Devil's Hole Pupfish

Cyprinodon diabolis

Description

The Devil's Hole pupfish, Cyprinodon diabolis, is the most distinctive member of its genus, characterized by its extremely small size, which rarely exceeds 0.8 in (2 cm) in length, its absence of pelvic fins, and the lack of vertical crossbars in mature males. It has a long tail, and a large head and eyes. It is distinguished from other members of the genus Cyprinodon by its lack of pelvic fins and scales in the preorbital region, and vertical crossbars in males, as well as by its posterior dorsal fin, long anal fin, and large head and eye.

Behavior

Little is known of Devil's Hole pupfish behavior. Its food supply is thought to consist entirely of algae. Algae growth, in turn, depends on the amount of sunlight that strikes the surface of the shelf pool within Devil's Hole. During the summer, the shelf receives about four hours of sunlight a day; no direct sunlight reaches the water surface during winter. Any decline in water level directly affects the amount of sunlight reaching the water, and thus food availability for the pupfish.

The Devil's Hole pupfish is primarily an annual species, living about one year, whose population fluctuates during the course of each year. Natural population fluctuations have been recorded from a maximum of 553 fish in the summer to a minimum of 127 fish in the winter.

Spawning occurs throughout the year, but reaches a peak in the spring. Fertilization occurs when eggs are singly deposited onto the substrate where they incubate. Growth during the spring varies between 0 and 0.025 in (0.06 cm)/wk, and little or no growth occurs during the winter.

Stomach analyses show they are opportunistic feeders whose diet includes Spirogyra or diatoms, depending on the season. Stomachs also contained invertebrates such as amphipods, ostracods, and protozoans.

Habitat

The spring pool of Devil's Hole (Nevada) is located some 60 ft (18 m) below the land surface, where there is a shallow rock shelf approximately 8 ft (2.4 m) by 16 ft (5 m). Just beyond the shelf, the spring descends to an unknown depth into a myriad of chasms, mostly unexplored. Most of the pupfish's reproductive and feeding activity takes place on the shallow shelf.

Distribution

This pupfish has probably been isolated within its current habitat, a limestone cave situated on the east central border of Ash Meadows, for many thousands of years. Small refugium populations have been established in the Amargosa Pupfish Station in Ash Meadows and in facilities constructed by the Bureau of Reclamation located near the base ofHoover Dam along the Colorado River. Devil's Hole is a deep, water-filled limestone cavern. Probable population is from 300-900 individuals.

Threats

Throughout the 1960s, pumping groundwater for irrigation lowered the water level within Devil's Hole. The reduction was so serious that in 1972, 27 Devil's Hole pupfish were moved to the Hoover Dam Refugium (Clark County), Nevada, to establish a captive breeding population. This captive population is reproducing, and numbers have fluctuated from 48-69 pupfish in recent years.

The primary threat to the pupfish's survival in the wild continues to be reduction of water levels needed to maintain the habitat. Other potential threats include surface runoff, which carries sand and silt into the underground caverns. Devil's Hole is part of the Ash Meadows National Wildlife Refuge, which has acquired water rights in the region.

Conservation and Recovery

The first goal of recovery is to stabilize the Devil's Hole habitat, but the species will probably remain threatened, even if pristine conditions are reestablished. For this reason, it is important to maintain the captive population. Scientists are concerned that the Hoover Dam population is not genetically pure, since these pupfish are larger in body size than the Devil's Hole population.

The status of the species has improved considerably in the past 10 years, but its populations are persistently small and localized. Prior to this, the removal of groundwater from wells pumping to support a cattle and alfalfa ranch reduced the water level within Devil's Hole. This decline was immediately evidenced in a decrease in the fish population attributed to the drying of areas utilized by the fish for feeding and reproduction. Litigation initiated by the U. S. Department of the Interior to protect Devil's Hole ended with a ruling by the U. S. Supreme Court which upheld a lower court decision mandating the maintenance of a minimum water level. The level being enforced today measures 2.7 ft (0.8 m) below a benchmark on the wall within Devil's Hole.

Recovery criteria include the requirement that all listed and candidate species be present in all locales they historically occupied within Ash Meadows; that listed species have reached self-sustaining populations; that the essential habitat be free of threats from all non-native animals, exotic plants and detrimental human disturbances; and that the springs have returned to historic discharge rates and water flow is reestablished into historic channels. In addition, the Devil's Hole minimum water level must be 1.4 ft (0.4 m) below the copper washer with a minimum pupfish population of 300 individuals during winter and 700 during late fall; two refugia populations must be established for the Devil's Hole pupfish; and native plant and aquatic communities and have been reestablished to historic structure and composition within all essential habitat.

To achieve these goals, the 1990 Recovery Plan recommends a variety of needed actions, including the securing of habitat and water resources for the Ash Meadows ecosystem; research on the biology of the species; management activities within the essential habitat; the reestablishment of populations and/or monitoring of new and existing populations; and the determination and/or verification of recovery objectives.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

Miller, R. R. 1961. "Man and the Changing Fish Fauna of the American Southwest." Papers of the Michigan Academy of Science, Arts and Letters 46: 365-404.

Minckley, C. O., and J. E. Deacon. 1975. "Foods of the Devil's Hole Pupfish." Southwestern Naturalist 20(1): 105-111.

U. S. Fish and Wildlife Service. 1980. "Devil's Hole Pupfish Recovery Plan." U. S. Fish and Wildlife Service, Albuquerque.

U. S. Fish and Wildlife Service. 1990. "Recovery Plan for the Endangered and Threatened Species of Ash Meadows, Nevada." U. S. Fish and Wildlife Service, Portland.

Williams, J. E. 1977. "Observations on the Status of the Devil's Hole Pupfish in the Hoover Dam Refugium." Report REC-ERC-77-11. U. S. Fish and Wildlife Service, Albuquerque.