400 Species Of Sharks essay example
Their teeth are short, broad and triangular shaped. The Leopard sharks (Triakis semifascicata) are active, fast sharks. They are nomadic, schooling sharks that roam inshore sand flats and rocky areas. They are known to feed on soles, bivalves, crustaceans, and other small bottom dwelling fish. Sharks have been around for 400 million years and out of that 400 million years about 100 million years the sharks and their close relatives have been closely unchanged in appearance. There are about 900 species of sharks and their close relatives.
There are about 400 species of sharks and more are been found and added to the list. What makes a shark a shark First its skeleton is made of cartilage, which is lighter, tougher, and more flexible than bone. The most noticeable difference is its teeth. Theyre jaw is lined with teeth, acting as a conveyor belt with new teeth replacing the old, broken and lost teeth.
As a matter of fact their entire body is covered in tiny tooth-like scales called dermal denticles, which, unlike those of bony fish, do not enlarge while the animal is growing larger. Another difference is that fertilization takes place inside the female with 1 of the 2 claspers inserted into her. The males use the claspers to inject the semen into her. The claspers are extensions of the pectoral fins. Unlike bony fishes, which usually spawn in great masses of tiny, immature young, most sharks produce large, well-develope offspring numbering, at the most, 100 to a litter. Most sharks are ovoviviparous, hatching the eggs within the female and bearing live young.
Some sharks are oviparous, however, laying their eggs externally. The eggs are often encased in leathery shells with tendrils that anchor them to rocks or seaweed. Others species of sharks are viviparous. Which means the yolk sac becomes a yolk placenta in the folds of the uterine wall and gives nutrients to the embryo. Embryonic development takes more than six months. The young are frequently born in protected closer to shore areas away from the males.
Sharks commonly fast for long periods during the breeding season and live on the vast reserves of lipids stored in their livers. This helps the sharks survive because it decreases cannibalism from the mother. The sharks tail is asymmetrical, with the vertebral column extended into the upper lobe. The fins and tails of sharks are rigid. Going against the popular image, the dorsal fins rarely project above water when the fish are close to the surface. They have strong digestive enzymes and a specialized epithelial fold that spirals the length of the small intestine, enabling the fishes to absorb a great diversity of foods.
Sharks, to a large extent, are scavengers, eating injured fish, garbage, and other waste from ships as well as animals such as seals, turtles, birds, whales, crabs, and a wide range of fishes. The most interesting difference is called the Ampoules of Lorenz ini, which detect faint electrical currents from other fish. All living things generate electrical fields due to the contracting of muscles and sharks have adapted to being able to use this as an advantage to find prey. Sharks have a very excellent sense of smell. They are able to detect small substances, such as blood in water and trace them to their source. Their sense of sigh allows the shark to catch dim movements of shadow and light in dark waters as it approaches its prey.
Sharks are particularly sensitive to sounds of low frequency and have fine directional hearing. Organs along their lateral lines and on the snout enable sharks to pick up weak electrical stimuli from the muscle contractions of bony fish. Their combination of keen senses accounts for the evolutionary success of sharks. The sharks also do not obtain a swim bladder, so they seem to be in constant motion. If the sharks stop swimming they will slowly sink to the bottom. They also have 5, 6, or even 7-gill slits instead of 1 that bony fish have.
The world has been tough on sharks. During a 17- month period in the 1930's, 1,500 sharks were caught by the mesh net method along the Australian beaches to keep swimmers safe. Up to 1,400 plus many dolphins are caught each year in South Africa. There is no easy way to keep sharks away from places where people swim, surf or scuba dive. Shark proof enclosures have been built, but these can only protect small areas because of the large coastlines. In South Africa and Australia, nets are used to trap sharks on popular beaches.
But the man- eating sharks arent the only victim of the nets. These nets also trap and kill many harmless sharks, dolphins, sea turtles and rays. Tests are being done to see if electrical barriers can be used, that wouldnt harm or kill the sharks and other animals in the process. An American scientist Dr. Eugenie Clark discovered that the Moses Sole from the Red Sea makes its own shark repellent.
When the Moses Sole is attacked, it secretes a milky, toxin ooze out of its skin and the shark will spit it out. This is another way to prevent shark attacks. Sharks play an important ecological role in oceans, similar to that of large predators on land. Sharks prey on weakfish, thereby helping a species to maintain its genetic strength. Because modern fishing methods have helped to deplete many food-fish species, however, the industry now views sharks as competitors, to the extents that shrimp trawlers frequently employ electrical shields by their trawls to keep sharks from destroying the catch. On the other hand, with the increasing scarcity and rising price of many food fishes, especially for United States consumers, shark meat is itself now selling at prices comparable to those for traditional table fishes.
The meat has long been eaten, especially in East Asian countries, but it is now increasingly being featured in United States markets and is often compared to swordfish. Also the sharks fins are made into soup. Sharks have a bad reputation as bloodthirsty killers. But only a handful of sharks are dangerous and attacks on people are rare. Shark experts are concerned that sharks are increasingly threatened by over fishing. In Florida, Lemon sharks are threatened due to the destruction of Mangrove Swamps, which are important nurseries for Lemon shark pups.
Many people begin to like and admire sharks as they learn about them. 1. web 2. OCEAN LIFE by Marty Syderman, The International Oceanographic Foundation Copyright date 1991 3. The Complete National Geographic 109 years of National Geographic Magazine on CD-ROM 4. Eyewitness Encyclopedia of Nature 2.0 Copyright date 1995 5. Ed marks Imagination Express DESTINATION: Ocean.