(Forsskål, 1775)
African softshell turtle
Recognition
Trionyx triunguis is a large softshell; an individual from Liberia that lived 53 years at the United States National Zoological Park, Washington, D. C. had a carapace length of 101.5 cm when it died. The carapace is olive to dark reddish- brown, sometimes without markings, but usually, at least in juveniles, with some light-centered, dark-bordered spots; it is often bordered with yellow. With increasing age, the light pigmentation fades and may disappear completely in old turtles. In juveniles, several longitudinal rows of tubercles lie on the carapace, but in large adults the dorsal surface is smooth. The anterior rim of the carapace is thickened over the neck. No preneural bone is present; a single neural bone separates the 1st pair of costals. The 8th pair of costals are complete (not reduced), and these and sometimes the 7th pair are at least partially in contact at the midline. Surfaces of all carapacial bones are coarsely pitted. The plastron is white to cream colored, usually unpatterned, but with a few faded anterior vermiculations in some. The hyo-hypoplastral and xiphiplastral callosities are well-developed and pitted in adults, and an additional callosity may be present on the epiplastron. A fontanelle is present, especially in young individuals, between the xiphiplastral bones (Atatür, 1979). Epiplastra are separated and the entoplastron is bent at right angles at the plastral midline. The skull is small, considering the size attained by adults, with its bony snout longer than the diameter of the orbit. The intermaxillary foramen is small, only about a third as long as the primary palate. No longitudinal ridge occurs on the maxilla, and a symphysial ridge is also absent from the mandible. The width of the mandibular symphysis is equal to or longer than the diameter of the orbit. Head and limbs are olive and heavily marked with small yellow or whitish spots and vermiculations. Both chin and throat contain a network of large white spots. The undersides of the limbs are yellow.
Males have long, thick tails with the vent near the tip.
Distribution
African softshells range over most of the continent except the waterways of southern and northwestern Africa. They are known from both the White (below Murchison Falls) and Blue Nile drainages downstream in the Nile to the Mediterranean Sea, Lakes Rudolf and Albert, the tributaries of the Congo River, and most drainages in West Africa. They have not been found in Lake Victoria. Trionyx triunguis also occurs in the Alexander River of Israel, and along the coasts of that country, Lebanon and Syria. In Turkey, it is found along the southern coast with important populations in the Dalyan delta and the Dalaman area (especially in Lake Kükürt) (Atatür, 1979; 1991; Gramentz, 1993a; Kasparek, 1994).
The African softshell has been exterminated in substantial parts of its former range, including its type locality, the (Egyptian) Nile (Balázs L. Farkas, pers. comm.). The total Turkey population is only about 500 individuals (Kasparek, 1994).
Habitat
The usual habitat is a slow-moving freshwater body, such as a large river, stream, pond, or lake, but Trionyx triunguis also enters brackish waters where its range meets the sea. A large specimen was caught in the ocean 3 or 4 km from the mouth of the Gaboon River (Loveridge and Williams, 1957), and it has been taken in waters of 33-42 ppm salinity in Israel and Turkey, where it is a nuisance to fishermen. African softshells seem to prefer the warmer parts of waterbodies (Gramentz, 1994).
Natural History
Courtship and mating have not been described. Nesting occurs from March to July, depending on latitude; nesting in Turkey occurs from early June to late July (Atatür et al., in press). Most nest cavities are dug in sand and earthen banks and on islands close to the shore (5-15 m, Atatür, 1979). Those living in brackish coastal waters may lay on adjacent sea beaches. Atatür (1979) reported that a nest he measured in Turkey had a diameter of 15-20 cm and a depth of 20-25 cm.
Several clutches may be produced per season (Atatür et al., in press). The white brittle-shelled eggs are spherical, about 32 mm in diameter; Atatür (1979) reported a mean of 35.3 mm (34.4-36.3) for 31 eggs in Turkey. A single female may contain 25 to more than 100 eggs, although Atatür (1979) only found 8-34 eggs in three nests. Incubation in the laboratory took about 56-58 days (Atatür, 1979).
Hatchlings are 42-54 mm long, and weigh 8-17 g (Gramentz, 1993a). They are greenish brown with numerous, conspicuous yellow spots with thin brown-black peripheral rings. With age, the ground color becomes darker and the light spots become smaller and more numerous.
Trionyx triunguis is mainly carnivorous, feeding on fish and gastropods (Atatür et al., in press), but anthozoans, aquatic insects, crustaceans, amphibians, reptiles, and vegetable matter such as palm nuts and dates have also been reported as food items. Both live and dead animals are accepted; Gramentz (1993b) saw up to four individuals feeding at the same time on a dead goat. Cansdale (1955) reported it will lie in ambush and then suddenly grab its prey when it comes within reach. Captives feed on frog meat and raw and slightly boiled liver (Atatür, 1979).
Trionyx triunguis is diurnally active, but some have been caught with fishing lines during night time (Atatür et al., in press). It will leave the water to bask, but is shy and difficult to observe. Basking durations in Turkey lasted from 29 seconds to 31 minutes (Gramentz, 1994). Aquatic basking in shallow water also occurs.
Remark
The name of the author of this species, Pehr (or Petrus) Forsskål, has often been misspelled as Forskål, as it was considered improper to write a double consonant before another consonant. See Leviton et al. (1992) for a discussion of this topic.
IUCN Red List Status (1996)
Not listed.