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Re: UNDER ATTACK
infoshark - 05.08.2007, 12:45UNDER ATTACK
UNDER ATTACK
I should never have looked at its teeth. For the past 15 minutes, this 6-ft. tiger shark has been hog-tied alongside our small flat-bottomed motorboat, tossing in choppy seas two miles off Waikiki Beach, in Honolulu. Carl Meyer, a graduate student at the University of Hawaii, has been busy the whole time--slipping a noose around the powerful tail, flipping the shark on its back to put it into a stupor, measuring it this way and that, then shouting the numbers to his colleagues on the larger boat that bobs in the waves nearby.
As he works, Meyer repeats under his breath, over and over, "No biting, no biting, no biting..." The object of his mantra gapes below us--a foot-wide crescent studded with hundreds of razor-sharp, serrated, half-inch-long triangular teeth. This fish is only half-grown--an adult tiger shark can surpass 14 ft. in length--but it could easily take off a hand or an arm, or a chunk of torso you wouldn't want to try and live without.
Meyer, luckily, is a pro. He has been working with sharks for years, and deftly avoids the open jaws. The last step before releasing the specimen is to tag it, a job Meyer assigns to me. I take a steak knife and stab an inch-long, inch-deep incision into the shark's back--no easy task, considering that its skin is as thick as a watermelon rind and as tough as leather. The shark doesn't even flinch. "That's nothing," Meyer reassures me, "compared with the wounds they inflict on each other during mating." I slip a barb-tipped wire with a white plastic tag into the incision and tug hard to anchor it in place.
"O.K., now you get in the water," orders Meyer. This is the scary part. The shark, having been manhandled and disoriented, may be too groggy to swim away, and unlike other fish, most species of sharks must swim constantly to keep oxygen-rich water flowing over their gills. Someone has to be ready in case it needs help getting restarted. And to my surprise and fear--the image of those teeth is still very clear in my mind--I have been elected. I slip over the side. Meyer unbinds the captive, and the huge fish and I are floating free in the crystalline blue water. This is the shark's element. What happens next is entirely up to him.
Biologists like to blame Peter Benchley's best-selling 1974 novel Jaws and the Steven Spielberg movie that followed for the shark's fearsome reputation as a mindless, relentless, consummate predator. The truth is that people have always been terrified by sharks, probably since humans first ventured into the sea. Who can blame them? As any survivor or witness well knows, a shark attack, especially by one of the larger species considered man-eaters--great whites, bull sharks, tiger sharks--is mind-numbing in its speed, violence, gore and devastation.
What most people don't realize is that it almost never happens. In a particularly bad year, as many as 100 people may be attacked by sharks. Of those attacks, a small minority--15% at most--prove fatal. Far more people are killed by bees, poisonous snakes and elephants, as well as bathtub falls and lightning strikes. It's much more dangerous to drive to the beach than to venture into the water once you get there.
Humans, in short, have little to fear from sharks. The reverse, however, isn't close to being true. Fish of all kinds are being hauled from the sea faster than they can reproduce, but until quite recently sharks were exempt from this reckless harvest. Not anymore. Each year between 30 million and 100 million sharks are caught for their meat (boneless and mild-tasting), their fins (a great delicacy in Asia), their hides (source of an exotic, high-quality leather), their jaws (worth thousands of dollars from collectors) and their internal body parts (made into everything from lubricants to cosmetics to "health" products of dubious value).
And at least one shark is accidentally killed, usually by longlines set by shrimp and tuna boats, for every one that is caught deliberately, according to the U.N.'s Food and Agriculture Organization. When you add it all up, each human who dies in the jaws of a shark is avenged roughly 6 million-fold.
Largely as a result of this relentless slaughter, the populations of some shark species have plummeted an estimated 80% over the past decade. "At the current rate," predicts marine biologist Merry Camhi of the National Audubon Society's Living Oceans Program, "some species will reach ecological extinction within 10 years."
That prospect spurred the U.S. government for the first time to slash fishing quotas for certain sharks in Atlantic waters in April. It also moved conservationists to put seven shark species on the IUCN-World Conservation Union's Red List of threatened species and prompted calls for even stricter safeguards for sharks before it's too late.
