Reply to Second Post on 06/29

…in the case of Mistaken Identity people are putting forward a theory that claims a shark with all its amazing sensory equipment and knowledge of prey can't tell the difference between a seal and a human being or other creatures!

Actually MI theory offers that sharks know the difference and choose not to attack because they're not interested in humans and most of the 100 or so attacks that happen annually are cases where they make a mistake. If swimmers knew how many times they had been checked out by a large shark and rejected they would never go back in the water again.

Maybe with less developed/smaller sharks but I doubt the great white swims around with its sensory system on standby mode or indeed turned off.

Define "less developed."

Sharks that aren't by their nature or evolution designed to hunt and kill specific difficult and dangerous prey like the white shark and therefore can be far less selective in their choice of prey and far less cautious in approach, therefore will attack and almost eat anything regardless, without any degree of thought or use even of sensory equipment. The white shark can't afford to be casual, to be mistaken.

Who said anything about a "standby mode?" MI doesn't mean you turn off your vision it means your vision is tricked.

Tricked by what, not that silhouette again. There is enough evidence on film that suggests the white shark will often get up close and personal with prey to size it up before striking, sometimes without the potential victim even realising and sometimes to even say hello to the potential victim. It has done this with seals before, swimming among them alerting them of its presence. Perhaps to panic them and force a break up so one becomes isolated and thus become easier to target. For all we know, a shark that has attacked a human, may have taken a good look from a distance of say 10-20 feet before striking, surely enough with its sight and all those other senses to make an informed decision as to whether this thing is a seal or some other creature. An attack on a human cannot be a simple case of MI, there must be more to it than that, surely. A human struggling at the surface splashing about is not some rubber seal being towed behind a boat at 30 nots at Dyer Island.

White Shark Attacks: Mistaken Identity or Something Else?

Clearly, White Sharks are capable of killing and consuming humans. But if White Sharks regard humans as 'fair game', why are so few people attacked by them each year? There is a widely repeated speculation that humans are attacked by White Sharks because - cruising along the bottom, some 60 feet (20 metres) or so below the surface - these predators occasionally mistake the silhouette of floating divers or surfboards for that of pinnipeds (seals and sea lions). Thus, according to this idea, humans are sometimes bitten by accident because we happen to resemble normal White Shark food in approximate size and shape. To put this another, more playful way:

The Great White Shark jangles our nerves With a reputation he hardly deserves Neither malice nor spite Will cause him to bite It's not his fault we look like hors d'oeuvres

According to a 1996 paper by George Burgess and Matthew Callahan reviewing worldwide patterns of White Shark attacks, of 157 cases only 41 (26%) were fatal. Although in some cases the victim's body is never recovered, the available data strongly suggest that very, very few of them were actually consumed by their attacker. How can a slow, 150- to 250-pound (70- to 110-kilogram), unarmed and barely-able-to-see primate so commonly escape a fast, 2,000- to 4,000-pound (900- to 1,800-kilogram) shark, equipped with a mouthful of razor-sharp, serrated teeth and exquisitely sensitive food-finding systems? In an influential 1985 paper, ichthyologist John McCosker proposed an answer to this mystery - the so-called "Bite and Spit" hypothesis. According to this scenario, a White Shark's usual strategy when preying upon pinnipeds features immobilizing the seal or sea lion with a massive, incapacitating bite, and then releasing it, whereupon the shark remains nearby at a safe distance, waiting for its prey to bleed to death before returning to feed. This pause between attacking and feeding allows the victim's brave companion(s) to effect his or her rescue, thereby short-circuiting the White Shark's feeding strategy. McCosker's nifty theory seemed to explain why so many human victims escape White Shark attacks relatively unscathed and fit the case histories accumulated up to that time reasonably well.

The 'Bite and Spit' strategy proposed by McCosker may well characterize the normal predatory behavior of White Sharks when attacking particularly huge and powerful pinnipeds, such as the Northern Elephant Seal (Mirounga angustirostris) - which may grow to 21 feet (6.4 metres) long and over 8,800 pounds (4,000 kilograms) in weight. However, recent observations in the wild of White Shark predatory attacks on smaller - more human-sized - pinnipeds indicate that, in many cases, there is often little or no hesitation between the shark's initial strike and consuming its prey. For example, when attacking a California Sea Lion (Zalophus californianus) at the surface, the White Shark is typically all business: smashing into the hapless animal with tremendous force - often lifting the 200- to 600-pound (100- to 300-kilogram) pinniped three feet (one metre) or more out of the water - typically knocking it unconscious or killing it outright in the initial strike, then promptly eating the carcass in two to five or so massive bites. In marked contrast to this apparently normal feeding behavior, a 1996 paper by McCosker and fellow ichthyologist Robert Lea analyzing 27 recent cases of White Shark attacks in the eastern Pacific reported that 15 (56%) resulted in "minor wounds, if any". Similarly, a 1996 paper by Marie Levine analyzing unprovoked White Shark attacks off the South African coast reported that of 63 cases, 29 (46%) of the victims were "bitten but sustained no tissue loss." None whatever! Why does the White Shark almost never capture and consume humans with the same fearsome efficiency with which it does pinnipeds?

