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Flatback Turtle (Natator depressus)

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Of the seven species of sea turtles, the flatback turtle has the smallest distribution range, habitat size, and population numbers. It is also the only sea turtle that is not found within United States waters. The only known reproduction grounds for the flatback are in Australia.

The flatback is named for its large, low-domed carapace with upturned edges. The scutes of the flatback carapace do not overlap and have an olive green-grey color.

A carnivorous animal, the flatback’s diet consists primarily of soft-bodied prey like jellyfish, corals, sea cucumbers, and anything they can find in subtidal habitats.

Taxonomy

Kingdom Animalia
Phylum Chordata
Class Reptilia
Order Testudines
Family Cheloniidae
Genus Natator (1)


General Description

  • 4 pairs or more of large scales on either side (costal scales) of the carapace
  • Non-overlapping carapace scales
  • Carapace low domed with upturned edges
  • Colour olive grey
  • Adult carapace approximately 0.9 metres

Diet
The flatback turtle is carnivorous, feeding mostly on soft bodied prey such as sea cucumbers, soft corals and jellyfish. They feed mainly in subtidal, soft-bottomed habitats.

Species Description

Adult carapace length: c. 90 cm

Adult weight: c. 73 kg

Hatchling carapace length: c. 6.1 cm

Hatchling weight: c. 43 g

Habitat

The flatback turtle inhabits coastal waters over soft-bottomed sea beds. Like other marine turtles, its lays its eggs on sandy beaches, either on the Australian mainland or on offshore islands.

The flatback turtle is endemic to Australia and all known breeding sites of this species occur only in Australia.

They feed in the northern coastal regions of Australia, extending as far south as the Tropic of Capricorn. Their feeding grounds also extend to the Indonesian archipelago and the Papua New Guinea coast.

Flatback turtles have a preference for shallow, soft-bottomed seabed habitats away from reefs.

Distribution

Having one of the most restricted ranges of any marine turtle, the flatback turtle is found only in the tropical waters of northern Australia, Papua New Guinea and Irian Jaya, and nests only in Australia.

Population trends

Flatback turtles nest on inshore islands and the mainland from Mon Repos in southern Queensland to Exmouth in northern Western Australia. There are four major nesting areas in Australia, representing four genetic breeding stocks.

On the east coast of Queensland, flatback turtles nest from Mon Repos in the south to Herald Island near Townsville in the north. Major rookeries include four islands on the inner shelf of the southern Great Barrier Reef, Peak, Wild Duck, Avoid and Curtis Islands. Nesting activity reaches a peak between late November and early December, and ceases by late January. Hatchlings emerge from nests from late December until about late March, with most hatching during February.

The largest nesting concentration of flatback turtles is in the north-eastern Gulf of Carpentaria and western Torres Strait. Other rookeries in the Gulf of Carpentaria are in the Wellesley Islands and the Western Gulf of Carpentaria. This population of flatback turtles nests all year round, but there is a peak of nesting activity in mid year.

In the western Northern Territory (and possibly eastern Kimberley) there is a mid-winter peak nesting season and low-density summer nesting.

In the Kimberley and Pilbara regions of Western Australia, from approximately the Lacepede Islands to Exmouth, there is a mid-summer peak nesting season.

Threats

There is a large range of threats which may be affecting populations of the flatback turtle. Flatback turtle eggs and hatchlings are threatened by tourism and recreation disturbing nesting beaches, the effects of light pollution, and harvesting by indigenous people. They are also vulnerable to predation by feral pigs, particularly on the Cape York Peninsula. Adult flatback turtles are harvested for their meat, and face additional threats such as entanglement in lost or discarded fishing nets, ingestion of marine debris, being struck by boats, and being caught as by-catch. Flatback turtles comprise the majority of the turtle by-catch (59 per cent) in trawls in the Northern Prawn Fishery. However, as one of the most poorly understood marine turtle species, there is insufficient information to determine to what extent the flatback turtle may be affected by these threats, and thus it has been classified as Data Deficient on the IUCN Red List.

Conservation efforts

The flatback turtle is classified as Vulnerable in Australia under the Environment Protection and Biodiversity Conservation Act 1999, and there are a number of measures in place to protect the marine turtles of Australia. Much of the flatback turtle’s habitat is protected. For example, 75 per cent of its nesting habitat is protected in Queensland and it occurs on the Great Barrier Reef, one of the world’s most extensive protected areas. In addition, in an effort to reduce by-catch, Turtle Excluder Devices were made compulsory in the Northern Prawn Fishery in 2000, resulting in turtle mortalities being reduced to just five per cent of what they were in 1989-90. A Recovery Plan for Marine Turtles in Australia was developed in 2003 and outlined a number of further measures necessary to reduce detrimental impacts on flatback turtles and other marine turtles of Australia. These included restricting boat speeds in areas of important marine turtle habitat, developing management plans for nesting beaches and a code of conduct for tour operators on beaches, as well as creating plans to ensure traditional indigenous harvests are undertaken in a sustainable manner.

Source: Australian government

-TSF-

#turtles #terrapins #tortoises #Flatback #TSF

 
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