Our crocs know there’s no place like home


IF crocodiles weren't scary enough, new research has shown they have the intelligence to return back to their capture point, even when relocated up to 300km away.

The research from Department of Environment and Natural Resources wildlife researcher Yusuke Fukuda saw five male salties, ranging from 3.03m to 4.02m, shifted and released 100-300km from their capture sites with satellite tracking monitoring their ability to return to their capture site.

"The translocated salties were highly mobile … and moved at sea in the direction of their original capture site," he said.

"(This) complicates management interventions aimed at reducing human-crocodile conflict."

However, Cobourg Peninsula may prove a saving grace for crocodile rangers in keeping crocodiles contained to the east of the Top End.

"They were unable or unwilling to swim around a geographic structure, Cobourg Peninsula, which prevented homing being achieved in all five cases," Mr Fukuda said.

"This is in contrast to what happens in Queensland, where Cape York is not an effective barrier to crocodile movement, at least for the larger salties."

While it was not known why it posed a barrier, Mr Fuduka's research suggested "ocean currents", a "significant deep channel" on the eastern side, and weather conditions such as large tides, strong winds and the onset of the monsoon could play a part on the migration hurdle.

Tissue samples collected from crocodile nests across the NT coastline showed genetic diversity between crocodiles, confirming that Cobourg Peninsula is a barrier separating genetic stocks across the NT coast.

"This suggests that more than 250 crocodiles the NT Government removes each year from the Darwin Harbour for public safety come from the western side of the peninsula," Mr Fukuda said.

When compared with three crocodiles, released at their captured site, the displaced crocs proved to be much more mobile, with two of the three controlled crocodiles remaining near their capture and release site.