OPINION: The secret life of sharks

OPINION: On MAR 3, 2012 | The views expressed in this opinion piece do not necessarily reflect the views of Animals Australia.
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THEY'RE our most feared predator, yet we know very little about great whites.

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I TURN my head for a moment to squint around the deep blue water, hoping to see what I know is out there. When I look back, the great white shark is surging towards me, teeth bared as its cavernous mouth snaps on the bait dangling in front of the cage. Inside, everyone instinctively pulls back in a sudden surge of fizzing bubbles as the predator shakes its prize free. And then it's gone, twisting its massive body to the right and gliding back into the blue.

Two metres below the ocean, four hours by boat out of Port Lincoln, we've just seen first-hand the speed, agility and power of a great white up close. My overwhelming impression is just how stealthy it is. I knew it was out there somewhere; I had no idea how quickly it could come at me.

It turns out there's a surprising number of things even scientists don't know about the great white. Our charter boat, the Calypso Star, is helping to find some answers. When it's not transporting thrill-seeker tourists, Calypso Star, along with Rodney Fox Shark Expeditions, is carrying researchers and helping tag dozens of white sharks (Carcharodon carcharias) off the Neptune Islands, 70km south-east of Port Lincoln, home to Australia's largest seal colony and a favourite hangout for roving great whites.

This day Calypso Star Charter's skipper Simon James reckons five sharks have turned up, the largest about 5m. Even from the safety of the cage, 40m above the sea floor, you can't feel completely comfortable.

Many of the sharks lunge and snap at the bait, all flashing teeth and tails. But one ignores the bits of tuna, and circles the cage, slowly, in a downward spiral, eyeballing us as though he is weighing up this possible prey and how to get to it. Creeped out, I'd really like to know what this one is thinking.

It's exactly the sort of question scientists are asking. "It's been a slow process getting information because they're not easy animals to work with," says Barry Bruce, a white shark expert from the Marine and Atmospheric Research department of the CSIRO in Hobart. It is striking how much we're yet to learn about these creatures which simultaneously fascinate and repulse us. There are practical reasons: the technology is expensive, the locations remote, and research money is harder to come by than it is when studying commercial fish stocks. The sharks themselves don't help. The habits and terrain of these scarce oceanic nomads are unpredictable, making them a frustratingly elusive target. White shark behaviour can't be pigeon-holed, says Bruce. "It's difficult to say they all do the same thing, because they don't all do the same thing at the same time," he says. "White sharks behave very differently in different environments and when they're preying on different things. Even the same individual will switch behaviours over a short space of time." This makes it impossible for experts to answer the one question we all want answered: why do sharks attack humans? "All we're doing is speculating," says Bruce. "There are very few patterns to work on."

What we do know is that few victims see a great white coming. This was explored at length in Coroner Anthony Schapel's inquest into the death of university student Jarrod Stehbens, killed by a shark in 2005 as he was ascending from a dive at Glenelg tyre reef, 6km offshore. Stehbens and his University of Adelaide colleagues had spent the day searching for cuttlefish eggs.

On his third dive, as Stehbens and his dive buddy Justin Rowntree ascended, a colleague aboard their small boat saw a "big grey shape" pass over the top of where they were submerged. They were 5m from the surface, on a three-minute safety stop, when the great white passed Rowntree with such force that it spun him around as it homed in on its victim. Stehbens had time to punch the 5m white pointer in the snout - stopping it momentarily - before the shark grabbed him below the knee and pulled him down. The 23-year-old was quickly, shockingly, gone. "There is no evidence as to what, if anything, caused the shark to identify Mr Stehbens in particular as an object of interest," the coroner said.

Bruce's work, tagging sharks near beaches frequented by swimmers, convinces him that sharks do not routinely and deliberately seek out humans for a meal. He tagged 18 whites in one day along a 6km stretch of beach, around Hawks Nest near Port Stephens in central NSW, "including some very close to the flagged areas". He has seen similar numbers at nearby Stockton beach. "Despite the presence of these large numbers of sharks in this area, there's never been an attack on that beach," Bruce says.

