Shark study to unlock secrets

Three nautical miles off Rottnest, a team of WA scientists crowds around a computer monitor as a line of submerged buoys looms into view.

Forty-five metres beneath the bobbing vessel a remotely operated vehicle - essentially an unmanned submarine - steadily approaches the line tethering the buoys to the sea floor.

With a deftness that occurs naturally among the video game generation, Department of Fisheries technical officer Silas Mountford angles a joystick until a hook on the ROV locks on to the line.

At the press of a button, a robotic blade snips the line and 30 seconds later, the buoys break the surface.

Covered in a year's worth of barnacles and seaweed, they resemble any rock lobster buoys but their bounty is so much more valuable.

A subsea data-recording acoustic receiver has detected every tagged shark or big fish swimming within 500m during the past 12 to 14 months.

This is world-leading stuff.

No other scientific outfit is using ROVs to harvest data from acoustic receivers.

The department's principal shark researcher Rory McAuley got the idea after using ROVs to survey wellheads as an oil and gas technician in the North Sea 25 years ago, but can't believe the technology at his disposal in his current job mapping WA's shark population.

"Ten years ago this would have been outside my wildest dreams of what was possible," he said.


The array of receivers placed 800m apart off Rottnest have been supplied by the Canadian Government as part of its ocean tracking network charting aquatic species globally.

The OTN dovetailed nicely into the WA Government's shark monitoring network, launched in 2009 and beefed up after a spate of shark attacks in 2011-12.

Between them, the OTN and SMN account for 240 acoustic receivers off the WA coast to monitor the movements of big sharks, mainly the great white.

Years of data is being analysed to produce the department's globally-anticipated study of the species, due out this year.

"What we are hoping to find out is when, where and why white sharks are moving along the WA coast and therefore when, where and why the risk of encountering them might be higher," Dr McAuley said.

Since 2009 there have been 15,000 individual detections of tagged great white sharks along WA's coast. "Already we're starting to see that sharks are coming close to people far more than what the bite statistics indicate," Dr McAuley said.