Sharks

Why Do Sharks Attack?

posted: 04/11/12
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Why Sharks Attack
Phil Mislinski/WireImage

Sharks attack and kill 10 humans per year, on average. Humans, in contrast, annually kill about 20 to 30 million sharks, according to the Florida Museum of Natural History's Department of Ichthyology. That shark death estimate, based on commercial and sport fishing landings, could even be conservative. It is therefore not too difficult to see which species poses the greater threat to the other. After 400 million years of shark evolution, we could potentially wipe out the world's sharks in a century's time.

The fact remains, however, that sharks can, and do, result in human deaths. Dogs and even traditionally mild-mannered animals like cows may kill people too, but the nature of shark attacks seems to fascinate and terrify us more. This year alone, two surfers from Mexico and two from California lost their lives after bleeding to death due to shark bites. The cluster of deaths puzzles researchers because, as shark numbers are declining overall, attacks seem to be holding steady, or are even rising, depending on the region.

Why Do Sharks Attack Humans?

After the recent deaths, some researchers are starting to wonder if certain sharks are developing a taste for humans. Jose Leonardo Castillo, chief shark investigator for Mexico's National Fishing Institute, recently announced that he and his colleagues are investigating this possibility, since criminal activity has resulted in bodies being dumped in the areas where the two surfers in Mexico died. It could be that, after repeatedly consuming other human flesh, one or more sharks could associate people with food.

Even if the food-human link is indirect, it likely explains most shark attacks in general. The National Oceanic and Atmospheric Administration (NOAA) explains that sharks do not normally hunt humans, but if they do attack, it is usually a case of mistaken identity. Assuming a large, predatory shark has not been exposed to human flesh before, it is probably used to biting into thick-tissued, fatty sea lions, seals and similar-bodied prey. Sometimes sharks will investigate potential food items by taking a taste. Unfortunately, given their many rows of sharp teeth, a few shark species can cause an individual to bleed to death after a single bite. The problem is compounded in lakes, rivers and estuaries, where freshwater sharks, such as bull sharks, often share water space with humans who are swimming, boating, fishing or engaged in some other form of recreation that might put them face to face with a shark.

How Sharks Attack People

According to author Murray Suid and George Burgess, a senior biologist and director of the International Shark Attack File, there are four basic types of shark attacks on humans. The first and, by far, the most common are provoked attacks. These occur when people in some way touch, or otherwise disturb, sharks. Fishermen removing sharks from their nets, for example, might lose a finger or limb if not careful. Sometimes divers have taunted or tried to grab a shark, with not-surprising consequences.

Unprovoked attacks can happen in three principal ways. The most frequent of this type are hit-and-run attacks — when the shark grabs, releases and leaves the scene. The shark could be investigating the individual, thinking he or she was its usual prey. It might also perceive the individual as a threat, similar to how a more aggressive, yet fearful, dog could attack anyone who mistakenly treads on its turf. The two other types of unprovoked attacks are sneak attacks, when a deep-sea shark moves upon a diver unawares; and, finally, bump-and-bite attacks, when a shark head-butts a person before it takes a bite.

Ways of Preventing Shark Attacks

The NOAA Fisheries Service offers the following tips on minimizing the risk of shark attack:

1) Stay in groups and do not wander away from your companions, since sharks are more likely to attack individuals.

2) Avoid being in the water during early morning and late afternoon, since sharks actively feed at those times.

3) Never go into the water if you are bleeding, even if the cut or injury is minor. Sharks possess very keen senses, and blood could attract one from several feet away.

4) Don't wear shiny jewelry when in the water. The glisten mimics fish-scale sheen and visually labels you as shark prey.

5) Stay away from sport or commercial fishermen when in the water, as their catches could attract sharks.

6) Avoid wearing brightly colored clothing in murky waters, since sharks easily perceive color contrasts.

7) Refrain from excessive splashing, which could mimic the movements of injured or disoriented prey fish and animals.

8) Sandbars, steep drop-offs and estuary inlets tend to be shark hangouts, so avoid swimming in these places.

While fear of sharks is well founded, the greater fear should be of shark extinctions, since no one really knows what could happen to ocean ecosystems without the managing presence of these elasmobranches. Since everything from total ocean system collapse to food shortages for humans, due to diminished fish catches, has been theorized, hopefully such fear can fuel conservation action before any of these unthinkable scenarios come to pass.

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