Sharks (superorder Selachimorpha) are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago.
Since that time, sharks have diversified into 440 species, ranging in size from the small dwarf lanternshark, Etmopterus perryi, a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark, Rhincodon typus, the largest fish, which reaches approximately 12 metres (39 ft 4 in) and which feeds only on plankton, squid, and small fish by filter feeding.
Sharks are found in all seas and are common down to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater, with a few exceptions such as the bull shark and the river shark which can live both in seawater and freshwater.
They breathe through five to seven gill slits. Sharks have a covering of dermal denticles that protects their skin from damage and parasites, and improves their fluid dynamics so the shark can move faster. They have several sets of replaceable teeth.
The Shark’s Body Structure
Sharks have a boneless skeleton made up of a tough, elastic substance. The name of this substance is "cartilage". Some of the shark species have rounded bodies like a torpedo. Others have flat bodies as thin as a playing card. Others have pectoral fins that help balance the front of their body.
harks have a large liver with oil that helps sharks from sinking. Still they must constantly swim to keep from sinking. Sharks have several rows of teeth. New teeth replace old ones regularly, every one to two weeks. Some have molar like grinding teeth, others have razor cutting teeth. Lastly, some have pointed teeth. Most sharks have their mouths on the undersides of their heads. A few have their mouths in front of their heads like the Whale and Angel Sharks.
Small tooth-like scales cover a shark's body. These scales are called placid scales, and they make a shark's skin very rough. Dried shark skin was called shagreen and was used for sandpaper. There are five to seven slits in the skin of each shark on each side of their head. Water passes through these slits after the oxygen is taken. Sharks can't pump water through their gills, so they rely on constant swimming to force water through their mouth and through the gills. This is called ramjet ventilation.
Species
Great white sharks
Tiger shark
Blue Shark
Mako Shark
Hammerhead
Habitats
Sharks are in equilibrium with the populations of their prey and thus play a role in maintaining a stable marine ecosystem.
In the oceans sharks are the most widely distributed hunters weighing more than 50 kg. They are called top predators because they are at the peak of the food pyramid. Some sharks are so-called super-predators which means they have no natural enemies except parasites and pathogens. White sharks, tiger sharks, oceanic whitetip sharks, as well as ocean mammals such as killer whales and sperm whales belong to the oceans' so-called super-predators.
Sharks play a key role as top predators. Directly or indirectly they regulate the natural balance of the populations of this food pyramid. Because they usually hunt older, weaker or sick prey, they also help maintain the health of the prey population. Healthy and strong individuals thus have a better chance of reproducing and passing on their genes.
Why are they endangered?
The reason that so many sharks are listed on the endangered sharks list today, and why so many more species are constantly being added to the list as time goes on, is mainly because of the actions of humans.
There is a huge market for the different parts of the shark such as the fins, teeth and cartilage. As one shark fin can be sold for up to $100.00! They use the fins in shark fin soup and the fins add no flavour to the soup and only texture! They die a cruel death. The result of the growth of this market is the increased need for shark fishing. Commercial fishing is to blame for the millions of shark deaths every year and unfortunately this number will continue to rise if something isn’t done to stop it.
The destruction of previous shark habitat is another cause for concern because it too can negatively affect the reproduction process of the shark. One of the most critical habitat environments known as the mangrove is constantly being destroyed by commercial fishing nets, large barge ships, cruise liners and their over-sized watercraft. The mangrove is the area where shark breeding takes place and without it, sharks do not have a safe place to raise their young. The constant slaughtering of sharks by humans and the destruction of precious habitat are two main causes for the massive decline in overall shark.
Examples of endangered shark species are shown as following.
- Angular angel shark
- Basking shark
- Bigeye thresher
- Bluegrey carpetshark
- Borneo shark
- Dusky shark
- Ganges shark
- Gulper shark.
- Oceanic Whitetip shark
- Pondicherry shark.
- Porbeagle shark
- School shark
- Smooth Hammerhead
- Smoothback angelshark
- Smoothtooth blacktip shark
- Speartooth shark
- Whitefin topeshark
The following are several organization which helps to conserve and preserve sharks.
i. Oceana
- The largest international organization focused solely on ocean conservation. Visit their website for more information at http://na.oceana.org/ .
ii. Shark Trust
- The Shark Trust is the UK charity for shark conservation. The Trust works to advance the worldwide conservation of sharks through science, education, influence and action. Have a look at their official website at http://www.sharktrust.org/
iii. Shark Research Committee (SRC)
- The Shark Research is conducting original research on the general biology, behavior and ecology of sharks indigenous to waters off the Pacific Coast, with particular emphasis on potentially dangerous species. Visit their website at http://www.sharkresearchcommittee.com/ to support them !
Prepared by,
- Keng Jean
- Le Ee
- Li Yin
- Rashmika
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