Not all sea turtles undertake epic migrations, contrary to what you might think, a fact that could help efforts to conserve them. Green sea turtles living off the remote Cocos Islands in the Indian Ocean travel only short distances every year to new feeding grounds – a trek of between 200 and 3000 kilometres is standard for turtles in other colonies.
Scott Whiting of Biomarine International, a consultancy based at Charles Darwin University in Darwin, Australia, used satellite tracking to study six female green sea turtles breeding on North Cocos Island. After laying its eggs, each turtle swam only about 35 kilometres to feed around the South Cocos atoll, a trip that took an average of just a few days. No other tracking studies have shown turtles living in such a small area, says Whiting. He suspects the turtles do not stray far from the nesting site because they are lucky enough to have feeding grounds so close by.
The shorter migration made by the Cocos turtles would seem to give the colony an advantage as it helps to reduce the females’ stress, allowing them to breed every year and thus produce more young, Whiting says. Other sea turtles that migrate longer distances only breed once every three to nine years, as females take time to store enough energy for the epic trip. This limits the number of hatchlings and makes turtles particularly vulnerable to human activities (Naturwissenschaften, ).
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Conservation of the Cocos turtles is easier to manage than in other colonies as a result of this, because they spend their lives in an area governed by one country – Australia -rather than migrating between areas in different countries.
“It’s a fabulous finding, and they’re spot on about the conservation implications,” says Brian Bowen of the Institute of Marine Biology, University of Hawaii. However, conserving the turtles will be a moot point if there are no islands left. Whiting points out that the Cocos Islands are no more than 3 metres high, making the nesting grounds vulnerable to rising sea levels.
