Overview

Comprehensive Description

Biology

Occurs in vegetated springs.
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Distribution

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.
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North America: Headwater springs of Clear Creek (in San Saba River system), Menard County in Texas, USA.
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endemic to a single state or province

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (<100 square km (less than about 40 square miles)) 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 kilometers west of Menard, Menard County, central Texas. Historical range probably included most of the spring run (about 5 kilometers), to its confluence with the San Saba River.

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Historic Range:
U.S.A. (TX)

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Headwater springs of Clear Creek, Texas, U.S.A.
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Physical Description

Size

Maximum size: 54 mm TL
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Max. size

5.4 cm TL (male/unsexed; (Ref. 5723))
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Length: 5 cm

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Type Information

Paratype for Gambusia heterochir
Catalog Number: USNM 164573
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Collector(s): J. Tilton, C. Hubbs, R. Strawn, W. Craig, T. Dobzhansky, A. Ellington & et al.
Year Collected: 1956
Locality: Clear Cr., Head Spring, 10.4 mi. W. of Menard, Menard Co., Texas., Menard County, Texas, United States, North America
  • Paratype:
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Ecology

Habitat

Habitat and Ecology

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
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Habitat Type: Freshwater

Comments: 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).

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Environment

benthopelagic; non-migratory; freshwater; brackish
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Depth range based on 1 specimen in 1 taxon.

Environmental ranges
  Depth range (m): 0.5 - 0.5
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 5

Comments: This species is represented by one occurrence.

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Global Abundance

1000 - 10,000 individuals

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

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Life History and Behavior

Reproduction

Female may store sperm for several months, fertile from March through September, capable of producing about 50 young every 7 weeks; live bearing (Matthews and Moseley 1990).

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
D2

Version
3.1

Year Assessed
2013

Assessor/s
NatureServe

Reviewer/s
Smith, K. & Darwall, W.R.T.

Contributor/s

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)
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Current Listing Status Summary

Status: Endangered
Date Listed: 03/11/1967
Lead Region:   Southwest Region (Region 2) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: E

For most current information and documents related to the conservation status and management of Gambusia heterochir , see its USFWS Species Profile

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National NatureServe Conservation Status

United States

Rounded National Status Rank: N1 - Critically Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G1 - Critically Imperiled

Reasons: Restricted to one spring in central Texas; vulnerable to habitat alteration (dewatering) and detrimental effects of non-native fishes.

Other Considerations: The owners of Wilkinson Springs have been instrumental in protecting the species' habitat.

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Population

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
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Global Short Term Trend: Relatively stable (=10% change)

Comments: Trend over the past 10 years or three generations is uncertain but likely relatively stable. Three generations is less than 10 years.

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Threats

Major Threats
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.
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Degree of Threat: Very high - medium

Comments: 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.

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Vulnerable (VU) (D1+2)
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Management

Conservation Actions

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.
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Global Protection: Unknown whether any occurrences are appropriately protected and managed

Needs: Protection of the Edwards-Trinity aquifer recharge zone is essential. Set aside headwaters of Clear Creek as wildlife sanctuary. Buy the land and maintain the dam.

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Relevance to Humans and Ecosystems

Risks

Stewardship Overview: 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.

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Wikipedia

Clear Creek gambusia

The Clear Creek gambusia (Gambusia heterochir) is a species of fish in the Poeciliidae family. It is endemic to the United States, particularly Menard County, Texas.

Life and habitat

The species is born live. Most births occur between March and September. The fish live their entire lives in the clear spring waters of the Clear Creek tributary of the San Saba River. The fish congregate around submerged aquatic vegetation that provides them with food and shelter. They have recently fallen victim to damming, relocation which has presented a change of climate, and nutria feeding. Thus, the Clear Creek gambusia was put on the United States' list of endangered species in 1967. [2]

References

  1. ^ Gimenez Dixon, M. 1996. Gambusia heterochir. 2011 IUCN Red List of Threatened Species. Downloaded on 12 September 2011.
  2. ^ Texas Parks and Wildlife
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