Turtles have been around for over 250 million years, since before the time of the dinosaurs. No-one knows how they managed to survive the extinction events that claimed so many other prehistoric creatures.
During a recent visit to Heron Island on the Great Barrier Reef, we were privileged to see green sea turtles haul themselves out of the water before dawn to lay their eggs.
Once the female turtle has found a suitable nesting site, she spends several hours digging a pit in the sand with her powerful flippers. It's important not to disturb her at this time, as sudden movements and flashing lights may cause her to abandon the nest and return to the water. When she begins to lay the eggs, however, the turtle enters a trance like state and it's safe to approach her more closely.
Turtles usually lay between 80 and 120 soft, round eggs, which are roughly the same size as a ping pong ball. After the eggs have been laid, the mother turtle begins the laborious process of covering the pit with sand. She will also usually make another mound nearby, to confuse predators about the location of the nest, before making her way back to the ocean.
Green sea turtle eggs take about two months to incubate. Interestingly, the temperature of the eggs during incubation influences the sex of hatchlings; lower temperatures tend to produce males, while higher temperatures tend to produce females.
The most dangerous time of a green turtle’s life is when it makes its first journey to the sea, particularly if it emerges from the nest after dawn or before dusk. As the hatchlings scamper across the sand, they become prey to multiple predators, including crabs and flocks of gulls. Although it's tempting to carry the hatchlings from the nest to the water, researchers think that it's important for the turtle's future navigation ability to make this perilous journey on their own.
And the dangers aren't over once they enter the ocean, with sharks, rays and other large predatory fish waiting to snap up the baby turtles before they're able to reach the relative safety of deeper waters.
Once they reach sexual maturity at about 25 years, female turtles tend to return to nest on the beach where they were born. This can be a problem if the nesting grounds have since been destroyed by erosion or coastline development.
Green turtles are listed as a vulnerable species but the good news is that recent research from Heron Island shows that their numbers may be increasing in the waters around Eastern Australia. Although turtles are a protected species, threats include boat propeller injuries, entanglement in fishing nets, depletion of their food supply (mainly seagrass and algae) and other problems caused by marine pollution. Turtles can also die when their stomachs become blocked with indigestible plastic waste. Sadly, despite their protected status, turtles are still killed for their meat and eggs in some parts of the World.
There are a few simple things we can all do to help ensure the survival of these amazing ancient creatures: limit the use of plastic bags and single use products, don't release balloons, dispose of waste (particularly fishing line) responsibly, participate in a beach or creek clean-up and avoid the use of fertilisers and pesticides that may pollute our waterways. When travelling abroad never eat turtle soup or buy souvenirs made from turtle products.
