In Sharkland, you’ll learn why species that are normally found oceans apart converge in this one relatively small stretch of coastline, and you’ll be introduced to many of these unique animals, including the catsharks of the Agulhas Bank a 155-mile-wide stretch of shallow warm seas off the southeastern tip of the continent, Southern Africa’s richest fishing grounds. You’ll also explore nature’s most extreme sharks – the fastest, fiercest, smallest, and strongest – and discover the innovative adaptations that have made the Great White such an efficient killing machine.

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Online content for Sharkland was originally posted May 2007.

Sharks come in a dizzying array of shapes and sizes. Here are profiles of just four of the more than 350 known species.

The Wobbegong

The Wobbegong, or Carpet shark, is a pudgy, toad-like bottom dweller common along the coast of Australia and the warm waters around other Pacific islands. As THE SECRET WORLD OF SHARKS AND RAYS shows, the Wobbegong has short, wiggly tendrils around its mouth that resemble seaweed, fooling small fish into thinking the shark is a place to hide. Off Australia, the Wobbegong “is usually the first shark a diver encounters,” says Stephen Bilson, a Down Under diver who runs a Web page dedicated to sharks. “The first time I ever saw a Wobbegong, I was down on the wreck of the ‘Scottish Prince’ on the Gold Coast of Queensland. The instructor called us to him and was pointing to a part of the wreck. When I got there, I got the shock of my life! Here within about 18 inches of my face were what I considered to be huge animals. There were a whole bunch of them lying on top of each other, the largest about five feet. It was a magical experience for me.”

“If you haven’t seen a Wobbegong,” Bilson says, “they are extremely well camouflaged. I’ve seen many divers kick them, stand on them, or run into them. That is really the biggest danger. It must always be remembered that these are big fish with teeth, not really scared of divers. I’m not saying they are a dangerous species of shark — I’m just pointing out that if you provoke one, it might bite you. If they do bite you, they have a tendency to hold on.”

Basking Shark

Though Whale sharks are the world’s largest shark, Basking sharks come in a close second, growing to over 30 feet long. Like Whale sharks, Basking sharks are gentle creatures that feed on plankton. They live around the world, cruising along the surface at five or six miles an hour, filtering plankton from the water with enormous gills, specially adapted to work like strainers. A single shark can filter a volume of water equivalent to that found in a 150-foot long swimming pool every day. Remarkably, the huge sharks, which can weigh more than 3 tons, sometimes make spectacular leaps out of the water, crashing back into the waves with an enormous splash. Researchers are not sure why the great fish make the leaps, but it may be to remove parasites or to communicate with other sharks. Unfortunately, Basking sharks are under heavy pressure from fishing fleets. Their livers, which can account for up to one third of their body weight, produce a valuable oil used to lubricate engines and manufacture cosmetics. And their dorsal fins, which can be six feet high, are valued for soup. As a result of overfishing, Basking sharks are now believed to be extinct in some areas they once inhabited.

Great White Shark

One of the gentle Basking shark’s closest relatives has a very different reputation: the 10- to 20-foot Great White shark has been celebrated in books and movies as a ruthless man-eater. But scientists say the Great White, which lives in the warm seas of the world, has gotten a bad rap. Although Great Whites do attack people, the attacks are rarely fatal and the threat is exaggerated.

In fact, other kinds of sharks are responsible for more fatal attacks and, overall, more people are killed in the U.S. each year by dogs than have been killed by Great White sharks in the last 100 years. Still, Great Whites are prodigious hunters, able to tackle giant tuna and even sea lions and dolphins. After eating a large meal, however, a Great White can survive up to a month without another morsel. Like most sharks, Great Whites sometimes lose teeth in the process of hunting, but they don’t mind this: the teeth regrow within days. Over a lifetime, in fact, sharks may go through thousands of teeth.

Researchers believe Great Whites spend most of their 40-year lifespans hunting alone, but because the sharks are relatively rare, very little is known about their habits. Some researchers believe that the biggest Great Whites are rarely seen, because they retreat to the depths of the ocean. Other scientists believe that the big sharks, like some other species, change sex when they reach a certain size: males become females. The switch may ensure survival by allowing the largest, most experienced sharks to give birth to young.

Tiger Shark

Though Great Whites have gotten the man-eating reputation, the Tiger shark is the fish people should fear. The menacingly-striped torpedo has been responsible for more fatal attacks on humans than any other shark. But as THE SECRET WORLD OF SHARKS AND RAYS shows, Tiger sharks don’t discriminate when it comes to snacking: they will eat almost anything from sea turtles to tin cans. They also eat other sharks. In one case, in fact, snagging a Tiger allowed an angler to catch four sharks at one time: the fisherman caught a Tiger that had a Bull shark in its stomach, which had a Blacktip shark in its stomach, which in turn had a small Dogfish in its stomach! Like Great Whites, Tigers apparently live nomadic lives, roaming the warmer coastal seas. They are known to travel more than 60 miles a day. The Tiger apparently lives up to 40 years and can grow up to 16 feet. Its name comes from the dark stripes that decorate its back, though some Tigers lose their colors as they age. Female sharks produce up to 80 young at a time. Luckily, the Tiger isn’t generally considered a valuable food fish, so its numbers have remained strong.

When most people hear the word “shark,” images of sharp teeth and fins slicing menacingly through the water instantly come to mind. Indeed, sharks include some of the planet’s most efficient killers: they are powerful hunters able to catch thousand-pound tuna, small whales, and occasionally people, with ease.