As mentioned earlier, Ralph Collier believes that the character of the initial strike by an unprovoked White Shark reveals much about its motivation. The very swift, violent, and ultimately fatal attacks on Shirley Anne Durdin and Theo Klein - which resulted in the victim, or a significant portion thereof, being consumed by the attacking shark - seem very likely to have been motivated by feeding. Yet about half of initial strikes against humans by unprovoked White Sharks are astonishingly gentle compared with the grievous damage these huge and powerful predators are clearly capable of inflicting. Consider the following cases:

• Rodney Orr, September 1990, off Jenner, California: while ventilating his lungs in preparation for a breath-hold dive, Orr was seized by the head and carried some 60 feet (18 metres) then released by a large White Shark; although the shark could have easily crushed his skull like an eggshell, Orr sustained only minor cuts to his face and neck.
• Heather Boswell, March 1994, offshore Chile: while taking an open ocean swim from a ship some 300 miles (480 kilometres) off the coast of Chile, Boswell was gently nibbled and released by a 12-foot (3.6-metre) White Shark which then casually circled around and bit her left leg, severing it above the knee before she could be pulled from the water; considering that the shark had the means and plenty of opportunity to remove large, bite-sized pieces and even consume her outright, Boswell got off remarkably lightly.
• Lewis Boren, December 1981, Spanish Bay, California: Boren disappeared while surfing; the next day, his surfboard washed ashore with a huge semi-circular bite removed, and the day after that, his body was recovered in much the same condition; from examination of the bites on the surfboard and Boren's body, Ralph Collier identified the attacker as a huge White Shark, perhaps as much as 23 feet (7 metres) in length - such an animal could easily have swallowed Boren whole, yet only a single (if devastating) bite had been removed, without evidence that the shark attempted any additional bites.

Or, perhaps most remarkable of all:

• Craig Rogers, August 1987, Tunitas Beach, California: Rogers' surfboard was grasped for 2 to 3 seconds by a 17-foot (5.2-metre) White Shark, resulting in a minor cut to his little finger as the shark's lateral teeth raked across the surfboard; surfboards are inherently unstable (overcoming this attribute is, of course, the very essence of the sport), yet Rogers' board was grasped by the shark so gently that no splash was produced and Rogers was not tipped from it - in fact, his first hint that the shark was there at all occurred when his board simply stopped moving, whereupon he turned around and saw the 2.5-foot- (0.8-metre-) wide head of the shark holding his board firmly between its teeth (two of which were left embedded in Rogers' board, confirming the species and size of shark).

It seems reasonable that these astonishingly 'gentle' attacks - and many more like them - are very different in motivation from all-out, violent feeding attacks. But what can that motivation be?

It has often been proposed that White Sharks attack humans because they initially mistake the victim for a seal or sea lion, releasing them when the shark realizes it had not caught what it expected. Shark behaviorist A. Peter Klimley has suggested that White Sharks reject human victims as low quality food - without a thick, insulating layer of blubber like that of a marine mammal, we humans are simply too bony to bother with. These are both interesting, complementary ideas. But neither theory explains why the initial strike by an attacking White Shark is often remarkably gentle and seemingly half-hearted.

Ralph Collier has questioned the widely accepted notion that - dressed in black neoprene - a surface-swimming diver closely resembles a seal or sea lion. Firstly, the color of a surface-borne diver's clothing is probably irrelevant, as - seen from below and backlit by the sun - it would appear a dark silhouette no matter what color it is. Secondly, the human silhouette does not closely resemble that of a pinniped: a floating skin or scuba diver presents a bottom-cruising shark with the shape of a strange, gangly, split-legged creature - quite unlike the sausage-like blubberiness of a seal or sea lion. Even surfboards, which are generally elliptical or lenticular in shape, do not offer pinniped-like silhouettes when paddled by a human rider. When ridden prone and paddled, the relatively thin arms of a human surfer and their exaggeratedly circular propulsive motions - vastly different from the alternating rear-flipper propulsive kicks of a seal or efficient, 'flapping' fore-flipper strokes of a sea lion - are readily apparent from below.

