G is for Green Turtle
Seafaring turtles may use smell to navigate during the epic ocean voyages they undertake to reach their breeding grounds, suggests a new satellite-tracking study.
Green turtles swim over 2200 kilometres from foraging grounds in Brazil to nest on Ascension Island, which sits in the middle of the Atlantic Ocean. How they find their way has puzzled scientists since Darwin.
Now Graeme Hays, at the University of Wales Swansea, and colleagues have shown that sniffing the air is at least part of the answer. The researchers abandoned turtles in the sea 50 kilometres from the island and found that those left downwind returned much more quickly.
“The hypothesis was confirmed.” says Annette Broderick, one of the Swansea. “There’s some smell off the island.”
“It’s an extremely useful idea” for explaining how the turtles navigate, says Michael Salmon, a sea turtle expert at Florida Atlantic University in the US. He thinks the olfactory cues might include odours from the beaches or vegetation. He notes that homing pigeons, some seabirds and salmon have also been shown to use smell as a navigation tool.
Lost at sea
Hays, Broderick and colleagues attached satellite transmitters to six female Chelonia mydas turtles which had just finished nesting on Ascension Island.
They then took the turtles by ship and left three 50 kilometres downwind of the island, to the north-west. These turtles found their way back easily, returning within one, two and four days.
The other three turtles were released 50 kilometres upwind, to the south-east. Two of these turtles managed to return after 10 and 27 days. But, after a frustrating 59 days looking for the tiny island, the third headed westwards back towards Brazil.
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