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Literature Review

Desert pupfish

Cyprinodon macularius macularius

USFWS: Endangered
CDFG: Endangered

Background

Distribution, Abundance and Trends. Historically, desert pupfish occurred in the lower Colorado River in Arizona and California, from about Needles downstream to the Gulf of Mexico and onto its delta in Sonora and Baja. In California, pupfish inhabited springs, seeps, and slow-moving streams in the Salton Sink basin, and backwaters and sloughs along the Colorado River. Desert pupfish also occurred in the Gila River Basin in Arizona and Sonora, including the Gila, Santa Cruz, San Pedro, and Salt Rivers; the Rio Sonoyta of Arizona and Sonora; Puerto Penasco, Sonora; and Laguna Salada basin of Baja California. The Quitobaquito pupfish, found only in Quitobaquito Spring, Arizona, was recognized as a subspecies of desert pupfish; however, a recent phylogenetic study supports the recognition of this pupfish, as well as pupfish from the Rio Sonoyta, as the species Cyprinodon eremus Miller and Fuiman (Echelle 1999).

In the Salton Sink, desert pupfish populations were remnants of those that inhabited ancient Lake Cahuilla. About 400-500 years ago, the Colorado River was diverted away from the lake and into the Gulf of California, leaving the pupfish isolated in certain springs. After the Salton Sink was flooded in the early 1900s by diversion of the Colorado River, desert pupfish colonized the Salton Sea. The Salton Sea, its tributary streams, irrigation drains, and shoreline pools, supported large pupfish populations until sharp declines began in the mid to late 1960s. However, a 1991 California Department of Fish and Game survey (Nicol et al. 1991) found pupfish in a majority of irrigation drains, some shoreline pools and several tributaries of the Salton Sea. Currently, California desert pupfish populations are restricted to portions of San Felipe Creek and its associated wetland, San Sebastian Marsh (Imperial County), portions of Salt Creek (Riverside County), some shoreline pools and irrigation drains along the Salton Sea (Imperial and Riverside counties), and various artificial refugia (Riverside and San Diego counties).

Naturally occurring populations of desert pupfish have been extirpated from Arizona. However, pupfish have been transplanted to a number of locations within the state. A large population of another desert pupfish subspecies is endemic to Quitobaquito Springs, Organ Pipe National Monument. In Mexico, desert pupfish are found at various localities along Rio Sonoyta, on the Colorado River Delta, and in the Laguna Salada Basin. In Sonora in Rio Sonoyta, pupfish inhabit several spring-fed marshes. In Baja California, pupfish occur on the Colorado Delta, in Laguna Salada, in a wetland associated with a geothermal power plant, and in a ditch downstream of this marshland.

In the Plan area, pupfish are found in upper and lower Salt Creek, the mouth of Salt Creek (Sutton 2000), several irrigation drains emptying into the Salton Sea, some shoreline pools, and several refugia: Dos Palmas; the Coachella Valley Preserve; Oasis Springs Ecological Reserve; The Living Desert; and Salton Sea State Recreation Area. The Plan area contains a substantial portion of remaining pupfish habitat, including one of only two natural tributary streams, most of the refugia, and some of the shoreline pools and irrigation drains.

A small, but stable, population exists in Salt Creek. The majority of fish inhabit an upstream portion of the creek, but a few pupfish were found at the mouth as recently as 1995 and again in 1999 (Sutton 1999). During 1997 surveys conducted by the Department of Fish and Game, 100 pupfish and 700 mosquitofish were captured in the upstream section of Salt Creek. In recent surveys conducted by the Department of Fish and Game, pupfish were found in approximately 30% of the irrigation drains emptying into the Salton Sea, significantly fewer than in 1991, probably as a result of a substantial increase in tilapia numbers during the past few years. Pupfish seem to be doing better along the west end of the Sea, where habitat is more suitable. Along the east end of the Sea, the substrate in many of the drains consists almost entirely of tilapia nests, and very little aquatic vegetation remains in these drains.

Adequate water quantity and quality must be maintained in desert streams, springs, irrigation drains, and shoreline pools. Surface and groundwater from upper Salt Creek Canyon and other canyons in the Orocopia and Chocolate Mountains may contribute to the groundwater system. Seepage from the Coachella Canal also contributes to the groundwater in the Salt Creek drainage system. Groundwater pumping, channel erosion, water diversion, contaminants, and other threats must be reduced to the extent possible.

Threats and Limiting Factors. Currently, the major threat is the presence of exotic fish species, particularly tilapia (Tilapia spp.), sailfin molly (Poecilia latipinna), and mosquitofish (Gambusia affinis) in habitats occupied by pupfish. These and other introduced fish species affect pupfish populations through predation, competition, and behavioral interference. In addition, the non-native bullfrog (Rana catesbeiana) is a serious predator of pupfish. Introduced plant species, such as salt cedar (Tamarisk) also pose a threat to pupfish populations. Evapotranspiration by salt cedar may result in a lack of water at critical times, especially in smaller habitats where water supply is limited. Salt Creek is particularly vulnerable to the effects of salt cedar. Other threats within the planning area include groundwater pumping, dewatering, water diversion, drain maintenance activities, off-road vehicle use, contaminants, the lining of the Coachella Canal, and fluctuations of the Salton Sea. The pupfish requires shallow, slow-moving clear water with a moderate amount of aquatic vegetation and soft substrate. The viable population size is considered to be a minimum of 500 overwintering adults (Ryman and Utter 1987, Soule 1987, Templeton 1990).

Special Considerations. The desert pupfish can experience large fluctuations in population in response to environmental conditions.