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Nature Life: Sharks And Nature

By Obiabin Onukwugha

Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head.

Sharks range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species that is only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length.

They are found in all seas and are common to depths up to 2,000 metres (6,600 ft). They generally do not live in freshwater, although there are a few known exceptions, such as the bull shark and the river shark, which can be found in both seawater and freshwater.

Yorubas call it “yanyan”, Ijaws in the Niger Delta call it “ɔfɪrɪma̰.”

Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They are also saod to have numerous sets of replaceable teeth.

Several species are apex predators, which are organisms that are at the top of their food chain. Select examples include the tiger shark, blue shark, great white shark, mako shark, thresher shark, and hammerhead shark.

Scientists say sharks have keen olfactory senses, located in the short duct (which is not fused, unlike bony fish) between the anterior and posterior nasal openings, with some species able to detect as little as one part per million of blood in seawater. The size of the olfactory bulb varies across different shark species, with size dependent on how much a given species relies on smell or vision to find their prey.

Sharks are a common seafood in many places, including Japan, Australia and other African countries. As a result of this, sharks has been listed as endangered.

Reports say in 2008, it was estimated that nearly 100 million sharks were being killed by people every year, due to commercial and recreational fishing. It was also estimated that the population of oceanic sharks and rays dropped by 71% over the previous half-century.

It is further reported that shark finning yields are estimated at 1.44 million metric tons (1.59 million short tons) in 2000, and 1.41 million metric tons (1.55 million short tons) for 2010.

Scientist say sharks use internal fertilisation. By this, the male reproductive organs, claspers, are inserted into the female’s, as opposed to other fish species where the female lays an egg, which is then fertilised by the male externally. They say sharks exhibit very little romance and no fancy courtship rituals or lifelong partners.

Some female sharks will mate with multiple males, or some have no need for a male at all. In a process called parthenogenesis, some female sharks have been observed giving birth to young without ever having encountered a male, instead producing a miniature copy of themselves. Thus the three main strategies for shark reproduction are viviparity (live birth), oviparity (laying eggs) and ovoviviparity, which is a strange mixture of the first two systems.

It is said that most sharks live 20 to 30 years, but some species can live far longer. At the extreme end of the longevity scale are Greenland sharks, which can live at least 272 years, making them the longest-lived vertebrates (backboned animals) in existence.

Sharks are an important element of healthy biodiversity. By feeding on prey species that are most numerous, sharks allow other species a chance to also grow in number, thus keeping food webs in balance and encouraging biodiversity to flourish.

Why the Shark and Monkey aren’t friends

Once upon a time Kee′ma, the monkey, and Pa′pa, the shark, became great friends.

The monkey lived in an immense “ogbono” tree which grew by the margin of the see, half of its branches being over the water and half over the land.

Every morning, when the monkey was breakfasting on the ogbono fruits, the shark would put in an appearance under the tree and call out, “Throw me some food, my friend;” with which request the monkey complied most willingly.

This continued for a long period of time, until one day the shark said, “monkey, you have done me many kindnesses: I would like you to go with me to my home, that I may repay you.”

“How can I go?” said the monkey; “we land beasts can not go about in the water.”

“Don’t trouble yourself about that,” replied the shark; “I will carry you. Not a drop of water shall get to you.”

“Oh, all right, then,” said Mr. Keema the monkey; “let’s go.”

When they had gone about half-way the shark stopped, and said: “You are my friend. I will tell you the truth.”

“Why, what is there to tell?” asked the monkey, with surprise.

“Well, you see, the fact is that our chief is very sick, and we have been told that the only medicine that will do him any good is a monkey’s heart.”

“Well,” exclaimed Keema, “you were very foolish not to tell me that before we started.”

“How so?” asked shark.

But the monkey was busy thinking up some means of saving himself, and made no reply.

“Well?” said the shark, anxiously; “why don’t you speak?”

“Oh, I’ve nothing to say now. It’s too late. But if you had told me this before we started, I might have brought my heart with me.”

“What? haven’t you your heart here?”

“Huh!” ejaculated Keema; “don’t you know about us? When we go out we leave our hearts in the trees, and go about with only our bodies. But I see you don’t believe me. You think I’m scared. Come on; let’s go to your home, where you can kill me and search for my heart in vain.”

The shark did believe him, though, and exclaimed, “Oh, no; let’s go back and get your heart.”

“Indeed, no,” protested Keema; “let us go on to your home.”

But the shark insisted that they should go back, get the heart, and start afresh.

At last, with great apparent reluctance, the monkey consented, grumbling sulkily at the unnecessary trouble he was being put to.

When they got back to the tree, he climbed up in a great hurry, calling out, “Wait there, Papa, my friend, while I get my heart, and we’ll start off properly next time.”

When he had got well up among the branches, he sat down and kept quite still.

After waiting what he considered a reasonable length of time, the shark called, “Come along, Keema!” But Keema just kept still and said nothing.

In a little while he called again: “Oh, Keema! let’s be going.”

At this the monkey poked his head out from among the upper branches and asked, in great surprise, “Going? Where?”

“To my home, of course.”

“Are you mad?” queried Keema.

“Mad? Why, what do you mean?” cried Papa.

“What’s the matter with you?” said the monkey. “Do you take me for a washerman’s donkey?” “It is a creature that has neither heart nor ears.”

And now,” said Keema to the shark, “you want to make a washerman’s donkey of me.

Get out of there, and go home by yourself. You are not going to get me again, and our friendship is ended. Good-bye, Papa,” said the monkey.

 

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