|Scientific Name:||Gambusia nobilis|
|Species Authority:||(Baird & Girard, 1853)|
Heterandria nobilis Baird & Girard, 1853
|Red List Category & Criteria:||Endangered B1ab(iii)+2ab(iii) ver 3.1|
|Reviewer(s):||Smith, K. & Darwall, W.R.T.|
|Facilitator/Compiler(s):||Hammerson, G.A. & Ormes, M.|
This species is listed as Endangered because extent of occurrence is less than 5,000 sq km, area of occupancy is less than 100 sq km and possibly less than 20 sq km, number of locations may not exceed five, and habitat is vulnerable to ongoing declines in quality/quantity due to reductions in water availability and impacts of non-native species.
|Range Description:||Range includes the Pecos River basin, Texas and New Mexico (Page and Burr 2011).
In New Mexico, the species occurred historically as far north as the Pecos River near Fort Sumner; now it is restricted to sinkholes or springs and their outflow on the west side of the Pecos River in Chaves and Eddy counties. Twelve populations are extant in the vicinity of Roswell; of these, natural populations are in two isolated gypsum sinkholes along with Sago and Dragonfly springs and their outflows, which combine to form the perennial portion of the Lost River (Bitter Creek drainage), all in Bitter Lake National Wildlife Refuge; other populations in the refuge are the result (in whole or in part) of introductions. An additional natural population occurs in Blue Spring, Eddy County, New Mexico. The species has been introduced in various areas of Salt Creek Wilderness Area and in artificial ponds at Living Desert State Park near Carlsbad, New Mexico. See Sublette et al. (1990).
In Texas, this species inhabits the headwaters of Phantom Lake (Jeff Davis County); San Solomon, Giffin, and East Sandia springs (Reeves County); and Diamond Y Draw and Diamond Y Springs (Pecos County) (Hubbs et al. 2008). Originally, it also inhabited Leon Springs (the type locality, approximately 16 km upstream from Diamond Y Springs) and also Comanche Springs (within the city of Fort Stockton) prior to their desiccation (Hubbs et al. 2008).
|Range Map:||Click here to open the map viewer and explore range.|
This species is represented by a small number of occurrences. It occurs in four main areas, two in New Mexico and two in Texas (Hubbs et al. 2002). These could be interpreted as four locations with respect to threats related to water availability.
Total adult population size is very large. New Mexico population was estimated to total about 933,500 in 1979 (Bednarz 1979). Texas populations: 113,000 adults in vicinity of Balmorhea, 1 million adults in Leon Creek, Pecos County (Echelle and Echelle 1980). Yet Page and Burr (2011) stated that this species is "uncommon and localized."
This species is less abundant now than in the past.
USFWS (1990) categorized the status as "stable". Recent trend has not been reported, but range extent, area of occupancy, and number of subpopulations probably have been relatively stable or declining at a rate of less than 30 percent over 10 years or three generations.
|Habitat and Ecology:||Habitat includes shallow margins of clear vegetated spring waters (pools and outflows) high in calcium carbonate, as well as more adverse gypsum sinkhole habitats (Lee et al. 1980, Page and Burr 2011). High salinities in gypsum sinkholes have precluded the success of most stockings in those habitats (Hendrickson and Brooks 1991). This fish is not tolerant of total hardness above 5000 mg/l CaCO3 (Bednarz 1979). Consistent habitat factors seem to be clear, clean water, stable flows, and fairly constant temperatures (Matthews and Moseley 1990). Abundance tends to be highest near spring sources (Minckley et al. 1991). Submerged cliffs and debris and aquatic vegetation are used for cover (Bednarz 1979).|
The most pervasive threat is drying of springs due to lowering water tables (e.g., via groundwater pumping, which eliminated populations at Comanche and Tunis springs in western Texas, and which probably will occur at other sites in the near future) (Echelle et al. 1989). Other threats include predation by introduced fishes (especially in sites lacking aquatic vegetation or shallow water), and competition and possibly hybridization with other Gambusia species. A renovation of Diamond Y Draw in 1998 removed Gambusia geiseri from that system (Hubbs et al. 2002). So far, hybridization has not had a significant impact. Introduced fishes (Green Sunfish) eliminated one transplanted population in Lake St. Francis and perhaps elsewhere on the Bitter Lakes NWR (Minckley et al. 1991). Alterations in the natural flow and physical conditions of the Pecos River have interfered with or eliminated movements of Gambusia among now isolated suitable habitats, which as a result cannot be naturally recolonized should local extinctions occur during drought years.
Jelks et al. (2008) categorized this species as Endangered due to (1) present or threatened destruction, modification, or reduction of habitat or range and (2) other natural or anthropogenic factors that affect existence, including impacts of nonindigenous organisms, hybridization, competition, and/or predation.
Efforts have been made to improve habitat and provide refugia in the Balmorhea area (Hubbs et al. 2002).
Minckley et al. (1991) recommended that annual or more frequent monitoring should be continued throughout the native range and that the search for new sites for possible introduction be continued and intensified (though previous attempts have not been especially productive).
Minckley et al. (1991) recommended that major efforts be made to maintain each of the existing natural populations. Populations most critical to maintaining present morphological variation are those in three springs in Toyah Creek drainage, Texas, and one in Blue Spring, New Mexico (Echelle and Echelle 1986). See also Echelle et al. (1989) for recommendations regarding preservation of species' genetic diversity (about half of genetic diversity due to differences between samples at different localities, and half due to variability within samples). Echelle and Echelle (1986) recommended that the genome of the Balmorhea area, Texas, be preserved at sites within the historic range but outside the Balmorhea area, where springs are declining in flow. See recovery plan.
|Citation:||NatureServe 2013. Gambusia nobilis. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 28 August 2015.|
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