The Devils Hole pupfish (Cyprinodon diabolis) is a species of fish native to Devils Hole, a geothermal aquifer-fed pool within a limestone cavern, in the Ash Meadows National Wildlife Refuge east of Death Valley. It has been described as the world's rarest fish, with a population of fewer than 200 since 2005. Genetic analysis indicates that the species evolved at the same time the cavern opened up to the surface, about 60,000 years ago.
The pupfish have been protected since being declared an endangered species in 1967. Conflicts over the ownership and use of the groundwater around Devils Hole caused litigation in the 1980s. The litigation triggered further protections of the pupfish. However, since the late 1990s, the pupfish population has substantially decreased. The reasons for the decrease are unknown. Attempts to establish refuge populations of the pupfish through 2013 have failed.
The Devils Hole pupfish is the smallest desert pupfish species in the genus Cyprinodon.
Devils Hole pupfish are less than 25 mm (1 in) long and resemble other pupfish in shape. They are the smallest of the desert pupfish species, averaging 19 mm (0.75 in) in length. They lack pelvic fins and have large heads and long anal fins. Breeding males are solid deep blue and have a black band on the caudal fin.
There are a number of pupfish species scattered near Death Valley. Earlier pluvial (wet) periods allowed colonization of present sites; subsequent xeric (dry) conditions served to isolate the aquatic habitats, with the result that the inhabiting organisms have differentiated and evolved into the relict species found today.
The Devils Hole pupfish is considered an annual species, with the historic spring populations ranged between 150 and 250; while the autumn population grew to 400–500 individuals.
Devils Hole and the pupfish are located in the Amargosa Desert ecosystem, in the Amargosa Valley, of southwestern Nevada, USA, east of Death Valley and the Funeral Mountains and Amargosa Range. The Amargosa River is part of Devil Hole and the region's aquifer hydrology.
Although pupfish have been found as deep as 80 feet (24 m), they depend on a shallowly submerged limestone shelf of only 2 metres (6.6 ft) by 4 metres (13 ft) in area for spawning as well as for much of their diet (primarily diatoms). Natural threats from flash floods to earthquakes have been known to disrupt this fragile ecosystem, but in the 1960s and 1970s, the major threat was groundwater depletion due to agricultural irrigation.
Research indicates that the annual fluctuation of population is caused by the amount of algae present on the shelf. The algal growth depends, in turn, on the amount of solar radiation the shelf receives and the concentration of nutrients in the water. Finally, recent evidence suggests that nutrient availability is highest when the cave is used by barn owls (Tyto alba) as a roosting/nesting site. The owls increase the pool nutrient levels by casting nutrient-rich pellets into the water.
The water level in Devils Hole is monitored daily by the National Park Service and occasionally by the U.S. Geological Survey. During the late 1960s, the water level dropped dramatically in response to pumping in the Ash Meadows area, in the immediate vicinity of the cavern. After the cessation of pumping, the water levels recovered until about 1986, when the water level began to decline. Pronounced changes in the water level resulted in response to the 1992 Landers/Little Skull Mountain earthquakes and the 1999 Hector Mine earthquake. Since December 2005, the water level in Devils Hole has been rising, and by December 2008, the water level had risen to its highest level since 1993.
The age of the species is subject to considerable debate. Some scientists argue that vertebrate species with small populations cannot persist for long, and estimate the age of the species to be 360 years. Recent high-resolution genetic analysis indicates that the species formed when the cavern opened up to the surface, 60,000 years ago.
C. diabolis was first noticed in 1890 but only identified as a unique and highly divergent species by Joseph Wales in 1930. Formal protection of the species began when Devils Hole was made part of Death Valley National Monument by presidential proclamation in 1952. Ten years later the NPS installed a hydrograph in the Hole to monitor water levels. Subsequently, the Hole was fenced after two divers drowned in its water. In 1967, the Devils Hole pupfish was officially listed as an endangered species.
In 1967, a farming corporation amassed 12,000 acres (4,900 ha) in the Ash Meadows area; by 1968, the hydrograph had begun to register a decline as large capacity wells were drilled and pumped in Ash Meadows. The water drop threatened to expose the critical spawning/feeding shelf and precipitated the formation of two groups to work for protection of Devils Hole: the Desert Fishes Council in the West, and the Desert Pupfish Task Force in Washington D.C.
