samedi 15 septembre 2012

Five Ways To Stay Safe From Sharks

One of the main reasons why people, kids and teens specifically, are afraid of going to the water is because of the scary presence of sharks. Movies like Deep Blue Sea, Jaws and Shark Nights have shown many different cases of shark attacks and how aggressive sharks can be when they are hungry. But not to worry, there are certain ways on how to prevent a shark attack when you are at the beach. Preparing for disasters such as a shark attack is of importance. Below are five ways on how you can avoid shark attacks when you are at the beach.

First is to try to stay near the shore of the beach. We have seen in movies like Jaws and Deep Blue Sea that most sharks stay in the deep recesses of the beach. Unless you can swim really fast and can out swim a shark, you can stay as far away from the beach as you can. But just to be on the safe side, do stay near the shore at all times. In case you want to go a bit further than the shore, make sure that you inform your companions so that they can check on your from time to time.

Third is to avoid going to areas of the beach where there are already warnings that it is a 'shark territory'. When a warning like this is placed in certain areas, please do avoid going there. Not only will you draw sharks to you but you can harm yourself, as well as your companions.

Another is to make sure to stay within the safe area of the beach. Commonly in beaches, there is a border lined with buoys or floaters which means that any swimmer should not go beyond that point. This is a disaster preparation to avoid people from drowning and from being eaten by animal creatures. Below these floaters holds a strong net that reaches to the bottom, held in the bottom by heavy things like anchors that will prevent huge aquatic animals such as sharks from going near the beach. If you go beyond the line, you are exposing yourself to danger, sharks in particular.

Last but not the least, in case there really is a shark and someone just got bitten or grazed by its teeth, make sure that you get hold of an emergency supply kit. Immediately cover and dress the wound to prevent further leaking of blood to the water which might draw the shark's attention. Carry the injured victim immediately to dry land.

For more safety tips to use at the beach, disaster preparation, as well as other tips and ideas, read more of Jackson Vanderson's articles and blogs.

Article Source: http://EzineArticles.com/?expert=Jackson_Vanderson




lundi 16 mars 2009

Sharks


sharks
Sharks (superorder Selachimorpha) are a type of fish with a full cartilaginous skeleton and a highly streamlined body. They respire with the use of five to seven gill slits. Sharks have a covering of dermal denticles that protect their skin from damage and parasites and improve fluid dynamics. They have several sets of replaceable teeth.[1] Sharks range in size from the small dwarf lantern shark, Etmopterus perryi, a deep sea species of only 17 centimetres (7 in) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 metres (39 ft) and which feeds only on plankton, squid, and small fish through filter feeding.
The bull shark, Carcharhinus leucas, is the best known of several species that swim in both seawater and freshwater, as well as in deltas.

Skeleton:
The skeleton of a shark is very different from that of bony fish and terrestrial vertebrates. Sharks and other cartilaginous fish (skates and rays) have skeletons made from cartilage, which is a flexible and dense connective tissue, but they are still considered bones. They function in the same way as human bones do. Like its relatives, rays and skates, the shark's jaw is not attached to the cranium. The jaw's surface, like its vertebrae and gill arches, is a skeletal element that needs extra support due to its heavier exposure to physical stress and its need for extra strength. It has therefore a layer of unique and tiny hexagonal plates called "tesserae", crystal blocks of calcium salts arranged as a mosaic.[3] This gives these areas much of the same strength found in real and much heavier bony tissue.
Generally there is only one layer of tesserae in sharks, but the jaws of large specimens, such as the bull shark, tiger shark, and the great white shark, have been found to be covered with two to three layers or more, depending on the body size. The jaws of a large white shark may even have up to five layers.
In the rostrum (snout), the cartilage can be spongy and flexible to absorb the power of impacts.
The fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling the horny keratin in hair and feathers.

Respiration:
Like other fish, sharks extract oxygen from seawater as it passes over their gills. Shark gill slits are not covered like other fish, but are in a row behind its head. A modified slit called a spiracle is located just behind the eye; the spiracle assists the water intake during respiration and even plays a major role in bottom dwelling sharks, but is also reduced or missing in active pelagic sharks.[4] While moving, water passes through the mouth of the shark and over the gills — this process is known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small subset of shark species that spend their life constantly swimming, a behaviour common in pelagic sharks, have lost the ability to pump water through their gills. These species are obligate ram ventilators and would presumably asphyxiate if unable to stay in motion. (Obligate ram ventilation is also true of some pelagic bony fish species.)[5]
The respiration and circulation process begins when deoxygenated blood travels to the shark's two-chambered heart. Here the blood is pumped to the shark's gills via the ventral aorta artery where it branches off into afferent brachial arteries. Reoxygenation takes place in the gills and the reoxygenated blood flows into the efferent brachial arteries, which come together to form the dorsal aorta. The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from the body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses. From there blood enters the ventricle of the heart and the cycle repeats.

