Crocodiles Surf Currents to Explore Their Realm

saltwater crocodile swimming photo

Image credit: Obliot/Flickr

The estuarine crocodile, more commonly known as the "saltwater crocodile," has the largest geographic range of any crocodile species. Spanning more than 10,000 square kilometers of ocean, the crocodiles make their home from India to Australia, Indonesia to China, and have turned up as far north as the Sea of Japan and as far east as the Pacific Islands.

To occupy such a vast marine realm, the crocodiles must be excellent swimmers—at least, that is what logic would suggest. In fact, there is a problem that has trouble scientists for years: The saltwater crocodile is a sub-par long distance swimmer.

saltwater crocodile range photo

The typical range of Crocodylus porosus. Image credit: Wikimedia Commons

So how does Crocodylus porosus manage long trans-oceanic voyages to reach the far-flung limits of its realm?

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The question baffled zoologists for decades, but now the first study to track the saltwater-loving reptiles on these long journeys has revealed that, in fact, the crocodiles don't swim much at all. Instead, they use surface currents to "surf" to their destination.

saltwater croc floating photo

Image credit: Obliot/Flickr

Craig Franklin, a zoologist at the University of Queensland in Australia, explained that "crocodiles ride the currents to cut the energy costs of travelling. They get a free ride." Along with a group of researchers that originally included the late Steve Irwin, Franklin tracked 20 crocodiles with acoustic devices that emit pulses through the water.

The devices radioed the body temperature and location of each crocodile back to the research team.

saltwater croc floating photo

Image credit: Obliot/Flickr

What the data revealed was that when the current was flowing opposite the crocodile's intended direction of travel, their body temperatures rose—indicating that the animals were basking in the sun on a riverbank.

When the currents shifted, the recorded body temperatures fell, showing that the crocodiles had slipped back into the water.

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Overall, crocodiles were observed traveling with the current 96 percent of the time while making long distance journeys. This contrasted with data showing that during short trips, the crocodiles move with and against the current equally.

Hamish Campbell, one of the members of the research team, explained:

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.

It is believed that this technique could explain why the many seemingly isolated populations of estuarine crocodile have not split into divergent species.

Read more about crocodiles:
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