According to the National Parks Service, biologists counted 263 Devils Hole pupfish in Devils Hole, Nevada, the highest count of this species in 19 years.
Devils Hole pupfish are a species of fish that only occur naturally in Devils Hole—a water-filled cavern in the side of a hill that is over 500 feet deep. It is part of Ash Meadows, a wildlife refuge that is a discharge point for a vast underground aquifer water system.
Parts of the area are thought to have been colonized with life in previous wet periods and subsequently isolated in dry periods. As a result, the Devils Hole pupfish are thought to have been isolated for between 10,000 and 20,000 years according to the U.S. National Park Service (NPS).
Inside the cavern the fish live and spawn exclusively on a shallow rock shelf near to the surface, feeding on algae. It is thought to be the smallest range of any vertebrate species on Earth.
Every year the Devils Hole pupfish population varies between 100 to 200 in the winter and 300 to 500 in the summer, depending on how much algae is present.
In the mid-1990s, the Devils Hole pupfish population began a mysterious and severe decline that has yet to be fully understood despite studies into water chemistry and pupfish genetics. The U.S. Fish and Wildlife Service has designated about 21,000 acres of the region to be essential habitat as part of a recovery plan in the 1980s.
The discovery of 263 of the fish this year followed a magnitude 7.6 earthquake in Mexico that generated 4-foot waves inside Devils Hole on September 19, according to the NPS.
This activity within the cave system sloshed around the algae and other organic matter in the water, making it easier for biologists to find the pupfish from the surface. The pupfish are counted using visual counters from the surface as well as scuba divers.
The count marks an increase from the average of only 90 fish over the past two decades or so, and could signal important changes in the ecosystem.
“I have never seen the population this robust before,” said Brandon Senger, a Nevada Department of Wildlife biologist who has been conducting scuba counts at Devils Hole since 2014, according to an NPS press release. “Fish of all size-classes were abundant. We scuba-counted more fish on one level than we have in total in previous counts.”
The fish that were counted appeared to be in good condition and were very active, with many courting and spawning pairs spotted.
The next pupfish count will take place in spring 2023.
