GREEN TURTLES - Chelonia mydas

Description
Adult green turtles have a smooth, high-domed carapace, are olive green in colour, with occasional brown, reddish-brown or black highlights. Hatchlings have a black carapace with white margins around the carapace (shell), flippers and on the plastron (bottom of shell). Green turtles have one pair of prefrontal scales between their eyes.

Distribution and Habitat
Green turtles are found in tropical, subtropical and temperate waters around the world and appear to be the most abundant of the six species of marine turtle found in the Great Barrier Reef World Heritage Area. They are found in subtidal and intertidal coral and rocky reefs and seagrass meadows of the continental shelf. Green turtles are principally herbivorous as adults, eating mostly algae, seagrass, mangrove fruit and jellyfish.

Two genetic stocks of green turtles breed within the Great Barrier Reef Marine Park, a southern and a northern stock. These two stocks are the two main management units. The southern stock has nesting concentrated in the Capricorn/Bunker group of islands, with an average annual nesting population estimated at 8000 females. The northern stock has nesting concentrated around Raine Island and Moulter Cay with an average annual nesting population of 30 000 females.

The proportion of a green turtle population that nests each year is highly variable (up to an order of magnitude difference) and is influenced by variations in the El Niño Southern Oscillation (ENSO) Index. Green turtles are the only species of marine turtle for which this correlation has been shown and it may be based upon nutrition.

For green turtles nesting and foraging in the Great Barrier Reef Marine Park, tag returns indicate migration to Indonesia, Gulf of Carpentaria, Arnhem Land, Torres Strait, Papua New Guinea, the Solomon Islands, Vanuatu and New Caledonia.

Breeding Areas
There is low density nesting on many islands and along the Queensland coastline. Although genetically distinct nesting aggregations are known, the stocks often occur in the same foraging habitat.

To date, there have been no detectable declines in the number of nesting green turtles at Great Barrier Reef nest monitoring sites. However, the 20 to 25 years of data for the key sites (Raine Island, Heron Island) do not cover a single generation for green turtles, and trends are difficult to determine with the large fluctuations in nesting numbers that can occur because of the El Niño Southern Oscillation. Additionally, population models using accumulated demographic data suggest that the northern and southern stocks may be exhibiting characteristics of populations under threat, including a decline in the size of nesting adults, increases in the non-breeding periods and a lack of expected increases of turtle numbers in dispersed feeding areas. In addition, climate change may be adversely affecting nesting success by, for example, increased flooding of nest chambers and altering chamber temperatures thus affecting the sex of hatchlings.

LOGGERHEAD TURTLES - Caretta caretta

Description
The loggerhead turtle was named for its large head. It has thick jaws that crush crustaceans and molluscs. Adults are brown and are often highlighted with light brown, reddish-brown and black on their carapace. The plastron is yellow. Hatchlings have a dark brown carapace and light brown plastron.

Distribution and Habitat
Loggerhead turtles are found in all tropical and subtropical oceans. They inhabit subtidal and intertidal coral and rocky reefs and seagrass meadows as well as deeper soft-bottomed habitats of the continental shelf.

Loggerhead turtles feed on benthic gastropod and bivalve molluscs, crabs, sea urchins, and jellyfish. Two genetic stocks inhabit Australian waters, one on the east coast and the other on the west coast.

For loggerhead turtles nesting and foraging in the Great Barrier Reef World Heritage Area, tag returns indicate migration to the Gulf of Carpentaria, Arnhem Land, Torres Strait, and Papua New Guinea.

Breeding Areas
In Queensland, breeding and nesting occurs mainly in the southern Great Barrier Reef (Capricorn/Bunker group) and adjacent mainland near Bundaberg. Approximately 95 per cent of all nesting marine turtles on the Bundaberg coast are loggerheads. A few hundred females now nest annually in the region.

The eastern Australian loggerhead turtle nesting beaches support the only significant stock of the species in the South Pacific Ocean. The population has declined since the 1970s from about 1000 breeding females. This combined with their long maturation and low reproductive rate, means that the remaining loggerhead population is at serious risk of extinction from any increases in mortality.

An annual loss of only a few loggerhead turtles could result in the extinction of the Queensland population. As female turtles return to nest in the area where they hatched, it is highly unlikely that a population that has ‘died out’ would be recolonised by turtles from another population somewhere else in the world.

HAWKSBILL TURTLES - Eretmochelys imbricata

Description
Adult hawksbill turtles have brown colouration, extensively variegated with brown and black on their carapace. The plastron is cream with occasional black spots. A distinguishing feature of the hawksbill turtle is their beak-like mouth and narrow head. The carapace of this species is characterised by overlapping scutes. Hatchlings are dark brown. Hawksbill turtles have two pairs of prefrontal scales between the eyes.