But as NATURE shows, not all sharks are sleek killing machines. The Secret World of Sharks and Rays reveals that the ocean’s 350 species of sharks have many eating habits and come in all shapes and sizes — from gentle 50-foot giants that graze on plants and tiny crustaceans to bizarre-looking bat-faced dwarfs that rarely budge from their cozy burrows on sandy sea floors. The Secret World of Sharks and Rays also reminds us that, while sharks get more attention, the seas actually hold many more kinds of their close relatives, the rays. Scientists believe the oceans support thousands of species of these flat fish, which use their wing-shaped bodies to soar through the depths.

Still, it is the sharks that fascinate and terrify us. Ironically, however, that fascination is not matched by a clear understanding of how sharks live. “We still know remarkably little about how most sharks live and reproduce,” says shark expert Jack Musick of the Virginia Institute of Marine Science in Gloucester Point, VA. “We lack some of the most basic facts of their life stories.”

Researchers do know that sharks and rays are some of Earth’s oldest fish. Once, more than 400 million years ago, the two groups shared a common ancestor that swam through the planet’s oceans long before the first dinosaur appeared. Today, to the untrained eye, that common origin isn’t obvious, because most sharks and rays look so different from one another. But the fish are, in fact, relatives with structural similarities. Instead of bones, their body frames are made of cartilage: the tough, fibrous tissue that gives our noses and ears their shape. Sharks and rays also share the same kind of skin: instead of scales, they have small tooth-like spikes called denticles. The spikes can be so sharp, in fact, that carpenters have long used shark skin as sandpaper!

Sharks and rays also share some acute senses, such as smell and the ability to detect the mild electric currents produced by other animals — including potential prey. Some sharks are reputed to be able to detect minute quantities of substances such as blood in water from several hundred feet away.

Though huge fossilized teeth suggest that larger sharks once existed, today the largest species is the Whale shark, a gentle 50-foot long fish featured in The Secret World of Sharks and Rays. Despite its size, the Whale shark feeds on some of the ocean’s smallest life, the tiny plants and crustaceans that drift near the surface. Even an infant two-foot long Whale shark, however, is longer than the world’s smallest sharks, such as the 10-inch long Dwarf shark, or an even smaller species named the Pygmy Ribbontail catshark. In fact, fewer than 50 shark species grow to be longer than six feet, and most rarely reach three feet long.

Sharks also vary in lifestyle. Sleek Mako sharks, for instance, may spend their days cruising the seas at up to 40 miles per hour, hunting fish and occasionally launching themselves into the air with acrobatic leaps. Angelsharks, however, prefer a more sedate existence. They bury their camouflaged, flat bodies in the sandy sea bottom and wait for unsuspecting crabs to scuttle by.

Most sharks, however, have to keep moving to breathe and stay alive. That’s because they breathe by swimming forward with their mouths open, allowing oxygen-filled water to sweep across their gills. The majority cannot stop for long or move backwards, as can most other fish.

Some sharks grow to be only a foot long. Despite this limitation, sharks have found ways to survive in virtually every oceanic nook and cranny, and they can have lifespans of more than 100 years. They eat everything in the water, from squid to seals. The Cookiecutter shark even survives by using a suction cup to attach itself to whales and large fish, then carving out a core of flesh with scalpel-like teeth. Only three dozen shark species, however, have ever been known to attack humans, usually by mistake. Off Australia, for instance, Great White sharks have been known to attack surfers — perhaps because the combination of surfer and board looks like a seal playing in the waves. While people are sometimes injured or killed in the attacks, often the shark gets only a bite of surfboard.

Whatever their lifestyle, sharks and rays share some of the most interesting child-rearing habits in the world of fish. While some species lay eggs — known to beachcombers as “mermaids’ purses” because of their soft, envelope-shaped shells — deep sea sharks give birth to live young who are ready to live and eat on their own. In fact, in the case of some live-bearing sharks, such as the Blue shark, baby sharks growing within the mother’s womb may have already consumed a few meals before being pushed through the birth canal: they eat some of their smaller brothers and sisters in a remarkable form of pre-birth cannibalism that researchers believe helps promote survival of the fittest.

Unlike the many fish that lay millions of eggs at a time, sharks bear relatively few young. Some egg-laying species can have more than 100 pups at a time. In sharp contrast, the deep-sea sharks usually give birth to just one or two young. This slow reproductive pace, unfortunately, threatens the survival of some sharks.

“People are killing some sharks faster than they can reproduce,” says Musick. “Many species are like humans,” he explains. “They live a relatively long time, reach reproductive age late in life, and then produce relatively few young. So it can take a long time to rebuild a population that has been overfished.”

Overfishing of some sharks is becoming a serious problem, Musick and other experts agree. As The Secret World of Sharks and Rays shows in sobering footage, some sharks are taken for their tasty meat. But others are killed just for their fins or cartilage, which are considered potent medicines in some parts of the world. Once the sharks are “finned,” their bodies are tossed overboard. Worldwide, fishing fleets kill an estimated 100 million sharks a year; scientists believe some species’ populations could be dropping by up to 2% per year. If nothing is done, researchers say, some species could become extinct within 50 to 100 years.

Some governments, however, are moving to protect sharks. In the U.S., for instance, Musick and other scientists helped convince regulators to scale back a growing East Coast shark-fishing operation that threatened some populations. Other conservationists are hoping that a growing interest in sharks as “watchable wildlife,” to be viewed by divers on underwater safaris, will create economic incentives to leave sharks in the sea rather than put them on the plate. As more people enter the fishes’ secret world, conservationists hope sharks will gain more fans committed to protecting them.