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Shark!

Colin Rowland was surfing about 100 kilometres up the coast from Port Stephens in NSW in December when a great white shark smashed into his board, propelling him metres into the air then dragging him and his board underwater.

Lisa Mondy was wakeboarding inside the heads at Port Stephens in 2011 when a great white shark surged from below and sent her flying. "At first, I actually thought I might have been hit by a boat," she says, "because it just hit so fast."

Both attacks prompted the usual media frenzy guaranteed to accompany almost any event involving sharks – and to bemuse and frustrate scientists and others angling to keep things in perspective.

Including Rowland's encounter, there have been 13 shark attacks on humans in the past two years on the northern NSW coast, leading to one death and prompting demands for action and explanations from scientists.

There were 36 unprovoked shark bites recorded in Australia in 2015 and 2016, three of them – one in Ballina and two in WA – were fatal.

Meanwhile, sightings of sharks off Victoria's Great Ocean Road and other beaches over Christmas have cut through any complacency among holiday-makers there.

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As summer draws millions of Australians to the beach, swimmers and surfers will be wondering if all the reported bites and sightings have raised the odds that a similar fate could await them when they plunge into the surf.

What's going on beneath our waves?

Taste testing

The teeth marks etched from Mondy's face down to her left arm told marine experts the shark that bit her was about four metres long.

That's on the large side: most white shark bites on humans involve juvenile or sub-adults of less than three metres in length, as are those animals that are tagged and released by authorities.

Rowland, who had surfed for five decades without seeing a shark, found himself surrounded by a pod of dolphins moments before a white shark rammed into his board at Bulls Park, off the Booti Booti National Park in NSW.

It's highly likely those mammals knew a major predator was nearby, one scientist says. Whether the shark – perhaps 3metres long – mistook him for its intended prey can't be known, although a shark's eyesight is not its strongest sense.

Rowland was pulled underwater by his leg rope and surfaced with lacerations to his foot as he kicked the shark in a bid to break free.

"The shark didn't really bite him," the scientist says. "He was incredibly lucky."

In fact, Rowland's encounter was not that uncommon among shark attacks, even fatal ones: most bites on humans are relatively gentle – by shark standards – implying a test or even a taste on the part of the predator.

As sharks grow larger, they need to "transition" from fish to fattier, more energy-rich prey such as seals and whales, says Nathan Hart, associate professor of biological sciences at Macquarie University. Juveniles are still learning what to eat and humans would hardly have featured on sharks' evolutionary menu that stretches back 400 million years.

Dr Barry Bruce, a senior CSIRO shark researcher, said sharks could be expected to vary their behaviour – depending on whether they were targeting a seal or a snapper or a ray.

It would also be wrong to consider all aggressive interactions to be about feeding – whether by sharks or other wildlife.

"There are many examples of sharks aggressively rushing someone on the surface, swimming, or on a surfboard, or underwater – yet they don't bite," Bruce says.

In some cases, it's a single bite, others involve several bites, and there are even cases of a surfboard being aggressively attacked when its owner has been rescued.

Between 1830 and 2015, 216 attacks in Australian waters were attributed to white sharks. Of the 182 cases where the number of bites were recorded, 114 – or almost two-thirds – involved just the single bite, according to Australian Shark Attack File data.

"Are all of these cases of predation or, in some instances, do sharks just not want us in their personal space? And how would we know?" Bruce says.

Other research also suggests that, rather than being attracted or stimulated by human blood, most sharks biting humans seem to sample and move on, which challenges the notion that human blood in the water is a shark "magnet".

In Mondy's case, as she struggled in the water, she still didn't realise she had been bitten until "I looked down towards my arm and – this is a bit graphic – but I honestly couldn't see through the water because of all the blood."

Luckily for her, the shark didn't return.

Encouragingly for those who rescue stricken surfers or swimmers there are few accounts of a second person being bitten, blood in the water or not.

Mondy, who was 24 at the time of the attack, attributes her survival to the quick response by those in the wakeboarding boat and the Westpac rescue helicopter, as well as to the surgeons who toiled for 16 hours at Newcastle's John Hunter Hospital to save her arm and her life.

