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The Great White Shark—Under Attack

The Great White Shark—Under Attack

 The Great White Shark—Under Attack

The largest carnivorous fish in the world, the great white shark is perhaps more frightening to humans than any other living thing. Yet, now it is a protected species in all or some of the waters surrounding Australia, Brazil, Namibia, South Africa, and the United States as well as in the Mediterranean Sea. Other countries and states are also considering extending protection. But why protect a known killer? The issue, as we shall see, is not that simple. Nor are public perceptions of the white shark always based on fact.

ALONG with the killer whale and the sperm whale, the great white shark * is at the top of the marine food chain. In the shark family, it is the king, the supershark. It will eat anything—fish, dolphins, even other sharks. But as it gets older, bigger, and slower, it develops a preference for seals, penguins, and carrion—especially dead whales.

In locating their food, most sharks use all their senses, including excellent vision. As for their sense of smell, let’s just say that the metaphor of a swimming nose is most appropriate! Yet, in addition, little escapes their ears—so little that sharks could also be called swimming ears.

The ears of the shark are aided by pressure-sensitive cells along each side of its body. Nothing escapes this eavesdropping system, which is especially attuned to the vibrations of struggle—a fish thrashing at the end of a spear, for example. Thus, it is prudent for underwater spear fishermen to get bleeding, thrashing fish out of the water as soon as possible.

Sharks also have a sixth sense. Thanks to the ampullae of Lorenzini—tiny ducts peppered around their nose—they can detect the weak electrical fields emanating  from the beating heart, the gill action, or the swimming muscles of potential prey. In fact, so keen is this sixth sense that it may even sensitize sharks to the interaction of the earth’s magnetic field with the ocean. As a result, sharks may know which way is north and which way is south.

Identifying the White Shark

Though it is called the great white shark, only its underside is white or pale. Its back is normally a dark shade of gray. The two colors abut along the side of the fish in a ragged line that varies from shark to shark. This feature enhances camouflage, but it also helps scientists to recognize individual sharks.

How big do white sharks grow? “The largest white sharks accurately measured,” says the book Great White Shark, “range between 19 and 21 feet [5.8 and 6.4 meters].” Fish this size can weigh in at over 5,000 pounds [2,000 kg]. Yet, thanks to swept-back triangular appendages that fuse with a torpedolike torso, these monsters glide through the water like missiles. Their nearly symmetrical tail, built for power, is another rarity in the shark world, as most other species of sharks have distinctly asymmetrical tails.

The white shark’s most distinguishing as well as fearsome assets are its huge conical head, its cold black eyes, and its mouth bristling with razor-sharp, serrated, triangular teeth. As these double-edged “knives” chip or drop out, a dental ‘conveyor belt’ nudges replacements forward.

Powered by Warmer Blood

The circulatory system of the Lamnidae family of sharks, which includes the mako, the porbeagle, and the white, is dramatically different from that of most other sharks. Their blood temperature is about 5 to 10 degrees Fahrenheit [3 to 5 degrees Celsius] above water temperature. Their warmer blood speeds up digestion and adds to their strength and endurance. The mako, which feeds on fast pelagic fish, such as tuna, can speed through the water at 60 miles per hour [100 kph] for short bursts!

When sharks swim, they get lift from their two pectoral fins. If they swim too slowly, they stall and sink just like an aircraft, and this in spite of a buoyancy-inducing cache of oil stored in a liver so big that it may account for one quarter of the shark’s total weight! In addition, many species of sharks must keep swimming to breathe, for in this way they drive oxygen-rich water through their mouths and gills. This accounts for their perennial cold grin!

A Man-Eater?

Of the 368 species of sharks presently known, only about 20 are dangerous. And of these just four are responsible for most of the some 100 attacks on humans that are reported worldwide each year. About 30 of these attacks are fatal. The four guilty species are the bull shark, which may have taken more human lives than any other shark, the tiger shark, the oceanic whitetip shark, and the white shark.

Surprisingly, at least 55 percent—and in some parts of the world, about 80 percent—of those attacked by the white shark have lived to tell the story. Why have so many survived an attack by such a feared predator?

Bite and Spit

The white shark is known to spit out its wounded prey after an initial, powerful bite. Then it waits for the victim to die before  eating it. When humans are the victims, this behavior provides an opportunity for rescue. This, at times, has been achieved by courageous companions, thus demonstrating the wisdom of the advice never to swim alone.

However, such rescue attempts would be practically suicidal were it not for another white-shark behavior. The smell of blood does not drive it into a feeding frenzy as it does certain other sharks. But why does the white shark use a bite-and-spit strategy?

It is because of its eyes, speculates one scientist. Unlike other sharks, the white has no eyelidlike membrane to protect its eyes; rather, it rotates them in their sockets when collision is imminent. At the moment of impact, the eye is left exposed, perhaps to the flaying claws of a seal. Therefore, for the white shark, a quick, mortal strike and release is common behavior.

Keep in mind, too, that white sharks behave much like human babies—everything goes straight into the mouth for an initial evaluation! “Unfortunately, when a big white [test] bites there can be disastrous consequences,” explains John West, a marine biologist in Sydney, Australia.

Though the white shark is a dangerous animal, it is not a demon craving human flesh. One abalone diver who spent 6,000 hours in the water saw only two white sharks, and neither of them attacked him. In fact, the white shark has often fled from humans.

While diving off the Cape Verde Islands, ocean explorer Jacques-Yves Cousteau and a companion chanced upon a massive white shark. “[Its] reaction was the least conceivable one,” Cousteau wrote. “In pure fright, the monster voided a cloud of excrement and departed at an incredible speed.” He concluded: “In pondering all of our experiences with the white shark, I was continually struck by the great gulf between what the public imagines the creature to be and what we saw it to be.”

The White Shark as Prey

The public image has been greatly colored by the 1970’s novel Jaws, which was turned into a popular movie. Overnight the white shark became evil incarnate, and “whole gaggles of trophy hunters raced to see who among them would be first to display the head or the jaws of the maneater over the fireplace,” says the book Great White Shark. In time, a mounted white shark tooth would fetch up to $1,000 (in Australia); and a full set of jaws, over $20,000.

By far the majority of white sharks, though, die in commercial fishing nets. In addition, millions of other sharks are caught annually to satisfy the burgeoning market for shark products, especially fins. In recent years, as the numbers taken have diminished, alarm bells have been ringing worldwide, especially for white sharks.

Understanding Is Coming

Sharks are known to scour the seas for the sick, dying, decrepit, and dead. Thus, a healthy shark population means healthy, hygienic oceans.

Recognizing the threat to the survival of sharks, the Species Survival Commission of the International Union for the Conservation of Nature has set up a Shark Specialist Group to study the whole shark problem. Studying the white shark, however, is not easy—they are not prolific, and they die in captivity. So they must be studied in their natural habitat.

As humans have gained greater understanding of sharks, their attitude toward these fascinating creatures has changed. But that doesn’t change the great white shark. Though not a fiend, it is, nonetheless, a dangerous animal and should be treated with caution and respect. A lot of respect!

[Footnote]

^ par. 3 The great white shark, or white shark, has a variety of common names. In Australia, for example, it is sometimes called the white pointer; in South Africa, the blue pointer.

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These sharks have large and fearsome mouths

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Photos by Rodney Fox Reflections

South African White Shark Research Institute