Extremely Rare Death Valley Fish Found in Highest Numbers in Decades

Take a deep breath and say this along with me: Biologists have found one of the world’s rarest fishes that lives in one of the smallest habitat ranges on earth, thriving at its highest numbers in over 20 years.

The Devils Hole pupfish (Cyprinodon diabolis) lives only in the top 24 metres of Devils Hole, located near Death Valley in the U.S. The pool plunges into a narrow desert cavern, and the unassuming fish lives only inside it and the shallow landing at the mouth of the cave. The unlikely habitat is the smallest range for any vertebrate on earth.

Scientists started SCUBA diving into the pool to count the fish in 1972. Generally counted during spring, the critically endangered fish commonly numbered under 100 for the last three decades. But on April 12, divers counted 175 fish, the most pupfish in 22 years.

Devils Hole pupfish count protocol and context

A patchwork of entities, including the National Park Service, U.S. Fish and Wildlife Service, and the Nevada Department of Wildlife, manages the site. They estimate the fishes’ population size by counting them throughout their habitat, according to a standard protocol.

devils hole divers

Photo: USFWS/Olin Feuerbacher


SCUBA divers descend to a depth below 30m, then start swimming upward to count fish in the cavern. Simultaneously, other scientists count fish on the shallow shelf at the surface. The final count includes both surface and underwater fish.

The count wasn’t the only thing that stood out about this season’s pupfish.

Brandon Senger, Supervising Fisheries Biologist for the Nevada Department of Wildlife, counted a surprising number of young fish below the surface, indicating robust spring reproduction coming out of winter. Other biologists noted the fish appeared both remarkably healthy and very active.

Higher numbers of pupfish in spring could also signal critical shifts in the Devils Hole ecosystem. Scientists in the area don’t know what it means yet. But Kevin Wilson, Aquatic Ecologist for Death Valley National Park, stated that “such shifts highlight the importance of maintaining long-term data as we work to find out what’s changed.”

‘Isolated’ for tens of thousands of years

Devils Hole slices into a limestone outcrop in Nye County, Nevada, to over 152m in depth.

Devils Hole opening

Photo: Ken Lund


The aquifer-fed pool’s surface is just 22m x 3.5m, and its floor has never been mapped. Its water temperature (33°C) and salinity are constants, giving a stable year-round habitat for its endemic pupfish.

Estimates indicate that the Devils Hole Pupfish have “been isolated” in the cavern for 10,000-20,000 years. The species relies on algae that grow on the shelf near the water’s surface.

devils hole

Photo: Stan Shebs via Wikimedia Commons


This week’s count re-confirms the Devils Hole pupfishes’ ongoing nine-year recovery from the all-time low of 35 fish.