Flatback turtle

Natator depressus

Description

The flatback turtle has a distinct low-domed flat carapace (shell) with upturned edges and covered by a thin skin and their plastron (bottom of shell) is white. Adults have olive grey flippers and head. Hatchlings are grey and have a white plastron.

Distribution and habitat

Flatback turtles are only found on the continental shelf of Australia. Although they feed around Papua New Guinea and Indonesia as well as within the Great Barrier Reef Marine Park, they nest only in Australia.

Hatchling flatback turtles are unique in that they do not have an oceanic pelagic phase, rather they are believed to inhabit inshore areas of clear reefal waters.

Flatback turtles inhabit subtidal soft-bottomed habitats of the continental shelf and feed on things such as soft corals, sea pens and jellyfish. Numbers in the east coast population in Queensland appear to be stable.

Tag returns up to 1300km between nesting and foraging areas have established movement between Australia and Indonesia (southern Irian Jaya) (Figure 1).

Breeding areas

All known breeding sites of the flatback turtle are in Australia. Breeding is centred in the southern Great Barrier Reef around Peak, Wild Duck, Curtis and Facing Islands (Figure 2).However, low density nesting by flatbacks occurs on many mainland beaches and offshore islands north of Gladstone.The largest amount of nesting occurs on Crab Island in western Torres Strait.

Whilst trends in population numbers of breeding flatback turtles are generally uncertain, their numbers are thought to be relatively stable on the Australian east coast including the Great Barrier Reef.

Figure 1 Indicative migration path of Great Barrier Reef flatback and hawksbill turtles

Map of Queensland, indicating flatback turtle migration routes

Dashed lines (- - -) represent movements of hawksbill turtles.
Solid lines (-) represent movements of flatback turtles.
All migration paths are indicative only.

Flatback turtle facts

Breeding season November to February
Years between breeding One to three years
Age at first female breeding 20 years
Nesting female length 94cm (range from 88 - 96cm)
Nesting female weight 82kg (range from 70 - 90kg)
Clutch size (number of eggs)
54 eggs
Hatchlings emerge January to April
Hatchling success 80 per cent
Hatchling size 6.1cm (range 5.66 - 6.55cm)
Hatchling weight 44g (range from 33.3 - 49.1g)
Predators of hatchlings Pelicans, ghost crabs, crocodiles and sharks
 

Figure 2: Great Barrier Reef flatback turtle nesting sites

Map of Queensland, indicating flatback turtle nesting sites