The shark is well-known as a dangerous and efficient killer. But its full nature is not understood, writes Ellen Bartlett
FOR all the exposure it gets every time it bites or kills someone, the great white shark is a poorly understood animal, maligned in science and fiction alike as an evil but mindless man-eater.
Perhaps Steven Spielberg can be forgiven the flights of fancy that created “Jaws” – a defamatory monster movie if there ever was one. But many scientists also have an “oral fixation” when it comes to Carcharodon carcharias. They look at the animal and see only the mouth – the multi-hinged jaw that changes shape to accommodate any prey, the rows of triangular jagged teeth.
The result, says Leonard Compagno, head of the Shark Research Center at the South African Museum, has been the rise of what he calls a “shark-attack science culture.”
Shark research in the United States, for example, was devoted to the development and testing of shark repellants, anti-shark armour and weapons, on shark-proof bags and shark-proof bubble “curtains” to protect shipwrecked sailors.
South African scientists’ interest in sharks could be summed up in a name, the Natal Anti-Shark Measures Board (now the Natal Sharks Board), founded in the early 1960s to combat perceptions of a shark threat to Indian Ocean bathers.
“Shark attack…!” says a brochure marking 20 years of combat against the “ocean’s supreme predator.” “There are few things more spine-chilling than the thought of being mercilessly attacked, torn and savaged by a shark.”
No doubt.
But what has been missing from the equation has been the sharks themselves, as individuals and as members of a species, as behavioural beings operating in a particular environment, adhering to a particular code of conduct.
That is slowly changing with new behavioural research being conducted in Australia and the United States, and off the Cape coast by the South African Museum and the University of Cape Town.
Compagno, who is the museum’s curator of fishes as well as head of shark research, and Mark Marks, an ecological behaviourist and graduate student from northern California, are finding that far from simple-minded solitary prowlers of the deep, the white shark is a social animal that engages in a variety of behaviours and in complex interactions with others of its species, and with other animals.
“Shark study has been anthropomorphic and egocentric,” Marks says. “We’re treating the animal as a top predator, not an animal shrouded in post-“Jaws” notoriety…
“I look at the shark in the same way that I would look at a lion, or a praying mantis, or a rattlesnake or a red-tailed hawk, or a bear. All predators are pitted against the same natural limitations and factors.”
Marks spent nearly three years studying great whites off Dyer Island, 20ha of low- lying and barren rock, about 5km off the Cape coast near Gansbaai. Dyer Island is separated from a smaller island, known as Geyser Rock, across a narrow channel; the channel has long been known as a congregating area for great whites.
Observing the sharks from three vantage points – an open boat, a viewing platform on the island and an underwater shark cage – he found they not only engaged in a wide array of behaviours, but also were capable of altering their behaviour according to changing circumstances.
Marks and Compagno have compiled a list of more than 70 distinct visually-observed behaviours. To each of the behaviours they have ascribed a motive. Some are social behaviours between white sharks; others are purely predatory, between white sharks and prey; others are “asocial” behaviours in which the sharks interact with other animals, but not because they want to eat them.
That sharks can and do communicate is indisputable. “In the same way that top terrestrial predators communicate, white sharks appear to do the same,” Marks says. “What we human observers can detect are the overt visual displays, and some of them are loud and clear.”
“Gape” for example, is an aggressive message, in which the shark opens its mouth wide and protrudes its jaws to show all of its teeth. A variation is “repetitive aerial gaping,” in which the shark sticks its head out of the water and gapes several times in a row. In “hunching” the shark arches its back and flexes its pectoral fins to reveal black blotches on either side of its body. In “tail slapping” the shark proves itself capable of aiming – at observers among other things.
“Headstand” is one of the more unusual predatory acts, in which the shark is vertical in the water, head down, tail in the air. Marks observed it during an attack on a seal. “It had the seal in its mouth, and held this vertical position for about four to six seconds,” Marks says. “I don’t know what was happening below the surface, one possibility was that there was another shark down there. Perhaps the shark was displaying to the one below it.”
