| Aussie turtles 'ride the EAC' to Peru|
|A marine biologist has helped fill in the so-called lost years of Australia's loggerhead turtles by discovering they are using ocean currents to undertake a 20,000-kilometre, round trip across the Pacific Ocean.|
Dr Michelle Boyle, of the School of Marine and Tropical Ecology at James Cook University, Queensland, and colleagues used genetic testing to track the migratory behaviour of the Australian-born loggerhead turtle (Caretta caretta), which hatches in rookeries on the Queensland coast.
Boyle says it appears the endangered turtles use the ocean currents that make up the South Pacific gyre to travel across the southern Pacific Ocean to the waters off Peru and Chile.
She says when the baby turtles hatch at Mon Repos beach near Bundaberg they head to the water and swim out to sea.
In scenes reminiscent of the animated movie Finding Nemo, they then pick up the East Australian Current (EAC), which they "ride" down the coast of eastern Australia.
"After the EAC swings away from the Australian coast, post-hatchlings using this current for transportation will most likely be directed eastwards into the Tasman Front," she says in the paper published in the recent Proceedings of the Royal Society B.
This current takes them past Lord Howe Island and to the north of New Zealand, across the southern Pacific Ocean, to the waters off the coast of Peru and Chile via the Humboldt Current.
Many unanswered questions
She says if the now juvenile turtles maintain their association with the South Pacific gyre, it "could be assumed that they return to coastal Australia waters via the SEC (southern equatorial current)".
Boyle concedes the research does leave many questions unanswered.
She says it is not known how long the journey takes, or how much of the turtles' migration is swimming and how much is passive movement with the current.
But, Boyle's finding do fill in some gaps in what is traditionally known as the "lost years" of the loggerhead.
"No one knew where they went or how long they went for," says Boyle, who adds there is currently no way of calculating the age of sea turtles.
When the turtles leave the Australian coast they measure about 5 centimetres in length, she says.
However they do not return to the Queensland coast until they are about 70-centimetre-long juveniles.
They then live in the coastal waters until ready to breed when they are about 30 years old.
To confirm the Pacific Ocean migration theory, Boyle used a variety of approaches that focused on the movement of the turtle in its post-hatchling life stage in the South Pacific.
She also took tissue samples from post-hatchlings that were found stranded on the Australian coast between 1996 and 2004, and from turtles captured in long-line fishing vessels operating off the Peruvian coast during 2002-2005.
Genetic analysis of the mitochondrial DNA haplotypes showed the South American turtles shared the same genetic background as hatchlings from the eastern Australian coast.
Boyle says while it may be hypothesised that the turtles return to Australian waters via the SEC, this needs to be verified using satellite technology to track the journey of open-ocean loggerheads.
The annual nesting population of loggerhead turtles in eastern Australia has dropped by 86% over the past three decades, the paper says.
However Boyle says improved habitat protection and the compulsory use of turtle excluder devices on trawl nets operating in Queensland waters has helped lift numbers.
She says her study highlights the need for international collaborations when developing management efforts.