The green turtle, Chelonia mydas, occurs throughout tropical waters and, to a lesser extent, in subtropical seas as well. They nest occurs in more than 80 countries worldwide.
Green turtles are slow growing and long lived; those that reach maturity may live to be 80 years old. Fully grown they are approximately 69 to 79 cm, and they reach sexual maturity between the ages of 26 and 40. Once they are mature, both male and female green turtles undertake breeding migrations of thousands of kilometres between foraging grounds and nesting areas. Their diet is algae and seagrass.
Turtles lay their eggs above the high-tide line on sandy beaches. The female comes ashore at night and digs a hole with her flippers then buries her batch of around 100 eggs in the sand. This keeps the eggs warm and safe until they hatch.
When hatchling turtles emerge from their nest they must make the journey into the sea and away from the shore as quickly as possible to avoid predation, from crabs, feral pigs and foxes on the beach or gulls, fish and crocodiles in the coastal shallows.
Green turtles can detect the orbital movement of waves and use this information to swim perpendicular to the waves’ crests. This means they swim directly offshore. Further out to sea they use the Earth’s magnetic field to maintain an offshore direction towards the open sea.
How turtles navigate remains a bit of a mystery. Not only can they maintain a fixed compass bearing, they can also return repeatedly to the same breeding beaches. Whilst geomagnetic cues may guide navigation over long distances, close to the goal, they may use wind-borne cues to home in on their target. It has recently been shown that juvenile greens can orient using the sun as their compass.
The IUCN (International Union for Conservation of Nature) lists Green Turtles as endangered. Hunting of turtles and their eggs is a widespread problem, but unintentional threats are actually more dangerous. These include ingestion of plastic, boat strikes, getting tangled in fishing nets, chemical pollution and habitat destruction (normally development along nesting beaches).