Buoyancy:
Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver, filled with oil that contains squalene. The buoyant liver may constitute up to 30% of their body mass[6]. Its effectiveness is limited, so sharks employ dynamic lift to maintain depth and sink when they stop swimming. Sandtiger sharks are also known to gulp air from the surface and store it in their stomachs, using the stomach as a swim bladder.
Because of this, most sharks need to constantly swim in order to breathe and cannot sleep very long, if at all, or they will sink. However certain shark species, like the nurse shark, have spiracles that force water across their gills allowing them to remain stationary at rest on the ocean bottom.[7]
Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility. Researchers have used this condition to handle sharks safely.[8].

Osmoregulation:
In contrast to bony fish, the blood and other tissue of sharks and Chondrichthyes in general is isotonic to their marine environments because of the high concentration of urea and trimethylamine N-oxide (TMAO), allowing them to be in osmotic balance with the seawater. This adaptation prevents most sharks from surviving in fresh water, and they are therefore confined to a marine environment. A few exceptions to this rule exist, such as the bull shark, which has developed a way to change its kidney function to excrete large amounts of urea.[6] When a shark dies the urea is broken down to ammonia by bacteria — because of this, the dead body will gradually start to smell strongly of ammonia.

Teeth:
The teeth of carnivorous sharks are not attached to the jaw, but embedded in the flesh, and in many species are constantly replaced throughout the shark's life; some sharks can lose 30,000 teeth in a lifetime. All sharks have multiple rows of teeth along the edges of their upper and lower jaws. They stick out of their mouth at angles of up to thirty degrees. New teeth grow continuously in a groove just inside the mouth and move forward from inside the mouth on a "conveyor belt" formed by the skin in which they are anchored. In some sharks rows of teeth are replaced every 8–10 days, while in other species they could last several months. The lower teeth are primarily used for holding prey, while the upper ones are used for cutting into it.[4] The teeth range from thin, needle-like teeth for gripping fish to large, flat teeth adapted for crushing shellfish. Their teeth are used on necklaces.

Shark senses
Sense of smell
Sharks, like this hammerhead, can use electroreception to detect changes in Earth's geomagnetic field.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. They are more attracted to the chemicals found in the guts of many species, and as a result often linger near or in sewage outfalls. Some species, such as nurse sharks, have external barbels that greatly increase their ability to sense prey.
Sharks generally rely on their superior sense of smell to find prey, but at closer range they also use the lateral lines running along their sides to sense movement in the water, and also employ special sensory pores on their heads (Ampullae of Lorenzini) to detect electrical fields created by prey and the ambient electric fields of the ocean.

Sense of sight
Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas, though their eyesight is well adapted to the marine environment with the help of a tissue called tapetum lucidum. This tissue is behind the retina and reflects light back to the retina, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some have nictitating membranes. This membrane covers the eyes during predation, and when the shark is being attacked. However, some species, including the great white shark (Carcharodon carcharias), do not have this membrane, but instead roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunting behavior is debated. Some believe that electro and chemoreception are more significant, while others point to the nictating membrane as evidence that sight is important. (Presumably, the shark would not protect its eyes were they unimportant.) The degree to which sight is used probably varies with species and water conditions. In effect the shark's field of vision can swap between monnocular and stereoscopic at any time.

Sense of hearing
Although it is hard to test the hearing of sharks, there are indications that suggest that they have a sharp sense of hearing and can possibly hear prey many miles away.[29] A small opening on each side of their heads (not to be confused with the spiracle) leads directly into the inner ear through a thin channel. The lateral line shows a similar arrangement, as it is open to the environment via a series of openings called lateral line pores. This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fish and tetrapods the external opening into the inner ear has been lost.

Shark sleep
It is unclear how sharks sleep. Some sharks can lie on the bottom while actively pumping water over their gills, but their eyes remain open and actively follow divers. When a shark is resting, it does not use its nares, but rather its spiracles. If a shark tried to use its nares while resting on the ocean floor, it would be sucking up sand rather than water. Many scientists believe this is one of the reasons sharks have spiracles. The spiny dogfish's spinal cord, rather than its brain, coordinates swimming, so it is possible for a spiny dogfish to continue to swim while sleeping.
It is also possible that sharks sleep in a manner similar to dolphins,[38] one cerebral hemisphere at a time, thus maintaining some consciousness and cerebral activity at all times.

