Sharks' winter holidays revealed
Scientists have found New Zealand's great white sharks are seeking relaxation in warmer climates as far away as Australia and New Caledonia.
The National Institute for Water and Atmospheric Research (Niwa) said data obtained recently from tags placed on great whites has turned up interesting results on the distances sharks travel each season.
While scientists knew great white sharks generally left New Zealand shores during winter, in June or July, the data has found in some cases they swim all the way to tropical waters such as Tonga, New Caledonia and the Great Barrier Reef.
"Ella, a 4.4 metre-long great white shark was tracked from Stewart Island to New Caledonia in both 2009 and 2011," said NIWA Principal Scientist Dr Malcolm Francis.
Another large great white shark, Phred, which was 4.8 metres long, was also tracked to Chesterfield Reef, in New Caledonia, in 2009.
The data showing their migratory patterns from years past had only just been downloaded off receivers set across Australia and the Coral Sea. It has provided the second year of stats on the movements of great white sharks in the Pacific area.
Niwa said there were seven receivers set up at the Chesterfield Reefs in the Coral Sea.
The receivers detected the acoustically tagged sharks as they travelled past them.
There were 46 acoustic receivers off Sydney in Australia with thirty-six of them arranged in a line between Bondi Beach out to the edge of the continental shelf.
The data has shown that an unnamed male shark had travelled from Stewart Island, where it was tagged in March last year, to the Chesterfield Reefs seven months later.
Francis said one shark in particular had achieved some serious mileage.
"In February 2012 a 2.8 metre-long shark known as Meadsy was picked up on a receiver 10 kilometres off Bondi Beach.
"It was picked up again at Stewart Island in March 2012 by our receiver array, having crossed the Tasman Sea in 21 days at an average speed of 96 kilometres per day."
The tracking project is a collaboration between Niwa, the Department of Conservation and Auckland University scientists.
They are hoping to be able to use the information to find out the size of the population of great whites in New Zealand waters, as well as narrow down the times they like to inhabit "hotspots" such as Stewart Island.
Scientists said last year that great whites left our shores at the end of June and started coming back between December and May.
Many of the same sharks were seen every year at Stewart Island, indicating an "amazing ability" to navigate back to the same spot after travelling thousands of kilometres across open ocean.
- © Fairfax NZ News
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