Sea turtles (or marine turtles) are some of the more conspicuous animals in the Great Barrier Reef World.

Six of the world’s seven sea turtles are found along the Great Barrier Reef.

  • Flatback
  • Green
  • Hawksbill
  • Leatherback
  • Loggerhead
  • Olive Ridley

About sea turtles

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Reptilia
  • Sub Order: Cryptodira

Sea Turtles are marine reptiles that must come to the surface to breathe.  The males live all life in the water.  At the same time, the females come up to the beach to lay their eggs.


Flatback Sea Turtle

Conservation Status: Threatened


Only found in Northern Australia and Papua New Guinea.  With nesting sites south of Bundaberg to the Torres Strait in North Queensland.  The flatback sea Turtle is found in 60 metres or less water depth and lives in shallow tropical and subtropical waters.


The Flatback is an Australian sea Turtle averaging between 76 – 96 centimetres and weighing between 70 to 90 kilograms.


The flatback sea Turtle has a flattened shell that is olive green to grey with a cream underside.  Their hatchlings are more significant than other sea turtles when they hatch.


Flatback turtles are sexually mature between 7-50 years of age, and adult females nest every two to three years.  The average hatch will contain 50 eggs around 55mm in size.

Hatchlings are to leave the nest in early December, and clutches will continue to hatch until late March.  Hatchlings’ sex is determined by the temperature of the sand where the eggs are laid.  Eggs will produce males if the temperature is below 29°C or females if the temperature is above 29°C.


Flatback turtles eat soft corals, sea cucumbers, jellyfish, shrimp and other invertebrates.  Occasionally they will feed on seagrass.

Green Sea Turtle


Conservation Status: Endangered with a population estimated between 85,000 and 90,000 nesting females.


The giant green sea turtles are on the Great Barrier Reef, and it is pretty standard for visitors to see green sea turtles daily.

Depending on their stage of life, green sea turtles roam between three different habitat types.  On the sand, they lay their eggs.  Most of their time is spent in shallow coastal waters with abundant seagrass beds by mature turtles.  The green sea Turtle lives in warm tropical and subtropical waters worldwide.

Ocean temperatures below 7 to 10 degrees Celsius are the environmental factor restricting turtles’ dispersal.  The green sea turtles typically stay close to the island and continental shores within their range.  The green sea turtles inhabit shallow bays and safe shorelines close to the coasts.

Most of a Turtle’s first five years are spent in convergence zones in the open, barren water surrounding them.  Due to their tendency to swim in deep, pelagic waters, these baby turtles are rarely seen.  Usually, green sea turtles swim at 2.5 to 3 km/h.


Adults grow to 1.5 metres long and weigh between 68-190 kilograms.


Green turtles are the largest of all hard-shelled sea turtles but have comparatively small heads.   They have teardrop-shaped dark brown, grey, or olive-coloured shells and a much lighter, yellow-to-white underside.  Green sea turtles have large paddle-like flippers.


The Great Barrier Reef has two genetically separate populations, one north and one south, off Australia’s northeastern and northern shores.  Twenty distinct areas of tiny islands and cays were found to be nesting sites inside the Reef.  On Raine Island, the most significant of these is located.  On Bramble Cay in the Torres Strait, there is a sizable rookery.  There are important breeding places in the Coral Sea.


As they get older, green turtles’ diets shift.  Young animals consume meat, but as they become older, they become omnivorous.  Young sea turtles consume molluscs, jellyfish, small invertebrates, worms, sponges, algae, crustaceans, and fish eggs.  In addition to feeding them red, brown, and green algae, coral reefs shield marine life from predators and violent storms.  Sea turtles have plenty of habitats thanks to the grass and algae that grow in salt marshes and seagrass beds.

Hawksbill Sea Turtle

Conservation Status: Critically endangered.


in Australia, Hawksbills’ habitat includes the entire far northern section of the Great Barrier Reef Marine Park and the Torres Strait.


On average, hawksbill sea turtles weigh between 45 and 68 kilograms as adults, and their shells typically reach a length of 0.8 meters.


The hawksbill sea Turtle has an oval-shaped body and is a small, agile Turtle.  The hawksbill’s name comes from its formidable toothless jaws and parrot-like “beak.” This beak is ideal for biting, tearing, and crushing food.  The carapace displays a tortoiseshell pattern with various orange, red, and black streaks that ranges in colour from dark to golden brown.  Hatchlings have 2.5 to 5-centimetre-long, typically heart-shaped, brown shells.  Yellow makes up the Turtle’s bottom shell.  The top shell’s back edge almost always bears overlapping horny plates called scutes and is serrated.  The hawksbill has four pairs of scutes on the sides of its carapace and two pairs of prefrontal scales on its head.