But why should anyone care? In fact, there are plenty of reasons, starting with the creature's pure elegance of design. Sharks first appeared on earth 400 million years ago, and after about 200 million years of evolutionary trial and error, nature pretty much ran out of ways to improve on its handiwork. Today more than 350 species swim the planet, ranging in size from the less-than-1-ft.-long dwarf shark and pygmy ribbontail catfish shark to the 50-ft. whale shark. Sharks have insinuated themselves into every marine environment from the Arctic to the tropics. One species, the bull shark, even ventures into rivers and lakes as far as 2,000 miles from the nearest salt water.
Beyond that, sharks have immense practical value. While shark cartilage does not, despite the claims, prevent cancer, it has been used to make artificial skin for burn victims. Shark corneas have been used experimentally for human transplants. Shark blood contains anticlotting agents. Shark-liver oil seems to aid white-blood-cell production; it is also an active ingredient in, of all things, Preparation H.
Sharks were the first creatures in evolutionary history to develop an immune system. Biomedical researchers believe that if we can figure out how theirs works we'll gain valuable insights into our own. A shark could someday save your life--if it isn't already extinct.
Sharks play a crucial role in keeping aquatic wildlife in balance. Scientists now understand that the ocean ecosystem has been evolving over hundreds of millions of years as an integrated whole--a biological machine in which each component has a vital function. For most sharks, that function is to serve as what biologists call an apex predator, the ocean equivalent of a lion or tiger or bear. Not only do they keep prey populations in check, but they also tend to eat the slowest, weakest and least wily individuals. In so doing, they improve the target species' gene pool, leaving the smarter, stronger individuals to reproduce.
When an apex predator is removed from the food chain, this carefully balanced machine tends to go haywire. Without wolves and mountain lions to keep them in check, for example, some deer populations in the U.S. have skyrocketed. And in just the same way, experts believe, overfishing of sharks off Australia and Tasmania years ago led to an explosion in the octopus population and a subsequent decline of the spiny-lobster fishery. Declining numbers of hammerhead sharks off the Florida panhandle may have allowed stingrays to reach record numbers there. "It's impossible to predict the implications of removing sharks from the food chain, but it could be disastrous," says shark specialist Sonja Fordham of the Center for Marine Conservation in Washington.
Fordham can't be more specific because biologists are only beginning to understand how sharks live and behave and what their relationship to other sea creatures really is. That's hardly a surprise, since sharks spend most of their time out of sight of human observers. Thanks largely to increasingly sophisticated electronics, though, scientists are finally opening a window on the life history of the shark.
To make reasonable but vague assertions like Fordham's more rigorous, for example, marine biologist Chris Lowe, a colleague of Meyer's at the University of Hawaii, has developed an ingenious way to measure the role of one shark, the hammerhead, in a well-defined environment. Every year thousands of hammerhead pups are born in Kaneohe Bay, on the east shore of Oahu. (About 40% of shark species lay eggs; the rest bear live young, and some of these carry their young just as mammals do, with an umbilical cord connecting the fetus to the uterus.) For the next 12 months or so, the baby hammerheads are an integral part of the region's ecosystem.
As it happens, the university's shark-research lab is located on Coconut Island, right in the middle of the bay, so Lowe can study them easily. In order to understand how much impact a hammerhead has on the bay ecosystem, Lowe is trying to learn how much energy it expends and how much food that takes. He has designed a miniature sensor that attaches to the baby shark's back and registers every beat of the tail as the shark swims along. By feeding the babies a precise amount of fish, then putting them in a tank with constantly flowing water--a sort of shark treadmill--he can determine just how many calories they burn in swimming a given distance.
In the second part of the experiment, Lowe puts a sensor-equipped shark into the open bay and follows it as it darts back and forth. After two days of nonstop tracking, he and his exhausted crew have a precise record of where the baby has gone and, by counting its tail beats, how much energy it has used. "We still have a lot of data to gather," he says, "but once we really understand what role the hammerhead pups play here, we can use that to begin understanding how adults fit into the ecosystem of the open ocean."
