Summit County Citizens Voice

A saltwater crocodile in the Adelaide River, Australia. PHOTO FROM THE WIKIMEDIA COMMONS.

New research from Australia sheds light on dispersal of world’s largest reptiles across huge expanses of Pacific Ocean

By Summit Voice

SUMMIT COUNTY — Salt water crocodiles colonized large swaths of the southeastern Pacific Ocean by riding surface currents to cross big expanses of open ocean, according to a group of Australian ecologists who recently tracked 27 adult crocodiles with underwater sonar.

The crocs are found in an area extending from East India to Fiji to southern China and all the way to northern Australia. Biologists have long wondered how they spread across such a large area without diversifying into different species. The research by Dr. Hamish Campbell from University of Queensland and colleagues from Queensland Parks and Wildlife Service and Australia Zoo shows the animals can easily travel more than 500 kilometers in just a few days by finding favorable currents.

“The estuarine crocodile occurs as island populations throughout the Indian and Pacific ocean, 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,” Campbell said.

There have been many reports of large crocodiles being sighted far out to sea, but this is the first study showing that estuarine crocodiles ride surface currents during long-distance travel, which would enable them to voyage from one oceanic island and another.

“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,” Campbell said.

The researchers worked in the remote Kennedy River in North Queensland, Australia, tagging 27 adult estuarine crocodiles with sonar transmitters and using underwater receivers to track their every move over 12 month

The data showed that crocodiles always began long-distance travel within an hour of the tide changing, allowing them to go with the flow, and that they halted their journeys by hauling out on to the river bank when the tide turned against them.

The team — which included the late Steve Irwin (“The Crocodile Hunter”) — also re-analysed archival data from the few crocodiles that have been satellite tracked while undertaking ocean travel. By overlaying the crocodiles’ movements with surface current estimates they found that ocean swimming crocodiles showed a similar behavioural strategy when at sea.

One satellite-tagged crocodile left the Kennedy River and travelled 590 km over 25 days down the west coast of Cape York Peninsula timing its journey to coincide with a seasonal current system that develops in the Gulf of Carpentaria.

A second crocodile travelled more than 411 km in only 20 days from the east coast of Cape York Peninsula through the Torres Straits to the Wenlock River on the west coast of Cape York. The Torres Straits are notorious for strong water currents, and when the crocodile arrived the currents were moving opposite to its direction of travel. It waited in a sheltered bay for four days and only passed through the Straits when the currents switched to favor its journey.

Filed under: endangered species, Environment, Marine biology, Summit County Colorado, wildlife Tagged: | Australia, marine biology, saltwater crocodiles, Summit County Colorado, Summit County News, wildlife