In pictures: the secret life of green turtles
Marine scientist and photographer Justin Gilligan reports on a project tagging turtles in New South Wales for the first time.
UP UNTIL RECENTLY, the movements of juvenile green turtles have been almost a total mystery. But since mid-2011 scientists have been using satellite tags to follow the movements of two young green turtles in the waters off Port Stephens – the first time turtles have been tagged this way in New South Wales.
Green turtles (Chelonia mydas) nest, forage and migrate across tropical northern Australia, though young turtles are known to occasionally drift into temperate waters to feed on seagrass and invertebrates. They take up to 30 years to mature, and may migrate more than 2600km between their feeding and nesting grounds. Nesting beaches are the same locations where they themselves hatched and emerged from the sand, scurried down the beach, and entered the sea for the first time decades earlier.
This year’s study – the most southerly satellite tracking of marine turtles in the world – will provide significant insight into the movements of sub-adults says Dave Harasti a scientist leading the project at the Port Stephens-Great Lakes Marine Park Authority.
Clues to foraging grounds
“Every time the turtles come to the surface to take a breath, the tags send a signal via satellite to notify us of their exact location,” he says. “We expect these turtles to reveal important foraging grounds, and help us to raise awareness of them in the marine park.”
Two turtles have been tagged by Dave’s team, they are both females that are about 60cm long and 15 years old. ‘Tracey’ was fitted with a tracking device and released at Fly Point in May, and is yet to venture further than 1km from this area. ‘Crabby’ was rescued from a crab trap off Soldiers Point and taken to Taronga Zoo’s Wildlife Hospital in Sydney for rehabilitation. Since her release in August, she has returned to the waters off Soldiers Point and has been detected there regularly.
The project has already yielded some insight into turtle movements. “We thought these turtles would move all around the Port, but it appears they like particular areas and don’t venture very far at all,” says Dave. His team will continue monitoring for the next six months, after which the tags will fall off.
Green turtles are listed as endangered on the IUCN’s Red List and classified as vulnerable in Australia.