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Nerodia paucimaculata 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Reptilia Squamata Natricidae

Scientific Name: Nerodia paucimaculata (Tinkle & Conant, 1961)
Common Name(s):
English Concho Watersnake, Concho Water Snake
Synonym(s):
Nerodia harteri ssp. paucimaculata (Tinkle & Conant, 1961)
Taxonomic Notes: Densmore et al. (1992) elevated Nerodia harteri paucimaculata to species status after Rose and Selcer had suggested that already in 1989. Other authors have pointed out that there is no single character that will allow separation of individuals from the two populations 100% of the time. Treated here as a good species.

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2007
Date Assessed: 2007-03-01
Annotations:
Needs updating
Assessor(s): Hammerson, G.A.
Reviewer(s): Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)
Justification:
Listed as Near Threatened because its extent of occurrence is not much more than 5,000 km², thus making the species close to qualifying for Vulnerable under criterion B1, and it is believed to be experiencing a continuing decline.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This species is restricted to the Colorado and Concho River drainages in Texas, in the south of the United States (Scott et al. 1989, Smith et al. 1996, Tennant 1998, Werler and Dixon 2000, Ernst and Ernst 2003). The probable historical range is estimated to have included, at a minimum, the Colorado River from Spence Reservoir downstream to the vicinity of Lake Buchanan; Elm, Bluff, and Coyote Creeks (Runnels County); and the entire Concho River (Tom Green and Concho counties) and its headwater tributaries, Dove Creek, Spring Creek, and the South Concho River (Irion and Tom Green counties) (Texas Parks and Wildlife Department). The historical range included about 450 stream km. The current range includes 396 stream km and about 25 km of lake (e.g., lakes Spence, Ivie, and Moonen [=Ballinger Municipal Lake]) (Scott et al. 1989, Smith et al. 1996, Tennant 1998).
Countries occurrence:
Native:
United States (Texas)
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:This species is represented by a small number of distinct occurrences (subpopulations) (Scott et al. 1989). The adult population size is unknown but presumably exceeds 10,000. As indicated by sample sizes in various field studies, this snake is locally abundant in proper habitat (Greene et al. 1994, 1999; Ernst and Ernst 2003). This snake has been eliminated from a small portion of its historical range (Scott et al. 1989). USFWS (1990) categorized the status as "stable." This snake is more abundant and more widely distributed than was previously thought (Scott et al. 1989, Dixon 1993).
Current Population Trend:Stable
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:This snake inhabits fast-flowing rocky streams and their margins, particularly shallow riffles and where flat, unshaded and unsilted rocks are at or close to the water's edge; it also occupies the shorelines of lakes, ponds, and impoundments (Werler and Dixon 2000). Individuals take cover under rocks or in vegetation along shore (Conant 1975, Tennant 1984, Scott et al. 1989, Ernst and Ernst 2004, Gibbons and Dorcas 2004). Juveniles use medium to large, flat rocks on unshaded shore for hiding, rocky shallows for feeding (species may be absent where juvenile habitat is lacking); adults inhabit rocky riffles as well as wider range of habitats in pools and lakes, and they use woody vegetation and flood debris along stream banks for basking and cover (Scott et al. 1989). At a large lake, snake presence was associated with rocky low gradient shorelines with silt substrate; retreat sites generally were within three metres of water but up to 15 m for gravid females (Whiting et al. 1997). Hibernation sites include crayfish burrows and rock piles (Werler and Dixon 2000).
Systems:Terrestrial

Threats [top]

Major Threat(s): Reservoirs have flooded many miles of former stream habitat. Below dams, restriction of stream flow and prevention of floodwater scouring have resulted in siltation of rocky streambeds, encroaching vegetation, and loss of riffle habitat required by young snakes (Texas Parks and Wildlife Department). Habitat fragmentation has left some populations isolated. Populations in reservoirs may not be viable or effectively connect adjacent riverine populations (USFWS, Federal Register, 2 August 1999). However, natural riffle habitat is not as essential as was previously believed; populations have survived for decades along reservoir shorelines. This species also has been found at all six artificial riffles constructed in 1989 in the 17 mile stretch of the Colorado River between the Robert Lee Dam and Bronte (Texas Parks and Wildlife Department). Diversion of water has reduced water levels and instream flows in some areas, threatening the fish preybase for the snake. An inadequate instream flow regime remains one of the most serious threats to the snake due to the prevalence of drought in Texas (USFWS, Federal Register, 2 August 1999). Pollution and degradation of water quality is a potential threat in certain areas. Non-point source pollution in the vicinity of San Angelo, petroleum production, refining, and transportation in the watershed, treated sewage disposal, pesticide use, and feedlot activities have been identified as water quality concerns that could affect the snake's habitat (Texas Parks and Wildlife Department). Despite all of these threats, this species has proven to be reasonably adaptable, and there is no evidence of a significant decline in numbers.

Conservation Actions [top]

Conservation Actions: As a condition of building Ivie Reservoir, the Colorado River Municipal Water District is required to release water from both Spence and Ivie reservoirs according to a schedule that is intended to maintain suitable watersnake habitat. These water releases include both continuous daily flows and flushing flows designed to maintain stream channels (Texas Parks and Wildlife Department). In conjunction with reservoir construction several artificial riffles have been built, and these now support populations of Concho Watersnake. The primary concern is balancing the need for habitat protection with an increasing human demand for the diversion of more water for residential and industrial use.

Citation: Hammerson, G.A. 2007. Nerodia paucimaculata. The IUCN Red List of Threatened Species 2007: e.T14631A4452043. . Downloaded on 15 October 2018.
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