Cyprinodon pecosensis

Allozyme data are consistent with the hypothesis that C. variegatus was ancestral to four recognized species (C. bovinus, C. pecosensis, C. rubrofluviatilis, and C. tularosa) from inland drainages associated with the western Gulf of Mexico (Echelle and Echelle 1992). Biogeography indicates that the C. pecosensis-C. bovinus clade may have evolved via vicariant peripheral isolation from C. variegatus (Echelle and Echelle 1992).

Cyprinodon variegatus was introduced into the Pecos River in Texas apparently in the early 1980s; interbreeding with C. pecosensis has led to the occurrence of a hybrid swarm, which by the early 1990s occupied about half the original range of C. pecosensis (Echelle and Connor 1989, Echelle 1991, Childs et al. 1996). High allozymic heterogeneity is associated with the relative isolation of subpopulations (see Sublette et al. 1990).

Restricted to small areas in New Mexico and Texas; current range is much less than historical range; recent management and a conservation agreement have reduced threats (security of exisiting populations, hybridization with introduced Cyprinodon variegatus) and stopped a severe population decline.

Historical range included the Pecos River system and nearby lakes, sinkholes, and saline springs, from the mouth of Independence Creek, 42 km SE Sheffield, Terrell County, Texas, to Roswell, Chaves County, New Mexico. As of the late 1990s, pure populations occurred in small reaches of the Pecos River and tributaries in Chaves and Eddy counties, New Mexico; in scattered sinkholes, lakes, and saline springs in New Mexico; and in the upper reaches of the Salt Creek drainage, Culberson and Reeves counties, Texas (populations in abandoned gravel pits near Grandfalls, Texas, are hybrid) (USFWS 2000).

This species is represented by several unhybridized populations.

In the late 1990s, the main threats to the Pecos pupfish were habitat loss caused by damming and dewatering of the Pecos River, excessive pumping of groundwater, and, since the early 1980s, hybridization with the sheepshead minnow (Cyprinodon variegatus). Subsequently, USFWS, BLM, New Mexico Department of Game and Fish, New Mexico Department of Agriculture, New Mexico Division of State Parks, and Texas Parks and Wildlife Department signed a conservation agreement that addressed the significant threats facing this species; the agencies made commitments to protect known extant populations, establish new populations, and prohibit the use of sheepshead minnow as bait (Federal Register, 28 December 1998; USFWS 2000).

Introduced Cyprinodon variegatus has negatively impacted the native gene pool of C. pecosensis. Apparently between 1980 and 1984, C. variegatus was introduced into Pecos River in Texas. By 1985, a hybrid swarm of C. pecosensis and C. variegatus occupied roughly one-half of historical range of C. pecosensis (Echelle and Connor 1989). Hybridization with C. variegatus in Red Bluff Reservoir on the Texas-New Mexico line raised concerns that New Mexico populations soon would be jeopardized by hybridization (Sublette et al. 1990). "The early history of the hybrid swarm is explained by genetic swamping, possibly mediated by selection for C. variegatus or C. variegatus x C. pecosensis, at a time when the normally abundant endemic species had been catastrophically depleted" (Childs et al. 1996).

Sinkhole populations are vulnerable to introduction of C. variegatus by anglers. Also, anglers may introduce toxins into sinkholes to eliminate unwanted fishes, including Pecos pupfish, prior to stocking them with sport fishes.

Populations have been depleted primarily as a result dewatering of habitat due to damming and excessive groundwater pumping, though many forms of habitat degradation have occurred. Lowered water tables have eliminated water flow between sinkholes, isolating these populations. Oil spills from pipelines into Salt Creek, Texas, have occurred and represent an ongoing threat to water quality and pupfish habitat.

River flooding may allow access of exotic fishes to sinkhole habitats. Sinkholes with introduced predatory fishes have smaller populations of Pecos pupfish than do sinkholes lacking game fish; predation could become a significant threat should the pupfish population continue to decline.

Algal blooms and large-scale fish kills have occurred in the Pecos River, Texas, and may threaten Pecos pupfish.