Fish
Devils Hole Pupfish
Cyprinodon diabolis · also called Devil's Hole pupfish
The Devils Hole pupfish lives in one pool, in one cavern, in one desert. A shelf of rock the size of a couple of table-tennis tables is the only place it can feed and breed. It is the vertebrate with the smallest natural range on Earth, and keeping it alive has taken decades of work and a Supreme Court ruling.
Overview
Cyprinodon diabolis is a small iridescent-blue fish, 2 to 3 cm long, found only in Devils Hole, a geothermal limestone pool in the Nevada desert inside Death Valley National Park. The water sits near 33 degrees Celsius and very low in oxygen, and the fish graze algae off a single shallow sunlit shelf.
On the edge
The wild population has swung between about 35 fish in 2013 and roughly 100 to 260 in recent years, counted individually by divers twice a year. A replica of the pool was built nearby to hold a backup population.
Saved in court
When 1970s groundwater pumping for farms dropped the water level and threatened to expose the spawning shelf, the 1976 Supreme Court case Cappaert v. United States ruled that protecting the pool carried an implied right to the groundwater it needed, and limited the pumping.
Status
Critically Endangered — earthquakes, flash floods, groundwater withdrawal, and its own tiny numbers all threaten a species that exists in a single pool.
Devils Hole Pupfish: common questions
Why does the Devils Hole pupfish live in only one place?
It is a relic. The Ash Meadows region of the Nevada desert was much wetter thousands of years ago, with lakes and connected springs, and pupfish spread through that system. As the climate dried, the water retreated to a scatter of isolated springs and pools, and the fish in each became cut off and evolved separately, which is why the area has several pupfish species and subspecies each confined to its own spring. Devils Hole is the most extreme case, a deep, narrow, geothermal cavern pool with just one small sunlit shelf where the fish can feed and spawn, isolated for perhaps 10,000 to 20,000 years, or possibly much longer.
How can a fish population survive at only a few dozen individuals?
With difficulty, and with a great deal of human help. A population that small is genetically impoverished, vulnerable to a single bad event, and prone to poor breeding success, and the Devils Hole pupfish has shown all of these problems. It is kept going by constant management. Divers count and monitor the fish twice a year, supplemental food is added to the shelf, eggs are sometimes removed to rear in captivity, and a full-scale replica of the pool has been built nearby to hold a backup population. Even so, the wild count dropped to about 35 in 2013 before recovering, and the species remains one bad year away from a crisis.
What was the Supreme Court case about?
It was about groundwater. Devils Hole was added to Death Valley National Monument in 1952 specifically to protect the pupfish. In the following two decades, a nearby ranch drilled wells and pumped large volumes of groundwater for irrigation, and the water level in Devils Hole fell, threatening to leave the shallow spawning shelf high and dry. In 1976, in Cappaert v. United States, the Supreme Court ruled that when the federal government set aside the pool it also implicitly reserved the right to whatever groundwater was needed to keep it functioning, and it ordered the pumping limited. The decision is a landmark in United States water law as well as in endangered-species protection.
Has anything else threatened the pupfish?
Yes, in several ways. Distant earthquakes, including large ones in Mexico, Japan, and Chile, have set the water in Devils Hole sloshing violently, scouring algae and eggs off the shelf. Flash floods have washed debris and non-native material into the pool. In 2016 three men broke into the site, and one waded into the pool and was filmed vomiting in it, and a dead pupfish was found afterward; the men were prosecuted. And the slow background threat of regional groundwater withdrawal never fully goes away. For a species living in one pool, almost any disturbance is potentially serious.