Distribution and Habitat
Hawksbill turtles occur in all oceans usually in tidal and sub-tidal coral and rocky reefs in tropical and subtropical areas. In Australia, hawksbills feed in rocky areas and on coral reefs. Their main feeding area is on the east coast, including the Great Barrier Reef. Sponges make up a major part of the hawksbill's diet, although they also feed on seagrasses, algae, sea cucumbers, soft corals and shellfish. The pointed jaws are well adapted to prising food from crevices in and around coral.

Tag returns for hawksbill turtles nesting or foraging in the Great Barrier Reef Marine Park indicate migration to Indonesia, Papua New Guinea, the Solomon Islands, and Vanuatu.

Breeding Areas
Hawksbill turtles are found all over the world. The entire far northern section of the Great Barrier Reef Marine Park and the Torres Strait region is internationally significant for hawksbill turtle nesting as the species numbers have declined in many parts of the world.

There are three main breeding areas in Australia - northern Great Barrier Reef (several thousand nesting females), north-eastern Arnhem Land (about 2000 nesting females), and Western Australia (several thousand nesting females).

Hawksbill turtles tend to nest in low numbers and in the Great Barrier Reef region, their nesting areas mainly occurs north of Princess Charlotte Bay and in the Torres Strait. The only Great Barrier Reef nesting population for which there is sufficient information is at Milman Island, where data indicates since 1990 there numbers of nesting females have been declining at about three per cent each year.

Tag returns for hawksbill turtles nesting or foraging in the Great Barrier Reef World Heritage Area indicate migration to Indonesia, Papua New Guinea, the Solomon Islands, and Vanuatu.

FLATBACK TURTLES - Natator depressus

Description
The flatback turtle has a distinct low-domed flat carapace. Its shell is flattened with upturned edges and is covered by a thin skin. Adults have olive grey flippers and head; their plastron is white. 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 primarily on benthic soft-bodied invertebrates (soft corals, sea pens, holothurians), and jellyfish. Numbers in the east coast population in Queensland appear to be stable.

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

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. 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.

OLIVE RIDLEY TURTLES - Lepidochelys olivacea

Description
The Pacific or olive ridley is the smallest of the marine turtles and has a round, grey to olive-grey carapace and has a cream-coloured plastron. Its carapace is domed from the front and is shaped like a heart. Hatchlings are black and have a light brown plastron.

Distribution and Habitat
Olive ridley turtles occur in tropical and sub-tropical regions of the Pacific and Indian oceans. In Australia, they are found in soft-bottomed, shallow, protected waters from southern Queensland, around northern Australia to Joseph Bonaparte Gulf in Western Australia.

Olive ridley turtles feed in continental shelf waters on benthic molluscs, crabs, echinoderms, shellfish and gastropods.

Breeding Areas
There are two main breeding areas for olive ridley turtles in Australia, one in the Northern Territory with about 1000 nesting females per year, and the other in the Gulf of Carpentaria with less than 100 nesting females per year. No nesting by the species has been recorded in the Great Barrier Reef World Heritage Area.

Olive ridley turtles are uncommon in the Great Barrier Reef and have received little scientific attention and the long-term trend in the population of the species on the Reef is unknown. The species has been little studied within Australia and much of its life history, breeding and population biology, and migration patterns remain unknown.

LEATHERBACK TURTLES - Dermochelys coriacea

Description
Coloured black with light spots, the leatherback turtle is the largest living species of turtle. It has a soft leathery skin with five ridges running down its back. Pale pink spots are present on top of the head and its features include a very pointed carapace. Hatchlings are black with white markings on the carapace ridges and plastron.

Distribution and Habitat
Leatherback turtles are found in all oceans of the world. Their feeding grounds are mainly in temperate waters but they breed in tropical areas. Leatherback turtles are oceanic and are rarely found close to shore in Australia.

Leatherback turtles feed and occasionally nest within the Great Barrier Reef Marine Park with nesting recorded at Wreck Rock and adjacent beaches near Bundaberg. There is sporadic nesting at other widely scattered sites in Queensland. Leatherback turtles nesting in Queensland probably represent strays at the extremes of their ranges, with the survival of the foraging population in eastern Queensland dependent upon the larger, but declining, nesting populations in neighbouring countries. Leatherback turtles are most commonly found in temperate waters feeding primarily on macroplankton (jellyfish, salps).

Foraging leatherbacks have been recorded as far south as Bass Strait and through the Gulf of Carpentaria.

Breeding Areas
No large rookeries for the leatherback turtle occur in Australia. Most leatherback turtles living in Australian waters are presumed to migrate to breed in neighbouring countries, particularly Papua New Guinea and Indonesia.  However, some Australian nesting occurs on the mainland coast near Bundaberg and on the coast of Arnhem Land in the Northern Territory. Fewer than 10 animals nest annually in Australia.

Leatherback turtles are uncommon on the Great Barrier Reef and have received little scientific attention. Whilst the long-term trends in the Great Barrier Reef population is unknown, given the broad scale decline in the South Pacific leatherback turtle stock, the animals that occur on the Reef are likely to be part of that declining population. This raises concerns for the species in the Great Barrier Reef.