Sharks

It may sound impossible, but some of the smallest sharks in the world prey on some of the largest, while the largest sharks of all only eat tiny creatures.

The jaws of a great white shark are lined with
triangular-shaped teeth several inches long. The teeth have serrated edges to help saw through prey.

Ask most people to draw a shark and they are likely to come up with a torpedoshaped fish with a large upright back (dorsal) fin, huge mouth, and fearsome teeth.Many sharks are like this, but they are outnumbered by other species that do not fit in with this popular image at all. The angel sharks, for instance, could not be more different.They have a flat body and an equally large, flat head.Their pectoral (chest) fins look like broad wings, their pelvic (hip) fins are a similar shape—only smaller— and their eyes are positioned on top of their head. And instead of actively hunting, angel sharks spend most of their time lying on, or buried in, the seabed,waiting for an unsuspecting victim to swim within reach.

Special Senses

Despite their different body shapes and feeding habits, all sharks are hunters.They go about hunting in different ways, although they tend to use the same senses to find their prey. The ears are particularly sensitive and can pick up low-frequency sound waves from a distance of over a mile. Low-frequency vibrations—such as those created by an injured fish or other animal—are picked up from a distance of about 300 feet by a special system known as the lateral line organ.This organ runs down both sides of the fish’s body. Sharks can also detect very weak electrical signals, such as those given off by fish and other prey animals.Using highly sensitive pits on their snout, which are known as the ampullae of Lorenzini, sharks can even detect their prey if it is buried under the sand or mud. The eyes, too, are very efficient.They can detect movement even in dim light, making sharks efficient night hunters. Some, such as the great white shark, also have good color vision that allows them to hunt in bright light. It is their ability to smell blood, however, for which sharks are most famous. It is why sharks are sometimes called “bloodhounds.”A blacktip shark has been shown to be able to smell grouper flesh (groupers form part of the diet of many sharks) at a dilution of one part of flesh to 10 billion parts of sea water! Many sharks can smell the tiniest hints of blood from distances of around one-third of a mile.

Shark Attacks

Sharks rarely attack humans, but when they do, it can often lead to serious injury and, occasionally, death. In total, there are only about seventy to one hundred officially recorded shark attacks on humans each year, although there may be others that go unreported. Despite the severity of some of these attacks, especially those from large species such as great white sharks and bull sharks, many people survive, although sometimes with major injuries.One reason why the victims survive is the “bite and spit” method used by some species of sharks, in which they let go of their prey after the first major bite.This may be the shark’s way of protecting itself from getting scratched or bitten by its prey, while it waits for it to bleed to death or become weak.At this time it is therefore sometimes possible for a swimmer who has been bitten to struggle to safety or be rescued before the shark returns for a second, and often final, bite. Attacks may sometimes be the result of a shark mistaking a human for a seal, sea lion, or turtle.Whatever the reason, there is no doubt that the consequences of being bitten can be very serious, even when the shark responsible is only a modest size. Even generally peaceful species such as nurse sharks, angel sharks, or wobbegongs may attack when provoked.

Sharks in Peril

Although sharks occasionally attack and kill humans, they have more to fear from us than we have from them. We kill countless millions of sharks each year.Many are killed accidentally by being caught in nets set out for other species. However,many more sharks are targeted directly for a variety of purposes, ranging from sport fishing to the shark fin soup industry. During the nineteenth and twentieth centuries, shark oil was in great demand as a useful fuel for lamps. It was also an excellent source of vitamin A. However, electricity replaced the need for oil lamps, and from the middle of the twentieth century, demands for shark oil for Vitamin A decreased greatly when it became possible to make the vitamin instead. Today, shark oil is still used for some cosmetics and soaps, as a high-quality machine oil, and in some dietary and other health products. Shark meat has also become quite popular since the 1980s, particularly in parts of the United States. Shark fins have been in great demand in the Far East for around 2,000 years as the main ingredient for shark fin soup. Shark skin is also used for handbags, purses, and other expensive goods.Other shark parts, especially teeth, are sold as jewelry, decorations, curios, knives, and ceremonial items. The result of this wide-ranging onslaught on shark populations has led to some species facing a serious threat to their survival. It is only relatively recently that shark protection and conservation programs and laws have been developed and put into action.

Tagged Aquatic life, sharks