Crocodiles 'surf' the seas, study finds

Crocodiles "surf" waves to cross many miles of ocean, scientists have learned.

The discovery explains how the estuarine crocodile - the world's largest living reptile - came to colonise numerous South Pacific islands separated by huge stretches of water.

It may also account for reports of large crocodiles being sighted far out to sea.

The formidable estuarine or saltwater crocodile, whose habitat extends over more than 10,000 square kilometres of the south-east Pacific, lives mainly in rivers, mangrove swamps and estuaries.

Known as "salties" in Australia, the creatures can grow up to 20ft in length. There have been many reports of them attacking and killing humans.

Scientists have long wondered how estuarine crocodiles manage to travel so far when they are poor swimmers.

The answer, according to new findings reported today in the Journal of Animal Ecology, is that they surf.

Australian researchers tagged 27 adult crocodiles with sonar transmitters and tracked their movements over the course of a year.

Satellite data on tracked crocodiles were also analysed.

The scientists found that both male and female crocodiles understood long-distance journeys, often travelling more than 50 kilometres (31 miles) from their river homes to the open sea.

Among the team was the late Steve Irwin, the crocodile-hunting wildlife expert and TV personality who was killed by a stingray in 2006.

The evidence showed that, like surfers catching waves, the crocodiles rode the ocean currents to cross large areas of open sea.

One 12.5ft male, travelled a distance of 590 kilometres (367 miles) in 25 days, timing its journey to coincide with seasonal currents.

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

Dr Hamish Campbell, from the University of Queensland, said: "The estuarine crocodile occurs as island populations throughout the Indian and Pacific ocean, and because they are the only species of salt-water living crocodile to exist across this vast area, regular mixing between the island populations probably occurs.

"Because these crocodiles are poor swimmers, it is unlikely that they swim across vast tracts of ocean. 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."