The Flatback sea turtle is native to the sandy beaches and shallow coastal waters of the Australian continental shelf. This turtle gets its common name from the fact that its shell has a flattened or lower dome than the other sea turtles. It can be olive green to grey in color with a cream underside. The females of this species are larger than the males in adulthood and also have longer tails than their male counterparts.
Flatback sea turtles are found in Northern Australia, the Tropic of Capricorn, and in Papua New Guinea. Within Australia, they are distributed in the areas of eastern Queensland, Torres Strait and Gulf of Carpentaria, Northern Territory, and Western Australia. These turtles inhabit the continental shelf and coastal waters of tropic regions. They can be found in grassy areas, bays, lagoons, estuaries, and any place with a soft-bottomed sea bed.
Flatback sea turtles spend all their life in shallow, soft-bottomed coastal waters. They do not travel long distances in the open ocean for migrations like other sea turtles and can typically be found in waters of 60 m (200 ft) or less in depth. Males never leave the water while females come out on land only to lay eggs and nest only at night. Flatback sea turtles spend their time on their own and move quickly in the ocean; however, on land, they are slow and also defenseless. They feed mostly on the prey found within the shallow waters where they swim.
Flatback sea turtles have a carnivorous diet. They feed mostly on soft corals, sea cucumbers, shrimp, jellyfish, mollusks, and other invertebrates. They will also occasionally feed on seagrasses, even though they rarely eat vegetation.
Flatback sea turtles breed every two to three years. The nesting season can go from November to January or can last the entire year. Females are able to lay up to 4 times throughout the nesting season, and the intervals between nesting can be 13-18 days. While using her front flippers to dig, the female will clear away the dry sand located at the top. After she clears the sand, the female will create an egg chamber using her back flippers. After she has laid her eggs, she will then cover the nest again using her back flippers, while also tossing sand back with her front flippers. She then returns to the ocean, leaving the eggs untended. The clutch will have an average of 50 eggs that are about 55 mm (2.2 in) long. The sex of the hatchling is determined by the temperature of the sand that the egg is in. If the temperature is below 29 °C (84 °F), the hatchling will be a male, and if the temperature is above this 29 °C it will be female. Baby sea turtles begin to leave their nests during the beginning of December, and the clutches will continue to hatch until late March. The peak of hatchling emergence can be seen during February. The young usually stay close to shore and will feed on the macroplankton present in their surface-dwelling environment. They will reach reproductive maturity and start to breed anywhere between 7-50 years of age.
Like all marine turtles, Flatback sea turtles are faced with threats such as habitat loss, the wildlife trade, collection of eggs, collection of meat, by-catch, pollution, and climate change. Flatback sea turtles are specifically threatened by the direct harvest of eggs and meat by the indigenous people of Australia for traditional hunting.[ These people are given the right to harvest by the government, but only if for non-commercial purposes. Another threat is the destruction of nesting beaches due to coastal development and the destruction of feeding sites at coral reefs and the shallow areas near the shore. Camping on these beaches compacts the sand and contributes to dune erosion, and the wheel ruts caused by vehicles driving on the beaches can trap the hatchlings on their journey to the sea. Coastal development contributes to barriers that make it difficult or impossible for adult turtles to reach nesting and feeding sites. Flatback sea turtles also fall prey to incidental capture. They are caught by fishermen, particularly by trawling, gillnet fishing, ghost nets, and crab pots. Lastly, pollution is a serious concern for this creature. Pollution can affect the timing of egg-laying, how it chooses its nesting site, how hatchlings find the sea after emerging, and how adult turtles find the beaches.
There is no overall population estimate available for the Flatback sea turtle. However, according to the Sea Turtle Conservancy resource, the total population size of the nesting females is between 20,000 and 21,000 individuals. Currently, this species is classified as Data Deficient (DD) on the IUCN Red List.
Flashback sea turtles play key roles in their ecosystem. They use beaches and sand dunes to lay their eggs. Such coastal environments are nutrient-poor and depend on vegetation to protect against erosion. Eggs hatched or unhatched, and hatchlings that fail to make it into the ocean are nutrient sources for dune vegetation and therefore protecting these nesting habitats for sea turtles, forming a positive feedback loop. Sea turtles also maintain a symbiotic relationship with Yellow tang, in which the fish will eat algae growing on the shell of a sea turtle.