Marine Turtles

Cheloniidae / Dermochelyidae Families

CLICK HERE FOR TURTLE FIELD GUIDE


Marine Turtles have roamed our oceans for 185 million years with only one natural predator - the Tiger Shark.

Amazingly they survived the mass extinction of dinosaurs but they now face and even greater threat, which we'll look at later in this passage.

Sea Turtles breath air and have lungs which require regular visits to the surface, their bodies can hold a great deal more carbon dioxide than us and other animals.

Some have been observed submerged for up to six hours.


Life Cycles

Generally speaking upon reaching sexual maturity females will mate every two to four years, males every year, both migrating from distant feeding grounds, returning to waters adjacent to beaches where they themselves hatched.
Two to four weeks later the female will come ashore at night, dig a pit with her fore flippers and lay between 100 - 120 ping pong ball shaped eggs in the sand, called a clutch of eggs. She'll do this as many as five or six times at 11 - 18 day intervals.

The total number of clutches she will lay varies depending on the species, the size of the clutch directly relates to the size of the females carapace and in one mating season she'll carry approximately 800 fertilized eggs.


The Temperature determines the sex of the eggs with lower temperatures producing males. Hatching occurs approximately two months later and working as a group the hatchlings dig their way out of the nest finding protection in numbers whilst various animals lie in wait for an easy meal. Mortality rates are high only about 1/1000 hatchling reach adulthood.

Those that make it to the open ocean will roam the seas for 3-7 years, known as  "Lost Years"
Little is known about the early existence of a turtle's life but it's thought they ride the ocean currents, feeding on small animals with flotsam for companionship until their shell length reaches 20 - 40mm.

The adolescents return to costal waters and mature, some years later they will mate and the cycle begins again.




New tagging information shows many more large turtles are out in the open ocean foraging for food than once was thought. Some migrations are amongst the longest in the world and it's thought turtles live for around 80 years.

Sipadan Island in the Celebes Sea is teeming with Green and Hawksbill turtles, so many that divers become blaze about seeing them.

Lets take a look at these two species in a little more detail.










Scientific Name: Cheonia mydas 
Common Name:  Green Turtle  

Green Turtles can be identified and differentiated by a set of two scales between the eyes. They are found throughout the world's oceans.

Reaching approximately 1m and 180kg this turtle gets its name from the algae and lime it feeds on which turns its fat tissue green, adults are herbivores but juveniles feed on plankton, jelly fish and fish eggs.
Its difficult to distinguish between sexes but mature males have a longer and thicker tail and develop a single mating claw on the trailing edge of the fore flipper.

Their carapace (top shell) is smooth and green and brown in colour, their plastron (belly shell) is a pale yellow tan colour.





Scientific Name: Eretmochelys imbricata
Common Name:  Hawksbill Turtle  

Unlike the Green Turtle the Hawksbill has two pairs of prefrontal scales between the eyes and has two claws on each flipper. It has a beak-like mouth; hence the name and mature females are approx. 87cm in length and 80kg.

They live on a diet of sponges and in costal waters can be found on rocky outcrops of reef and solid substrates, which are optimal sites for sponge growth.


Nesting occurs on high and low energy beaches, due to their smaller body size they can often cover fringing reefs where other species cannot. Their nesting season is longer than most, lasting up to six months opposed to two months.




Threats to Turtles

Sadly, owing to Mans harmful activities over the past 200 years turtles are now close to extinction.

WWF's Endangered Species list includes the Green Turtle, Hawksbill, Kemps Ridley, Loggerhead and Leatherback Turtle. Sexual maturity comes late, most turtles will not mate until at least the age of 25 years old some much later, and a great number are killed before they reach this age reducing their numbers to the point of critical depletion.
They face numerous threats; their meat, eggs and oil are sought after for human consumption and seen as a delicacy in parts of Asia.

Their shells, especially that of the Hawksbill is beautiful and used to make jewellery and household ornaments. Many become entangled in fishing nets and long line nets. 


Turtles accidentally swallow plastic bags, which block up their digestive system and cigarette butts, which are toxic. In recent years dead turtles have been found with grapefruit size tumors, the cause of which is uncertain but most likely a result of increased chemical pollutants in our oceans.

It's a sad state of affairs, perhaps awareness and education can help save our Turtles and each of us can make a small difference. Take a look at our News and Events page and see how you can help protect Marine Turtles.





CLICK HERE FOR TURTLE FIELD GUIDE