During the blistering heat of last summer, which was accompanied by unusually warm waters to the east of the Philippines and the Nansei Islands, a juvenile hammerhead shark wandered into the Sea of Japan. After being sighted off Shimane Prefecture it was hunted ruthlessly -- but apparently never caught. No doubt thoughts of the thrilling, but grossly misleading "Jaws" movies led the story-hungry media to magnify the story, which duly appeared in news releases nationwide. Near panic followed among bathers on the Japan Sea beaches.
At roughly the same time, a boy lost an arm (later sewn back on) to a shark in Florida. It was one of a small spate of attacks in that area that threw the media into a feeding frenzy.
The Florida sharks were probably all sandbar sharks. This is an aggressive, but usually not especially dangerous species, with closely related species widespread in the warm-water oceans. It is not a man-eater. Nonetheless, these media reports (in both countries) were followed by revenge killings of sharks. We often respond to tragedies with fear, then anger and an urge for retribution. And often innocent individuals suffer -- whether they're "collaterals" in Afghanistan or sharks in U.S. or Japanese waters.
Let's examine the facts, beginning with statistics from Florida showing shark attacks were fewer than average in 2001. As for causes, the sandbar shark is so-named because of its habit of swimming rapidly over shallow sandbars in search of mullet or other prey fish. When people ignorant of shark behavior swim out to these shallows and then stand there or walk about, a hungry sandbar shark may mistake the feet and ankles of the human intruder as edible fish, and attack.
The blacktip reef shark, a related, harmless species, behaves similarly. Swimming over shallow coral reef patches in search of parrotfish, etc., it sometimes mistakes the feet of wading humans as prey, again resulting in serious bites.
During my fish studies in 1981 at One Tree Island on the Great Barrier Reef, I had to anchor my small boat about 40 meters from the beach and swim or walk ashore and, the following morning, get back to my boat. There were always two or three blacktips en route, and because I have a some knowledge of shark behavior, I never waded. I always swam all the way to shore, up to a "tummy-scratching" depth of 20 cm. I never had a problem.
Other related species, such as the gray reef shark of the Western Pacific, also occasionally attack scuba divers as a result of human misunderstanding of their normal behavior. This species defends so-called "moving territories" around their swimming bodies when they are hunting alone, and warn intruders before they attack. The body is swung back and forth, in gradually widening arcs, as the back is hunched and the pectoral fins are lowered. When the head of the displaying shark swings at roughly 180 degrees, the animal is ready to attack.
The attack usually consists of slashing the intruder with open jaws as it swings its head by. This can cause series injury to humans.
As for hammerheads, there are no authenticated records of any attacks by them in Japanese waters, and worldwide there have been only 17 recorded unprovoked attacks in more than 200 years. Not long ago, while searching for bottlenose dolphins at Mikura-jima, our boat approached a young hammerhead. I jumped into the water, hoping to photograph the sleek, beautiful creature, but it raced away in panic. From the shark's perspective, I was the dangerous one.
Hammerheads normally dine on fish, which they seek out with an astonishing "sixth sense" called "electrosense." Electrosense organs, known as ampullae of Lorenzini, are small pouches beneath the skin, lined with hair cells and connected to openings in the skin that are filled with conductive jelly. The organs are clustered on the head and lower jaw, but their tubes spread outward to separate pores on the skin. Using this sense, sharks can detect electric fields as slight as 5 billionths of a volt per centimeter. This enables them to detect the weak electric field generated by all animals, resulting from electric activities of the muscles, such as a beating heart.
Hammerheads can detect stingrays even when they lie buried under sand. Scientists believe the strange shape of these sharks' heads may expand the range of their electrosense organs.
One August evening in 1976, I was in Miyake-jima studying Japanese angelfish, which are gorgeous reef fish that live in small single-male "harems." My study site was about 400 meters offshore, along an undersea cliff where the depth plunged 12-26 meters. Using scuba, I was lying quietly on a boulder at the edge of the cliff, watching the mating behavior of angelfish.
It was still fairly light, and hundreds of plankton-eating damselfish and basslets were feeding in the water above my head. Suddenly, with a clearly distinct "whoosh," all the planktivorous fish above me rushed to the shelter of the deep. I looked up, as a giant 4-meter hammerhead cruised slowly about 3 meters above my head, and then, still slowly and with an almost indescribably graceful beauty, swam off into the darkening waters.
The unnecessary slaughter of sharks worldwide, due to ignorance and fear, is tragic. Along the Florida coast, a person is said to be 100 times more likely to be killed by lightning than by a shark. Yet sharks remain greatly feared and little attention is given to their protection.
Shark populations are decreasing drastically from overfishing and other human abuse. An ocean without sharks would be like the plains of Africa without lions, leopards and hyenas. Our ignorance of the role of sharks is only part of a widespread, environmentally dangerous ignorance of the many delicate ecological webs of life in our seas.