In all parts of their habitat, hawksbills mate twice a year in secret lagoons near the beaches where they lay their eggs.  Mexico, Seychelles, Indonesia, Sri Lanka, and Australia have the most extensive nesting beaches.

The Atlantic hawksbill’s breeding season typically lasts from April to November.

Populations in the Indian Ocean, like the Seychelles hawksbill population, breed between September and February.

Females haul their bulky bodies high onto the beach at night after mating.  With the aid of their rear flippers, they clear a space of debris, create a nesting hole, place clutches of eggs within, and then cover everything with sand.  About 60 different countries’ beaches contain their nests.


After around two months, hatchlings, which typically weigh less than 24 g, emerge at night.  Hatchlings have dark colouring and a 2.5 cm long, heart-shaped carapace.  They are drawn by the moon’s reflection in the water and instinctively scramble into the ocean (disrupted by light sources such as street lamps and lights).  Hatchlings that do not reach the sea by daylight are preyed upon by shorebirds, shore crabs, and other predators, even if they emerge in the shadows.



As they migrate through the Indo-Pacific, hawksbills eat various foods, including sponges, invertebrates, and algae.  Hawksbills are omnivorous, eating seagrasses, sea urchins, barnacles, small animals, and their favourite food, sponges.

It’s interesting to note that some of the sponges and other small invertebrates that hawksbills eat are poisonous.  Although the meat of hawksbill sea turtles may be harmful to humans, their body fat allows them to absorb the toxins without becoming ill.  Despite this, hawksbills are still harvested for their meat.

Leatherback Sea Turtle

Conservation Status:  Vulnerable


Leatherback sea turtles around found in the open ocean and are known to travel 20,000 kilometres in 674 days.  They prefer deeper water during the day and shallow during the night.

Leatherback sea turtles have the most extensive distribution and are found in subtropical and tropical waters as well as Alaska, Norway and New Zealand.


The leatherback sea Turtle is the largest of all sea turtles.  The largest on record was almost 305 cm from the tip of its beak to its tail, weighing 916 kilograms.

The leatherback skin is soft leathery rather than a hard shell with bone-like jagged edges referred to as teeth.


Two cusps and a deeply notched upper jaw on the head.  The only marine Turtle that doesn’t have a hard shell is the leatherback.  Its vast, extensible, flexible shell has seven unique ridges traverse the animal’s length.  The carapace lacks scales except in hatchlings and is made of a layer of thin, firm, rubbery skin that is reinforced by hundreds of microscopic bone plates.  Flippers are all devoid of claws.  The plastron is white to black and has five ridges, while the shell is dark grey or black with white or light patches.  On their shell, hatchlings feature white spots.


At sea, couples mate.  Unlike females, who build their nests on land, males never leave the water once they have entered it.  The male utilises head movements, nuzzling, biting, or flipper movements after encountering a female (which may release a pheromone to advertise her reproductive status).  While females only mate every two to three years, males can mate yearly.  Internal fertilisation occurs when numerous men mate with a single female.  The children of this polyandry do not receive any particular benefits.  The female leatherback sea Turtle has the lowest interrogating period of any sea Turtle since she can nest up to ten times in one nesting season.

Leatherback sea turtles may select a different beach within the region, unlike other sea Turtle species that virtually always return to the beach where they hatched.  Because hard rocks easily harm their softer shells and plastrons, they prefer beaches with soft sand.  Additionally, nesting beaches have shallower seaward approach angles.  Due to how quickly such beaches deteriorate, this puts turtles at risk.  They build their nests at night when predation and heat stress are least likely.  The eyes of leatherback turtles are not well suited for night vision on land because they spend most of their lives in the water.  Dark forested terrain close to the beach makes up the traditional nesting environment.  Females are given direction by contrasting this dark forest and the lighter, moonlit ocean.  They build their nests towards the night before returning to the light and the water.

Leatherback sea Turtle Hatchlings

With their flippers, females dig a nest above the high-tide line. Nine clutches from a single female are possible throughout a mating season.  Every nine days, a nesting event occurs.  One hundred ten eggs, on average, make up a clutch, and 85% of those eggs are fertile.  The female carefully backfills the nest after she has laid her eggs, hiding it from predators with a sprinkling of sand.


with a diet of jellyfish.  Small crustaceans, fish, sea urchins and snails.

Loggerhead Sea Turtle


Conservation Status Endangered


The loggerhead sea Turtle is found in the Atlantic, Indian, and Pacific Oceans and the Mediterranean.


Loggerhead sea turtles grow to an average size of 90 cm when fully grown, weighing approximately 135 kg.


The skin colour range from yellow to brown.  The male’s town is thicker and shorter than the females.

The loggerhead sea Turtle, the slightly more giant than the green sea Turtle,

is the world’s most famous hard-shelled Turtle.  In addition, it is the second-largest living Turtle in the world after the leatherback sea Turtle.

