Can Science Explain the Marked Increase in Shark Attacks?

  Authorities in Western Australia have failed in their attempt to hunt down and kill a great white shark that took the life of a 32 year old American diver, George Wainwright last  Saturday.  This is the fourth fatal attack by sharks in Australia in the last 14 months—three times the annual average.  There have been 13 shark attack deaths world-wide this year, and statistics show that the number of shark attacks have increased steadily for decades. 

I studied sharks for my MA and PhD degree in Biological Oceanography; I’ve been diving with them, and I’ve seen them explode into a feeding frenzy attacking their normal prey.  So after this recent attack I contacted some of the world’s leading authorities on sharks and shark attack to get their expert opiniosn.

John West, of the Taronga Zoo, in Australia and Curator of the Australian Shark Attack File, indicated in an e-mail for this article that shark attack numbers in Australia have increased steadily over the last 20 years.  “We are talking about an average of 4.6 cases per year in the 1970’s, 6.4 in the 1980’s, 8.2 in the 1990’s, and 16.1 cases per year in the 2000’s.”

George Burgess, shark researcher and curator of the International Shark Attack File at the Florida Museum of Natural History, confirms a similar trend from his data.    “If one looks at the last eleven decades from 1900 through 2010, what one finds is that there is an increase in the number of attacks each decade, without fail, which would suggest to the casual viewer, that we’re under siege,” he says.  Both experts agree that there a scientific explanation for these alarming data and the spike in recent fatal shark attacks. 

The steady increase in shark attacks is easily explained by the increase in human population and growing popularity of water related sports and recreational activities.  “The increase in shark attacks is largely a function of human demographics and growth.  The number we get in any given year is purely a function of how many people went into the water,” says Burgess. 

There are, however, some new patterns emerging from Burgess’ data on shark attacks.  “There has been an increase this year [in shark attacks] in a number of areas where we have not traditionally had such attacks, undoubtedly by white sharks, most notably the three series of attacks in Russia in areas of cold water most of the time,” he says.  This, he explains is due to warming of waters, possibly associated with global warming, that are allowing sharks to expand their range farther north and south into waters that they normally do not go, and also because warmer water induces more people entering the sea.    

Contrary to the sensational scenes in the movie Jaws portraying maniacal sharks stalking and terrorizing bathers, most attacks on humans are mistakes.  “We all need to remember that we are not a natural part of the marine environment,” Burgess observes.  “So therefore we are not likely to be a preferred food item of any animal in the sea, simply because we are foreign objects every time we are encountered.  In fact, most commonly sharks will move away from us as we represent an unknown entity and the natural reaction is to show caution.”

“Here in Florida where we have more shark bites than anywhere else in the world.  These interactions are almost surely mistaken identity, because the animals involved are small—six feet or less in size—and species of sharks that are typically shrimp eaters that don’t normally go after large prey items.  Their teeth are not designed evolutionarily for tearing, but rather for grabbing and swallowing whole.”  When these sharks feed in the murky surf zone where the jostling of waves and currents forces them to rely on quick grabs to feed, a flailing leg or arm of a bather frolicking in the surf can be mistaken for the animal’s normal prey.

There are exceptions, however.  “Other animals like white sharks, tiger sharks, bull sharks, of large size whose teeth are designed for shearing and who normally go after large prey item can in some cases see humans as simply representing an appropriate sized and perhaps appropriately behaviored image of the normal prey item.”  The silhouette of surfer in a black wetsuit paddling on the surface can resemble a seal, for example.  “You can’t dismiss all bull shark and white shark attacks on humans as cases of mistaken identity; a human simply looks like something worthy of a trial.” 

What can be done to prevent such predatory attacks on humans?  Some, as has happened after the recent fatal attack in Australia, argue for “culling” the shark population and hunting down and killing the suspected killer shark.  This, Burgess argues, is futile. 

“Obviously trying to kill the killer is just really a waste of time and public resources, simply because you can’t identify the individual shark in any other way than to kill the shark and open the stomach and hope to find a piece of human in it.  That’s a shot in the dark.  The chances of finding a killer are pretty much slim to none.”

