Making Heads or Tails of Shark Attacks

| posted on July 22, 2010

Sometimes it seems as if sharks are their own worst enemy– at least as publicists. Just as the summer run of Discovery Channel’s Shark Week is about to swing into full effect, a run of shark attacks has drummed up more bad press than Dennis Rodman at a Newport Beach keg party. The recent spate of attacks and encounters that have grabbed the attention of the public and the media in the past few weeks, a series of events that have reminded everyone, surfers and non-surfers alike, that once humans step into the ocean, we no longer occupy the top spot on the food chain.

But what’s the deal really? Why the flurry of shark activity all at once? Can it be explained through patterns in their behavior? Is it us? Is it the media drumming up attention? As was the case with the summer of 2001, otherwise known as “The Summer of the Shark,” recent attacks and sightings have seemed to pile in one on top of another. The past month alone has been stacked with incidents that have received ample attention from both the surf and mainstream press.

In mid-June, it was reported that three surfers were scared out of the water at Point Mugu in California by what they believe was a 10- to 13-foot great white. On June 18th, lifeguards at Leo Carillo State Park spotted another white shark in the surf, this one approximately 13 feet in length, and were forced to close the beach. In Florida, 14-year-old Jamie Daigle was attacked and killed by an 8-foot bull shark on the 25th, followed two days later by another bull shark attack on 16-year-old Craig Adam Hutto. Hutto, who lost his leg in the attack, was hit while surfcasting just 80 miles east of where Daigle was killed. June was then capped off by another reported bull shark attack on a 64-year-old male surfer at Nine Palms in Cabo San Lucas. The attack did significant damage to the unidentified surfer’s foot that was later repaired with reconstructive surgery by local doctors.

These three tragic attacks at the end of last month, coupled with the sightings in California, seem to suggest that something unusual is afoot with respect to shark behavior, or at least with regard to how they are interacting with humans. However, according to marine biologist R. Aidan Martin, director of The ReefQuest Center for Shark Research, what seems to be a pattern of behavior is most likely nothing more than coincidence. In response to the overwhelming media attention he and other shark specialists received during the summer of 2001, Martin created a page on the ReefQuest website entitled, “What’s Up With All These Shark Attacks?” as a means of quickly answering many of the most poignant questions posed when a string of these type of incidents seem to clump together.

“It’s an illusion when it appears that there are more attacks than usual, closer together than usual,” explains Martin on his site. “I’m not suggesting that the attacks themselves are not real, but that their apparently unusual pattern isn’t. It all comes down to the statistics that describe interval patterns of rare events. Statistically speaking, shark attacks fall under a class of entities termed ‘random, independent events.’ In this respect, shark attacks are similar to a series of heads-or-tails coin tosses using a fair, un-weighted, coin.”

“Think of it this way: the odds of tossing a heads, for example, on any given coin toss is the same as the odds of tossing a tails; 50 %. Therefore, in a series of coin tosses you would expect about half to end up heads and half to come up tails. However, because each coin toss is independent of previous tosses, it’s certainly possible to have a whole series of heads in a row without a single tail. This sort of clustering of random, independent events is so common there’s even a name for it. It’s called a ‘Poisson Burst’ after the French mathematician who first described it,” explained Martin. “It might seem weird, and it might seem that the next toss would have to be tails, but the odds of getting either a heads or a tails are exactly the same on every coin toss; 50/50.”

“It’s the very same with shark attacks. They can seem to occur in clusters, as they did during the summer of 2001. But the likelihood of any one individual being attacked by a shark at a given time and place, and the average interval between any two attacks, remains constant.”

According to Martin’s explanation, shark attacks occur so randomly and sporadically that by their very nature they are purely a matter of chance. And as opposed to a coin toss, in this case, the deck is neatly stacked in your favor.

Martin explains: “The risk posed by shark attack has been compared to all sorts of mostly irrelevant things, including death due to lightning, bee stings, injuries caused by domestic dogs, and my personal favorite, farm-yard pigs. The risk of death or injury due to a shark attack is far less than any of these. But you can’t compare terrestrial and marine injury statistics in a mathematically rigorous way. A far more realistic comparison is afforded by comparing the rates of deaths by drowning or injuries. According to a study by the Centers for Disease Control, 4,406 people drowned in America during 1998. That’s about 550 times as many deaths as those caused by sharks in an average year.”

“Or you could compare the rate of injuries to surfers from their own boards. According to a survey conducted by the Harvard Medical School, between May and December 1998, 451 surfers from 24 countries reported a total of 636 surfing-related injuries, of which 426 (66%) were lacerations caused by collision with the sharp nose or skegs of their boards. This means that about eight times as many surfers were injured by their own boards than were attacked by sharks.”

Anyone who has paddled out at a log-jammed SoCal hotspot can certainly attest that an errant board is a far greater health concern to the average surfer than aggressive sea life. Comforting information to be sure; however, this is not to say that the odds in the attack equation cannot be tipped. Obviously, if an area is known to be sharky it should be avoided, and along those same lines of thought, it stands to reason that the more people swimming in the ocean as a whole, regardless of location, the greater the chances of someone, somewhere being hit. “The high percentage of victims from Florida waters reflects the enormous number of people entering the sea in that state,” says Martin. “Accurate numbers are hard to obtain, but it seems likely that the number of people entering the ocean off Florida each year would be on the order of tens of millions.”

As is the case when mankind encroaches on any animal’s natural habitat, encounters and attacks are simply a matter of time, and obviously, these days, humans are taking to the water in massive numbers. What Dr. Martin describes as “accidents waiting to happen,” are bound to happen, and in the U.S., the public and the media seem to have a morbid fascination with these types of incidents, rendering shark attacks as extremely newsworthy items. When one occurs, much less two or more in close proximity, we’re going to hear about it. We’re going to hear a lot about it.

But what about the flipside of the coin? Who is actually coming up tails on the human vs. shark coin toss with “Poisson Burst” regularity? As you probably guessed, it’s not us. The price sharks pay for their cohabitation of the planet with mankind is far greater than the occasional human pound of flesh that gets such enormous publicity in the press. Aside from already having a disreputable image, which contributes to our general disregard and disinterest in their protection, sharks are heavily fished worldwide for their meat, fins, and cartilage. According to the Global Shark Attack File (GSAF), a database of information maintained by the Shark Research Institute in Princeton, New Jersey, “every year 600,000 to 700,000 tons of sharks are caught and slaughtered.” Noting that the average weight of each shark is only roughly 10 to 20 kilograms, the GSAF concludes that yearly, about 100,000,000 sharks are killed. That figure, when combined with the considerable pressure human development has put on coastal waterways and mangroves, the areas sharks naturally seek out as breeding grounds and nurseries, suggests that mankind is waging a war on sharks at both ends, a process that if continued unchecked, threatens to wipe them out.

Any death or disfigurement is tragic, and the recent attacks in Florida and Cabo San Lucas are certainly no exception. However, a tragedy just as great is the pervading misunderstanding about sharks and shark attacks, a misconception that is often fueled by a sensationalist mainstream press. “Sharks are not vicious,” says Dr. Martin, “which may be defined as evil, malicious, or prone to violence. Sharks simply lack a moral code, which is a necessary prerequisite for choosing to behave in a manner that could be called evil. They do what they do without ill will or premeditation. Sharks are not unduly forceful or even particularly aggressive. In fact, sharks are a lot less violent or aggressive than many other animals, including humans.”