Categories of White Shark Attacks
Motivation is the key to understanding shark attacks on humans. To facilitate analysis, shark attacks are often divided into a number of discrete categories. At the International Shark Attack File (ISAF), for example, George Burgess divides unprovoked shark attacks into three broad categories: 1) Hit and Run, 2) Bump and Bite, and 3) Sneak. While these catchy titles provide neat, discrete conceptual handles for media and other lay people to grasp, Ralph Collier of the Shark Research Committee suspects that Burgess is sub-dividing different gradations of a single spectrum of unprovoked shark attacks, creating false and possibly misleading categories. Always tending toward pragmatic parsimony, Collier believes that – when it comes to shark attacks – the only meaningful distinction to be made is between provoked and unprovoked. Anything more is assuming much that is unsupported by empirical data about the attacking shark's motivational state.
A provoked shark attack may be defined as any physical contact with a human by a shark that was apparently precipitated by the former cornering, pursuing, striking, grabbing, spearing, hooking, shooting, or otherwise molesting the latter. Since any wild animal will defend itself if stricken, provoked shark attacks reflect poorly on the decision-making abilities of the human 'victim' and reveal little useful information about the motivation of an attacking shark. To deliberately provoke any shark – no matter how small or harmless it may seem – is at best unnecessary and at worst highly dangerous. To deliberately provoke a large, free-swimming White Shark can only be described as colossally stupid.
White Sharks are also infamous for their occasional attacks on boats. It has been suggested that White Sharks may sometimes attack boats because they are attracted by the electric field generated when dissimilar metals – such as the zinc or magnesium anti-rust plates on a metallic hull – corrode in seawater. This corrosion does produce a weak galvanic effect that could, conceivably, be confused with bioelectricity. However, ion-rich seawater moving through the Earth's magnetic field and populated with countless billions of bioelectricity-generating life forms generates so much background static, it seems unlikely that a shark could detect this artificial field at distances greater than 5 to 8 feet (1.5 to 2.5 metres) or so. In any case, White Shark attacks on boats have occurred off the shores of many countries, including Australia, the United States, and even Canada. For some unknown reason, False Bay, just south of Capetown, South Africa, is the White Shark boat attack 'capital' of the world. More than a dozen attacks, some of them quite fierce, have been launched by White Sharks against boats in this Bay. According to accounts in a 1978 popular book by Tim Wallett, White Sharks in False Bay have repeatedly rammed boats head-on, slammed into them broadside, and bitten the hull, swim-step, or propeller. In one particularly dramatic case, occurring August 1977 off Macassar Beach, a 16-foot (5-metre) White Shark actually leapt into a 20-foot (6-metre) ski-boat, landing almost squarely on top of Alex Mamacos, crushing his pelvis and rupturing his bladder; even in its death throes, the shark thrashed violently and savagely bit the fuel and control lines, eventually clamping down on the gunwale. In almost all cases in which a boat was attacked by a White Shark in False Bay, the vessel was actively engaged in fishing – either playing a hooked teleost sportfish or had hooked the shark which subsequently attacked the boat. Since a fish actively fighting on a line is well known to highly stimulate sharks and hooked sharks often turn on their tormentors, these boat attacks may tentatively be regarded as provoked.
Unprovoked attacks by White Sharks on humans are far more dramatic, frightening, and potentially informative than provoked attacks of any kind. An unprovoked shark attack may be defined as any contact with a human by a shark that was apparently not precipitated by any action on the part of the former. Although such is often the case, an unprovoked shark attack need not result in injury to the human; the only defining factor is the context in which the attack occurs. Why a White Shark would attack a human 'for no apparent reason' is a subject of much speculation and debate. For example, if a White Shark attacks a human 'out of the blue', whereupon the victim strikes the shark – causing it to bump, mouth, or bite in response – is the first attack unprovoked and the second provoked? Based on his four decades of research on the subject, Ralph Collier has come to believe that the nature of the initial contact can reveal the motivation of the attacking shark. Any subsequent contact or contacts by the shark may be regarded as reactions to what the victim did or, perhaps, did not do. For example, a 1981 paper Collier co-wrote with colleague Daniel Miller found some evidence suggesting that a White Shark is more likely to remain in the vicinity and attempt to inflict further bites if the victim fights back or otherwise resists the initial strike. So what motivates a White Shark to attack a human in the first place?
According to a 1996 paper by George Burgess and Matthew Callahan reviewing worldwide patterns of White Shark attacks, in 122 (92.4%) of 132 cases, the initial contact with the victim was characterized as "sudden and violent". Some researchers have suggested that sharks may become more aggressive at certain times of the year, perhaps due to endogenous hormonal cycles. While recent research by Louis Rasmussen and her co-workers has demonstrated that blood testosterone levels in some male sharks reach astronomical levels at certain times of the year, there is neither a simple nor a direct relationship between serum concentrations of testosterone and aggressive behavior. Further, any hypothesis linking testosterone levels to incidence of shark attack presupposes that these incidents are motivated by aggression – an assumption that is premature at best. Others have suggested that sharks attack humans when we blunder into their territory, much like bears, wolves, or big cats are reputed to do. Although many sharks have well-defined home ranges and there are a few anecdotes that suggest site-related aggression occurs in certain species, the evidence is far from conclusive. However, my own field research has made it clear that many sharks, like humans, have a clear sense of idiosphere, the limits of which they definitely will defend if broached – violently if necessary. But an attack resulting from such a situation is defensive in nature, and thus provoked.
Most speculations about what motivated an unprovoked White Shark attack on a human are predicated on the notion that the animal was attempting to feed on the victim. Some cases seem to strongly – and gruesomely – support this idea. The much-publicized attack on Shirley Anne Durdin provides an excellent case in point. In March 1985, Durdin was snorkelling for scallops with her husband and another man in about 7 feet (2 metres) of water in Peake Bay, just north of Port Lincoln, South Australia. Suddenly, before the eyes of her companions and several witnesses on the beach, Durdin was bitten in half and consumed by a White Shark estimated to be some 20 feet (6 metres) in length. It is difficult to regard this case as anything other than a feeding attack.
Perhaps even more compelling is the case of Theo Klein. In April 1971, Klein was swimming beyond the breakers in Buffalo Bay, South Africa, when he was attacked by a White Shark of undetermined length. Klein was disemboweled in the initial strike and collapsed within a few swim strokes. A nearby surfer, who did not witness the attack, took Klein to be a drowning victim. As the surfer paddled over to try to assist, he noted blood in the water and saw a White Shark swim between him and Klein's body. The surfer retreated and, as hundreds of horrified onlookers watched, the shark returned repeatedly and tore pieces from Klein's lifeless body. The total time between the initial attack on Klein and recovery of his badly mutilated body was about 20 minutes. What makes this case particularly interesting is that a White Shark – probably the attacking animal – swam between Klein's body and the would-be rescuer. This behavior strongly suggests competitive exclusion – that the shark was attempting to discourage access to Klein's body, which it may have regarded as a food resource.
Important New Book on Shark Attacks!
The culmination of four decades' of research by my friend and colleague Ralph Collier, President of the Shark Research Committee, this book is the first scientific study of every verified shark attack that occurred along the Pacific Coast of North America during the 20th Century. Vivid accounts of attacks by survivors, rescuers, and witnesses are punctuated with chilling, never-before published photos. Patterns in shark attacks are identified, possible motivations for attacks are discussed, and activity-specific safety guidelines for swimmers, divers, surfers, and sea kayakers are offered. The individual case histories are fascinating; the general conclusions and safety guidelines are applicable word-wide. If you are interested in Great Whites or shark attacks, this is a Must Have book.