Sharks Life

The shark. Perhaps no other sea creature is as well known, or as feared, as the shark. Sharks conjure images of horror in many people's minds. Much has been written of the shark's appetite for human flesh. There are those who will not set foot in the ocean, for fear of being eaten alive by this fearsome creature of myth and folklore. But are these myths true? Are sharks really the bloodthirsty man-killer we have labeled them, or have we created this myth through centuries of exaggerated stories? Should we fear the shark or admire it? Join us as we search for the truth about these magnificent but greatly misunderstood animals.

Sharks have lived in the seas for at least 400 million years. Before there were any dinosaurs roaming the Earth, there were sharks. Today, sharks inhabit all of the world's oceans at all latitudes and ocean temperatures. Some live in shallow water, while others live in water so deep that the sun never reaches them. No matter where you go, there are sharks to be found.
Sharks also come in many sizes. From the tiny dogfish to the enormous Whale Shark and of course the classic streamlined Caribbean reef Shark.

Biologically, sharks are fish, having both gills and fins. The sharks are different from ordinary fish in that they have a cartilaginous skeleton as opposed to a bony one. This makes their bodies very flexible. Fish with cartilaginous skeletons are grouped together in a special class which also includes the skates and rays, close relatives of the sharks. All of these cartilaginous fishes have another trait marking their difference from the bony fishes: the absence of a swim bladder.

A swim bladder provides a bony fish with a means of controlling its buoyancy by allowing it to add or remove air from this organ. Sharks have no swim bladders and instead they have a relatively big liver full of a oil or gas which is lighter than water and keeps the shark balanced and so they wont sink, however some species must keep swimming because they are still heavier than water.The skates simply stay on the bottom, feeding on worms, crustaceans and mollusks which live in the sand.

The rays use their large wing-like pectoral fins to actually fly through the water. Just as birds use their wings to fly through the air, rays actually do need their wings to keep from sinking! Here, a manta ray uses its 12 foot wingspan to swim in a strong current. The Manta feeds like the whale shark, by filtering plankton from the water. A shark works more like an airplane than a bird. It uses its tail fin in a back and forth motion to provide forward thrust, while its pectoral fins, which are shaped just like airplane wings, provide lift to keep the shark from sinking. Just like an airplane, if the shark stops moving forward, it will sink and crash into the bottom! Because the tail is designed for producing power, while the pectoral fins are designed to produce lift, sharks are fast, but not as agile as most bony fishes. For this reason, many animals which could otherwise serve as food for sharks can get away from them using their superior maneuverability. In order to capture prey, sharks rely both upon the surprise attack and their superior senses.

Sharks have several interesting senses which are well adapted to the their lives as perfect predators. First of all, they have an extremely good sense of smell.

They have 2 more senses than people. They have a Lateral Line (which is located along the sharks body from the snout to tail, as a line) and the Ampullae of Lorenzini System (located in their snouts as tiny dots). This allows the shark to locate injured prey from quite a distance. It takes only seconds for a reef shark to find and devour this small tuna.

With these 2 organs Sharks can sense minute electrical disturbances in the water which are generated by the swimming muscles of fish. Sharks are among the most sensitive to electric currents of all ocean creatures. Sharks have an extensive network of pores on their bodies which are connected to specialized sensory organs for sensing electric pulses. This electro-sensory system is so sensitive, that it enables sharks to detect the small bioelectric currents produced by the muscles of prey fish at a distance of up to one meter or so.

This allows many types of sharks to feed quite readily in complete darkness. This is also an useful tool to know what are their surroundings and to navigate in a reef or in open water.

It is a popular misconception that sharks have such good senses to make up for poor eyesight. In fact, this is completely untrue. Sharks have excellent eyesight, not only in daylight, but also in very low light. They do see in colors.

Sharks have a unique eye with a mirror behind the retina. This mirror reflects light back through the retina a second time, increasing sensitivity in low light. For this reason, it is believed that sharks can see reasonably well in nearly complete darkness. Starlight is plenty of light for a shark.

Because their eyesight is so important to them, sharks are very careful about protecting their eyes.

Many species of sharks, including the Great White, have a special protective eyelid, called a nictitating membrane, which is used to cover and protect the eye when engaged in aggressive behavior such as fighting or feeding.

The membrane rolls over the eye from below, and minimizes the chance that a struggling fish or other shark could poke the animal's vulnerable eye.

Because sharks enjoy life at the top of the food chain, they don't have to worry much about being eaten (except perhaps by bigger sharks). Still, they do have camouflage. This camouflage is intended to help them sneak up on their prey. Shark camouflage is called “countershading”, and it is found on most sharks. Countershading means that the dorsal surface of the animal is dark in color while the ventral surface is white. When looking down on a shark, the dorsal surface blends in better with the darker water below, while the white belly of the shark blends in better with the lighter water above.