Bruce says white sharks are inquisitive creatures, and like to nose around novel objects on the water's surface that could prove to be edible. Their powerful bite is so devastating that even a curious "test" of possible prey with their razor teeth can prove fatal. But he dismisses the theory that sharks mistake humans for seals, for two reasons: the mammals form only a minor part of the white shark and bronze whaler's diet, and sharks have such acute senses, such enviable eyesight, that it is unlikely they would routinely confuse the flailing limbs of a swimmer or surfer for the sleek bodies of a familiar prey.

He also gives the rogue shark theory popularised by Jaws the flick. Given there is an average of one fatal attack around Australia each year, "by god, it must be hungry because it isn't eating much," he says. "These animals have enormously complex behaviours and we don't understand them," Bruce says. "The question that should be asked is: Why don't they attack us more? They have plenty of opportunity, but they don't."

The numbers support his question. The first record of a fatal attack in Australia was in 1791, when an Aboriginal woman was said to have been "bitten in two" at Port Jackson. Since then, there have been 884 attacks, 214 of them - or about one in four - fatal. Another 523 left survivors with injuries, and the rest proved terrifying but otherwise harmless - often because the shark was punched or somehow deterred. Great whites have been responsible for 63 deaths in Australia.

SA has seen 62 shark attacks since 1836, and 19 fatalities - each by a great white. The most recent victim was abalone diver Peter Clarkson, off Coffin Bay in February last year. His skipper Howard Rodd said the experienced diver was taken by two great whites as he was surfacing.

Bruce does not support calls for culling sharks in response to fatal attacks, for the simple reason that finding the culprit is unlikely. "Although sharks can remain resident in a region for periods of days to weeks, their movement patterns will generally take them well away from the site of an attack afterwards," he says. "So a day later a shark can be 75km-80km away."

While there are more questions than answers, years of tagging and observation have laid to rest some myths: that sharks love eating seals, and that berleying - the spreading of bloody bait mixture in the water - attracts them close to shore. Seals are only a very small part of their diet - in human terms, they spend as much time eating seals as we do eating Easter eggs.

And it seems that berleying doesn't lure all sharks within a blood-sniffing radius, although it may make sharks already in the vicinity hang around for longer than they usually might, according to Charlie Huveneers, senior shark ecologist at the South Australian Research and Development Institute and Flinders University lecturer. On one trip Huveneers was surprised to find that some sharks ignored the blood in the water. "At the same time, we also see sharks that are potentially staying at the Neptune Islands longer than they used to ... if you apply that to jetties, it might mean that berleying off jetties - not just with crabpots but even recreational fishing - might make some sharks stay around that area longer than they're used to."

The berleying research complements an earlier report, co-authored by Barry Bruce, which found that white sharks appear to be staying longer at North Neptune Island than they did a decade ago, a behaviour it links to the increase in berley activity by tourism operators since 2007. That report recommended that berleying be reduced at North Neptune, prompting authorities to halve the number of tourism permits to two operators when the existing licences expire on June 30.

SCIENTISTS have been astonished by the animals' range and confounded by their different seafaring habits in Australian waters compared with South Africa, New Zealand or California. Here, great whites seem to favour travelling in water between 60m and 120m deep, and appear to follow reefs - the remnants of ancient coastlines - which researchers think act as underwater highways that help them navigate. Sharks will swim in anything from warm beach shallows to up to 1100m down in the cold, black depths. "What they're doing at those depths is unknown; we have no idea why they go down there," says Bruce.

Sharks tagged around New Zealand and California will often make for the open ocean and can spend months roaming thousands of kilometres out to sea. They consistently cover 70km to 80km a day, occasionally taking up temporary residence for a few days or weeks in spots where the menu is especially toothsome.

