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Anatomy of a Shark Bite
Kate Roach
December 2003
Up to his hips in bait-filled water and surrounded by sharks, Dr Erich Ritter conducts a television interview. 'As long as you don't move,' he assures the less-than-confident TV presenter, 'we're not a threat to them; they couldn't care less.' Moments later a large female bull shark grabs Ritter by the leg and attempts to drag him into deeper water, where she'll devour him. Ritter survived, but the calf muscle of his left leg didn't. In Anatomy of a Shark Bite, part of Channel 4's BodyShock series, Dr Erich Ritter is on a mission to find out when and why sharks bite humans.
Jaws
'I turned around and I saw this dorsal fin, it was huge, you know, it was towering over me in the water.' One gruesome moment later and Heather Boswell had completely lost her left leg to the jaws of a great white shark. A more terrifying ordeal is hard to imagine. This is exactly the kind of sad story that gives the media (and Hollywood) the ammunition to portray the shark as a bloodthirsty maneater. Titillating sensationalism has long been the stock-in-trade of shark attack stories in the media and feature films.
Clearly we all have a deep-seated fear of the beast, and one that is well-founded at that. For any large carnivore, shark, lion or leopard, is capable of ripping us to bits in a matter or seconds. The poor old shark though seems to get top marks for the horror factor, probably because of his silent approach, his huge ugly teeth and his expressionless face. So are we right to have built him up as marauding mass murderer of the high seas? Sorry Hollywood, sorry media, but the facts really don't support the story.
Sharks attack 50-90 people each year worldwide, with perhaps 5-10 fatalities. In the year 2000, an estimated 264,000,000 people visited beaches in the US alone. Of those, 71,000 people were given medical treatment by lifeguards and 132 died by drowning or other water sport injuries. In the same year in the US, there were just 23 shark attacks, with no fatalities. And on a global scale consider how many millions of people enter the water each year, and how many millions of sharks inhabit the same waters. Now the shark doesn't really seem to live up to his image, does he?
Every year, more people are injured by lightening strikes and by dog bites than by sharks. And take flu, for example, do you quake with fear at the thought of contracting the flu virus? No? You should. The World Health Organisation estimates that every year between 250,000 and 500,000 people die as a result of flu in industrialised countries alone. Our mass murdering sharks seem rather tame in comparison, with a measly 5-10 deaths a year to their name. This is not to diminish the trauma and terror of a shark attack, but it is time to see the shark for what he really is.
There are about 400 species of shark altogether, but only 32 of those have been documented in attacks on humans. In fact, 80% of shark species grow to less than 1.6 metres and are simply not big enough to hurt people. An additional 36 species are considered potentially dangerous, but have never been recorded in aggressive encounters with humans.
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Sharky factoids
Sharks have been around for longer than crocodiles, dinosaurs and man. They first appeared in the seas about 450 million years ago – 200 million years before the dinosaurs.
Sharks have skeletons made of cartilage not bone. Better for buoyancy because it's lighter than bone – an advantage for a fish that has no gas-filled swim bladder, like other fish.
The smallest shark, the spined pygmy or dwarf shark, is only 20-25 centimetres long.
The whale shark is the largest fish in the sea, reaching a gargantuan 20 metres when fully grown. Thankfully whale sharks prefer plankton to humans.
The great white shark is the largest predatory fish in the sea, reaching a maximum length of 6.8 metres.
The female great white is bigger than the male.
The largest marine predator that ever lived is the extinct shark Carcharoden megalodon which exceeded 15 metres in length and weighed in at 52 tonnes.
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Why do sharks attack?
Erich Ritter, is the Chief Scientist for Global Shark Attack File, one of the large databases that documents all aspects of shark attacks. The database is maintained at the Shark Research Institute in Princeton, New Jersey. Ritter's hope is that by carefully investigating all the factors leading to 'shark accidents', as he calls them, the number of attacks might be reduced and our almost supernatural fear of the great fish might be allayed a little.
The trouble is that sharks large enough to threaten humans are huge predators. And no matter how much we come to understand shark behaviour, all animals are unpredictable – a fact that Ritter himself can sadly testify to. Realistically, almost any shark in the right size range, roughly 1.6 metres or greater, is a potential threat to humans, even when a bite is not intended as a direct feeding attempt. Ritter has demonstrated that the actual bite force of sharks' jaws is not as great as we might at first imagine. But combine the bite with rows and rows of pointed teeth together with the momentum created by swimming and a quick nibble for a shark becomes a deadly bite for a human.
Three species are repeatedly identified as the culprits in attacks on humans – the great white (of Jaws fame), the tiger and the bull. All three are found worldwide, reach large sizes and, most importantly, all three eat large prey species like sea lions, seals and sea turtles.
