Sharks Falling Prey To Humans' Appetites
for National Geographic News
|June 3, 2002|
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Summer is around the corner, and soon beach lovers will flock to their favorite coastal areas to soak up the sun and plunge into the surf. Many of them, however, will be keeping a nervous lookout for one of Earth's most misunderstood predatorsthe shark.
Thanks to the perennially popular movie Jaws and other dramatic portrayals of vicious attacks, many people think sharks are savage predators posing a grave threat to anyone entering the water. The truth is that while attacks do occur, and are a potential threat to humans, they don't deserve a very prominent place on our list of worries.
Bees, wasps, and snakes are responsible for far more deaths each year than sharks, according to data compiled in the International Shark Attack File (ISAF). The ISAF is a compilation of all known shark attacks maintained by the American Elasmobranch Society and the Florida Museum of Natural History.
Worldwide, sharks attack only about 50 to 75 people each year, and only 8 to12 of the attacks are actually fatal. In the United States, the annual risk of being killed by a lightning strike is some 30 times greater than the risk of death by shark attack. In fact, more people are killed driving to and from the beach than by sharks.
But while shark attacks against humans are relatively rare, the human onslaught on shark populations is another matter.
"The United Nations Food and Agriculture Organization estimates that we're catching one billion pounds of sharks each year," said Robert Hueter, director of the Mote Marine Laboratory's Center for Shark Research. "That's many, many millions of animals."
Man Bites Shark
For the past 100 million years or so, sharks have inhabited the world's seas in basically unchanged form. They are successful predators that have long been ensconced at or near the top of the food chainuntil recently.
Today, heavy human pressure is making a big impact on shark populations. "By the population measures we have, numbers are down," said Hueter. "In some cases it's subtle but in some cases it's a pretty dramatic drop within the last 25 years."
Sharks are falling victim to an ever more efficient global fishing industry, which sometimes operates with little regulation. "Worldwide, sharks are taken for their meat," Hueter said. "In a lot of developing nations, [shark] is a major source of protein in people's diets. In some countries, Mexico is an example, they don't target one species while fishing, they just bring in what they catch. They're catching a lot of sharks."
The problem is compounded by population declines of other fish species. As worldwide demand for fish increases, the stocks of some species have been overfished. As a result, sharks are targeted by fishermen in areas where they were previously left alone.
A Costly Delicacy
While shark meat has become an important staple of some diets, in other cultures the animal holds a more special place on the menu. Because shark fins, which can net fishermen more than $25 per pound, are more profitable than shark flesh, fishermen sometimes take merely the fin.
Once the rigid, cartilage-supported fins are sliced off, the sharks are then dumped overboard, either already dead or doomed to die. After being dried and processed, the fins eventually end up in shark fin soup, a popular and expensive delicacy in Chinese cuisine.
"It's a big problem, because there is lots of demand and little regulation of finning," said Christine Snovell of the National Coalition for Marine Conservation. "These fins are worth a tremendous amount of money, so the law of supply and demand is in effect."
"Fins to these sharks are analogous to the horns of rhinos," added Hueter. "Even fishermen who catch sharks unintentionally, as bycatch, will now take the finsotherwise they are throwing money away."
Sharks are also a tremendous source of cartilage. Unlike many fish, which have bony skeletons, shark skeletons are made entirely of cartilage, which grows throughout the animal's life. Shark cartilage pills are advertised as cure-alls for any number of ailments and diseases.
Scientists like Hueter, however, are skeptical about the efficacy of shark cartilage pills in treating disease in humans. "There's research ongoing," he said, "but as far as we can tell it's not having major value in terms of fighting diseases, although that is how it's being marketed."
Shark carcasses serve other purposes as well. Different parts of the animal are put to commercial use in products ranging from cosmetics to hemorrhoid creamwhich makes liberal use of shark liver oil.
Altering the Ocean Ecosystem
The popularity of shark products means that the animals are being pulled from our oceans faster than ever before. Dropping shark populations could spell big trouble for the ocean ecosystems so crucial to life on Earth.
"Sharks are an apex predator," points out Snovell, "like lions or wolves on land. If you remove that important link from the top of the food chain, you're going to have some real problems all the way down the line."
Shark biology compounds the problem. Sharks have a long life span, don't reach sexual maturity until they are 12 to 20 years old, and even then have a low reproductive rate. Reduced populations mean fewer sharks reproducing, at well below the replacement rate necessay to keep pace with the number lost to fishing fleets.
This reproductive timetable was in balance with an ecosystem in which a limited number of sharks sat atop the food chain. It may prove inadequate, however, to sustain shark populations in an ocean ecosystem increasingly dominated by humans.
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