One of Earth's Rarest Fish Sees 'Remarkable' Return From Near-Extinction

A critically endangered species of fish that lives in a very bizarre place is coming back from the brink of extinction.

The National Park Service (NPS) announced that the Devil's Hole pupfish has hit a 25-year spring population high, with 191 individuals being counted in their secluded cavern home.

The spring population of these rare fish—considered to be one of the most endangered species of animal in the world—hit an all-time low in 2013 at only 35, having declined from between 200 and 250 before the mid-1990s. This year's population is the highest spring count that conservationists have found since 1999.

"It was really encouraging to see such a large number of young fish during these spring dives. Conditions within Devils Hole looked healthy, so we have hopes of high recruitment over the coming months that will lead to a large population in the fall," Brandon Senger, a supervising fisheries biologist for the Nevada Department of Wildlife, said in an NPS statement.

The Devils Hole pupfish (Cyprinodon diabolis) is found exclusively in Devils Hole, a 92-degree water-filled cavern in the Mojave Desert, located within the Ash Meadows National Wildlife Refuge in Nevada. These fish live in the smallest habitat of any known vertebrate animal in the world, spending their time in the upper 80 feet of the 500-foot-deep cave, and relying on the 11 by 16-foot shelf to feed and reproduce.

These pupfish are small, typically no larger than an inch or so in length, and they feed on algae, detritus, and microorganisms. Their population fluctuates throughout the year, ranging between only 100 to 200 in the spring to 300-500 in late summer, with this cycling thought to be linked to the amount of algae available in the cave.

According to the NPS, this count was done between April 6 and 7 by SCUBA divers who examined the upper 100 feet of the cave. They noted that the fish appeared in "remarkable condition."

"It's exciting to see an increasing trend, especially in this highly variable population. Increasing numbers allow the managing agencies to consider research that may not have been possible in the past, when even slight perturbations of habitat or fish had to be completely avoided. We're excited about the future directions with respect managing this species," Michael Schwemm, senior fish biologist for the U.S. Fish and Wildlife Service, said in the statement.

The species faces numerous threats, ranging from habitat changes, groundwater pumping, and climate change. Several conservation measures have been implemented to protect and recover the population, including habitat restoration, careful monitoring of water levels and quality, and even the establishment of a refugial population in a separate facility to serve as a backup should the wild population face catastrophic decline.

The fall count of 2022 was also significant at a 19-year high, with 263 of the fish being found. This came just after a magnitude 7.6 earthquake in Mexico triggered 4-foot waves inside Devils Hole on September 19, 2022, which can be catastrophic to the fish as it disturbs the algae on their crucial feeding shelf. However, the number of these fish remained higher than in previous decades.

This year's record-breaking spring count is hoped to mean that the pupfish population is finally on the rise for good.

"Recent high spring and fall counts show the importance of maintaining long-term data as we work to find out what's changed," Kevin Wilson, an aquatic ecologist for Death Valley National Park, said in the statement.

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