One reason that Ritter believes sharks might go for humans is a case of mistaken identity. The silhouette of a surfer on a board or a swimmer paddling along on the surface might, when viewed from below, resemble a sea lion or a seal. Surfboards in particular are seal-shaped. Indeed, swimmers took the brunt of most attacks in 1960s but by the 1980s attacks on surfers were much more common. The trend doesn't reflect a change in shark preferences, rather it is a reflection of the increased popularity of surfing. So, if you surf, be sure to avoid areas where marine mammals congregate, because sharks will be hanging around there too.
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Sharks help fight cancer
Sharks, it seems, have an uncanny ability to resist disease. They do get sick, but not as much as other fish do. According to the Registry of Tumors in Lower Animals, a database held at the Smithsonian Institute in the US, of the thousands of cancerous tissues that are listed from fish, only 8-10 are from the shark family. The low incidence of cancer in sharks has prompted medical researchers at the Mote Marine Laboratory in the US to explore the mechanisms underlying this incredible tumour resistance.
Mote scientists first tried to induce tumours in sharks with carcinogenic chemicals that cause cancer in humans. Some of the chemicals had similar effects in sharks and mammals, but no changes in the target tissues or their genetic material ever resulted in the formation of cancerous tumours in the sharks.
Research interests are now focussing on the shark immune system, which is more primitive than the human one, but is clearly remarkably effective. Since some new approaches to cancer therapy involve stimulating immune cell production, Mote researchers are planning to compare shark immune systems with mammalian ones. An understanding of how sharks' immune cells are controlled may some day aid in the control of immune regulation in human cancer patients.
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The great white
The infamous great white has been credited with more fatal attacks on humans than any other species of shark. And yet some 80% of all shark accidents occur in the tropics or the subtropics where the great white is relatively rare and other shark species dominate. A statistic that suggests that the great white either has a particular penchant for human flesh or is especially offended by humans that stray into its path. Neither of course is true.
One reason is simply that humans prefer warmer waters for recreation and so there are more humans to have a go at in tropical regions. But the belief that great whites are mistaking humans for seals seems suspect in light of the fact that they will bite inanimate objects of many different colours, shapes and sizes that don't resemble marine mammals at all. Some researchers have suggested that great whites strike unfamiliar objects in exploration. Grasping might be the only way a shark has of determining palatability. But one exploratory grasp from a super predator with 3000 razor sharp teeth could spell the end for a puny creature like a human.
The exploratory bite scenario is borne out by shark accident data. The majority of attacking great whites, will bite their victims only once and then leave the scene. Researchers believe that they prefer prey that is rich in fat, like marine mammals – a preference that would explain why they generally spit out humans who make relatively low-fat foods. In support of this idea is the observation of aggregations of great whites feeding selectively on the blubber, but not the muscle layers, of whale kills. Marine birds and sea otters also seem to be rejected for being too low in fat; these animals are commonly found having suffered injuries from encounters with great whites, but are rarely ingested.
Another reason for the apparent propensity that great whites have for humans is their huge size and power combined with their feeding style. One of the drawbacks of being a top predator is that your size might alert your prey to your presence. Other shark species often approach prey with caution, swimming around and bumping the prey before attacking (as did the bull shark that bit Ritter). But the great white often goes straight in for the kill, relying on stealth to catch the victim off guard. When hunting, most great whites swim just below the surface until their intended dinner is within a metre or so, then they attack suddenly by deflecting the head upward and emerging out of the water. Another favoured approach is to swim vertically upward in the water column and to rush up at the last minute, biting down on the victim with an explosive splash.
It isn't only feeding sharks that we should be wary of either. Great whites and other species are poorly understood, but are believed to engage in social behaviours like territorial defense, communal feeding and of course mating. Disturbing any of these communal activities is just asking for trouble; it's sensible to keep well away from any aggregation of sharks. Sandbars, steep drop-offs in the ocean floor, channels or river mouths and sewage outfalls are all areas where sharks are known to congregate. Swim there at your peril.
Shark fin soup
As an apex predator, the great white has little to worry about from other predators. Killer whales, larger sharks and humans pose the only real threats to an adult great white. But despite its relative rarity, the rate of capture by humans is alarmingly high. This is in part due to trophy-hunting and the increasing monetary value of great white jaws and teeth. And in part due to the growing trade in shark fins of all species. Shark fin soup is considered a delicacy in many parts of the world, and fisherman can often get a better price for the fins than they can for the shark meat itself. This has led to the wasteful and cruel practise of finning, where fins are cut off live sharks, and the bodies dumped back in the ocean. Finning is now banned in many countries.
