Biological notes

Biological notes:

Green Turtle

Class: Reptilia
Order: Testudines
Family: Cheloniidae
Species: Chelonia mydas

Adults have a smooth, high-domed carapace, olive green in colour, with occasional brown, reddish-brown or black highlights. The ventral surface is whitish-cream. Males are often darker and have a lower domed carapace than females. Hatchlings are black dorsally with white margins around the carapace and flippers, and white ventrally.
Greens are large turtles, having an average curved carapace length of 107 cm and average weight of 130 kg.
Worldwide distribution in tropical and subtropical waters, inhabiting tidal and subtidal habitats including coral and rocky reefs, seagrass meadows and algal turfs on sand and mud flats.
Abundant on the GBR, with major rookeries located in the Marine Park. These are islands of the Capricorn and Bunker Groups in the southern GBR (in particular North West, Wreck and Hoskyn Islands); and Raine Island, Moulter Cay, No 7 and No 8 Sandbanks in the northern GBR.
There are two genetically distinct breeding populations on the GBR - the northern GBR and the southern GBR.
Breeding season: In the northern GBR mating occurs from August to December and while nesting can occur all year round, it is most prevalent from October to March. In southern areas of the GBR the breeding season commences in September and ends in March. The female will lay around five clutches in a nesting season with greater than 100 eggs per clutch.

There is a two-week interval between the laying of each clutch.

The female will migrate to the breeding site after an interval of greater than five years, while the male migrates every two years.
Hatchling emergence in the northern and southern GBR takes place from December to May.
As with most species of marine turtles, greens may take between 30 to 50 years to reach maturity. At maturity, females have an average curved carapace length of 107.6 cm, and range of 91 to 124 cm.
Herbivorous, feeding principally on seagrasses, algae and mangrove fruits.

Leatherback Turtle

Class: Reptilia
Order: Testudines
Family: Dermochelyidae
Species: Dermochelys coriacea

Adults have a black carapace with five distinct longitudinal ridges and very pointed posterior. Pale pink spots are present on top of the head and pale blue spots may occur on the carapace. Hatchlings are black dorsally and ventrally with seven ridges on the carapace.
Leatherbacks are the largest of the marine turtles, with an average carapace length of 162 cm. Adults may weigh up to a tonne.
Distributed worldwide, throughout tropical and temperate oceans, in deep, open water habitats.
There have been no major breeding aggregations of leatherbacks recorded in Australia. There are records of low density nesting, by one to three females a year in the GBRR, at Wreck Rock and on coastal beaches at Mackay, Round Hill and Bundaberg.
Nesting commences in the GBRR around December and finishes in February. The eggs incubate around eight to nine weeks before the hatchlings emerge.
The female lays up to four clutches in a breeding season, with around nine days between each nesting activity. There are an average of 86 eggs laid in each clutch.
Females have an average curved carapace length of 162.4 cm at maturity, with a range of 150.5 to 174.5 cm.
Carnivorous, feeding largely on jellyfish, tunicates and other soft bodied invertebrates. They feed at all levels of the water column from the benthos to the surface.

Flatback Turtle

Class: Reptilia
Order: Testudines
Family: Cheloniidae
Species: Natator depressus

Adults have olive grey flippers and head, although the anterior of the head is yellow and the carapace is a darker olive grey. The ventral surface is cream in colour. They have a distinctive, low domed carapace with upturned lateral edges. Hatchlings have a grey dorsal surface with scales outlined in black. There is a white outline around the edge of the carapace and flippers, and white ventral surface.
Medium to large adult turtle with an average carapace length of 92 cm and average weight of 82 kg.
Flatbacks are of special significance as they are endemic to Australia. They have only been recorded nesting within continental shelf waters.
The species is distributed throughout tropical and subtropical waters of northern Australia. They are abundant in Queensland waters, where they inhabit shallow coastal waters and inter-reefal soft bottom habitats, feeding in shallow turbid waters.
Nesting principally occurs on the beaches of inshore continental islands and the mainland between Gladstone and Mackay. Major rookeries in the Marine Park are located at Peak, Wild Duck and Avoid Islands, in the southern and central regions of the GBR. Low density nesting also takes place on mainland beaches between Bundaberg and Cairns.
The breeding strategy adopted by this species is very different to greens. Green turtles lay several large clutches in a single breeding season, being active for a limited number of seasons. Flatbacks nest over a greater number of seasons, however each season is much shorter, and the female only lays a few, small clutches.
The breeding season extends from October to January. Females come ashore around two to three times during a season to lay their clutches, averaging 50 eggs in each clutch. The interval between nesting is about 16 days. Females migrate to the breeding site every one to three years.
At maturity, females have an average curved carapace length of 92.3 cm, and a range of 88 to 96 cm. Omnivorous, feeding on a variety of crustaceans, molluscs, jellyfish and algae.

