(Hartweg, 1939a)
Big Bend slider
Recognition
This poorly studied turtle has an oval, weakly keeled (juvenile) to smooth (adult) carapace (to 25.9 cm) with a slightly serrated posterior rim. The vertebrals are wider than long. The carapace is light olive-brown with a reticulate pattern of curved orange lines, often surrounding small ocelli, on the pleurals and vertebrals. A dark spot is present on vertebrals 1-3, and usually present on the 4th. Each marginal has a single, curved, orange bar and a dark-bordered ocellus at the lower, posterior corner of its upper surface. At least in males, melanism may develop with age. The ventral surfaces of the marginals have large dark-bordered ocelli at the seams, and the bridge is patterned with narrow, transverse dark lines. The hingeless plastron is cream to orange or light olive, usually with a large, dark, central figure formed by a series of elongated narrow lines that may spread laterally along the transverse seams. The central figure is usually continuous from the gulars to the anals. The plastral formula is abd > an > fem > pect > gul > hum. The skin is light olive to orangish brown; forelegs are striped with yellow or orange; and vertical yellow or orange stripes occur on the hind quarters. An oval, black-bordered, red to orange postorbital spot is well-separated from the orbit. The chin is medially striped, with lateral stripes shortened to ovals that are almost ocelli. The upper jaw is slightly notched, and the toes are webbed.
Males are smaller and less domed than females, and have long, thick tails with the vent beyond the carapacial rim, and slightly concave plastra. Mature males lack elongated foreclaws. Females have short tails with the vent beneath the carapacial marginals, and flat plastra.
Distribution
The Big Bend slider is found in the Rio Grande from the Big Bend upstream to at least the Bosque del Apache Refuge, New Mexico, and in the Rio Conchos watershed of western Texas, New Mexico, Chihuahua, and Coahuila.
Geographic Variation
No subspecies have been described, but Trachemys scripta hartwegi may yet prove to be a subspecies of T. gaigeae.
Habitat
This species is found in scattered pools, often bordered by sand or gravel bars, and sloughs in the Rio Grande; presumably it wanders from pool to pool during dry periods. It also has been found in adjacent cattle ponds and tanks.
Natural History
Legler (1960c) reported that females were sexually mature at 16.9 cm and males at about 10.3-11.5 cm. Male courtship does not involve stroking the female's face with elongate foreclaws. Instead, the male chases the female and bites at her tail and hind quarters (Ernst et al., 1994).
Four females examined by Legler (1960c) contained 6-11 oviducal eggs in June; a female collected in Socorro County, New Mexico on 8 June contained 10 eggs that appeared close to oviposition (Degenhardt et al., 1996). Stuart and Painter (1997) reported an unusually large clutch of 29 T. gaigeae eggs dissected from a 22.4 cm female around 1 July; 24 were in the oviducts and five in the abdominal cavity. The eggs measured 34.5-40.3 x 21.5-24.0 mm. Another small (13.6 x 11.1 mm), ovoid, shelled egg was also present in the oviduct, but was not included in the count of 29 full sized eggs. In addition to the eggs there were two additional distinct sets of enlarged ovarian follicles, 16 which measured 15 mm in diameter and six that were 10-12 mm. The enlarged follicles suggest the female could have produced 1-2 additional clutches that year.
Stomachs examined by Legler (1960c) only contained aquatic plants. Digestive tracts of several New Mexico adults contained filamentous algae and possibly the plant Potamogeton (Stuart, in Degenhardt et al., 1996). T. gaigeae is attracted to traps set with fresh fish, canned sardines, or lettuce (Degenhardt, et al., 1996). Captives readily accept fish.
Remark
Trachemys gaigeae was first described as a subspecies of Trachemys scripta by Hartweg (1939a). Stejneger and Barbour (1939) first elevated it to specific rank, but gave no reason for their decision. This arrangement was virtually ignored until Weaver and Rose (1967) re-elevated it to a full species on morphological grounds. For a more complete taxonomic history of T. gaigeae, see Ernst (1992).
IUCN Red List Status (1996)
Vulnerable (A1c, D2).