterious part: The water in Devil’s Hole was first exposed to the surface about 60,000 years ago, and since then, it’s never been connected to any other surface water. So although scientists can track the pupfish’s origins from the California desert back 200 million years to Pangea (the landmass that would eventually split into seven continents), no one’s quite sure how the Devil’s Hole pupfish managed to negotiate the last few miles.
We do know this much: Devil’s Hole is the smallest known range of any vertebrate species—an opening in the earth about 60 feet by 100 feet, where a small pool of water leads to a submerged cavern. In fact, everything about the Devil’s Hole pupfish is small: An adult pupfish is smaller than your thumb. A pupfish’s lifespan is roughly nine to ten months—one year, tops. In recent years, its population has ranged from 200 to 500 with large seasonal variations, but it now hovers between 125 and 200. Whereas most fish produce thousands of eggs during a reproductive cycle, spawning pupfish produce about ten eggs annually. Given all those factors, the margin of error for the species’ survival is pretty small, too. Thankfully, the pupfish is able to deal with a lot of adversity.
“Pupfish are incredibly adaptable—they’ve been successful in the desert because they’re capable of surviving wide ranges of salinity and temperatures,” says James Deacon, PhD, former professor of environmental studies at University of Nevada, Las Vegas. “Pupfish species can live in water that’s very hot or near freezing—when it gets really cold, they’ll just bury themselves in the mud until it warms up.” In Devil’s Hole, air temperatures often hover around 100 degrees Fahrenheit, and water temperatures often reach 90 degrees, making this the warmest place you’ll find a fish outside of a bouillabaisse.
But even the pupfish has limits. Its spawning activity occurs on a shelf covered in shallow water about 6 inches to 24 inches deep. Pupfish stay in this shallow area to reproduce and to eat algae, aquatic insects, and invertebrates, so every inch of water is vitally important.
In fact, years ago, when water levels in Devil’s Hole fell because of agricultural uses, a 1976 Supreme Court decision confirmed that water rights attached to Death Valley prohibited farming interests from pumping ground water from the source, protecting the pupfish’s habitat, and setting a precedent for water rights that’s still taught in law schools today. Although that move boosted water levels and pupfish counts, the last ten years have seen another decline.
“These fish are already living at the margins of their thermal tolerance, and they’ve been doing so throughout history,” says Wullschleger. “But a relatively small change in water depth could change conditions enough that they couldn’t maintain themselves anymore.”
NPCA’s recent State of the Parks report focusing on the California Desert Parks highlights the effect of increasing development in the West and the resulting competition for scarce water re-sources, all of which affect the desert pupfish and other rare and endangered species. Because most of the springs in this region appear to be supplied by the same aquifer, many researchers believe that the Devil’s Hole pupfish is the proverbial canary in the coal mine— one of many wildlife species that can survive in harsh desert conditions until the scale is tipped too far in one direction.
For now, researchers are doing all they can to learn more about the pupfish and bolster its numbers. But when you’re working with a small population of animals in a single area, every action has major consequences. Last fall, a flash flood washed researchers’ collection devices into the water, a bizarre mishap which inadvertently captured and killed dozens of pupfish before it was discovered. And every time an earthquake or flash flood pours sediment into the shallow ledge, researchers must decide if they should clear the ledge themselves or let natural processes unfold, and hope the species finds a way to survive. Although the Devil’s Hole pupfish has managed to last this long on its own, now its fate is in the hands of humans—the biologists fighting for its survival on one side, and the millions of others competing for the one vital resource that none of us can live without.
Scott Kirkwood is senior editor for National Parks magazine. |
