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Shark attacks? Humans kill sharks in far greater numbers.

Shark attacks may make headlines, but it's the human attacks on sharks that are having a far greater impact on our oceans' ecosystems.

By Charles Q. ChoiOurAmazingPlanet Contributor / June 21, 2010

Shark attacks on humans are quite rare compared to the inverse: Populations of many species of sharks have plummeted in recent years due in large part to commercial fishing.

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As dangerous as sharks may have seemed to people after watching "Jaws," which was released on June 20, 1975, the recent disastrous plunge in their numbers reveal that people have proven far more dangerous to sharks.

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In the waters off the U.S. eastern seaboard, populations of many species of sharks have dropped by 50 percent and some have fallen by as much as 90 percent, said George Burgess, director of the Florida Program for Shark Research in Gainesville. Overall, nearly a third of all sharks and rays worldwide may be threatened with extinction.

This catastrophic decline is due in large part to commercial fishing of sharks. "The market for shark fins in East Asia opened up thanks to changes in their economy, increasing their ability to spend money on things such as shark fin soup," Burgess said.

IN PICTURES: Top shark attack locations

However, the biggest worry for sharks and their relatives, the skates and rays, which are suffering a similar fate, "is how they are killed incidentally when fishermen try and take other fish — the problem of bycatch," Burgess explained. "They may be thrown back afterward, but they're still dead."

When it comes to why one should save sharks, Burgess said, "I could give you the philosophical answer that all creatures deserve to be here — that they each have their own place in the grand web that is our world, and no one animal is more important than the others."

There is also the more grounded answer that sharks are at the top of the food chain, he added, and that by removing such apex predators, one could wreak havoc on the rest of their ecosystems. Indeed, research has shown that the alarming decline in sharks is causing other species to suffer as well. With the large predators gone, their prey — smaller rays and sharks — are free to feast on lower organisms like scallops and clams, depleting valuable commercial stocks.

The crux of the problems behind bringing sharks back "is that they're not the same as other fish," Burgess said. "Sharks are slow growing and slow to reach maturity. Sharks are live-bearers, which means females keep their young in their body just like us, but instead of nine months, it takes 12 to 18 months or more in sharks. Also, sharks generally can't give birth again until a year after they've given birth — sometimes they're on a three-year cycle. So once you get a shark population knocked down, this 'life in the slow lane' means that recovery is measured in decades rather than years."

For instance, "the smalltooth sawfish, a close relative of the shark, was the first endangered marine species in U.S. waters," Burgess said. "I'm on the recovery team for it, but the recovery plan for that is over the course of 100 years. So I won't see them recover, nor will you, nor will your children. That's what it means when these animals go down — they're down a long time."

Any measures aimed at saving sharks must not only consider bycatch, "which is the real killer right now," but also encourage international cooperation, Burgess said.

"Sharks are very migratory, and many species cross borders," he said. "We can protect them only by getting many governments to come aboard. That's the hardest part about this."

IN PICTURES: Top shark attack locations