Giant south-american river turtle, Arrau side-necked turtle

Language English

Onglets

Description

Distinguishing features

The Giant South American turtle is a large semi-aquatic turtle with a flattened oral‑shaped carapace that is slightly wider at the rear. It is the largest of the river turtles in South America, with the females being considerably larger than the males.

Giant South American turtles have a long neck that does not retract in between their front legs, as is the case with most other turtles in North America and Eurasia. Instead, they fold their necks sideways into the carapace across the front of their forelegs.

Reproduction

Giant South American turtles reproduce during the dry season, when water levels are very low and provide easy access to the banks of sandy or fine gravel beaches for egg laying. These turtles are faithful to their nesting site, where they gather in very large numbers.

Females climb the banks at night to dig 60-80 cm deep nests in which they lay between 75 and 132 eggs. Clutch size depends on the size of the female: larger females lay more eggs. The eggs, which weigh about 40 g and have a flexible shell, incubate for 42‑48 days. The hatchlings emerge when the rains return and the rivers start to flood.

Diet

Giant South American turtles feed almost entirely on fruit, but they also eat seeds, roots, leaves, freshwater sponges, small fish, crustaceans and molluscs.

Predators

Giant South American turtles (and their eggs) are widely consumed in the Amazon. In fact, they are considered a prized delicacy in local cuisine, which means these turtles are often heavily harvested despite it being illegal. Farming attempts are currently underway in an effort to supply this market without harming the species. Giant South American turtles are also in high demand for pet stores.

The fact that these turtles lay large numbers of eggs on exposed, readily accessible sandbars makes them easy prey and provides a very “profitable” opportunity for harvesters.

The coati (Nasua nasua), crab-eating fox (Cerdocyon thous), Tegu lizards (Tupinambis teguixin), and birds such as vultures, caracara (Polyborus plancus) and jabiru (Jabiru mycteria) eat the eggs and juveniles, whereas caimans, piranhas and other carnivorous fish prey on the young turtles that reach the river. Jaguars are the only known predators of the adults.

Habitat

Giant South American turtles are highly aquatic. They rarely leave the water except to bask in the sun or to lay eggs. These turtles are indigenous to the tropical rainforests of the Amazon, Orinoco and Guiana basins. Large populations are also found in the rivers of the Cerrado (Brazilian savannah).

During the rainy season, Giant South American turtles invade the flooded forests (varzea and igapó) in search of fruit trees. When the floodwaters recede, they return to ponds or rivers and then travel to sandbars where the females lay their eggs.

Ecology, behaviour

Giant South American turtles belong to the suborder Pleurodira. This small group of turtles share several surprising characteristics, such as the fact that they cannot retract their necks in between their limbs as do most of the northern hemisphere turtles we are familiar with. Pleurodira have necks that fold sideways, just in front of their forelegs—a position that leaves them partially exposed (less protected). However, their long, highly flexible necks provide them with easier access to food and allow them to strike quickly to capture prey.

These turtles are diurnal and most active during the hottest period of the day. As with most turtles, the sex of the hatchlings is determined by the temperature at which the eggs are incubated—higher temperatures produce females whereas lower temperatures result in males.

French name

Podocnémide élargie, Tortue arrau

Scientific name

Podocnemis expansa

Phylum

Chordata

Class

Reptilia

Order

Testudines (Chéloniens)

Family

Podocnemididés

Size

Maximum carapace length: 107 cm Average carapace length of female: 80 cm Average carapace width of female: 60 cm Average carapace length of male: 40-50 cm

Weight

Average weight of female: 60 kg Maximum weight: 90 kg

Life span

Over 20 years in the wild Up to 25 years in captivity

Status

Least concern according to the IUCN (2018). Protected species (CITES, Appendix II).

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