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Gambusia heterochir

Status_ne_offStatus_dd_offStatus_lc_offStatus_nt_offStatus_vu_onStatus_en_offStatus_cr_offStatus_ew_offStatus_ex_off

Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA ACTINOPTERYGII CYPRINODONTIFORMES POECILIIDAE

Scientific Name: Gambusia heterochir
Species Authority: Hubbs, 1957
Common Name/s:
English Clear Creek Gambusia

Assessment Information [top]

Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2013
Date Assessed: 2012-02-03
Assessor/s: NatureServe
Reviewer/s: Smith, K. & Darwall, W.R.T.
Facilitator/s: Hammerson, G.A. & Ormes, M.
Justification:
This species is listed as Vulnerable because it occurs in only one location and area of occupancy is less than 20 sq km. Trend is unknown, but the population probably is not undergoing a continuing decline.
History:
1996 Vulnerable
1994 Vulnerable (Groombridge 1994)
1990 Vulnerable (IUCN 1990)
1988 Endangered (IUCN Conservation Monitoring Centre 1988)
1986 Endangered (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description: This species is restricted to a very small area of impounded headwaters (Wilkinson Springs) of Upper Clear Creek (San Saba River system) on the Clear Creek Ranch, 16 kilometres west of Menard, Menard County, central Texas. Historical range probably included most of the spring run (about 5 kilometres), to its confluence with the San Saba River.
Countries:
Native:
United States
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: This species is represented by one occurrence.

Total adult population size is unknown but presumably exceeds 1,000.

Historically, the area of occupancy likely was larger but declined after the habitat was modified.

Trend over the past 10 years or three generations is uncertain but likely relatively stable. Three generations spans fewer than 10 years.
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: Habitat consists of springs and outflow streams with clear, clean water; this species prefers areas with dense aquatic vegetation (e.g. Ceratophyllum) and nearly constant temperatures throughout the year (USFWS 1982, Page and Burr 2011).
Systems: Freshwater

Threats [top]

Major Threat(s): USFWS (2010) summarized threats as follows:

The primary threats are: (1) habitat loss from the potential loss of spring flow due to a decline in groundwater levels, and (2) hybridization or competition with Western Mosquitofish initially due to the local habitat modifications, but now caused by the failure of the upper dam to maintain a barrier between spring outflow and downstream habitats. Available information does not indicate that impacts to spring flows from significant increase in groundwater use or declines in recharge is imminent (defined as likely to occur in the next 10 years) at this time. However, it is likely to occur over the foreseeable future of 50 to 100 years as a result of climate change and the increasing human need for more water resources. The magnitude of impact on the Clear Creek Gambusia if this threat were realized is extremely high. Because the range of the species is limited to one small, isolated location, habitat modification due to a decline in spring flows could result in its extinction. The threats associated with hybridization and competition may be occurring now due to the recent erosion of the upper dam allowing renewed access to the upper spring pool by Western Mosquitofish. If the impacts of these threats are the same as observed in the past between 1953 and 1978, then the population of Clear Creek Gambusia will be depressed, but not eradicated until the upper dam can be repaired. Therefore, the magnitude of the impact of this threat on the species is considered moderate to high. Secondary threats include habitat modification from water quality degradation, local habitat changes, lack of regulatory mechanisms, and introduction of a disease, parasite, or nonnative species (resulting in competition or predation). None of these concerns acting alone result in substantial threats to the species, but together any of these could negatively impact the Clear Creek Gambusia. Climate change is another source of potential threats to the species. All possible impacts associated with future climate change cannot presently be reliably predicted. However, accelerating climate change will exacerbate any of the threats already considered or could result in whole new threats that are not conceived at this time. Either way, subtle but significant changes in the ecosystem of the Clear Creek Gambusia resulting from climate change in the foreseeable future of 50 to 100 years could cause the species extinction and is a threat of high magnitude. All of these threats, both primary and secondary, must be considered in the context of a fish with an extremely small range with no opportunity for movement, a relatively small population size, and a very short life span. Because of these factors, the magnitude of impact of any potential threat or future stochastic event is exceptionally high. Any events negatively affecting the species or its habitat could result in complete extinction of the Clear Creek Gambusia.

Conservation Actions [top]

Conservation Actions: Reconstruction of "Dam 1" was important in reducing the negative effect of non-native species. This dam should be maintained in good condition.

Population monitoring to detect factors that may affect the Clear Creek Gambusia population and determine the current genetic status of the population should be continued.

Protection of the Edwards-Trinity aquifer recharge zone is essential. Set aside headwaters of Clear Creek as wildlife sanctuary.
Citation: NatureServe 2013. Gambusia heterochir. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 24 April 2014.
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