Owens Pupfish

Cyprinodon radiosus

Description

The Owens pupfish, Cyprinodon radiosus, is a small (2.5 in; 6.4 cm) deep-bodied fish with a laterally compressed shape. The sexes display differing size and color patterns. The larger males are olive above and slate gray beneath, with an overall bluish cast. Their lateral bars are deep purplish with posterior bars having some gold. The lower head is silver and blue, and the dorsal and anal fins are blue with an orange-amber border. The smaller females are deep olive with brown lateral blotches and purplish vertical bars.

Behavior

Pupfish are omnivorous and feed on algae, aquatic insects, crustaceans, and plankton. The spawning season begins in April when water temperatures reach 68°F (20°C). When spawning, males turn bright blue and become territorial, defending their spawning area from other male pupfish and from other fish species. Females can deposit 50-200 eggs during the season but rarely lay more than one or two eggs at a time. Eggs hatch in seven to 10 days, depending on water temperature. Newly hatched pupfish larvae begin feeding the day they hatch. Pupfish fry, which live along the shoreline where warmer water supports abundant food, mature in three to four months.

Habitat

Basic habitat requirements for the Owens pup-fish consists of good quality water, aquatic vegetation, and a silt-or sand-covered bottom. It is normally found near the margins of bulrush marshes, in wide, well-vegetated shallow sloughs, or in spring pools.

Distribution

The Owens pupfish has been found in east-central California in the Owens River and adjacent springs as far south as the springs around Owens Lake in Inyo County. In 1915 the species was plentiful along the Big Bend areas of the Owens River northeast of Bishop, but had mostly disappeared by 1934. During the 1940s the Owens pupfish was considered extinct. In 1956, however, a small population was discovered in Fish Slough. This population has been the source for all Owens pupfish populations that have been reestablished and exist today.

The Owens pupfish is now confined to four springs in the Fish Slough area north of Bishop (Mono County), California. The protected area includes the Owens Valley Native Fish Sanctuary and a Bureau of Land Management spring refuge. There are no current population estimates.

Threats

Most Owens pupfish habitat was destroyed when dams and upstream diversions on the Owens River prevented seasonal flooding of shallow marshy areas. Groundwater pumping for irrigation continues to threaten aquifers supplying water to the remaining spring habitats, and vandals have destroyed structures built to help maintain the habitats.

Conservation and Recovery

The sanctuary at Fish Slough was created in the late 1960s to provide protected habitat for the speckled dace, the Owens sucker, and the federally listed Owens tui chub (Gila bicolor snyderi ) as well as the pupfish. Fish Slough, a unique wetland in an arid environment, contains a number of rare species besides the Owens pupfish, including the Fish Slough milkvetch and an undescribed species of mollusk. Recently, recovery efforts at the sanctuary received a setback, when it was discovered that the predatory largemouth bass had penetrated the Owens pupfish refuge at Fish Slough. In a single year, the bass managed to invade all four habitat springs. California Fish and Game personnel suspect that the bass were purposely introduced above fish barriers to threaten the survival of the pupfish. Repeated efforts to eradicate the bass have been only partially successful. Because much of the habitat within the historic range can never be restored, U. S. Fish and Wildlife Service personnel hope to transplant the fish to the adjacent Adobe Valley, where good habitat still exists.

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

Brown, J. H. 1971. "The Desert Pupfish." Scientific American 225: 104-110.

Soltz, D. L., and R. J. Naiman. 1978. "The Natural History of Native Fishes in the Death Valley System." Natural History Museum of Los Angeles County Science Series 30:1-76.

U. S. Fish and Wildlife Service. 1984. "Recovery Plan for the Owens Pupfish, Cyprinodon radiosus." U. S. Fish and Wildlife Service, Portland.