Sea turtles are under threat and in decline the world over. Of the seven species of marine turtles, six occur in Australian waters.
Swimming gracefully through the water, sea turtles evoke a sense of serenity and freedom. With large, hard shells (called carapaces) on their backs to fend off predators, they spend most of their time underwater using their strong paddle-shaped flippers to swim around.
Loggerhead Turtles have been recorded measuring up to 280cm in length and weighing up to 450kg!
Sea turtles that occur in Australian waters are:
- Flatback Turtle (Natator depressus)
- Green Turtle (Chelonia mydas)
- Hawksbill Turtle (Eretmochelys imbricata)
- Leatherback Turtle (Dermochelys coriacea)
- Loggerhead Turtle (Caretta caretta)
- Olive Ridley Turtle (Lepidochelys olivacea)
Four of these are supported through work on our reserves and partnerships – the Green Turtle, the Flat-backed Turtle, the Olive Ridley Turtle and the Loggerhead Turtle.
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Where do marine turtles live?
The Great Barrier Reef, itself in alarming decline, is home to the largest populations of sea turtles in the world, along with the Caribbean Islands.
Some sea turtle species, such as the Green Turtle and Loggerhead Turtle, can be found across the globe, travelling great distances between their nesting and feeding sites.
The Loggerhead Turtle inhabits the coastal waters of more than 140 countries, in and around shallow lagoons, coral reefs, salt marshes and seagrass beds near the shore.
Olive Ridley turtles occur along the coast from southern Queensland and the Great Barrier Reef, northwards to Torres Strait, and across to the Joseph Bonaparte Gulf in WA. Other sea turtles are more choosey. The Flat-back Turtle is found only in the waters around the continental shelf of northern Australia.
Sea turtles live in a range of coastal habitats, with most species’ hatchlings preferring the open sea, where they’re exposed to fewer predators before their shells have a chance to harden.
Interestingly, juveniles have a carnivorous (meat-based) diet during this time in the open sea, while most species have a herbivorous (plant-based) or omnivorous (meat and plant-based) diet by the time they’re adults and inhabit shallower waters closer to shore.
Marine turtle behaviour
Some sea turtles, including Loggerheads, are known to spar over access to feeding grounds. This confrontation begins with circling behaviour and can escalate to direct confrontations and snapping at each other’s jaws.
Some sea turtles are also known to hibernate in the cooler months, submerging for up to seven hours and surfacing for only seven minutes afterwards to breathe. The amount of time turtles can hold their breath underwater depends on their activity levels.
Perhaps one of the most intriguing habits of marine turtles is the long journeys they make across oceans to mate and then deposit their eggs on specific beaches – sometimes the very same beaches where their lives began.
After mating, female sea turtles pull their heavy bodies onto the beach and carefully select a nesting site. They use their powerful hind flippers to dig a hole, where they deposit up to 200 eggs per ‘clutch’ before covering the nesting hole with sand and returning to the water.
The early life of hatchlings is a battle for survival. After emerging up to 70 days later, en masse and at night, they must immediately survive a gruelling trek across the sand towards the sea and relative safety.
Threats to sea turtles
Sea turtles face many threats and are in decline. According to the Internaional Union for the Conservation of Nature, the Green Turtle is endangered, while the Olive Ridley and the Loggerhead Turtle are vulnerable.
Eggs and hatchlings are easy prey for feral predators, in particular foxes, which can dig up and consume almost all the nests in an area if left uncontrolled.
It’s estimated that only 1% of sea turtles survive until sexual maturity at the age of 30 to 50 years, depending on the species.
Climate change is also a threat for sea turtles as the temperature of the sand in which their eggs are laid determines the sex of the young. While the ideal temperature of about 30°C creates an even balance of male and female young, increased or decreased temperatures can create a gender imbalance. Fishing nets, pollution and habitat destruction are also threats.
Natural predators include birds and crabs (when hatchlings are making the treacherous journey across the sand to the water) and sharks.
What’s Bush Heritage doing?
November to February, when the tides are high, Loggerhead, Green and Flatback turtles come from the Coral Sea to nest on beaches adjacent to our Reedy Creek Reserve near Agnes Water on the Queensland central coast.
Controlling foxes in the area is crucial to ensuring as many hatchlings as possible survive.
Flatback Turtles are also culturally important to the Wunambal Gaambera people on the far north-west coast of the Kimberley. Since 2011 we’ve worked in partnership with the Wunambal Gaambera, to help plan and implement conservation works. The Karajarri people, whose land is known as the gateway to the Kimberley, also support nesting Flatbacks.
Donate today to help us continue this and other vital conservation work.
FlickR photos above are reproduced under a Creative Commons Licence.
