Barbour's Map Turtle
BARBOUR’S MAP TURTLE
Photo Credit: U.S. Geological Survey
SCIENTIFIC NAME: Graptemys barbouri (Carr and Marchand)
OTHER NAMES: Barbour’s Sawback Turtle.
DESCRIPTION: A large (females, 20-30 cm [8-12 in.] carapace lengths; males, rarely >13 cm [5 in.]) aquatic turtle exhibiting a remarkable degree of sexual dimorphism. Females develop massive heads that appear disproportionate to bodies; males achieve only 20 percent of body mass of average female. Carapace with a median keel accentuated by prominent, black-tipped spines or knobs on second through fourth vertebrals; spines retained by males but become inconspicuous in adult females. Carapace typically olive green to tannish with light yellow, circular to C-shaped markings on costals and marginals; these markings frequently obscured in older females as the ground color darkens. Plastron pale yellow and unmarked except for narrow dark lines along the sulci (seams). Head has olive green background with a large, yellowish, pale green, or tan blotch behind each eye. Chin with an isolated light bar paralleling the jaw, followed by a light, inverted, U-shaped mark. Limbs and tail striped (Cagle 1952, Carr 1952, Carr and Marchand 1942, Ernst et al. 1994, Sanderson 1974, Sanderson 1992). In the Graptemys pulchra species group, a group of Gulf Coast map turtles in which the females develop broadly expanded jaw surfaces, extreme sexual dimorphism is exhibited, and vertebral scutes develop into a spine-like keel. The character that distinguishes Barbour’s map turtles from the other species in the group is the curved or transverse bar on the underside of the chin. No subspecies recognized (Ernst et al. 1994, Lovich and McCoy 1992).
DISTRIBUTION: Previously thought to be restricted to the Apalachicola River system, including the Chipola (from which it was first described) and Apalachicola Rivers in Florida, the Flint River in Georgia, and the Chattahoochee River along the Alabama-Georgia border. In Alabama, occurs northward at least to Russell County but is exceedingly scarce throughout. Some Alabama tributaries of the Chattahoochee and Chipola Rivers are possibly inhabited (Carr and Marchand 1942, Ernst et al. 1994, Mount 1975). An individual unidentified Graptemys was first observed in the Choctawhatchee River in 1996 (Godwin 2002); Barbour’s map turtle was documented from the Pea River (Choctawhatchee River system) in 1997. From recent surveys, now known from both the Choctawhatchee and Pea Rivers in Alabama, and the Choctawhatchee River in Florida. Also of note, the Escambia map turtle has been documented from the Pea and Choctawhatchee Rivers in Alabama. This species was previously considered to be endemic to the Escambia River system (Conecuh and Yellow Rivers in Alabama, Escambia and Shoal Rivers in Florida). Putative hybrids of Barbour’s and Escambia map turtles also have been collected (Godwin 2002).
HABITAT: Exclusively rivers and associated habitats. Greatest numbers occur along stretches with considerable amounts of exposed limestone and abundant snags and stumps for basking. Occasionally may be found in river swamps or impoundments, but these habitats are suboptimal (Carr 1952, Ernst et al. 1994, Sanderson 1992, Godwin 2002).
LIFE HISTORY AND ECOLOGY: Nesting occurs during late spring and early summer with most females presumably nesting three to four times during this period. Four to 11 eggs typically laid in a cavity a few centimeters beneath the surface, within a few meters of the water, on sandbars and riverbanks. Although males may mature in three to four years, females may take as long as 15 to 20 years to achieve sexual maturity. Wholly carnivorous. Diets of males and small females consist primarily of caddisfly larvae and other aquatic insects. Adult females use massive head musculature and expanded oral crushing surfaces to feed almost exclusively on molluscs, particularly native snails of the genus Elimia and the introduced Asian clam (Cagle 1952, Ernst et al. 1994, Mount 1975, Sanderson 1992, Wahlquist and Folkerts 1973).
BASIS FOR STATUS CLASSIFICATION:. Alterations to the occupied drainage systems makes species highly vulnerable. The Apalachicola River system repeatedly has been impounded for reservoirs, dredged for barge traffic, and poisoned and otherwise polluted through human negligence. Additionally, females have been depredated by humans in the past for food. Although effects of these multiple threats to the species have not been analyzed, their impact on a late-maturing, mollusc-feeding species could be severe. The species also has considerable demand in the pet trade, which could contribute to the decline of some populations. Injuries and mortalities from boat traffic occur, but may be a minor impact (Jackson 1986, Ernst et al. 1994, Godwin 2002).
Author: James C. Godwin