Literaturdatenbank
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Simpson, T. R., & Rose, F. L. (2007). Distribution of cagle's map turtle (graptemys caglei) in the blanco and san marcos rivers.(report). Texas Journal of Science.
Added by: Admin (15 Mar 2009 13:31:40 UTC) |
| Resource type: Journal Article BibTeX citation key: Simpson2007 View all bibliographic details  |
Categories: General Keywords: Apalone, Apalone spinifera, Emydidae, Graptemys, Graptemys caglei, Graptemys geographica, Habitat = habitat, Kinosternidae, Nordamerika = North America, Pseudemys, Pseudemys texana, Schildkröten = turtles + tortoises, Sternotherus, Sternotherus odoratus, Systematik = taxonomy, Trachemys, Trachemys scripta, Trionychidae Creators: Rose, Simpson Collection: Texas Journal of Science |
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| Abstract |
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Abstract. -- Cagle's Map Turtle (Graptemys caglei) is a small emydine aquatic turtle described in 1974. At that time, it was known from the Guadalupe and San Antonio river systems, including the Guadalupe, San Antonio, Blanco, and San Marcos rivers. Its presence in the Blanco and San Marcos rivers was based on few documented specimens. Surveys in 1991 and 1992 failed to detect the turtle's presence in the Blanco River or the upper reaches of the San Marcos River. Grapemys caglei was listed as threatened by Texas Parks and Wildlife in 2000 and is classified as vulnerable by the IUCN Red List due to the diminished distribution. In 2003, a male and female G. caglei were found at one location in the Blanco River. Systematic searches begun in 2005 revealed small-scattered populations of G. caglei in the Blanco River from near Fisher to San Marcos in Hays County. No G. caglei were observed in the upper reaches of the San Marcos River (Hays County); however, they were observed at several sites on the San Marcos River in Guadalupe and Gonzalez counties. Extensive surveys and trapping efforts over 15 years resulted in 4,000 individually marked turtles in Spring Lake (Hays County), the initial source for the San Marcos River, and no Graptemys were observed. The river dynamic (extreme drought to extreme flood) of the Blanco River probably plays a dominant role in the turtle's life history. This dynamic is muted in the lower San Marcos and the Guadalupe rivers ********** Raun (1959) reported two juvenile and one subadult Graptemys pseudogeographia from the San Marcos River near Ottine, Gonzales County, Texas. Members of the genus Graptemys, at that time, were not known to occur west of the Colorado River. Proper species allocation of these three turtles was possible when Cagle's map turtle (Graptemys caglei) was described by Haynes & McKown (1974) from the Guadalupe River system in south-central Texas. The new species was distinguished from other members of the genus by its transverse yellowish chin bar and a conspicuous "V" dorsal head marking. It belongs to the narrow-headed group of map turtles (Dobie 1981). Although extensively studied, little has been published about its natural history. It is an inhabitant of the Guadalupe River where it may be the most common species of aquatic turtle in DeWitt County (Vermersch 1992). It is known to occur upriver to the Kerrville area in Kerr County, but its distribution in the Guadalupe River across the Edwards Plateau is poorly documented. Haynes & McKown (1974) report a specimen from 15 km NW of San Marcos, which is in the Blanco River (Hays County); however, Porter (1992) found no Cagle's map turtles on the Blanco River during his surveys and stated, "Cagle's map turtles seem to be disappearing from areas previously reported to support populations." A review of the literature confirms that actual sightings of this turtle in the Blanco River were minimal and Killibrew et al. (2002) stated that the turtle "... is currently found only in segments of the Guadalupe and San Marcos rivers ..." Because of its presumed diminished distribution, the Texas Parks and Wildlife Division (2000) classified the turtle as "threatened" and it was listed as "vulnerable" by the IUCN Red List (Tortoise & Freshwater Turtle Specialist Group 1996). A male and female Graptemys caglei were captured by hand within 10 minutes of each other at one location in the Blanco River, Hays County, in 2003. Because of these two individuals a systematic search for the turtle in the Blanco and San Marcos rivers was begun in 2005. More intense searches of the San Marcos River were begun in 2006. The results of those systematic searches are presented in