Physiological studies by Gruber and Cohen of the White Shark retina suggest that this species has exceptionally keen bright-light (day-time) vision. An elegantly simple grass-roots experiment conducted opportunistically by Wesley Strong in Spencer Gulf, South Australia, provides strong behavioral evidence that White Sharks are indeed sharp-sighted. Strong tossed an empty cigarette carton - measuring perhaps 1 by 2.5 by 4 inches (2.5 by 6.4 by 10.2 centimetres) - into the water, which promptly attracted the attention of a large White Shark cruising along the bottom. The small floating target elicited an oriented approach, snout prodding and gentle nibbling by the shark. A 1996 paper by Scot Anderson and his co-workers at the Farallon Islands, California, reported results of experiments on visual discrimination in the White Shark. Results of this work suggest that White Sharks will examine almost any floating object, first cruising by for a visual inspection and then - if this swim-by does not elicit a disconcertingly strong reaction by the object - frequently mouth or nip it. Such behaviors suggest that, rather than resulting from hunger or mistaken identity, many White Shark attacks on humans may be exploratory, motivated by something approximating sheer curiosity.

Perhaps the attack case that most strongly suggests a White Shark investigating a human is one described in a 1993 paper by Ralph Collier. In September 1974, commercial abalone diver Jon Holcomb was diving alone off the southeast end of North Farallon Island, California. Pinnipeds were seen in the water 300 feet (100 metres) north of his location. Holcomb was on the rocky bottom at a depth of about 35 feet (11 metres), using hookah gear (a regulator attached to a surface air supply by a pressurized hose). The normally abundant fish life was conspicuously absent, and what few remained were - in Holcomb's words - "very spooky". Holcomb had been in the water for about 90 minutes and was unaware of any shark in the area. Suddenly, while swimming quickly over the bottom looking for abalone, he was struck violently on his right side, then grabbed by his right arm and shaken for 3 to 5 seconds before being released. Holcomb's attacker, a 13- to 16-foot (4- to 5-metre) White Shark, then bumped him three or four times in the chest with its snout. At some point during his attack, Holcomb dropped his abalone iron (a sharp, square-edged tool used for prying abalone from hard substrates). The shark then grasped Holcomb's left arm and shook him for another 3 to 5 seconds before letting him go again. As the Great White turned to swim away, Holcomb picked up his ab iron and struck the shark on the flank as it swam past. After being struck, the shark swam some 15 feet (5 metres) away, bent its body in half "as though made of rubber", turned and charged Holcomb. The shark bumped Holcomb in the chest with its snout, then paused momentarily - as though waiting for some manner of response. As the shark swam past, Holcomb grabbed the corner of its open mouth - hoping to prevent the shark from biting him again. The shark swam off, dragging Holcomb through the water at a speed of 5 to 10 knots (9 to 18 kilometres per hour), the force of the rushing water pulling his diving mask down to his chin. When Holcomb saw the light of the surface a short distance above him, he let go. Surfacing some 40 feet (12 metres) from his tender boat, Holcomb alerted his companions and was promptly rescued. Holcomb was flown by US Coast Guard helicopter to a nearby medical center in San Francisco. Holcomb had suffered three lacerations to his right forearm, 1.5 to 2 inches (3.5 to 5 centimetres) in length, a 3 to 4-inch (8- to 10-centimetre) laceration to his left forearm, and a single 3-inch (7.5-centimetre) laceration to the left thigh. Holcomb was discharged 10 days later with both arms in long casts.

Jon Holcomb's attack is interesting in several respects. Unlike the vast majority of White Shark attacks on humans, in which the victim is bumped or bitten while floating more-or-less motionless at or near the surface, Holcomb was bitten while swimming close over the bottom. Considering the grievous bodily harm a 13- to 16-foot (4- to 5-metre), 1,800- to 3,500-pound (820- to 1,600-kilogram) White Shark with a mouthful of 1- to 1.5-inch (2.5- to 4-centimetre) serrated teeth could easily have inflicted, Jon Holcomb got off very easily indeed. Holcomb's wounds were remarkably minor - especially given the fact that he had struck the shark with an edged weapon, potentially inciting a devastating retaliatory strike. But what is even more remarkable is the shark's behavior during the attack. Although the attack seemed sudden and violent from Holcomb's perspective, the initial strike was surprisingly gentle. That the shark bumped Holcomb repeatedly in the chest, grasped one of his arms, shook and released him, then swam around to the other side, grasped his other arm, shook, and released him is very uncharacteristic of the no-nonsense, full-force way White Sharks usually employ when attacking prey.

