How crocodiles cross oceans

How did the world’s largest living
reptile, the saltwater crocodile, reach so many South
Pacific islands separated by huge stretches of water despite being a poor
swimmer?

Apparently, like a surfer catching
a wave, these goliaths can ride currents on the ocean surface
to cross large areas of open sea, researchers now reveal.

The saltwater or estuarine
crocodile is a ferocious giant that can grow at least 23 feet long and weigh
more than 2,200 pounds. These scaly monsters have been known to devour sharks,
and even attack things they can’t eat, often assaulting boats in the mistaken
belief they are rivals or prey, biting down with nearly 2 tons of pressure –
powerful enough to crush bone or punch through aluminium hulls.

These deadly predators hunt in
tropical areas throughout eastern India, southeast Asia, northern Australia,
and on an untold number of the islands in-between. Although these crocodiles
spend most of their lives in saltwater, they cannot be considered marine reptiles the same way sea turtles are, because the
crocs rely on land for food and water.

There were already many anecdotal
accounts of large crocodiles sighted far out at sea, but nothing confirmed.
Now, for the first time, using sonar transmitters and satellite tracking,
scientists now find that saltwater crocodiles actually do
ride surface ocean currents for long-distance travel, enabling them to voyage
from one oceanic island to another.

“Because these crocodiles are
poor swimmers, it is unlikely that they swim across vast tracts of ocean,”
said researcher Hamish Campbell, a behavioural ecologist from University of Queensland in Australia. “But they can
survive for long periods in saltwater without eating or drinking, so by only
travelling when surface currents are favourable, they would be able to move
long distances by sea.”

Working at the remote Kennedy River
in northeastern Australia, the team of scientists –
which included the late Steve Irwin, “The Crocodile Hunter” – tagged
27 adult seawater crocodiles with sonar transmitters, employing 20 underwater
receivers deployed along a 39-mile-long stretch of the river to track the
reptiles’ every move for more than 12 months. They found both male and female
adult crocodiles undertook long-distance journeys, regularly travelling more
than 30 miles from their home area to the river mouth and beyond into open sea.

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