The difficulty of identifying the killer, which popular folk lore would have terrorizing a local coastal community, is compounded by the biology of large sharks.  “White sharks are highly mobile and they move 40 to 50 miles a day.  So the chances of the killer shark being caught after an attack are pretty much nil, because that animal has probably long gone.” 

 Moreover, this eye-for-an-eye approach to shark attacks can have devastating ecological effects.  The studies of Gregor Cailliet, Professor Emeritus, Moss Landing Marine Laboratories and Program Director for the Pacific Shark Research Center, have highlighted the vulnerability of sharks to predation by humans, because unlike many fish, sharks take a long time to reach sexual maturity and most species only have a small number of offspring.  “In my opinion Jaws (the movie) and Shark Week, etc., are not good things, but rather sensationalize the situation,” he says.

Moreover, the number of shark species that are dangerous is exceedingly small.  “Remember there are almost 1,200 species of sharks, rays and chimaeras worldwide and the white, bull and tiger sharks [most often implicated in attacks on humans] are only three of these,” observes Cailliet. 

The experts advise that understanding and respecting the biology and ecology of sharks can enable one to avoid becoming shark bait.

“People need to use common sense in deciding where and when to be in the water and doing what.  For example, areas where pinnipeds [seals and sea lions] have pupping grounds, and often costal points outside of kelp beds, are “hot spots” off California, says Professor Cailliet. 

The most recent fatal attack on the diver in Australia took place in an area where white sharks would have been expected to be feeding.  “The place where he was [attacked] was close to a seal colony.  We see a number of shark attacks on humans around seal colonies,” Burgess says. 

Moreover the location of the attack is in the migratory route for whales.  “Whales move through this area at this time of year, every year, and where there are migratory whales there are white sharks following.  We see this right along our coast–the East Coast–in the winter as the Right Whales head south off of Georgia and Florida, white sharks follow them as well.  The only time we see white sharks in Florida is in the winter time when they follow the whales down.” 

It also appears from initial reports that this diver was engaged in spear fishing.  If so, this attack would be classified in the shark attack files as a “provoked attack” because the blood and frantic movements of speared fish would attract sharks to the area and provoke them to feed. 

“Sharks have more to fear from humans than humans have from sharks,” observes John McCosker, an expert on white sharks at the California Academy of Sciences in California.  He advises people to avoid areas where there is a history of attacks, and that the new thrill-seeking “shark dives” being offered adventurous divers runs counter to common sense.  “I suspect that this is contributing to an unrealistic perception of the risks associated with such stupidity; however, surprising, I’m not aware of a significant increase in attacks [in such dives].  The risk of diving with white sharks in the Northeast Pacific, as is done in California and Guadalupe Island, Mexico, will increase if people think that it is safe to leave the protection of a cage.” 

One needs to keep the risk of shark attack in perspective.   These are very rare events.  “Over the past 50 years there is an average of around one person killed by a shark each year in Australia, yet there is also an average of 87 people that drown every year at our beaches [in Australia], says John West. 

All of the shark authorities consulted for this article agree that the general population has a distorted and sensationalized view of sharks.  “I think the only words most people hear or read and retain are ‘dangerous’ and ‘predator’ even when an article or documentary is balanced,” West says.  “Of all the people I have spoken to over my 40 years involved with sharks, 99.5%  have never seen a live wild shark yet 99% are fearful of sharks—where do they get this fear from?  I think it is the media and associated movies.” 

People seem to have forgotten the basic biological facts with respect to humans and sharks.  “When we enter the sea, we need to understand that we are visiting a foreign environment,” Burgess observes.  “We are terrestrial animals.  Our evolution occurred on land.  We don’t have gills.  We can’t swim very well, and as such every time we enter the sea it is a wilderness experience for us.  One of the mistaken impressions that we as humans have is that we are owed the right to be safe 100 percent of the time wherever we go in the world.  That’s a pretty haughty view that humans have– that we should be able to control every phase of the world we live in.  In the sea we should accept a certain amount of risk, and it is incumbent upon us to reduce the chances of risk by being smart.  But any way you look at it, when you enter the sea it is a wilderness experience.”

 Further Reading:

Fields, R. Douglas (2007)  The Shark’s Electric Sense.  Scientific American, August, p. 75-81. 

http://www.scientificamerican.com/article.cfm?id=the-sharks-electric-sense