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Other common names: Australian Flatback, Flatback Seaturtle

The Flatback Sea Turtle, Natator depressus, is a medium sized sea turtle with an elliptical, flattened shell characterized by upturned edges. Its olive-gray shell has a thin, waxy surface that can easily be damaged. Its range is much more restricted than other sea turtles, as it is found only in the waters surrounding Australia. It is the only sea turtle with no pelagic phase.

Female flatbacks weigh from 70 to 80 kg (155 to 175 lbs) and their shell is about 85 to 95 cm (33 in to 37 in) in length. Males are generally a bit smaller. Their bodies are olive-gray with a creamy white underside.

Flatbacks have a lower dome than other sea turtles, thus giving them their name. The upturned edges of their shell often collect sand when they flip sand backwards while concealing their nests. The keratin which covers the scutes of this turtle is so thin that blood can be drawn by running a fingernail firmly across its shell.

Flatback sea turtles were once thought to be a variation of Green Sea Turtles, Chelonia mydas, and were originally placed in the same genus. Like Green Sea Turtles, they have one pair of long prefrontal scutes between their eyes, and four pairs of lateral scutes on their shell. The tracks they leave while nesting also resemble green sea turtle tracks. These similarities notwithstanding, flatbacks are now recognized as being very distinctive from Green Sea Turtles with their own genus. Features that distinguish them from Green Sea Turtles are their non-pelagic behavior and limited range, their distinctive flattened shells, their larger head and shorter flippers, and the smaller scales on their flippers.

Flatback sea turtles are endemic to Australia, with their northern range extending to southern Papua New Guinea. They inhabit the east and west coasts of Australia only as far south as the warmest temperate areas. Their preferred habitat is shallow, murky waters with muddy bottoms away from coral reefs. All nesting sites are thought to be in Australia.

Flatback Sea Turtle
Picture of Australian flatback sea turtle, Natator depressus, heads back to ocean after nesting in beach dunes, Curtis Island, Queensland, Australia. Image #: 004040

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Reptilia

Order: Testudines

Suborder: Cryptodera

Superfamily: Chelonioidea

Family: Cheloniidae

Genus Species: Natator depressus

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Flatbacks feed on soft-bodied invertebrates, such as sea cucumbers, soft coral, squid and jellyfish. As sea cucumbers are common in their preferred habitat, they may be considered the fatback’s main food source.

Flatbacks exhibit some unique sea turtle characteristics. They often bask in the sun at the ocean’s surface, providing a perch for seabirds. They have also been found laying eggs in daylight. Their shells generally do not become fouled with barnacles, possibly as a consequence of natural chemicals covering their waxy scutes.

Flatback sea turtles reach adulthood at about 20 years of age, and females nest on the same beach where they were born. They lay eggs once every one to four years during the Australian summer, in November and December, and lay up to four clutches in a season. There are an average of 54 eggs to a clutch, a number which is half that of other sea turtles. The eggs, however, are larger than those of other species, and the hatchlings emerge larger than any sea turtle species except the leatherback. It takes 50 to 55 days for hatchlings to emerge.

Because flatback hatchlings are larger than other sea turtle hatchlings, they have a better chance of surviving attacks by crabs, gulls and fish when they leave the nest. They are also strong swimmers, which allows them to fight ocean currents and remain near the Australian shore where they spend most of their lives.

Flatback sea turtles and turtle nesting sites are well protected by the Australian government, but large numbers of these turtles are picked up in shrimp trawlers in international waters. Since 2000, shrimp trawlers have been required to use TEDs (Turtle Excluder Devices), which should help reduce flatback drownings. While aboriginal people consume some turtles and their eggs, they are not considered a serious threat to this species, as the numbers taken are low. Predators of flatback turtle eggs include pigs, foxes, rats, dingos, lizards, herons and crocodiles. Hatchlings are eaten by pelicans, sea eagles, sharks and crocodiles.

The IUCN lists the flatback sea turtle as Data Deficient, which means the organization lacks enough information to detail the risk of extinction for this species. Because of the flatback’s limited range, many scientists fear they are most at risk if sudden changes occur to their habitat.