Adults typically weigh between 135 and 80 kilograms with a straight-line carapace length between 70 cm and 95 cm.

The heaviest documented weight is 545 kg, and the most extensive reported length is 213 cm (presumed total) (84 in).  The underside usually is a pale yellow, while the head and carapace, or upper shell, can be any colour between yellow-orange and reddish brown.  The Turtle’s neck and sides are brown, while the sides and bottom are yellow.


Between 17 and 33, female loggerhead turtles begin to spawn, and their mating season can last up to six weeks.  They court their partners, although this conduct hasn’t been studied in depth.  Male courtship behaviours include head and flipper movements, biting, and nuzzling.  According to studies, females emit cloacal pheromones to signal their capacity for reproduction.

A male approaches a female and tries to mount her before mating, but she resists.  The male and female then start to circle one another.  The female could allow the males to fight each other if the male has rivals.

The winning male then mounts the female, frequently causing damage to the female’s shell’s shoulders with his curved claws.  While the male is trying to mate, other courting males bite him, injuring his flippers and tail and possibly exposing bones.  The guy may have to dismount due to this damage, which could take weeks to heal.

Nesting and Hatchlings

Females typically lay 3.9 egg clutches while nesting, after which they go into dormancy and stop laying eggs for two to three years.

Unlike other sea Turtle species, female sea turtles typically engage in courtship and mating while travelling between their feeding and breeding areas.  Recent data suggests that mating induces ovulation in loggerhead turtles.  The female releases eggs during mating, and the male fertilises them.  Since mating-induced ovulation is uncommon outside of mammals, this is unusual.  Loggerheads mate in the Northern Hemisphere from late March to early June.  The nesting season is brief between May and August in the Northern Hemisphere and October and March in the Southern Hemisphere.

Loggerheads may show more than one paternity.

Sperm preservation makes it feasible for several fathers to exist.  The female can keep multiple male sperm in her oviducts until ovulation.  One clutch can have up to seven different fathers, each of whom provides sperm for a portion of the clutch.  Positive correlations exist between multiple paternity and female size.  Two theories explain this association.  One theory holds that because huge females are thought to be more fertile, males prefer them (the ability to reproduce).  According to the others, larger females have more extended mating periods because they can swim to mating grounds more quickly.

Laying the eggs

Every sea Turtle exhibits the same fundamental nesting habits.  During the nesting season, females return to the beach where they were hatched to lay eggs at intervals of 12–17 days.  After emerging from the water, they climb the sand to create a body hole.  They make an egg chamber with their rear limbs, where the eggs are laid.

After covering the corpse pit and egg chamber with sand, the females finally return to the sea.  This procedure lasts one to two hours and takes place on open sand areas or on top of dunes, ideally close to dune grasses that the females can utilise to conceal the nest.  Because it impacts traits like fitness, emergence ratio, and sensitivity to nest predators, the nesting habitat must be carefully chosen.  The typical clutch size for loggerhead turtles is 112.4 eggs.


The loggerhead sea Turtle is an omnivore that mostly consumes invertebrates that live on the ocean floor, including gastropods, bivalves, decapods, and horseshoe crabs.  Hatchling turtles (including members of its species), algae, and vascular plants are among the additional food sources.  Loggerhead turtles consume jellyfish, floating molluscs, floating egg clusters, squid, and flying fish while migrating through open water.


Olive Ridley Sea Turtle

Conservation Status Vulnerable

Habitat in Australia

Olive Ridley turtles often reside in shallow, protected waters with soft bottoms.  They can be found in Australia along the coastline from southern Queensland and the Great Barrier Reef up north to Torres Strait and through to Western Australia’s Joseph Bonaparte Gulf.


Olive Ridley is the second smallest sea Turtle growing to around 61 centimetres in length and weighing between 25 to 46 kilograms.  Hatchlings usually weigh around 12 -23.3 grams.

Reprod Adults have different sexual types.  The mature male has a longer, thicker tail employed during copulation, and his front flippers have expanded, hooked claws that enable him to grab the female’s carapace.  The female’s carapace is spherical and dome-shaped, whereas the males are more extended and tapered.  The male’s plastron is likewise more concave, which is thought to be another adaptation for mating.  Additionally, the male plastron could be softer than the females.


Olive Ridley turtles’ diet is omnivorous, eating mostly crabs, shrimp, jellyfish, and snails.  They will also eat seaweed and algae.



All six Australian sea turtles are protected under the National Parks and Wildlife Conservation Act 1975.

On Fitzroy Island in Cairns is the Cairns  Turtle Rehabilitation Centre.  This team of volunteers, outstanding people, cares for and rehabilitates sick or injured turtles.   If you would like to donate to this fantastic cause to help, your donation will be greatly appreciated.

Interesting facts about sea turtles