this report. METHODS AND MATERIALS Initial searches for Graptemys caglei suggested that the populations were dispersed. Therefore, systematic searches of selected sites for presence or absence of G. caglei was the chosen method. Search sites were selected based on access and the presence of optimal habitat characteristics for G. caglei, including riffles, shallow pools, moderate water flow and sand or gravel bars (Haynes & McKown 1974; Killebrew 1991; 1992; Babitzke 1992). Searches were conducted on foot or from kayaks. Dip nets were used to capture basking or swimming turtles. Search site coordinates were recorded with a GPSMAP 60cs unit (Garmin International, Inc., Olathe, KS). For identification, dorsal head and cheek patterns, wide forearm and post femoral yellow stripes, and ventral chin patterns were considered definitive for Cagle's map turtles. The primary head and cheek patterns are: (a) post orbital stripe forming a crescent beginning underneath the eye and extending vertically upward on the side of the head (Figure 1a), (b) v-shaped pattern formed by medio-dorsal extensions of the post-orbital stripe on top of the head, and (c) unbroken transverse crescent underneath the chin (Figure lb.) (Haynes & McKown 1974). The Texas river cooter (Pseudemys texana) is the only other species with which G. caglei might be confused within an appropriate size range. Typical P. texana head markings in the area of sympatry include a large yellow post-orbital spot, bold supralabial and infralabial stripes, and numerous ventral medial stripes. However, head patterns of P. texana are geographically variable. Whereas, juveniles of the two species are morphologically similar, the three juvenile G. caglei that were observed during the study were distinctive, with brightly colored, wide yellowish carapacial markings. Vertebral "knobs" are not definitive because juvenile P. texana can have prominent extensions that may be tipped in black and the more prominent "knobs" of G. caglei are reduced ontogenetically. Observers adhered to the general rule: If there is confusion about the visual identification, the species at hand is P. texana. RESULTS Blanco River. -- Initially, two Graptemys caglei were found on a private ranch in the Blanco River (29 59'N, 97 58'W) nine km west of Kyle by students in a field class in 2003. During 2005 and 2006, 453 search hours were conducted at 10 sites. Graptemys caglei was identified from four sites on the Blanco River. One individual was seen in a pool (29 54'N, 97 53'W), 8.2 km above the confluence of the Blanco and San Marcos rivers. Two adults and 3 juveniles were visually identified at Dudley Johnson Park, Hays County (29 57'N, 97 54'W), 13.7 km above the confluence with the San Marcos River. One small individual (83 mm carapace length) was captured ~30 km upstream of the confluence of the Blanco and San Marcos Rivers (30 00'N, 97 58'W). One large female (158 mm carapace length) was captured and five adults were observed 3.5 km downstream (29 58'N, 98 12'W) of the Fischer School Road crossing, Blanco River, Hays County. No individuals of G. caglei were found in Blanco State Park (30 05N, 98 25'W) in Blanco, nor within 4 km upstream or downstream of the park. Visits to sites upstream of Blanco State Park revealed little habitat compatible with turtles. San Marcos River. -- Numerous search and trapping efforts have been done in Spring Lake (29 53'N, 97 56'W) and the upper San Marcos River within San Marcos, Hays County, from 1993 to present. Although, more than 4000 turtles were captured and marked at these sites, no Graptemys caglei individuals were seen or captured. Searches for Graptemys caglei on the San Marcos River were oriented to road and highway crossings in most instances. Each of 17 road and highway crossings between San Marcos and Gonzalez were visited and searched a minimum of three times for a total of 110 search hours. Map turtles were observed at four of these sites. Four G. caglei individuals were identified visually with spotting scopes at Farm to Market (F.M.) 20, Gonzalez County (29 45N, 97 46W). Two G. caglei individuals were identified at F.M. 2091 (29 35'N, 97 35'W), Ottine, Texas. One individual of G. caglei was visually identified at the crossing of County Road 232 (29 33'N, 97 32'W) and at U. S. Highway 90a (29 30'N, 97 29'W). DISCUSSION The Blanco River presents several challenges to aquatic vertebrates: (1) floods frequently alternate with severe droughts during which there is no flow, (2) the substrate is limestone based and during the summer, higher temperatures in shallow water limit the