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| Sunday, 15 May 2005 |
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Junior Observer |  |
| News Business Features Editorial
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Mighty jaws
However, such attacks are not very common. The chances of being attacked by a shark are surprisingly low and most attacks happen in quite shallow water. Several types of sharks are known to attack man, and they include the carpet shark, the tiger shark and the hammerhead. But the most fearsome of these so called 'man-eaters' is the great white shark. The great white shark which is a fierce predator of fishes and other sea creatures such as whales, porpoises and turtles can grow to a length of 7.6 m (25ft). Divers suspended inside steel cages, in order to study these massive fish, have reported hair-raising stories about how these huge specimens have tried to lunge through the bars of the cages or have grabbed the cages in their mighty jaws and shaken the cages violently, as if in frustration that they could not eat the occupants of the cage. The great white shark's hunting technique
The great white shark, up to 6 m (20 ft) in length, is large enough to attack humans but, it is unjustly feared because it prefers to eat seals and other large fish than humans. Let's check out the complex and sophisticated 'attack' strategy the white shark uses, to find, hunt and finally dispatch its prey. When seeking a prey, the first of the shark's senses that comes into play is smell. Did you know that the nasal sacs in a shark's nostrils can detect minute quantities of blood, as low as one part in 1,000,000,000 - seeping from an injured animal? Once the blood smell is detected, the shark promptly swims towards its source. It can detect the low-frequency sounds the injured prey makes from about one kilometre away. If you are aware that sharks have no external ear holes, you may wonder how it detects such sounds. Well, it does have a pair of inner ears, flanking its brain case. Each of these ears is connected to an external pore on top of the shark's head which detects sound, especially low-frequency sounds which travel through water.
The shark then swims closer and using its sophisticated eyes that can see colour, spies its victim. Once this is done, it circles the prey to ensure it is suitable to 'eat', before opening wide those amazing killer jaws to attack. However, at this point, its eyes serve no function. In fact, the shark rolls its eyes back out of harm's way and becomes temporarily blind, guided only by its sensory armoury - which is activated at this time. Now, what exactly is this 'sensory armoury'? Beneath the skin, in its snout are numerous tiny, electrosensitive organs which are known as 'ampullae of Horenzini'. Each of these organs are linked to the outside world by an external pore. These detect the minute electrical fields produced by the shark's victim and allows it to home in on its prey.
After its first bite, a shark usually waits for its prey to die before devouring it. The shark may nudge the prey only at the very end, in order to find out more about its texture and size from the tiny touch receptors located on its snout. Now do you understand what a lot of senses come in to play before a shark attacks its victim? **** Fact file Most popular varieties * There are more than 90 varieties and some of them are the zebra shark, whale shark, blue shark, blacktip shark and the blind shark. * Sharks become immobile when upside down. * The great white shark is the only shark that sticks its head out of the water to look around. * Only a few sharks including the great white shark, jump out of the water. * The bull shark can live in both fresh and salt water. * Sharks have been around in some form, for about 400 million years. * Sharks belong to the class of fish, Chondrichthyes. * Sharks have the most powerful jaws on the planet. Unlike most animals' jaws, both the shark's upper and lower jaws move. * A shark bites with its lower jaw first and then its upper. It tosses its head back and forth to tear loose a piece of meat which it swallows whole. * Each type of shark has a different shaped tooth depending on their diet. You can tell he's a carnivore just by looking at those sharp, pointy teeth! * A shark may grow and use over 20,000 teeth in its lifetime! * Sharks never run out of teeth. If one is lost,another spins forward from the rows and rows of backup teeth. *** Lateral line system
The lateral line system consists of a horizontal grove running along
each flank and onto the head. At this point it splits into three shorter
grooves within which is a line of tiny sense organs known as neuromasts.
They consist of tiny sensory cells.Neuromasts also cover the entire
surface of a fish's skin and can serve as normal touch receptors. |
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| Politics | Produced by Lake House |
Many of you would have watched or at least heard of the famous movie
Jaws, which leaves one's nerves on edge. It's about a man-eating shark.
And what the movie portrayed is not pure fiction. Sharks do attack humans,
and whenever a shark-attack occurs, it makes headline news. 
Sharks have not changed much since they first swam the prehistoric seas
some 350 million years ago. They have an astounding ability to coordinate
their senses to catch their prey, earning a reputation as 'killer
machines'. Of all the creatures in the animal kingdom, the white shark
stands out as an animal with great sensory coordination on record. 
Running along the side of the shark is its lateral line system, where,
sensory cells within this line system allows it to sense the presence of
other creatures by their movements. Both splashing and swimming motions
can be felt by the shark's 'distant touch' sense, from about 200m (650 ft)
away. 
It is the ability to use these complex multiple senses that usually
makes a shark's aim accurate and its first bite generally deadly. 
The lateral line system is a kind of underwater sonar and is very
similar to the sonar-based navigation system employed by bats.This system
forms the basis of a sophisticated mode of navigation that uses
water-borne vibrations to give the fish an accurate picture of its
surroundings.While bats listen to ultrasonic squeaks that bounce back from
solid objects, fish feel the movement of water reflected back against
their body from objects around it. 
