Devils Hole Pupfish

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Updated April 2011... The Devils Hole pupfish (Cyprinodon diabolis) was listed as endangered in 1967. This iridescent blue inch-long fish's only natural habitat is in the 93 degree waters of Devils Hole, located within the Ash Meadows National Wildlife Refuge, Nye County, Nevada, which is a detached unit of Death Valley National Park . Although the cavern is over 400 feet deep, the pupfish are believed to spawn exclusively on a shallow rock shelf just under the waters surface.

Since population surveys began, Devils Hole pupfish numbers have not exceed 553 individuals. For reasons that are still unclear, the population of Devils Hole pupfish began to decline in the mid 1990’s. By the fall of 2006, an estimated 38 fish remained in the wild and two refuge populations were lost.

Past research demonstrated that their population naturally cycles in Devils Hole with the largest number of pupfish occurring in the fall and declining over the winter. Although they spawn year round in the constant 93°F water, the adults that survive the winter produce most of the next generation of pupfish in the spring.

In 2006, the Service, National Park Service, and Nevada Department of Wildlife launched an emergency effort to reverse the decline of the species. Working with partners as diverse as Shark Reef Aquarium at Mandalay Bay in Las Vegas, they struggled to find innovative ways to reverse the population decline.

Suspecting that the food source may be a limiting factor, an artificial food was developed and an automatic feeder installed in Devils Hole. Originally a stop gap measure, this has proven to be so successful that it has remained in operation. Another critical decision was to limit access into Devils Hole and not remove pupfish for experimental or captive propagation until the fall population exceeds 200 fish and an increasing population trend is demonstrated for three years.

Biannual adult population surveys in April and in October continue. In addition to a surface count, cave divers enter Devils Hole and descend approximately 100 feet to count the number of adult pupfish. The average of these dives is used to determine the spring and fall population estimates.

Since 2007, the population estimates have started to swing upward. The fall 2008 count was estimated at 127 fish; the first time triple digits have been estimated since 2004, and the first three year upward trend since 1996. The average number of pupfish estimated in April 2011 is 104.

If you would like additional information about the Devils Hole pupfish and recovery actions, please contact the Las Vegas field office at 702-515-5230