organisms that can live there, and, (3) the scoured substrate has limited attached aquatic plants and few invertebrates, including snails and young clams, that could serve as food. The most numerous chelonians observed at all search sites in the Blanco River were the red-eared slider (Trachemys scripta) and Pseudemys texana, in roughly equal numbers. However, densities of all turtle species were low compared to numbers observed on the San Marcos River. Results of this study support the summation that whereas Graptemys caglei does inhabit the Blanco River, its densities are low, and the turtles are probably restricted to areas where deep pools provide suitable habitat during drought. Basking and nesting sites might also be limiting. No Graptemys caglei were observed in or upstream of Lake Blanco (Blanco County). However, significantly more turtles were observed within the lake, including the common musk turtle (Sternotherus odoratus) and the spiny softshell turtle (Apalone spinifera). The negative environmental factors that probably limit turtle distributions in the Blanco River are accentuated upstream of Blanco Lake, especially during times of drought. In addition, the area between Dudley Johnson Park (Hays County) and the confluence with the San Marcos River is also deemed environmentally challenging for G. caglei for the same reasons. Distributions downstream might be enhanced by floods; however, once water levels recede, habitat quality for maintenance of healthy G. caglei populations is limited. The San Marcos River has significant flow and has not gone dry in recorded history (Brune 2000). Turtle densities are high, yet the presence of G. caglei has been documented infrequently in its upper reaches, and there are no records in the San Marcos River above its confluence with the Blanco. There are several substantial dams on the San Marcos River above Interstate Highway 10. The three largest, Luling City Park Dam (Luling), Martindale Dam (Martindale), and Cummings Dam near the confluence of the San Marcos and Blanco rivers), probably limit upstream migration. In addition, the deep water produced by these dams is not thought to be optimal habitat for G. caglei populations (Killibrew, et al. 2002). Although these surveys confirm that there are viable local populations of G. caglei in the Blanco River, it should be emphasized that these are scattered and densities are low (about 10 turtles/453 search hours). This confirmation does not diminish the need for continued surveillance and protection. ACKNOWLEDGMENTS We thank S. Franklin, J. Scalise, and R. Swanson for their help in the field and G. Amoan, P. Way, and W. Johnson for access to segments of the Blanco River. We also thank the Texas Nature Conservancy, Texas Rivers Center, and Texas Department of Transportation for funding. Permits were provided by Texas Parks and Wildlife (permit number SPR-0993-638) and Texas State University Institutional Animal Use and Care Committee (permit number 06-0632515E7F). LITERATURE CITED Babitzke, J. B. 1992. An analysis of population size of Graptemys caglei. Unpublished Masters Thesis, 47 pp. Brune, G. 2002. Springs of Texas, Vol 1. 2002. Texas A & M University Press, College Station, Texas, 566 pp. Dobie, J. L. 1981. The taxonomic relationships between Malaclemmys Gray, 1844 and Graptemys Agassiz, 1857 (Testudines: Emydidae). Tulane Studies in Zoology and Botany, 23:85-102. Haynes, D. & R. R. McKown. 1974. A new species of map turtle (Genus Graptemys) from the Guadalupe River System in Texas. Tulane Studies in Zoology and Botany, 18:143-152. Killibrew, F. C. 1991. A petition for threatened status listing of Graptemys caglei (Testudines, Emydidae). Letter to U.S. Fish and Wildlife Service, Corpus Christi Ecological Services Field Office. April 8, 1991, 15 pp. Killibrew, F. C. 1992. U.S. Fish and Wildlife Service scope. A synopsis of information on Graptemys caglei. Unpublished report for U.S. Fish and Wildlife Service, Austin, Texas, 10 pp. Killibrew, F. C., W. J. Rogers & J. B. Babitzke. 2002. Assessment of instream flow and habitat requirements for Cagle's map turtle (Graptemys caglei). Report to Edwards Aquifer Authority, contract #00-52-AS, 60 pp. Porter, D. A. 1992. Distribution survey on Graptemys caglei. Unpublished report to U. S. and Wildlife Service, Austin, TX, 6 pp. Raun, G. G. 1959. Terrestrial and aquatic vertebrates of a moist, relict area in Central Texas. Texas Journal Science, 11(2):158-171. Tortoise & Freshwater Turtle Specialist Group. 1996. Graptemys caglei, In: IUCN 2006. 2006 IUCN Red List of Threatened Species. Added by: Admin |