'Salty' Aussie crocs go long-distance surfing: study

The world's biggest type of crocodile rides ocean currents for hundreds of miles (kilometres), effectively surfing to places way beyond its reach merely by swimming, a new study says.

Scientists were at a loss to explain how the estuarine or saltwater crocodile - known as "salties" in Australia - can be found across numerous South Pacific islands separated by huge expanses of water.

So the experts, including the late Australian television nature show presenter Steve Irwin, attached sonar transmitters to 27 adult specimens of the croc - Latin name Crocodylus porosus - to see exactly how they did it.

"The study demonstrates that C. porosus dramatically increase their travel potential by riding surface currents, providing an effective dispersal strategy for this species," added the researchers.

Specifically, the crocs - the world's largest living reptile - stayed near the surface when currents there were in the right direction, but dived deeper if flow direction became unfavourable."

The crocodile species can grow up to 20 feet (6.1 metres) in length. One 12.5 foot male travelled some 590 kilometres (367 miles) in 25 days, timing its journey to coincide with seasonal currents.

Another 16-footer covered more than 411 kilometres (255 miles) in just 20 days. Again, the crocodile utilised fast-moving ocean currents to reach its destination.

Hamish Campbell of the University of Queensland, said the C. posorus live in islands throughout the Indian and Pacific ocean.

"Because these crocodiles are poor swimmers, it is unlikely that they swim across vast tracts of ocean," he said of the study, published in Britain's Journal of Animal Ecology.

"But they can survive for long periods in salt-water without eating or drinking, so by only travelling when surface currents are favourable, they would be able to move long distances by sea.

"This not only helps to explains how estuarine crocodiles move between oceanic islands, but also contributes to the theory that crocodilians have crossed major marine barriers during their evolutionary past."