Back in Honolulu, on the other side of Oahu, the tiger-shark tagging is another high-tech effort to understand a different aspect of shark behavior. In 1992 two people were killed by tiger sharks in Hawaiian waters, the first such deaths there in three decades. An earlier spate of killings had provoked an all-out program to eradicate tiger sharks, but it was never clear whether that slaughter had been really effective.
This time Kim Holland, director of the shark lab, suggested a more judicious approach: first figure out how the sharks actually behave. If they keep to a small territory, a locally targeted eradication program could reduce the danger. But if they have no territorial allegiance, an aggressive animal might kill and disappear, never to return, and slaughtering the sharks that remained might not help at all.
With funding from the federal Sea Grant Program and help from students, including Lowe and Meyer, Holland began hooking tiger sharks off Waikiki Beach. Smaller specimens get old-fashioned tags; if a tagged shark is recaptured, the scientists know that it has returned to the same spot at least once.
Sharks that are at least 10 ft. long get a 6-in.-long cylindrical beeper deposited inside an incision in the belly. Every time the shark nears an acoustic receiver anchored on the ocean floor, it leaves a record of its visit. Based both on these records and on open-ocean shark chases, Holland has come to several conclusions. "First," he says, "we've established that tiger sharks do have home ranges." Those ranges, however, are huge: Holland's crew has tracked sharks all the way to Molokai, 25 miles away.
Moreover, the sharks patrol these ranges randomly. They may return to a given spot twice in one week, then not again for months. "It's clear," says Holland, "that you can't significantly reduce the local shark population by fishing for a limited time in a single area. You'd have to reduce the general population to have any effect--and that's not acceptable anymore."
Signals from beeper-equipped tigers have revealed that they dive much deeper than anyone had suspected--as far down as 1,000 ft. and back within 15 min.--and that they can swim in an absolutely straight line for miles at a time. "Every time you get a chance to follow a shark around in its natural environment," marvels Holland, "you get a new, incredible insight."
Halfway across the Pacific, marine biologist A. Peter Klimley of the University of California at Davis has for decades been getting his own incredible insights into shark behavior, frequently by taking risks others would call insane. While a graduate student in the 1970s, Klimley became the first scientist ever to swim directly into schools of adult hammerhead sharks. He dived as deep as 70 ft. without scuba gear so his air bubbles wouldn't disturb the skittish fish.
By observing sharks repeatedly over the years, Klimley was able to solve the long-standing mystery of why hammerheads gather in schools. It's clearly not for protection, since nothing preys on what Klimley calls "the big tough guys of the ocean." It turns out that they gather, at least in part, for an elaborate mating ritual, in which large, dominant females fight their way to the center of the school. The males know which females are most desirable by their position in the pack.
Klimley also discovered what may be the reason the hammerheads school year after year at an undersea mountain known as Espiritu Santo, 15 miles east of the Baja Peninsula. The metal-rich seamount, he found, has a particularly strong magnetic field. So do bands of ancient congealed lava that radiate from the seamount like spokes from a wheel. The hammerheads, he believes, can detect this magnetism and use it for navigation. The seamount is essentially a depot: the hammerheads gather there before going out to their feeding grounds.
This idea hasn't yet been confirmed by other shark researchers, but they don't dismiss it either. They know that sharks are extremely sensitive to electromagnetic signals; a "sixth sense" lets them home in on faint electricity generated by another fish's movement, gill action or even heartbeat. Indeed, Holland's team in Hawaii routinely tricks baby hammerheads at Coconut Island into striking at electrodes dangling in the water. Adult sharks, apparently drawn by the same process, have been known to bite through undersea cables. Holland is planning to investigate what sorts of electric signal might repel rather than attract sharks--protecting not just hardware but people as well.
While any shark 6 ft. long or more is potentially dangerous to humans, some species are more aggressive than others. None is considered deadlier than the great white. This huge fish, which can exceed 20 ft. in length and 2 tons in weight, is relatively rare among sharks but is responsible for more recorded attacks than any other species. Most of those have occurred off California, in the so-called Red Triangle, which extends from Monterey Bay to San Francisco to the Farallon Islands, 30 miles offshore.