Loggerhead Turtle

Class: Reptilia
Order: Testudines
Family: Cheloniidae
Species: Caretta caretta

Adults are brown dorsally often highlighted with light brown, reddish-brown and black, while the ventral surface is yellow. Hatchlings are dark brown dorsally and lighter brown ventrally.
Loggerheads are large turtles with an average carapace length of 95 cm and average weight of 100 kg.
Worldwide distribution throughout tropical and subtropical oceans, occurring in subtidal habitats such as coral and rocky reefs, seagrass beds and soft bottom habitats of mud and sand. Widespread throughout Queensland waters, including the Marine Park.
There are two nesting stocks in the GBRR, with major rookeries in the Marine Park located on the islands of the Capricorn and Bunker Groups, especially Wreck, Tryon and Erskine Islands, and the cays of the Swain Reef. Nesting in the Region also occurs on the mainland coast from Bundaberg to Round Hill, in particular at Mon Repos and Wreck Rock beaches.
Breeding season: Mating commences in October and extends to December. Nesting takes place from October to March. Hatchlings emerge from December through to April.
The female lays an average of 125 eggs in a clutch, laying around three clutches during the nesting season. On average, there is a 14-day interval between clutches. Loggerheads migrate to their chosen breeding site every three to four years.
As with all species of marine turtles, the females show a strong faithfulness to their chosen nesting site, returning to the same beach for each clutch and on successive nesting seasons. A high level of fidelity is also displayed towards their feeding ground.
Females reach maturity at an average curved carapace length of 95.8 cm, with a range of 80 to 113.5 cm. Males have an average curved carapace length of 96.6 cm at maturity, and a range of 88 to 113 cm.
Carnivorous, largely feeding on molluscs and crabs although occasionally feeding on other animals such as jellyfish, holothurians, sea urchins and fish.

Olive Ridley Turtle

Class: Reptilia
Order: Testudines
Family: Cheloniidae
Species: Lepidochelys olivacea

Adults are a uniform grey to olive grey in colour on the dorsal surface, and whitish ventrally. The carapace is similar in appearance to a heart shape. Hatchlings are black brown on their dorsal and ventral surfaces.
Smallest marine turtle in the Indo-West Pacific region, with adults having an average carapace length of 71 cm and average weight of 37 kg.
Widespread distribution throughout the world’s tropical and subtropical oceans, including northern Australia. They inhabit inter-reefal, soft bottom habitats. The species has not been recorded in coral reef, or coastal seagrass habitats.
Feeding populations are present in the Marine Park, however no major breeding populations have been recorded on the east coast of Australia.
Studies from Northern Territory breeding sites have indicated that nesting occurs all year round, although a peak in activity is evident in the cooler, dry season months. Females lay around 100 eggs per clutch, which incubate for approximately two months before the hatchlings emerge. There is no available information on the number of clutches per season, or how frequently the female returns to her chosen breeding site, for Australian olive ridley populations.
At maturity, females have an average curved carapace length of 71 cm.
Carnivorous, principally feeding on gastropod molluscs and small crabs.