In August 1971 a federal court issued an injunction to halt further pumping, that threatened to completely expose the natural shelf. Further litigation finally resulted in the landmark Supreme Court decision of 1976 (Cappaert vs. U.S.). It recognized the prior water right of Devils Hole vis-a-vis its designation as part of a national monument. The permanent injunction did not halt pumping, but limited it to a level which guaranteed sufficient water to inundate the natural rock shelf.
In 1980, the U.S. Fish and Wildlife Service designated as essential habitat about 21,000 acres (8,500 ha) acres where the groundwater most influenced the water level in the Hole. One of the identified goals of the recovery plan was to maintain the aquifer at such levels that the population fluctuates from 300 in winter to 700–900 in late summer. The water source for the Devils Hole pupfish was now adequately secured, but the remainder of Ash Meadows was as yet unprotected. A land development company bought the Ash Meadows land from the farm corporation in 1980, planning to subdivide the area into 34,000 residential lots. Furthermore, in 1982, the U.S. Fish and Wildlife Service emergency-listed as endangered two more of the fish species in Ash Meadows, thereby conferring protection to all the pools in the area. Finally, in 1984, Ash Meadows National Wildlife Refuge was established by Congress. The Nature Conservancy bought the bulk of the land from the development company and resold it to the USFWS. By 1986, the USFWS had drafted a recovery plan for the entire Ash Meadows area, including Devils Hole.
In April 2016 the National Park Service recorded three men firing a shotgun and leaving beer cans, vomit, and boxer shorts in the water of Devils Hole that may have caused at least one pupfish death. The men were charged with killing an endangered animal and other property crimes.
In 1970, a floating artificial shelf, artificially lighted, was suspended in Devils Hole to substitute for the partially exposed natural rock shelf. The fish never used the artificial shelf.
A number of artificial "refugia" (concrete tanks approximating conditions in Devils Hole) were attempted to ensure species' survival should the natural population at Devils Hole die out; one at Hoover Dam established in 1972, and two near Devils Hole itself within the Ash Meadows National Wildlife Refuge established in 1980 and 1991.
In May 2005, nine pupfish were moved from the hole and a federal hatchery to both a Las Vegas Strip casino aquarium, at Mandalay Bay, and another federal hatchery in hopes of augmenting the population.
In 2006, five younger pupfish were moved to the Willow Beach National Fish Hatchery in Arizona to establish the pupfish in aquaria.
As of 2013, none of the previous attempts to establish refugia were successful. Studies have been undertaken to better understand energy flow in the system, water chemistry, pupfish genetics, organisms living in the water, and other factors.
From 1970 through 1996, the average population was 324. Since 2005, the population at Devils Hole has been below 200 individuals, although the population fluctuates depending on the season. Low algae growth and other winter conditions cause spring populations to be 35–65% of the autumn population. The reasons for the decline of the population are unclear.
In November 2005, divers counted just 84 individuals in the Devils Hole population, the same as the spring population, despite observations of egg-laying and baby fish during the summer. As many as 80 fish – one-third of the population – was estimated to have been destroyed during the summer of 2004 when a flash flood pushed a quantity of scientific equipment (fish traps) which had been left sitting on the edge of the hole into the hole; later, about 60 cubic feet (1.7 m3) of debris, washed into the cave by floods, was removed.
In 2007, between 38 and 42 fish were left in Devils Hole.
In 2008, the National Park Service began to feed the pupfish a special food to attempt to restore the population. The Devils Hole pupfish count rose in the autumn of 2008 to 126, the first steady increase in more than 10 years.
As of April 2013 U.S. Fish and Wildlife reported only 35 fish remain in their natural habitat, but increased to 92 when measured again in 2014.
As of spring 2016, a periodic count found 115 of the fish living in the waters.
All the various surviving local Cyprinodon species and subspecies (pupfish), including the Devils Hole pupfish, are on the IUCN Red List of endangered species:Ash Meadows pupfish, Cyprinodon nevadensis mionectes
Amargosa pupfish, Cyprinodon nevadensis amargosae
Death Valley pupfish, Salt Creek pupfish Cyprinodon salinus
Shoshone pupfish, Cyprinodon nevadensis shoshone
Tecopa pupfish, Cyprinodon nevadensis calidae (extinct)
Desert pupfish, Cyprinodon macularius
Owens pupfish, Cyprinodon radiosus