Number crunching

After the recent series of shark bites off NSW, the Baird government stepped up its research on sharks, including expanded tagging of sharks caught on so-called smart drum lines arrayed along the coast.

The Rowland incident prompted the government to announce the deployment of five of those lines – baited hooks trailing from drums that send a signal when an animal is caught – within hours of the attack, even though the beach had never reported a shark bite before.

The NSW Department of Primary Industries (DPI) has tagged 68 white sharks and 88 bull sharks with tracking devices before releasing them since August 2015.

Of sharks tagged in the current program, "most have been less than three metres", says CSIRO's Bruce, who has studied whites for three decades. Soon after shark nets and drum lines were introduced to the Ballina region, four whites measuring three metres or less were tagged and released, and a fifth was 3.2 metres.

Despite descriptions of those sharks as "massive", they are well shy of adult size. A female white will typically grow to about five metres before it starts to reproduce, a process that can take 40-50 years, says Bruce. Even then, female great whites may produce offspring only every two or three years, with a litter of about 10 pups. Whites, bulls and other large sharks are apex predators, which don't reproduce often in any case – part of nature's way of maintaining balance in an ecosystem.

"Adult female white sharks are big – at greater than five metres – and rarely caught, indeed rarely seen," Bruce says. "Less than 3 per cent of all white sharks sighted at the Neptune Islands, the site of cage diving in South Australia, are adult females, and this is similar to other such areas in the world."

Despite sharks' natural dominance of their domain, a quarter of the world's 1200 species are vulnerable, with another predator – humans – killing tens of millions, perhaps even 100 million sharks every year. The losses are from deliberate targeting of sharks such as for their fins – a favourite in east Asian cuisine – but also from fishing bycatch.

"We know larger size makes them more vulnerable," says Colin Simpfendorfer, director of the Centre for Sustainable Tropical Fisheries and Aquaculture at James Cook University. This is why great whites have been protected in Australian waters for the past two decades.

Despite anecdotal evidence that white shark numbers are on the increase – perhaps even surging in regions such as off Ballina – there is little science to back that up.

Whale numbers, which have been rapidly recovering after the end of most whaling, may help account for a build-up of shark numbers but do not explain why shark bites have clustered in one part of the coast.

Vic Peddemors, a DPI senior research scientist, told a CoastalWatch audience in October that the breeding population in Australia probably totals about 1500 whites. These are split into two distinct populations – those swimming westward from Bass Strait all the way to Western Australia and beyond, and an eastern group circling Tasmania and ranging up to Queensland and as far east as New Zealand.

"It certainly looks like the east coast population [of whites] to be less than 6000," Peddemors told the gathering in Ballina, citing genetic studies that can extrapolate from close kin relations. As for population trends, "if you squint a bit, you start to see, in the last couple of years, a slight increase", Bruce says. A gain, of course, was "the objective of the protection".

As Peddemors told the Ballina group, the government stepping up aerial surveys means "we're seeing sharks everywhere". "We're looking more – is that why we're seeing more?"

A shore thing

Shark counts are one thing but scientists are also trying to understand why there appears to be more movement of the mostly juvenile whites to inshore waters – and apparently to areas such as the Ballina-Byron region.

"We know so little about white shark movements and it surprises just about everyone," Peddemors told the group, later adding "these animals are just mooching along really close to shore and we don't know what they are doing".

One theory being explored is whether changes in the East Australian Current, which is strengthening and pushing further south with climate change, may be a factor in producing more upwellings of plankton-rich cooler waters, favoured by sharks, along parts of the coast. WA's Department of Fisheries has speculated that a jump in shark bites in the state's south-west in 2011 may have been triggered by a marine heatwave further up that state's coast, prompting whites to move further south.

Researchers at the Sydney Institute of Marine Science and Macquarie University are also investigating whether water temperatures may be a guide to shark movements.

Bruce, though, is doubtful that the evidence is there to support such links to temperature. "There have been some upwelling events in the past when there've been no shark attacks," he says.

In any case, the chances of bites – and fatalities – remain tiny. As the Australian Shark Attack File maintained by associates of Taronga Zoo notes, over the past half century, 47 deaths have been blamed on unprovoked shark bites, or slightly fewer than one per year. Visits to Australian beaches are now roughly 100 million a year.