It was here, in the early 1980s, that Klimley first saw an attack by a great white, on a 400-lb. elephant seal. The shark rose almost entirely out of the water, with the massive seal in its jaws. "It was stunning," he recalls. "The shark ambushed the seal, then came back several times to take three or four bites out of it. I had never seen anything like it." Since then Klimley has analyzed more than 130 videotaped white-shark attacks. All seem to follow a pattern. The powerful first bite usually takes place underwater, and the first sign of an attack is often a blood slick on the surface. Within 20 min., a sea lion or seal pops to the surface with a big chunk taken out of it. Then the shark appears, seizes the carcass and finishes it off.
Where Jaws went astray was in portraying great whites as mindless eating machines. Ken Goldman, a shark researcher from the Virginia Institute of Marine Science, in Gloucester Point, has been studying great whites in the Farallons for the past seven years. Says he: "Their attacks are very controlled, as is their feeding behavior." Klimley agrees: "The white shark is a skillful and stealthy predator that eats with both ritual and purpose."
That purpose does not include the deliberate consumption of humans--another misconception spread by Jaws. Great whites, most experts believe, prefer high-fat prey because fat is packed with calories. People are too scrawny, which is why, after taking a first bite--perhaps because a human, especially one wearing a black wet suit and flippers, looks something like a seal--a great white will usually turn up its nose at whatever remains. Most other shark attacks are probably also cases of mistaken identity: a swimmer's flapping feet and hands may look like the movements of a fish darting through the water.
About the only time sharks attack humans on purpose is when their territory is invaded or their courtship rituals are interrupted. And just about the only time they eat humans is when there's lots of blood in the water, after an airplane or ship accident, for example.
While marine biologists like Klimley and Holland are trying to unravel the mysteries of sharks' behavior and their role in the marine food chain, immunologists and physiologists are attempting to understand the animals' biochemistry. The idea that sharks can actually be beneficial to human health was established decades ago: vitamin A came primarily from shark-liver oil until 1947, when it was first synthesized in the laboratory. The unctuous liquid is also, for reasons still unknown, highly effective in shrinking human hemorrhoids.
Today biomedical scientists are on the trail of deeper mysteries. It has been known for some time that sharks have a low incidence of disease in general and extremely low rates of cancer. Known carcinogens injected into sharks by researchers don't trigger malignancies; they don't even cause the sorts of genetic damage that leads to tumors in other animals.
No one knows why. One clue may be that the chemical squalamine, found in the stomach, liver and gallbladder of the dogfish, can inhibit the growth of human brain tumors. Sharks also have a primitive but highly active immune system, which may play a role. Their resistance to cancer, however, has nothing to do with their cartilage, despite extravagant claims by people who peddle shark-cartilage pills. While the cartilage has proved promising as an ingredient in temporary artificial skin for burn patients, no proof whatever exists that it can prevent tumors in humans.
Assertions that it does are based on a tiny grain of scientific truth. Shark cartilage--and cow cartilage, for that matter--does contain minute quantities of a compound that inhibits blood-vessel growth, and tumors depend on the rapid growth of internal blood vessels that can feed them. But this substance is locked up in the cartilage and doesn't leak out to the rest of the body. To extract it, scientists have to soak huge amounts of cartilage in harsh chemicals for weeks at a time.
Nevertheless, shark cartilage is hot, and sharks are being slaughtered wholesale to produce it; a single processing plant in Costa Rica reportedly turns 235,000 sharks into cartilage pills every month. Sharks are also taken by the millions for their fins--a practice that scientists and conservationists find especially disturbing. Often the fins are hacked off and the sharks are thrown back into the water, alive but mortally wounded, to bleed to death.
It isn't as though the fins are being fed to starving children. They're used in Asia for shark-fin soup, a delicacy that fetches up to $150 a bowl. The market for shark fins is incredibly profitable; U.S. fishermen earn as much as $25 per lb. for fins, compared with 50[cents] per lb. for shark meat. The trade has grown dramatically since commerce with China began expanding in the 1980s: some 125 nations are now involved.