Hawksbill Turtle

Class: Reptilia
Order: Testudines
Family: Cheloniidae
Species: Eretmochelys imbricata

Adults have brown colouration, extensively variegated with brown and black on the dorsal surface. The ventral surface is cream with occasional black spots. Another distinguishing feature is a beak-like mouth and narrow head. Hatchlings have a dark brown dorsal surface and light brown ventral surface.
Small to medium sized turtles with an average carapace length of 83 cm and average weight of 51 kg.
Distributed worldwide in tropical oceans, living in association with coral reef systems and other hard substrate habitats. This species is prevalent in the northern GBR.
Hawksbills are the most tropical of marine turtles, nesting only at the extreme north of the GBR. Nesting occurs all year round although a peak is evident from January to April. Recorded nesting on the GBR is largely on the inner shelf cays and islands, north of Princess Charlotte Bay. A major rookery is located at Milman Island.
Females nest from two to four times in a breeding season, laying up to 150 eggs in a clutch. There is an interval of 15 to 20 days between nesting activity. The eggs incubate for a period of 50 to 70 days, depending on the temperature. While it is not yet certain, it is believed that the migration interval back to the breeding site is two to six years, or possibly more.
The most serious problem affecting the long-term viability of hawksbill populations is the tortoiseshell (Bekko) trade.
At maturity, females have an average curved carapace length of
83.2 cm, with a range of 75.5 to 92.5 cm.
Omnivorous species, eating molluscs, crustaceans, sponges, soft corals and marine algae.

Dugong

Class: Mammalia
Order: Sirenia
Family: Dugongidae
Species: Dugong dugon

Dugongs have a wide geographical distribution in shallow tropical and subtropical waters of the Indo-Pacific Region. Their range includes waters of 43 different countries, extending from eastern Africa to Vanuatu and between 27° north and south of the equator. However, many dugong populations are relict or extinct. In Australia, their range is from Shark Bay in Western Australia, across the north to Moreton Bay, Queensland. There are an estimated 80 000 dugong in Australian waters, about 12 000 of them in GBRMP waters.
Dugongs look similar to a rotund dolphin or seal, although they are less streamlined. They have short flippers and their tail flukes are broad, similar to those of whales. Their head can look more like that of a pig, with a large, downward-pointing mouth. The body has a grey-bronze colouration, which is darker on the dorsal surface, than the ventral.
Adult dugongs can grow to lengths greater than 3 m and weigh in excess of 400 kg.
Despite their appearance, dugongs and their relatives (manatees and the now-extinct Steller's sea cow) are more closely related to elephants than to other marine mammals.
Dugongs have a life span of about 70 years. Females, which are called cows, have their first calf between 9 and 17 years. Calves are born singly, with an interval of 3 to 7 years between each calf being born. The gestation period is 13 months, and calves suckle for 18 months. During this time there is a strong bond between the cow and calf.
Most calves are born in the months from September to November, and reports indicate that calving occurs in specialised areas. These are often in shallow waters, removed from seagrass beds.
Dugongs are the only strictly marine herbivores, feeding almost exclusively on seagrasses.

Other Relatives:

Manatee

There are three species of manatee: the West Indian manatee, the Amazonian manatee and the West African manatee. Manatees are less streamlined than dugongs and have a rounded, paddle-shaped tail rather than flukes.
The range of the West Indian manatee is in the Caribbean region, from southern United States to the eastern extremity of South America. This species grows to about 3.8 m and weighs about 1600 kg.
The Amazonian manatee inhabits the Amazon basin and has not been known to enter marine waters.
The West African manatee lives in the rivers and coastal waters of West Africa.

Steller's Sea Cow

The Steller’s sea cow was the closest relative to the dugong and grew to 8 m long and weighed more than 6000 kg.
The last populations were found in the Bering Sea in 1741,
but previous populations had occurred along the Pacific rim from Mexico to Japan. The entire estimated population of 2000 became extinct by 1768 due to intensive hunting by seal hunters, taking them for their meat.
The species fed on kelp and became so well adapted to shallow waters that it could no longer dive, making it easy prey for hunters.
The Steller’s sea cow was the first marine mammal recorded as becoming extinct, in recent times.