"You're more likely to get killed by bees or by horses than by sharks," says Culum Brown, an associate professor at Macquarie University.

To net, or not

The shark attacks, though, have undoubtedly caused widespread anxiety in the northern coastal towns of NSW, prompting the Baird government to backflip on its opposition to introducing shark nets to the region.

"We've been described as 'the shark attack capital of the world' and that it's dangerous to go into the water," says Donny Munro, president of the local Le-Ba Boardriders Club, which covers the Lennox Head-Ballina strip of beaches.

Munro, whose work involves supplying the surfing industry, is one of many with falling revenues as surf tourism takes a dumping from the media focus on the region.

The government has now begun to install seven nets on five beaches in a bid to restore confidence, a move that can't come soon enough for Munro. "We stand to lose a whole generation of young kids who won't surf," he says.

Munro and his daughter had their own close call recently when a very large shark came within metres of them as they surfed. "People on the beach were going berserk," he says.

Supporters of shark nets say it was unfair that beaches from Wollongong to Newcastle and much of Sydney had been protected by nets since the 1930s, but northern beaches hadn't enjoyed the safety.

"People are feeling like they're used as an experiment with modern technology," Phil Myers, a local surfer, told the CoastalWatch group.

An oft-repeated statistic is that there's been only one death at a netted beach in NSW – in 1951 at Merewether near Newcastle. That death was attributed to a white but is hard to confirm, Bruce says.

Scientists such as Simpfendorfer say it's impossible to know whether there would have been more deaths without the nets. Greater lifesaving and other surveillance efforts are likely to be in place at those more populous beaches, with medical teams often not too far away too.

The nets rarely encompass a beach. Instead, they are typically 150-200 metres long and six metres high, sitting in 10-12 metres or deeper waters. Creatures can swim around, over or under them.

"According to the data, 17 per cent of attacks in NSW have been on netted beaches since the program began," Bruce says, adding that seven of the attacks were by whites and more than a third attributed to small wobbegong sharks.

Professor Hart, from Macquarie University, says the decision to introduce the nets to northern NSW was "largely political and not necessarily based on science".

Fear fighters

Shark researchers such as Professor Chris Lowe at the University of California note that no US beaches are netted. "The most popular beaches tend to be the safest places and [this] argues against sharks being out to eat humans," Lowe says. "If they were, these places would be Costco for sharks – one-stop shopping. We don't see that."

Bruce is doubtful that large crowds necessarily scare off sharks, noting that marine life is often severely depleted near urban areas where beachgoers tend to congregate.

That's also one reason why more remote places such as Ballina are so attractive to sharks – the region is famous for its fishing and other marine life such as fish, turtles and dolphins.

"It's always been a shark hot spot," Bruce says. "Just why we get these clusters of shark attacks every so often, that's the question that we don't have the answer for."

Advances in technology, such as tagged sharks setting off warning sensors, do point towards safer conditions.

Still, Bruce has some concerns about having ever more information. For instance, people might avoid a beach with a tagged shark detected nearby but instead unwittingly swim in an area with more untagged sharks.

Surfers and swimmers may take greater risks, too, if they are carrying shark repellents such as electronic devices which may anyway have only a limited deterrent effect on a "really motivated" animal.

"One of the real challenges in the future is not so much what we can do to mitigate the chance of a shark attack but how we mitigate the fear by telling them every day there's a shark near them," Bruce says. "There was probably always a shark near them [in the past]; they didn't know, and nothing happened."

Mondy and Rowland share some of these sentiments about recognising the ocean as the domain of sharks and other wildlife.

For Rowland, the allure of the surf is undiminished. Still recovering from his injuries, he says: "As soon as I can stand on my back foot, on the back of my surfboard, I'll be back out there."

Mondy has not just overcome her fear of sharks but has got into shark cages to see whites up close. "I scuba dive and snorkel with grey nurse sharks quite often," she says. "I absolutely love it."

On the day we speak with Mondy, she is at a rally protesting against shark nets. "I still know that shark nets aren't keeping us safe and they have no place in our waters," she says. "Most of what's caught in the nets poses no risk to humans and the toll on the wildlife ... I think we can do better than that in this day and age."