Shark warnings and hi-tech solutions such as underwater gliders and overhead drones may prove the best hope of reducing the number of fatal shark attacks in West Australian waters, according to researchers.
Debate over shark mitigation polarised the public and been politicised in the wake of the attack that claimed the life of 17-year-old surfer Laeticia Brouwer near Esperance.
The Liberal Federal Government seized on the issue by offering support for a shark cull, while the newly-elected Labor State Government refused to overturn its no-cull policy and called for a measured, evidence-based response.
The public remains divided, with fearful swimmers, surfers and divers split over whether killing more sharks is the best way to reduce the risk to the public.
Peter Sprivulis, a Perth-based emergency physician and professor of emergency medicine at the University of WA, is an expert on the subject of risk.
He is also a scuba diver who checks cray pots in the waters off Rottnest, and said he had shared the growing unease of many after a spate of seven fatal attacks in three years from 2011.
But unlike most of us, Professor Sprivulis carefully tested his fear against the data and applied his expertise in risk assessment to a simple question: what is the risk of a shark attack in WA?
From his analysis, he was able to predict WA would experience two fatal shark attacks each year between 2014 and 2018.
In the time since his paper was published, his predictions have been disturbingly accurate, with four fatalities in two years.
"Sadly, yes. I really think that's a consequence of people being in denial of the risk," he said.
Professor Sprivulis was able to discern risk conditions and locations he believed could warn people of the dangers.
He said he had been surprised surfers and even experienced medical colleagues seemed unaware of the risk posed by certain locations, seasons and conditions.
"If you are doing something in deep water, in water that is cool, near a source of food for a white shark, you are doing something much more dangerous than having a casual swim at the beach in the warm weather of Perth in summer," he said.
His conclusions, published in a 2014 paper, tracked the pattern of shark attacks in an effort to build an evidence-based risk profile along the WA coast.
Assessing the risk of a shark attack
Professor Sprivulis could not determine exactly when and where a shark attack would occur, but he said he could reliably predict when and where an attack was more likely.
Water temperature, depth of water and distance from shore were critical, he found.
Summer swimmers in shallow, warm water close to shore — less than 25 metres — faced a tiny risk of encountering a shark.
But if you were a diver or surfer in cold water more than 25m from the shore or more than 5m deep, the risk of attack escalated dramatically.
The risk also shifted with the location and seasons, with an attack more likely on WA's south coast and south west in winter and spring — coinciding with the migration of a growing population of humpback whales.
"There was a very strong seasonal correlation with the fatal bites from white sharks with the migration of the humpback whales down the coast in winter and spring," he said.
Professor Sprivulis said preventing individual attacks may be reliant on the future evolution of highly-effective personal protective devices to deter sharks.
But he believes people should be given clear information about the risk of shark attacks in specific areas, similar to the public bushfire warnings issued on high-risk fire days.
"I think we could be providing the same kind of real-time warnings to people who are intending to undertake activities in our wild oceans," he said.
No hard data on white shark numbers
As the debate escalated during the week, the political rhetoric papered over the big gaps in the data.
Federal Environment Minister Josh Frydenburg claimed "blind Freddie" could see the number of sharks off the WA coast had increased.
But whatever the perception, the hard data in successive studies has produce no conclusive estimate of the number of white sharks in WA waters — or whether that number is increasing, decreasing or remaining stable.
"What we do know is there is no such thing as south-west West Australian white sharks," Professor Sprivulis said.
"We know that they migrate very large distances. Our sharks turn up in South Africa, in South Australia, off the coast of Tasmania.
"I find thoughts that we might attempt to cull what is a global species, rather than a local issue, somewhat illogical."
'Not about sharks before humans'
University of Western Australia marine researcher Jessica Meeuwig believes we still know so little about the size, location and behaviour of white sharks, and that embarking on a cull would not only be irresponsible, it would waste of money on a measure that would not save lives.
Fatal shark attacks in WA since 2000
- Surfer Laeticia Brouwer: Kelp Beds, April 17, 2017
- Diver Doreen Collyer: Mindarie, June 5, 2016
- Surfer Ben Gerring: Mandurah, May 31, 2016
- Spearfisher Jay Muscat: Cheynes Beach, Dec 29, 2014
- Surfer Chris Boyd: Gracetown, Nov 23, 2013
- Surfer Ben Linden: Wedge Island, July 14, 2012
- Diver Peter Kurmann: Geographe Bay, March 31, 2012
- Diver George Wainwright: Rottnest Island, Oct 22, 2011
- Swimmer Bryn Martin: Cottesloe Beach, Oct 10, 2011
- Surfer Kyle Burden: Bunker Bay, Sept 4, 2011
- Surfer Nick Edwards: Gracetown, Aug 17, 2010
- Snorkeller Brian Guest: Port Kennedy, Dec 27, 2008
- Snorkeller Geoffrey Brazier: Abrolhos Islands, Mar 19, 2005
- Surfer Brad Smith: Gracetown, July 10, 2004
- Swimmer Ken Crew: North Cottesloe, Nov 6, 2000
Professor Meeuwig said the Barnett government's drum line policy captured no white sharks and did not reduce the risk of attacks.
"We didn't learn anything except that we're really good at catching tiger sharks," she said.
"It's not about putting sharks ahead of humans. I don't know any of my colleagues who would say that. It's about making your investments wisely, and lethal methods don't make people safer."
Professor Meeuwig said more research was desperately needed — including a resumption of shark tagging — to carefully define the risk areas and time periods.
But she said the biggest challenge was finding a way to provide real-time monitoring and alerts in remote locations like WA's south west and far south coast.
Underwater gliders currently used for mapping the sea floor could be equipped with shark detecting and alerting technology, she said.
"You could set up underwater patrols, for instance," she said.
She said aerial drones launched along regional beaches offered another potentially cost-effective means of shark surveillance in remote areas.
"The waters around Esperance are so clear that you would have no problem whatsoever identifying a shark against that turquoise and white sand background," Professor Meeuwig said.
While the debate over shark mitigation continues, Professor Sprivulis follows the advice of his own research, enjoying the ocean on days and in ways that make an unfriendly confrontation with a white shark the least likely.
"I've never been one to do anything in deep water, cooler water, at the time of year when there are lots of prey about for white sharks," he said.
"I don't think it's a wise activity."