endemic to a single state or province
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (<100 square km (less than about 40 square miles)) Known range is confined to San Felipe Creek, Val Verde County, Texas (Page and Burr 2011); this fish was not found there before 1997, despite earlier collecting efforts (Garrett and Edwards 2003). Probably the species was there in low numbers and became more numerous and detectable after favorable habitat changes occurred. Numerous collections in adjacent streams (Pinto Creek, Devils River, Cienegas Creek, Sycamore Creek, and Las Moras Creek) over the last 15 years yielded no specimens of G. clarkhubbsi (Garrett and Edwards 2003).
Habitat and Ecology
Habitat Type: Freshwater
Comments: This fish inhabits a spring-fed stream; it appears to prefer vegetated margins or quiet pools in close association to areas with significant spring flows (Garrett and Edwards 2003, Page and Burr 2011).
Non-Migrant: No. All populations of this species make significant seasonal migrations.
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.
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 (subpopulation) (Garrett and Edwards 2003, USFWS 2007).
2500 - 100,000 individuals
Comments: Total adult population size is unknown but presumably is at least several thousand. In collections since 1997, this species often comprised 50% of the Gambusia in collections of 30 to several hundred individuals (Garrett and Edwards 2003).
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N1 - Critically Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G1 - Critically Imperiled
Reasons: Small range in one creek in Texas; voluntary management has improved habitat conditions in recent years.
Total adult population size is unknown but presumably is at least several thousand. In collections since 1997, this species often comprised 50% of the Gambusia in collections of 30 to several hundred individuals (Garrett and Edwards 2003).
Population size apparently increased in the early 2000s. A major flood (1998) that affected the springs and streambed may have improved conditions for G. clarkhubbsi (Garrett and Edwards 2003). Also, improved watershed management practices likely have contributed to habitat improvement and population increase (USFWS 2007).
Degree of Threat: Low
Comments: San Felipe Creek, an urban stream, has been modified for bank stabilization, flood control, public access, road bridges, and diversion of irrigation water (Garrett and Edwards 2003). Potential water quality problems include elevated nitrate, phosphate, and orthophosphate, which may be in part related to adjacent land use practices (e.g., golf course) (Garrett and Edwards 2003). However, the City of Del Rio and the San Felipe Country Club have instituted voluntary management plans that have improved creek habitat (USFWS 2007). Other potential threats include habitat loss through groundwater mining and the introduction of non-native fish species that could be detrimental through predation, competition, and/or hybridization. USFWS (2007) concluded that these factors do not now pose a significant threat to the species.
Management Requirements: In an effort to aid in conservation of Dionda diaboli, the city of Del Rio and the local golf course are in the process of developing watershed management plans designed to protect the creek environment; some creek-friendly management has already been implemented (Garrett and Edwards 2003).
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