Yahoo! News
Secret Revealed: How Crocodiles Cross Oceans
Charles Q. Choi
LiveScience Contributor
LiveScience.com charles Q. Choi
livescience Contributor
livescience.com Mon Jun 7, 1:06 pm ET

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 (Crocodylus porosus) is a ferocious
giant that can grow at least 23 feet long (7 meters) and weigh more than
2,200 pounds (1000 kilograms). 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 aluminum 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
behavioral ecologist from University of Queensland in Australia. "But
they can survive for long periods in saltwater without eating or
drinking, so by only traveling when surface currents are favorable, they
would be able to move long distances by sea."

Crocodile river travel

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 (63 km) to track the reptiles' every move for more than 12
months. They found both male and female adult crocodiles undertook long-
distance journeys, regularly traveling more than 30 miles (48 km) from
their home area to the river mouth and beyond into open sea.

The scientists also discovered the "salties" always began long-distance
travel within an hour of the tide changing, allowing them to go with the
flow. They halted their journeys by hauling out onto the river bank or
diving to the river bottom when the currents turned against them.

The researchers originally were just aiming to investigate the
territorial habits of the crocodiles and how they divvied up land among
themselves.

"I never thought they would be making these long-distance journeys out to
sea," Campbell told LiveScience.

Riding ocean currents

After they made their discovery on the river, Campbell and his colleagues
re-analyzed archival data from the few crocodiles that have been
satellite tracked while undertaking ocean travel. By overlaying the
reptiles' movements with surface current estimates, they found the
strategy of ocean-swimming crocodiles was similar to what they employed
with rivers.

One satellite-tagged crocodile, 12.6-foot-long male (3.8 meters) - left
the Kennedy River and travelled 366 miles (590 km) over 25 days, timing
its journey to coincide with a seasonal current system that develops in
the Gulf of Carpentaria.

Another croc - a 15.8-foot-long male (4.8 meters) - traveled more than
255 miles (411 km) in only 20 days through the Torres Straits, which are
notorious for strong water currents. When the reptile arrived at the
straits, the currents were moving opposite to his direction of travel -
he then waited in a sheltered bay for four days and only passed through
the straits when the currents switched to favor his journey.

These findings could explain why this crocodile species did not split
into many other species despite occupying islands across such a large
range, where in principle populations could have been isolated and
diverged from their relatives over time.

"Regular mixing between the island populations probably occurs," Campbell
said. "Crocodilians have crossed major marine barriers during their
evolutionary past."

Although scientists now know that salties seem to make long-distance
journeys on purpose, "we presently do not know what these are for,"
Campbell noted. However, it was recently discovered that considerable
numbers of the reptiles congregated to feast on an annual fish migration,
so these long trips might be a way for the predators to satisfy their
hefty appetites.

The scientists will detail their findings June 8 in the Journal of Animal
Ecology.

http://news.yahoo.com/s/livescience/secretrevealedhowcrocodilescrossocean
s/print