Sharks in Australian waters might zip up the east coast to the Great Barrier Reef in autumn and winter and return south during spring, or follow migrating whales up the West Australian coast to Exmouth and Ningaloo Reef in spring with a return ticket booked for summer. More seem to congregate around SA's Neptune Islands in winter and spring, and follow the snapper swarming through the gulfs during spring and summer. Despite the easy pickings of New Zealand fur seals and Australian sea lions at the Neptune Islands this is only a temporary pitstop. "It's almost as if it's important physiologically to feed on seals ... but perhaps if they feed on too many they become fat and lazy," Bruce jokes.

The numbers at the Neptunes vary considerably from year to year and, he says, "sometimes you don't see any at all when you expect to see them". This happened over late 2009 going into 2010. The populations hadn't crashed, as might be assumed, they were just "somewhere else", he says. "We know there are shifts from year to year in the overall distribution of sharks," Bruce says. "We don't know what drives those patterns."

These sharks are rarely observed feeding. Unlike in South Africa, where they will leap out of the water off False Bay to snag a cape fur seal, those loitering around the Neptunes are much less frenzied and obvious in their habits. Huveneers says of the 10 times he has visited the Neptune Islands, he has only once witnessed the many sharks there capture a seal.

Most of the sharks tagged by researchers are juveniles, so their breeding habits remain a closed world. Researchers have never nabbed a pregnant great white in Australian waters (and perhaps only half a dozen have been studied worldwide). White sharks tend to produce only a handful of razor-toothed pups each litter and they don't breed often - once every three years at most. Their 1.5m, 30kg offsping - born fully-formed and independent - is the reason why female whites, contrary to many animals, grow larger than the males. Females are 5m long before they reach reproductive maturity, and 15 to 20 years old - at least halfway through their life. The largest Bruce's team has captured was a 5.3m female which weighed 1500kg, and the largest white ever measured was 6.1m, but Bruce reckons they can get up to 7m.

While Australian researchers have no idea where mating occurs, they know of at least two nurseries in Australian waters - one around Port Stephens, just north of Newcastle, and another around the Corner Inlet and 90 Mile Beach area in southeastern Victoria. Juvenile white sharks will move between these two nurseries for about five years until they are mature enough to venture into the open seas. Bruce believes it is probable there is also a nursery in SA waters because there appears to be a pupping area at the western end of the Great Australian Bight, around Fowlers Bay, west of Ceduna. This is where, after 18 months of gestation, females travel to give birth.

SINCE late December, the Department of Primary Industries and Resources' Shark Sighting Log has reported 13 sightings of great whites, including a small one 50m from shore at Victor Harbor, and others kilometres off Elliston, the Glenelg tyre reef, Streaky Bay and Coffin Bay. Shane Daw, the aerial services officer in charge of the Westpac Lifesaver Rescue Helicopter Service and state manager of Surf Life Saving South Australia, has seen barely a dozen great whites off Adelaide's beaches during 25 years of patrols. "The great whites that we're seeing close to the shorelines are probably 1 per cent out of all the sightings," he says. "The rest would be bronze whalers and hammerheads."

The yellow and red rescue helicopter is a familiar sight on summer weekends above Adelaide's beaches. The helicopter can easily make out sharks roving too close to swimmers and surfers. From the air, "bronzies" are distinctive for their slim bodies compared with the unmistakable torpedo-shaped bulk of great whites. The helicopter uses the downwash of its rotors to chase the loitering animals out to sea - sometimes encountering the same shark repeatedly over a few days. "We sight as few as 60 sharks in a year (season) up to around 140, 150 sharks in any one summer," Daw says. "On occasions, we've seen sharks within probably a couple of metres of people. They haven't been posing any threat to the people, just swimming, and we've actually seen sharks as close as you and me" - indicating across the small table - "swim straight past a person. It probably happens more than we realise."

Maria Moscaritolo for AdelaideNow

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