All sharks tend to be near the top of their food chain and as apex predators they are believed to play an important role in regulating numbers of the prey animals they catch. Sharks also grow slowly, mature late and give birth to few young, which means that they are very vulnerable to over-fishing. Once over-fished, stocks take a long time to recover. Many sharks are now protected and 77 species are listed on the IUCN's (The World Conservation Union) Red List as somewhere between vulnerable and critically endangered.
So next time you watch Jaws, spare a thought for the 1.3 million tonnes of sharks and rays fished from the sea each year. That equates to well over 100 million individuals – now who's the mass murderer?
Find out more
Channel 4 is not responsible for the content of third party sites
Websites
Biology of Sharks and Rays
www.elasmo-research.org/education/
white_shark/mistaken_identity.htm
Information on the biology of sharks and specifically on the reputation of the great white.
A Masterpiece of Evolution – The Shark
www.ncf.carleton.ca/~bz050/
HomePage.shark.html
Answers questions like, do sharks have tongues? The site looks at the evolution of these creatures and explains the differences between the different types of shark.
Reef Quest Centre for Shark Research
www.elasmo-research.org/shark-sites.htm
Offers a list of recommended shark sites that provide a wealth of information.
Shark Attacks – Victims Files
www.sharkattacks.com/bites.htm
News and information on shark attacks with some gory images; strictly for those who aren't squeamish.
The Shark Foundation
www.shark.ch
Houses an excellent shark database; although still under construction it will contain more than 460 species. There is also information about the main threats to sharks worldwide and how the foundation is working to protect them.
The Shark Trust
www.sharktrust.org
Excellent UK site that focuses on shark conservation, with tonnes of information and news, a kids' zone, downloads and video footage of shark hunting.
The Tragedy of the USS Indianapolis
www.ussindianapolis.org/pfinnstory.htm
This site provides detailed information about the sinking of USS Indianapolis in 1945 and the terrifying shark attacks that followed. There are eyewitness accounts from survivors.
Shark Info
www.sharkinfo.ch/SI1_99e/gsaf.html
This site holds details of the Global Shark Attack File.
Mote Marine Laboratory
www.mote.org
Find out all about current shark research, including the shark's uncanny ability to resist cancer.
Books
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The Basking Shark in Scotland: Natural history, fishery and conservation by Denis Fairfax (Tuckwell Press, 1998)
The basking shark, the largest fish in Scottish seas, is often in the news as conservationists press for its legal protection. Here the history of the fishery for the shark is fully treated. Also covered is the anatomy of the basking shark and its biology, in so far as is it is known, as there is still much that is unexplained about the life of this enormous plankton-eating fish.
Get this book |
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Great White Shark by Richard Ellis and John McCosker (Stanford University Press, 1995)
Lavishly illustrated, this book is the definitive account for general readers of everything that is known about the great white shark, the most feared creature in the world's oceans. It's based on extensive research into the scientific literature and lore of this superbly adapted predator, on analysis of historical records, and on the most up-to-date information.
Get this book |
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In Harm's Way by Doug Stanton (Bantam, 2002)
In July 1945, the USS Indianapolis was steaming through the South Pacific on her way home, having delivered the bomb that was to decimate Hiroshima seven days later, when she was torpedoed by a Japanese submarine. Of a crew of 1196 men, an estimated 300 were killed on impact; the remaining 900 sailors went into the sea. Undetected for five days, they struggled to stay alive, fighting off sharks, hypothermia and dementia. By the time rescue arrived, only 317 men were left alive.
Get this book |
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Shark Attacks: Their causes and avoidance by Thomas B Allen (Constable & Robinson, 2001)
Contains harrowing personal stories of shark attack survivors, expert opinions from marine biologists and the latest scientific studies of shark behaviour. The author explains why so many attacks occur in water less than five feet deep; which species are killers; what triggers shark behaviour just before an attack; whether shark nets increase swimmer safety levels; environmental and seasonal conditions that contribute to an increase in attacks; and why is it better to be below a shark than above it.
Get this book |
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The Shark Watcher's Handbook: A guide to sharks and where to see them by Mark Carwardine and Ken Watterson (BBC Publishing, 2002)
Nearly a quarter of a million people have an intentional encounter with sharks every year; shark-watching has become a multi-million dollar business. The ultimate shark-watcher's guide, this generously illustrated and informative book is for any marine enthusiast who wants to navigate the waters of those who consort with sharks.
Get this book |
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Sharks: Informania by Christopher Maynard (Walker Books, 2000)
The author invites kids to get their teeth into sharks, before they get their teeth into you. He presents news and views on the ocean's oldest and meanest predators, including gory tales of shark attacks, presented in the form of a pupil's term project.
Get this book |
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