Sharks are voracious carnivores, meaning that they eat meat, usually in the form of fish or invertebrates. But they do not always have to kill what they eat. Sharks are opportunistic scavengers, and will frequently eat whatever they can find (except us) which is already dead . This does not mean that sharks are indiscriminate eaters: sharks will sometimes refuse food that they find objectionable.
If it is necessary for the shark to hunt for food, it will usually search for something which is easy to catch. Generally, sharks seek out sick or injured prey, as do wolves, tigers, and other large predators. Not only does this make capturing a meal easier for the shark, but it serves the purpose of keeping the gene pool free of weak animals. This is a very important way in which nature keeps natural populations healthy. Therefore, the shark is an essential part of the ecosystem, serving the purpose of “keeping clean” natural populations and the ecosystem. In addition, the role of top predators in the food chain is very important for maintaining balance in the oceans. Without the top predators feeding on the smaller fish, the fish populations would grow unchecked and could soon outnumber their food resources. For these and other reasons, sharks are absolutely essential in the world's oceans.

Sharks are frequently seen with traveling companions. One such companion is the remora, a fish with a suction cup which it uses to attach itself to sharks, whales, turtles or other large marine animals. Contrary to popular belief, the remora does not harm its host. It gets a free ride and feeds from its host's leftover scraps. Although remoras may sometimes annoy the shark, they perform an important service by removing parasites from the shark’s skin. Other traveling companions are the so-called pilot fish. Pilot fish are so named because people used to believe that they guided, or "piloted" the shark to food. We now know that these fish are, in fact, looking for a free meal. But if they aren't careful, the pilot fish themselves may end up being the meal!

Any discussion of sharks usually ends up with the question of how dangerous they are to people. But Sharks are not dangerous at all. The number of people who have been injured by sharks is minuscule compared with the number of people who have been injured by dogs, or injured in car accidents. Even lightning has killed more people than sharks. Yet we still call them maneaters! Certainly sharks are capable of killing people, but in general, people simply are not their preferred food!
Unfortunately, humans on surfboards have an uncanny resemblance to a seal as seen from underneath. And, the added fact that a human on a surfboard is by no means as graceful as a healthy seal, makes the shark think it has found a very easy meal.

Most sharks are discerning about what they attack and prefer fish to people. But the presence of fish blood in the water could possibly create an unpredictable situation, and accidents could happen in the confusion. Shark attacks are either accident or a simple case of mistaken identity, not because the shark was hungry.

The jaws of the shark are its most formidable weapon. Without their jaws and teeth, sharks would be practically harmless. The teeth of most sharks are extremely sharp and numerous. As teeth are worn out or broken, new ones rotate into place from behind the old ones giving the animal a constant supply of new, sharp teeth.

The shark's jaws have powerful muscles, which can generate well over 100 pounds of force in larger sharks. Needless to say, with that much power, it takes very little effort for a shark to bite through bone and tissue.

Most sharks are discerning about what they attack and prefer fish to people. But the presence of fish blood in the water could possibly create an unpredictable situation, and accidents could happen in the confusion. Shark attacks, which should be called shark mistakes, are either accidents or a simple case of mistaken identity.

Although sometimes we tend to think of sharks as cold-booded killers who are completely indiscriminate about what they eat, this doesn't seem to be the case. In general, sharks are afraid of people and will not approach divers.

Most Sharks must swim to survive. However, many species such as the nurse, white tip or caribbean reef shark, can periodically rest on the bottom, able to move water through its gills quite well in this position by swallowing water like most other fish. Every year, more and more species of sharks are "caught in the act" of doing the impossible: resting on the bottom.
Recent interest in shark research has made another fascinating discovery about these fish. Sharks seem to have a natural immunity to cancer. While cancer is common in humans, it is unheard of in sharks. Scientists are hoping that some day soon, a cure for cancer in humans may come from that animal we love to hate...the shark.

Like all life in the sea, the shark has a place in the food chain, and without the shark, the world's oceans wouldn't be balanced. Already, many species of sharks are endangered because they are being ruthlessly killed out of ignorance. Additionally, sharks are killed for their fins, which, in many Asian countries, are used to make Shark's Fin soup. Frequently the animal is killed just for its fins, and the rest of the animal is discarded, or thrown back into the sea alive, to die a slow and painful death. Not only are these fishing practices cruel, but they are extremely wasteful of the resources of the sea.
It's a shame that this beautiful and elegant creature is so misunderstood by so many people. Like many other predators in the world, the shark is feared as a threat to man based more on myth than on fact. When we understand that sharks are designed by nature as predators, we begin to see the importance of the role they play in the ocean ecosystem and the true beauty of these remarkable animals. We need to remember that sharks, like all animals, have a place in the ecosystem and perform a function. Sharks are not bloodthirsty maneaters, but simply animals trying to survive. As visitors to the shark's world, it is our responsibility to treat the shark with the respect that a wild animal deserves. Only then can we truly begin to understand sharks and how they live.

Cheers,
Save Sharks
Isa