Krokodil als zeevaarder

Nieuws | de redactie
8 juni 2010 | Zoutwater krokodillen uit India en Australië zwemmen slecht, maar zijn in staat grote afstanden over zee af te leggen. Hoe was onbekend. Dat raadsel is nu opgelost. Zij blijken een soort surfers van het dierenrijk, ook als ze 1000 kilo zwaar zijn.


Apparently, like a surfer catching a wave, these goliaths canride currents on the ocean surface to cross large areas of opensea, researchers now reveal. The saltwater or estuarine crocodile(Crocodylus porosus) is a ferocious giant that can grow atleast 23 feet long (7 meters) and weigh more than 2,200 pounds(1000 kilograms). These scaly monsters have been known to devoursharks, and even attack things they can’t eat, often assaultingboats in the mistaken belief they are rivals or prey, biting downwith nearly 2 tons of pressure – powerful enough to crush bone orpunch through aluminum hulls.

They hunt in tropical areas throughout eastern India, southeastAsia, northern Australia, and on an untold number of the islandsin-between. Although these crocodiles spend most of their lives insaltwater, they cannot be considered marine reptiles the same waysea turtles are, because the crocs rely on land for food andwater.

There were already many anecdotal accounts of large crocodilessighted far out at sea, but nothing confirmed. Now, for the firsttime, using sonar transmitters and satellite tracking, scientistsnow find that saltwater crocodiles actually do ride surface oceancurrents for long-distance travel, enabling them to voyage from oneoceanic island to another.

“Because these crocodiles are poor swimmers, it is unlikely thatthey swim across vast tracts of ocean,” said researcher HamishCampbell, a behavioral ecologist from University of Queensland inAustralia. “But they can survive for long periods in saltwaterwithout eating or drinking, so by only traveling when surfacecurrents are favorable, they would be able to move long distancesby sea.”

After they made their discovery on the river, Campbell and hiscolleagues re-analyzed archival data from the few crocodiles thathave been satellite tracked while undertaking ocean travel. Byoverlaying the reptiles’ movements with surface current estimates,they found the strategy of ocean-swimming crocodiles was similar towhat 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 25days, timing its journey to coincide with a seasonal current systemthat develops in the Gulf of Carpentaria.

Another croc – a 15.8-foot-long male (4.8 meters) – traveledmore than 255 miles (411 km) in only 20 days through the TorresStraits, which are notorious for strong water currents. When thereptile arrived at the straits, the currents were moving oppositeto his direction of travel – he then waited in a sheltered bay forfour days and only passed through the straits when the currentsswitched to favor his journey. [bron: LiveScience]

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