Homing crocodile: One of the crocodiles in the study is captured prior to relocation. 'Crocodile hunter' Steve Irwin is one of the authors behind the research.

Credit: Craig Franklin

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PERTH: Relocated saltwater crocodiles have been found to rapidly navigate vast tracts of open ocean to return home, according to a satellite tracking study.

A team of Australian scientists report that one crocodile made an astonishing journey of over 400 km in 20 days, which included circumnavigating Queensland's Cape York Peninsula. Crocodiles have the homing skills and stamina to swim between 10 and 30 km a day to travel back to their original capture sites, they said.

"We often thought crocodiles tired very quickly, but here we show very clearly that they are capable of moving marathon distances for days on end," said zoologist and lead author Craig Franklin, of the University of Queensland in Brisbane.

Relocation issues

The discovery suggests that moving 'problem' animals to remote river systems is not an effective solution. "Moving crocodiles to isolated waterholes which are surrounded by land might prove to be an effective impediment to them returning home," said Franklin.

For the study – which is detailed in the open-access journal PloS One – a team of wildlife scientists captured three, large, male saltwater crocodiles (Crocodylus porosus) in northern Queensland. They were then moved by helicopter to remote locations between 50 and 130 km from their capture sites.

Over the next few weeks the researchers used satellite tracking systems (tags, strapped to the back of their heads) to follow the path the animals took. Though the crocodiles spent a little time poking around their new residences, they were able to rapidly and purposefully negotiate open seas and coastlines to return to their original locations.

Nifty navigators

The study represents the first time that GPS technology has been used to track the movements of crocodiles. Crocodiles are renowned for being secretive and difficult to track, said Franklin, and satellite devices provided access to the animal's movements in difficult to access locations, such as along the coastline and in open oceans.

Franklin believes that the crocs may be using a suite of factors for orientation and navigational purposes. These might include: the position of the Sun, the Earth's magnetic field and other clues such as visual landmarks and smells. Though migratory navigation is well understood in turtle and birds, which are related species, further studies are needed to explain the phenomenon in crocodiles.

The study was a collaboration between researchers at the University of Queensland, Australia Zoo and Queensland Parks and Wildlife Service, with the late 'crocodile hunter', Steve Irwin as a major driving force.