Know About Shark Article From TamilYoungsters.com

It weighs three tonnes, can reach speeds of 60km/h and is armed with

300 razor-sharp teeth: the great white shark is one of the last superpredators

on the planet. But marine expert Mike Rutzen says they’re

not mindless killing machines. AND he can understand them…

15 MINUTES WITH A GREAT WHITE SHARK

It’s arguably the most dangerous laboratory in the world. Fishermen and scientists are working together on a boat owned by non-profit organisation OCEARCH in order to carry out 12 different tests on great white sharks and equip each animal with a sensor. The shark is attracted with bait, caught, then hoisted onto the boat using a special lift. Skipper Brett McBride manoeuvres the shark onto the deck by hand. From that point, the researchers have 15 minutes to examine the animal. A dark towel over its eyes and a constant stream of water over its gills calm the shark while the workers take blood and tissue samples and attach a sensor that will allow them to track the shark’s movements once it’s released back into the sea.

1.NAVIGATION NOSE   

The nose of a great white is so sensitive that it can determine the exact direction that a smell is coming from. How? A smell of blood coming from the right will hit its right nostril fi rst, then the left.

2.FEARSOME BITING TECHNIQUE

Shortly before the shark bites into its prey, it shoots its jaws forwards and yanks it head back. The lower jaw hits the victim fi rst, before the teeth of the upper jaw saw into the fl esh. The entire process lasts just under a second.

3.THE EATING MACHINE

With a single bite this marine predator can devour 9-13kg of meat. A great white shark will ingest around 11 tonnes of sustenance annually. By comparison, an average-sized human consumes around half a tonne of food per year.

4.FLEXIBLE EXOSKELETON

The skin contains a thick layer of collagen that overlays the muscles, protecting the shark like a suit of armour. It also ensures that the muscles work effectively.

Lets ask about this to guy who was familiar with Shark Gansbaai, South Africa. Mike Rutzen sits on the stern of his craft, his feet dangling in the water. A few metres below the sea surface, a streamlined shadow circles Rutzen’s fishing boat. The fish is what biologists refer to as an apex predator – with a body length of up to six metres, it sits at the very top of the food chain in its habitat. It’s a great white shark – and most of us would regard what Mike Rutzen is about to do next as insane… The 44-year-old tightens the straps on his flippers and gracefully glides into the water of the Atlantic Ocean – with no metal cage and no harpoon. Once underwater, Rutzen comes into closer contact with the great white shark than most researchers would dare. “I want to understand the animals better,” he says. “To do that I have to get into the water with them, observing them without a boat or cage.” Such objects, says Rutzen, alter the sharks’ behaviour.

During these unprotected encounters, Rutzen’s survival rests on just one thing: the South African’s uncanny ability to ‘converse’ with the sharks. “They communicate using body language,” he says. “If you know the signs and how to react to them, you can talk with them.” But these shark/human conversations are akin to a potentially fatal game of chess. One false move or misjudged moment, and it’s curtains. “Great whites aren’t mindless eating machines,” says Rutzen, “but they do have less patience than all the other animals that I have dived with.” He won’t get into the water, then, with just any old shark, and will keep his distance from particularly aggressive great whites who bite his boat or angrily bare their teeth. “I’ll only ever swim with a shark that seems relaxed and is calmly circling the boat.” 

HOW DO YOU KEEP YOUR DISTANCE

FROM A SIX-METRE PREDATOR?

These risky encounters have three key factors. One: Rutzen must awaken the shark’s curiosity so that he can spend as much time as possible with the animal; Two: the shark must view Rutzen as a predator, in order to respect him; Three: Rutzen, however, must not appear threatening, or he’ll either scare off the shark or risk a defensive attack. Rutzen must walk an extremely fine line between dominance and humility – but how can he ensure he doesn’t cross that line? The moment the researcher is submerged in the water, he pulls his legs up to his chest and embraces himself, making himself as small as possible. The shark – a female – cannot resist the temptation, and swims over to investigate Rutzen. What is that in the water? Is it edible? The female draws closer, slowly, with her mouth closed – a sure sign that she’s relaxed. “As a shark approaches me, I make myself bigger,” says Rutzen. He stretches out his legs and turns towards the shark. This causes the great white to maintain its distance, alter its course and swim past Rutzen “The animal notices that I don’t feel comfortable at this distance, and gives me more space.” Suddenly, a second shark appears – and this one isn’t as friendly as the female. It wants to identify Rutzen by having a taste of him, and chomps at his fl ippers. “This ‘test-bite’ is the shark’s only way to inspect an object more closely,” explained Ron Taylor, the late Australian shark-expert, who recently died of cancer. As soon as the shark has latched on, it uses thousands of taste buds to analyse the object and to decide whether it’s prey or not. It’s a worrying moment for Rutzen: even if the predator applies this test using only a fraction of its maximum biting strength of 1.8 tonnes, it could still bite off his leg. The situation is critical. Rutzen must ensure these two adult super-predators stay in his line of vision while also keeping them at a distance. Fleeing is not an option. “Anything swimming away just awakens the animal’s hunting instinct and is judged as prey,” says Rutzen. It is the shark that ultimately decides when the encounter is over. Unfortunately, the agitated newcomer isn’t eager to bid Rutzen farewell. It swims directly at him, teeth bared. The next few moments represent a fierce psychological battle in which Rutzen must emerge as the dominant force, if he is to escape with his life. Once again, Rutzen does something that appears to be suicidal: he swims down, rather than up, and positions himself beneath the shark. “This is a power position for great whites,” he explains, “as they will often attack from below. If I place myself in the same power position, the shark judges me as an equal.” The manoeuvre is still extremely risky, as the shark could overtake Rutzen as he dives downwards before swooping in to attack him. But the South African’s plan proves successful: shark number two retreats, and Rutzen makes his way back up to his boat.

