|Scientific Name:||Graptemys caglei|
|Species Authority:||Haynes & McKown, 1974|
|Red List Category & Criteria:||Endangered A2c+4c; B2ab(iii) ver 3.1|
|Assessor/s:||van Dijk, P.P.|
|Reviewer/s:||Horne, B.D., Mittermeier, R.A., Philippen, H.-D., Quinn, H.R., Rhodin, A.G.J. & Shaffer, H.B.|
Graptemys caglei warrants Red List status as Endangered as its range has reduced by half to two-thirds since 1974, and the species is now restricted to a single stretch of about 120 km of the lower Guadalupe river, where the population appears to be under continuing threat from habitat degradation, disturbance and water diversion. Further distribution and population trend data may document that the species warrants listing as Critically Endangered.
Recorded on the Guadalupe River system of south-central Texas (segments of the Guadalupe and San Marcos rivers in Kerr, Kendall, Comal, Guadalupe, Gonzales, Dewitt, Hays, and Victoria counties) as well as the adjoining San Antonio River (although continued occurrence in the San Antonio is unconfirmed – Vermersch 1992, Ernst and Lovich 2009). Overall, the vast majority of the species’ individuals appears restricted to the lower 120 km of the Guadalupe River.
Native:United States (Texas)
|Range Map:||Click here to open the map viewer and explore range.|
At the time of description (1974), Graptemys caglei was described as locally abundant in the lower Guadalupe River, some other sections of the Guadalupe, in the San Antonio system, and in several smaller tributaries (Haynes and McKown 1974).
The species is nearly invisible along the upper Guadalupe (above San Marcos confluence) and any populations there are likely severely fragmented. The population in the San Antonio river system may have been extirpated (Ernst and Lovich 2009). The species has thus suffered an effective range reduction of 50–67% since 1974.
Killebrew data from the early 1990s, focused on the lower Guadalupe area, estimated a total population of 11–13,000 animals; the surveys were repeated in 2000–2001, with similar results (Lindeman, pers.comm.).
Graptemys caglei was considered the rarest of all Graptemys by Lindeman (pers. comm 6 Aug 2009) based on extensive basking surveys.
|Habitat and Ecology:||
Graptemys caglei occurs in riverine habitat with limestone bedrock bottoms interspersed with pools with silt and gravel, and with gravel bars connecting long pool areas with a shallow average depth and a muddy moderate flow; optimal habitat appears to include both riffles and pools; males may spend much of their time in gravel bar riffles and transition areas between pools and riffles; basking sites include fallen trees and shrubs, logs, rocks, and cypress knees.
Males and juveniles apparently feed mainly on aquatic insects, while females reportedly are predominantly mollusc feeders (Haynes and McKown 1974, Porter 1990 in Lindeman 1999, Killebrew in Ernst and Lovich 2009).
Females reach a maximum carapace length (CL) of 21.3 cm, while males become no larger than 12.6 cm CL.
Males were calculated to mature towards the end of their second or in their third year of growth (Lindeman 1999). Females produce one or perhaps up to three clutches of 1–6 eggs (Wibbels et al. 1991, Vermersch 1992). Longevity has not been reported but likely exceeds 20 years. Generation time has not been calculated.
Specific documentation of the threats impacting Graptemys caglei have not been published in detail. Habitat alteration and disturbance are likely factors, and the effects of groundwater depletion from the Edwards aquifer is likely to be significant. Being an exceedingly shy species with a physiological need for extensive basking, human disturbance of river areas is likely long-term low-level detrimental.
Graptemys caglei is included in CITES Appendix III (United States) since 14 June 2006. It has been listed as Threatened in Texas since 2000. It was a candidate for Federal protection under the ESA until 2006, when it was found not to warrant ESA status based in part on actions taken by the Texas Parks and Wildlife Department (TPWD) to increase protection of the species against collecting and shooting.
Updated distribution and status surveys are urgently needed, followed by a program of population monitoring. Much better understanding is needed of the threats facing this species, and appropriate measures to address these threats.
|Citation:||van Dijk, P.P. 2011. Graptemys caglei. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 24 May 2013.|
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