A 4.8 m male estuarine crocodile ready for release with satellite transmitter. This crocodile traveled over 590 km by sea. (Courtesy/University of Queensland)
Next time you’re out sailing the high seas and think you’ve spotted a crocodile hanging ten, no need to get your eyes checked just yet. Turns out crocs do surf ocean currents, albeit sans boards and all the crazy wipeouts.
The behavior tracked by researchers out of Queensland, Australia, helps explain why the reptiles are so widespread, yet genetically similar.
Estuarine crocodiles which typically live in saltwater habitats like rivers and mangroves occupy a range covering about 10,000 km2 stretching from East India to Fiji and southern China to northern Australia, said the study. Geographic isolation tends to support the evolution of different species. But despite living in places separated by thousands of miles of open ocean, a crocodile living in Fiji is likely the same kind of croc living in Australia.
“The estuarine crocodile occurs as island populations throughout the Indian and Pacific Oceans, 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,” said Hamish Campbell with the University of Queensland, and study lead in a press release.
But until now, scientists weren’t sure how. Stories have floated in over the years of ocean-bound crocodiles, even though the toothy predators are no Mark Spitz when it comes to swimming. Campbell and his colleagues from Queensland Parks and Wildlife Service and Australia Zoo set out to monitor the mobile capacity of crocs. They used acoustic and satellite tracking to follow the movements of 27 adult crocodiles over the course of a year. The crocodiles revealed an astonishing range of movement, regularly traveling 50 kilometers or more from their stomping grounds to the mouth of the river and out into the sea.
Croc’s, it seems, like to “go with the flow,” according to the researchers. Tides and currents dictate the timing and extent of a crocodile’s swim, with crocs typically beginning a swim within an hour of a changing tide, following the movement of the water, and returning to shore when water is no longer headed in the desired direction. Similar behavior applies to swims in the open ocean, where crocs ride the currents.
One croc, a roughly 15-foot- long male, traveled more than 400 kilometers in 20 days from the east coast of Cape York Peninsula through the Torres Straits to the west coast of Cape York, according to the study. At one point, the croc stopped on the shore of the Torres Straits and stayed there for four days waiting for more ideal currents.
Campbell explains that this type of behavior, “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.”
The full paper is available in the British Ecological Society’s Journal of Animal Ecology.
The Nature Files 