Though far less profitable, shark meat has also enjoyed a sales boom since the early 1980s. Tuna and swordfish stocks began to dwindle at that time, and the U.S. government encouraged fishermen to pursue other targets. That may have been a big mistake. Traditional food fish, like cod and tuna, grow quickly and lay millions of eggs at a time. Sharks, by contrast, can take two decades to reach sexual maturity, have a long gestation period and bear only a few young at one time. Killing a relatively small number of females can dramatically limit the reproductive potential of an entire species.
To date, only four countries--the U.S., Australia, New Zealand and Canada--have implemented any sort of shark-management plan, and only a handful have enacted laws protecting especially vulnerable species. Probably the most comprehensive undertaking is the U.S. National Marine Fisheries Service's Atlantic shark-fishery management plan, which since 1993 has limited the catch of 39 species in the Atlantic Ocean, Caribbean Sea and Gulf of Mexico. The plan sets annual quotas, bans finning and mandates species-specific tracking programs to help scientists. "It's having an impact," says NMFS's Rebecca Lent. "The 1996 assessments show that the large coastal sharks are still being overfished, but the rate has slowed down."
To slow it down further, NMFS announced last spring that it was cutting this year's quota for large coastal sharks by 50%, to 1,285 metric tons, as well as establishing the first quota ever for small coastal sharks and banning commercial harvests of five species considered especially prone to overfishing--whale, basking, white, sand tiger and bigeye sand tiger. Outraged fishermen have responded by suing the Secretary of Commerce. Conservation is important, agrees Robert Spaeth, head of the Southern Offshore Fishing Association, but he argues that shark populations are difficult to count accurately--an assertion biologists agree with--and that the government's statistics are therefore suspect.
NMFS stands by its numbers, however, and is considering even tougher restrictions, such as limiting the number of shark-fishing permits and setting minimum size requirements for each species. Another option, which requires cooperation from individual states but is enthusiastically supported by environmental groups, is to close critical inshore pupping and nursery grounds.
In the Pacific, conservationists' most immediate concern is finning. Every year at least 50,000 blue sharks landed by longline fishermen off Hawaii are stripped of their valuable fins and tossed back in the water. While the regional fisheries councils responsible for U.S. Pacific waters haven't yet addressed this problem, California has: the state legislature in 1993 passed a bill protecting white sharks from being caught or killed by commercial fishermen, along with more limited restrictions on other species and rules against killing sharks for their fins alone.
International regulations on shark fishing are much harder to implement than local laws. Three years ago, the member nations of the Convention on International Trade in Endangered Species ordered an investigation into the status of sharks worldwide. A preliminary version of that report, issued last December, warned of commercial fisheries collapses, local species extinctions and depletion of highly migratory stocks unless action was taken soon.
Nevertheless, two shark-related protection proposals were defeated at the recent biennial CITES meeting in Zimbabwe. Several nations successfully argued that fisheries management should be handled on a regional rather than a global basis. That makes no sense to marine biologists, since some shark species migrate thousands of miles. The Audubon Society's Camhi and other shark specialists hope to make a more convincing case at the next meeting, in 1999.
Perhaps they could make their point more strongly if they could get CITES to meet in Honolulu next time and take the other delegates out to visit the tiger sharks on their home turf. Arguments about the impact on marine ecosystems and about the destruction of creatures whose biochemistry might one day save lives are, in the end, somewhat dry and academic.
But there is nothing academic about a tiger shark bobbing in the preternaturally clear Hawaiian sea. I am now in the water, and Meyer has released the measured, tagged shark. Another student stands by to help it get moving, but that turns out to be unnecessary. With an almost imperceptible flick of its muscular tail, the massive fish is suddenly ten yards away, a graceful, pale white torpedo gliding effortlessly down into the measureless blue depths. In the face of such beauty, dignity and grace, I almost forget my fear.
--With reporting by Greg Aunapu/Miami, Andrea Dorfman/New York and Jeanne McDowell/Los Angeles
Quelle: Time
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