flatback turtle

flatback turtle (Natator depressus) is a species of sea turtle endemic to the continental shelf of Australia. It is the only extant member of the genus Natator and is distinguished by its relatively flat carapace. The species has a restricted range compared to other marine turtles, primarily nesting on northern Australian beaches and foraging in shallow, coastal waters of the Arafura Sea and Coral Sea.

Description and taxonomy

The species was first described by American zoologist Samuel Garman in 1880, initially placed within the genus Chelonia. It was later reclassified into its own monotypic genus, Natator, a taxonomic distinction supported by both morphological and genetic studies. Key physical characteristics include a smooth, olive-grey carapace that is distinctly flattened compared to the more domed shells of species like the green sea turtle or loggerhead sea turtle. Adults typically reach a carapace length of about 90 centimeters, making it a medium-sized sea turtle. Its unique plastron is a pale yellow, and it possesses a single pair of prefrontal scales on its head, a feature it shares with the hawksbill sea turtle.

Distribution and habitat

The flatback turtle has one of the most geographically restricted distributions of all sea turtles, being found only in the waters of the Australian continental shelf. Major nesting beaches are concentrated in Queensland, the Northern Territory, and Western Australia, with significant rookeries on islands like Crab Island and the Wellesley Islands. Its foraging grounds are limited to the shallow, turbid waters of northern Australia, including the Gulf of Carpentaria, Torres Strait, and the Great Barrier Reef lagoon. Unlike other sea turtles, it does not undertake extensive pelagic migrations across deep ocean basins, remaining largely within the warm, coastal seas of its native range.

Behavior and ecology

The flatback turtle is primarily a carnivorous feeder, with a diet consisting mainly of soft-bodied prey such as sea cucumbers, jellyfish, soft corals, and other invertebrates found on the seafloor. Its foraging behavior is adapted to the soft sediments of its inshore habitat. Key predators of hatchlings and juveniles include ghost crabs, seabirds like the silver gull, and various species of shark and fish. Adults face fewer natural predators, though they may occasionally be taken by large sharks such as the tiger shark. The species exhibits strong philopatry, with females returning to nest on or very near the beach where they hatched.

Reproduction and life cycle

Nesting occurs primarily at night on mainland and island beaches from October to February. Females lay fewer but larger eggs per clutch than other sea turtles, typically around 50 eggs, which have a larger yolk sac. The incubation period is approximately 50-60 days, influenced by sand temperature. Hatchlings are notably larger than those of other species, measuring about 6 centimeters in length, which may confer a survival advantage. After emerging, hatchlings swim directly to offshore waters but do not enter the oceanic gyre system; instead, they remain in neritic developmental habitats. The age at sexual maturity is estimated to be between 10 and 20 years, though precise data is limited.

Conservation status and threats

The flatback turtle is listed as Vulnerable on the IUCN Red List and is protected under Australian law, including the Environment Protection and Biodiversity Conservation Act 1999. Major threats include bycatch in trawl and gillnet fisheries, particularly in the Northern Prawn Fishery, coastal development leading to habitat loss and light pollution at nesting beaches, and climate change impacts such as sea level rise and increased sand temperatures affecting hatchling sex ratios. Conservation efforts are coordinated by the Australian Government in partnership with state agencies, indigenous ranger groups like the Dhimurru Aboriginal Corporation, and research institutions such as CSIRO. Key actions include the mandatory use of Turtle Excluder Devices in trawl fisheries and extensive monitoring programs at major rookeries. Category:Sea turtles Category:Reptiles of Australia Category:Vulnerable fauna of Australia