by Whit Gibbons

May 4, 2014

Warm weather at the coast plus the media’s thirst for hype plus the public’s craving for high drama can only mean one thing: shark attacks will soon be in the news.

Why do sharks attack people? How often do attacks actually occur? Must we really contemplate a visit to the beach with terror? Such questions come to mind as shark season approaches. Fortunately, the answer to these and many other shark questions can be found in “Sharks: The Animal Answer Guide” by Gene Helfman and George H. Burgess (Johns Hopkins University Press, 2014). “Sharks” is available in paperback and as an ebook.

The book answers more than a hundred questions about the taxonomic group of cartilaginous fishes known as Chondrichthyes. The group includes not only the characteristic torpedo-shaped, large finned, toothy creatures we think of as sharks but also the familiar rays and skates. All have cartilaginous skeletons rather than being bony like other fishes.

For most of the world’s species of animals and plants, even those that are seemingly well studied, many biological questions remain only partially answered or even completely unresolved. Why, for instance, does a shark swim with its dorsal fin above the surface even in deep water? One explanation is that because of their amazing sense of smell, sharks swim near the top of the water to detect floating or maybe even airborne scents. If so, the extended fin would be merely an artifact with no obvious function. The authors do point out that fins circling a swimming person make “life easier for Hollywood filmmakers during dramatic, suspenseful moments.”

The assertion that sharks have to swim continuously to keep breathing is only partially true. Not all sharks swim all the time. Some take breaks to lie on the bottom. These sharks breathe by sucking water into the mouth or through spiracles, two openings on the top of the head. For sharks that must stay on the move, water enters the mouth and exits through the five to seven vertical gill slits on the side of the head. The obvious slits--along with the bullet-shaped nose, big teeth, and distinct dorsal fin--make it easy even for children to identify the stereotypical image of a shark.

As for the question concerning your odds of being attacked by a shark, the answer is simple, straightforward, and not at all terrifying. In the United States, your chances of being attacked by a shark are less than 1 in 11 million. You are more likely to win a $1 million Powerball payout (assuming you buy a ticket) than you are to be attacked by a shark. According to the book, the chance of being killed is “less than 1 in 264 million.” Clearly, the danger of being attacked or killed by a shark while you’re at the beach should be quite low on your list of things to worry about.

As to why sharks attack people, the book presents both facts and speculation. Some bites are attributed to defensive or aggressive responses by sharks in special situations. Some are believed to be actual feeding attempts. But whether the human was mistaken for a common prey item, such as a seal, or the shark was actually trying to feed on a human would be hard to determine. Experts believe that most people along U.S. coasts are bitten not by great white or other well-known predatory species but by common blacktip sharks, which reach a length of less than 7 feet.

One question in the book I had never thought to ask: “what is the best way to take care of a pet shark?” Apparently, that is a question some people actually ponder and the authors provide the answer. So if you have a pet shark or plan to acquire one, you will definitely want to get this book. You might also do so if you are merely curious about this remarkable group of animals that share the world with us.

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