WHICH STRATEGIES DOES A GREAT

WHITE SHARK USE TO KILL?

If Rutzen had remained on the water’s surface, his outing could have ended fatally, because an upwards attack is the preferred strategy of a great white. In South Africa the sharks have developed an additional hunting strategy: breaching. The prey hunted using this method are young seals; a shark creeps up on a seal from below, accelerating from zero to 60km/h in seconds and racing towards the water’s surface like a rocket. The shark seeks to ram its prey, render it immobile with a bite and then devour it immediately. To achieve this, the predator accelerates so fiercely that it actually hovers over the water for a moment before crashing back beneath the surface. Another tactic popular with several shark species is the ‘bump and bite’: the shark circles its victim, bites it just once, then vanishes for a short while. So why does it not chow down immediately? Despite its strength, a shark’s sensory organs are vulnerable, and a seal or turtle could seriously injure its eyes with surprising ease. “If a shark loses an eye, it can die,” Rutzen explains. This super-predator is completely dependent on its senses, and for that reason it will do everything in its power to avoid close combat. So after a shark has bitten its prey, it leaves it to bleed out, only returning a few minutes later. The prey is now either weak or already dead. A great white will spear the flesh with the teeth in its lower jaw, then slice it using its upper teeth like a steak knife. According to the International Shark Attack File, there have been 279 recorded instances of people being attacked by a great white shark; of these, 78 died of their injuries. Why does this perfect predator allow human prey to survive and escape so often? “Shark attacks are relatively common because the creatures get humans confused with seals and turtles,” says aquatic biologist Dr John McCosker of the California Academy of Sciences. “A person who’s floating on the water’s surface using a surfboard or boogie board looks very similar to these types of prey. In reality, only 7% of all shark attacks end fatally.” Many humans manage to escape from bumpand- bite attacks because the shark leaves them for a while so that they can bleed out; the bite victim will then seize this opportunity to flee or be rescued. If humans actually were on the shark’s menu, there would be fatalities every day. Great white sharks can see ten times more acutely than humans and sniff a single drop of blood in a 50-metre swimming pool. “They can also swim at a depth of just one metre, and can come closer to the shore than my boat,” says Rutzen. “If people were prey they’d simply lie in wait for us, close by the beach. Humans are the slowest form of protein available. Given what an easy catch we are, sharks could eat us in very large numbers – if they were so inclined. “I take calculated risks in order to learn about the sharks for conservation reasons,” says Rutzen. “If you try to be Rambo in this game, you will die.

 Let Us see about Shark Anatomy:-

1. NOSE

Great white sharks can smell a single drop of blood in a 50-metre swimming pool. Little wonder: its olfactory radar for blood and other bodily fl uids takes up 20% of its brain.

2. EYES

Great white sharks see in colour and their vision is ten times better than a human’s. They even possess low-light amplifi cation. In spite of this, split seconds before an attack a shark will go blind, as a membrane known as a third eyelid covers its eyes to protect them.

3. SIXTH SENSE

Using its ampullae of Lorenzini – gel-filled cavities – a shark can sense electric fields. That’s how it notices movements in the water, and possibly also within the Earth’s magnetic field.

4. EARS

The great white can hear for many kilometres and pinpoint the locations of sound waves. The otolith – or ‘ear stone’ – responds to gravity, ensuring that the shark always knows where it is in the water. 

5. TEETH

The great white has fi ve rows of teeth, numbering around 300 in total. They’re all self-renewing: new teeth from the back rows are pushed to the front, while old teeth from the front row regularly fall out to facilitate this.

6. BITE FORCE

When a great white bites down, it presses a weight of 1.8 tonnes down onto its prey. The predator can also shift its bite forwards so that its teeth grip into the fl esh of its victim more securely.

7. SKIN

A shark’s skin is covered in small scales – known as denticles – which are pointed from front to back, and sharp. If a shark brushed against your skin it would feel like you were being rubbed with sandpaper.

8. PECTORAL FINS

These are used for communicating and also give a great white shark buoyancy in the water. The basic principle is the same as that used for aeroplane wings.

9. TAIL

The tail fi n, strengthened with collagen, normally moves slowly through the water. The shark generally swims at a speed of just 3.5km/h. During hunting, however, it can reach 60km/h. Great whites cannot swim backwards.

10. LIVER

Sharks do not have swim bladders. Instead, they achieve buoyancy in the water via the fat found in their livers, which can weigh around 230kg. 

11. REPRODUCTIVE ORGANS

Great white sharks give birth to live young, which hatch from eggs in the stomach and are between 1.2 and 1.5 metres long at birth. The mating process remains a mystery: to this day no one has successfully witnessed it.

12. BODY HEATING

Great white sharks are capable of keeping their bodies 14°C warmer than the water surrounding them. Their network of blood vessels transform movement-energy into warmth. They can dive down to 1,000 metres without freezing.

13. SKELETON

The skeleton is made of cartilage and is therefore lighter than bone. Like the trunk of a tree, a shark’s age can be deduced from the growth rings on its cartilage. Life expectancy was thought to be 29, but scientists have identifi ed a male great white that lived into its 70s.

14. UNIQUE FEATURES

The line along which the grey back meets the white stomach is as individual to every great white as a fi ngerprint. This varied colouring acts as camoufl age: the shark is diffi cult to spot from both above and below.

15. LATERAL ORGAN

The great white can sense prey via hairs in a liquid-fi lled canal that runs along its body. These hairs measure changes in water pressure to a range of 100 metres.