“Jumping over” involves a shark in a high- speed chase with a seal. The shark anticipates the seal’s attempts to outmanoeuvre it, and by mimicking the motions, outmanoeuvres the seal.
Both behaviours call into question previous descriptions of the white shark as slow and clumsy, an animal that can only catch its prey using rote ambush techniques. “The white shark is a highly manoeuvrable, fast, active predator that uses an array of techniques to catch a variety of prey,” Marks says.
But among the most intriguing behaviours are those that are non-predatory, because they corroborate the scientists’ belief that sharks are far more discriminating than they have ever been given credit for.
“Toss,” for example, is a complicated manoeuvre in which the shark catches a seal in its mouth, throws it into the air, and then leaves it. “It lets the seal swim off,” Marks says. “It wasn’t like it missed it or lost it, it was still within range of the animal.”
In “bashing” a shark approaches another animal – it could be a fellow shark, or a penguin – and strikes down on it with its upper teeth.
What is notable about penguinbashing is that a white shark could just as casually bite the penguin in two. That it does not eliminates the explanation that it is predatory behaviour and opens up a number of other possibilities – that non-fatal attacks on penguins are a form of displaced aggression, or perhaps just target practice.
“Just because they take something into their mouths doesn’t mean they’re going to eat it,” Marks says. “White sharks use their mouths as a human would use a hand. They can use very gentle pressure, as exhibited by being able to release prey from its mouth with barely a nick to the animal. The shark is exhibiting a lot of control.”
A number of behaviours are being observed for the first time. In “piggybacking”, a shark descends upon the back of another and the two swim in unison. Marks has watched sharks swim in that fashion for several metres, and then separate and swim on, staying parallel to one another. He speculates it could be a courtship-related behaviour, but cannot say for sure because he was unable to determine the sex of the two sharks.
He also has seen what he believes is evidence of co-operative hunting among white sharks – multiple shark attacks carried out on multiple seals almost simultaneously.
“I can qualitatively and quantifiably say that a white shark is a very complex predator … It exhibits such a degree of behaviours that you then have to take the next speculative leap, which is that I believe white sharks to be cognisant – and this is the real stretch of the imagination – sentient predators. Repeatedly the animals have demonstrated, for lack of a better word, body awareness, eye-tail co- ordination. I have seen individuals make decisions, go into one behaviour, change behaviours, obviously making a choice.
“Look at the spectrum of prey they are feeding on … among other things, they’re feeding on large-brained social animals, they capture dolphin, porpoise, seals, sea otters, sea birds … In order to do that you have to be able to operate on a level higher than the simple machine mentality.
“The story is by no means straightforward. To suggest that, as has been done in the past, is doing an injustice to the animal and to the science of studying him.”
Overcoming the shark stereotype has been only half the battle; the other half was conducting the study itself.
“You can spend your life studying white sharks and still not have a complete picture, because in your life it’s unlikely that you’re going to be able to spend so much as a week in the water with one animal,” he says.
There were individuals he recognised from repeated sightings over the course of the three years, but none he could say he got to know, not as Jane Goodall knew her chimpanzees, or Cynthia Moss her elephants.
White sharks are nomadic, and capable of covering enormous distances. Their migratory habits remain a mystery, as do their domestic ones, such as reproduction. “As I see it,” Marks says, “we can no better put ourselves in their shoes than they can put themselves in ours.”
Marks and Compagno stress that their research is limited to visual study of the sharks that happen to congregate in the waters off Dyer Island. It’s a little like studying long-distance truckers by watching them as they hang out at a bar on their route.
What they have learned so far tells them there is far to go.
“If you had as many people working on shark behaviour as there are on mammalian behaviour we’d know a lot more about sharks and we’d know a lot more about them intimately as behavioural animals,” Compagno says.
But one thing they can say about the subject of white shark-human interaction is that it is rare, and even more rarely fatal. Studies of the stomach contents of hundreds of white sharks have found no human remains. Statistics show that white sharks are far less dangerous to people than predators like tigers, lions, hippos, and crocodiles.
“Big sharks are a minimum danger to the
public,” says Compagno, “because they attack people so seldom.”
But when the nearly impossible does happen, that’s not much consolation, is it?