Hundreds of extremely rare fish were recently discovered in Nevada after an earthquake revealed their location.
According to the National Parks Service, biologists counted 263 Devils Hole pupfish in Devils Hole, Nevada, the highest number for this species in 19 years.
Devils Hole pupfish are a species of fish that occur naturally only in Devils Hole, a water-filled cavern in the side of a hill more than 500 feet deep. It is part of Ash Meadows, a wildlife refuge which is a discharge point for an extensive underground aquifer water system.
Parts of the area are believed to have been colonized by life during earlier wet periods and subsequently isolated during dry periods. As a result, Devils Hole pupfish are believed to have been isolated between 10,000 and 20,000 years ago according to the US National Park Service (NPS).
Inside the cave, the fish live and spawn exclusively on a shallow rocky platform near the surface, feeding on algae. It is believed to be the smallest range of any vertebrate species on Earth.
Each year, Devils Hole’s pupfish population varies between 100 and 200 in winter and 300 and 500 in summer, depending on the amount of algae present.
In the mid-1990s, the Devils Hole pupfish population began a mysterious and severe decline that has not yet been fully understood despite studies of water chemistry and pupfish genetics. The U.S. Fish and Wildlife Service designated about 21,000 acres of the area as critical habitat under a recovery plan in the 1980s.
The discovery of 263 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 took place around algae and other organic matter in the water, which made it easier for biologists to find the pupfish from the surface. Pupfish are counted using visual counters from the surface as well as by scuba divers.
The count marks an increase from the average of just 90 fish over the past two decades or so, and could signal significant changes to the ecosystem.
“I’ve never seen the population this robust before,” said Brandon Senger, a Nevada Department of Wildlife biologist who has been conducting dive counts at Devils Hole since 2014, according to an NPS news release. “Fish of all size classes were abundant. We counted more fish at one level than we had 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 the spring of 2023.