Entertain for a moment the intriguing possibility that the shark's visual acuity was such that it could tell that John Holcomb was clearly not a fish or a pinniped. What are we to make of this attack then? The shark's relative gentleness seems investigatory rather than predatory in nature. Further - until Holcomb short-circuited the process by striking the shark - its exploration of Holcomb seems remarkably systematic. Is it feasible that, recognizing that Holcomb was not something familiar, the shark performed simple, tactile 'experiments' to help it determine just what sort of creature he was?

Consider the following thought experiment: if you had never seen a certain large, noisy animal before, would your first inclination be to try eating it? Of course not. You would probably investigate the unfamiliar creature visually, from what you hope is a safe distance. But a visual inspection can reveal only so much about novel objects. Imagine that you had never before seen a tin opener. Without picking it up or manipulating it in any way, do you think you could discern the use for which it was designed? Probably not. Yet - without benefit of hands - a shark has little recourse for investigating a novel object other than gently mouthing it. As described in the previous section, the White Shark can control its jaws with astonishing dexterity and its teeth and gums are highly sensitive. This sensitivity can provide a great deal of tactile information about unfamiliar objects, including information that could be useful in determining its potential value as food.

Now consider the unusual specter of a primate in the ocean. No matter how good a swimmer some of us might be in human terms, by the standards evolved over countless eons by life in the sea, we are clumsy and awkward. Although we may choose to enter the ocean for commerce or recreation, clearly we do not belong there. When we enter the sea, we impose a change in its rhythms, awkwardly announcing our presence to every resident creature that has some manner of sensory equipment that can detect our presence. Yet determining the nature of a novel object is particularly difficult divorced from its normal context. (What would a Kalahari bushman, far removed from technologies most of us have long taken for granted, make of a tin opener, I wonder?) Compared with the dimensions of most marine life, we are relatively large creatures. Our unfamiliar aspect, noisy movements, and large size conspire to make us rather frightening to most marine animals. No wonder that most actively swimming marine creatures - such as squids, fishes, sea turtles, and dolphins - simply avoid us. But experience eventually teaches most large sharks - such as Great Whites - that they have little to fear in their liquid realm. Combined with a predatory life characterized by perpetual ambush and investigation of potential new food sources, it stands to reason that humans would attract attention without inspiring sufficient fear to discourage the curiosity of a large White Shark.

So, why do White Sharks occasionally attack humans? Some White Shark attacks on humans may be due to mistaken identity, that the large predator simply failed to distinguish our form from that of its usual prey. But, given the White Shark's sensory acuity, such misidentifications seem likely to occur only very rarely. A few White Shark attacks on humans may be motivated by feeding, pure and simple. The shark was there and hungry, a hapless human blundered by - appearing awkward and easy-to-catch - and the outcome is usually overwhelmingly one-sided. But, given that in so many cases their nature is remarkably gentle, I would suggest that many - perhaps most - White Shark attacks on humans are motivated by investigation rather than predation. I find this idea to be far more interesting than attributing White Shark attacks to either mistaken identity or feeding. Any one - or any fish - can make a mistake. And all animals, including ourselves, need to eat. But to be investigated by an alien intelligence in an environment where it has every advantage over us is a chilling and altogether humbling possibility.

We are a remarkable species. But - for all our achievements in science, technology, culture, and so on - we remain mammals, subject to the same biological rules and constraints as all other animals. When we enter the sea, our smug sense of superiority grants us no special privileges. There is no politics in the sea. There is only producer and consumer, predator and prey. In the brutally rigorous laws governing marine creatures, the bigger and better armed eat the smaller and less well armed. This consequence of natural law is neither cruel nor 'unfair' (a uniquely human notion). It is simply the way things are. Whether we enter the sea for sport or commerce or science, we are nothing more than big - but relatively helpless - animals.

In a time when human mastery of our terrestrial realm grants us the illusion that we can control everything from atoms and genes to the destiny of our planet, it is humbling that something as simple as a big fish can put us back in our place. In a 1987 interview with Time magazine, "Far Side" cartoonist Gary Larson put our situation into irreverent and incisive perspective: "I think it's wonderful that we live in a world in which there are things that can eat us. It keeps us from getting too cocky."

Food for thought?

A gruesome paper published in January 1909 by Italian zoologists M. Condorelli and G.G. Perrando describes a 15-foot (4.5-metre) White Shark captured off Sicily that contained the complete bodies of three people - two adults and one child, the latter still clothed; the account and rather graphic photos included in this paper suggest that they had all drowned as a result of the December 1908 seaquake and were consumed together.