Habitat
Sharks are found all around the globe from the north to the south in all seas, they generally do not live in freshwater except for a few exceptions like the bull shark and the river sharks which can swim both in seawater and freshwater. Sharks are common down to depths of 2,000 metres (7,000 ft), and some live even deeper, but they are almost entirely absent below 3,000 metres (10,000 ft). The deepest confirmed report of a shark is a Portuguese dogfish that was found at 3,700 metres (12,000 ft).

Shark fishery
An estimate states that, every year, 26 to 73 million (median value is at 38 million) sharks are killed by people in commercial and recreational fishing.[43] Over 11,000 sharks are killed each hour, amounting to near 100 million a year [44]. In the past, sharks were killed simply for the sport of landing a good fighting fish (such as the shortfin mako sharks). Shark skin is covered with dermal denticles, which are similar to tiny teeth, and was used for purposes similar to sandpaper. Other sharks are hunted for food (Atlantic thresher, shortfin mako and others), and some species for other products.[45]
Sharks are a common seafood in many places around the world, including Japan and Australia. In the Australian State of Victoria shark is the most commonly used fish in fish and chips, in which fillets are battered and deep-fried or crumbed and grilled and served alongside chips. When served in fish and chip shops, it is called flake. In India small sharks or baby sharks (called sora in Tamil language, Telugu language) are caught by fishermen routinely and are sold in the local markets. Since the flesh is not developed completely it just breaks into powder once boiled and this is then fried in oil and spices (called sora puttu). Even the bones are soft and these can be easily chewed and considered a delicacy in coastal Tamil Nadu. In Iceland, Greenland sharks are fished to produce hákarl or fermented shark, which is widely regarded as a national dish.
A 14-foot (4 m), 544 kg (1200 pound) Tiger shark caught in Kaneohe Bay, Oahu in 1966.Sharks are often killed for shark fin soup: the finning process involves the removal of the fin with a hot metal blade. Fishermen will capture live sharks, fin them, and release the finless animal back into the water. The immobile shark soon dies from suffocation or predators. Despite claims that this practice is rare, it has become a major trade within black markets all over the world with shark fins going at about $220/ lbs. Millions of sharks a year are being illegally poached for their fins and not many governments are enforcing the laws of protecting these apex predators. The dish is considered a status symbol in Asian countries, and is considered healthy and full of nutrients, with some even claiming they prevent cancer and other ailments.[46] There is no scientific proof that supports these claims; at least one study has shown shark cartilage of no value in cancer treatment.[47] The shark fin trade is a major problem and has gained international controversy.
Sharks are also killed for their meat. Conservationists have campaigned for changes in the law to make finning illegal in the U.S. The meat of dogfishes, smoothhounds, catsharks, makos, porbeagle and also skates and rays are in high demand by European consumers.[48] However, the U.S. FDA lists sharks as one of four fish (with swordfish, king mackerel, and tilefish,) that children and women who are or may be pregnant should refrain from eating. For details see mercury poisoning.
Shark cartilage has been advocated as effective against cancer and for treatment of osteoarthritis. (This is because many people believe that sharks cannot get cancer and that taking it will prevent people from getting these diseases, which is untrue.) However, a trial by Mayo Clinic found no effect in advanced cancer patients.
Sharks generally reach sexual maturity slowly and produce very few offspring in comparison to other fish that are harvested. This has caused concern among biologists regarding the increase in effort applied to catching sharks over time, and many species are considered to be threatened.
Some organizations, such as the Shark Trust, campaign to limit shark fishing. According to Seafood Watch, sharks are currently on the list of fish that American consumers, who are sustainability minded, should avoid.

Teeth:
The teeth of carnivorous sharks are not attached to the jaw, but embedded in the flesh, and in many species are constantly replaced throughout the shark's life; some sharks can lose 30,000 teeth in a lifetime. All sharks have multiple rows of teeth along the edges of their upper and lower jaws. They stick out of their mouth at angles of up to thirty degrees. New teeth grow continuously in a groove just inside the mouth and move forward from inside the mouth on a "conveyor belt" formed by the skin in which they are anchored. In some sharks rows of teeth are replaced every 8–10 days, while in other species they could last several months. The lower teeth are primarily used for holding prey, while the upper ones are used for cutting into it.[4] The teeth range from thin, needle-like teeth for gripping fish to large, flat teeth adapted for crushing shellfish. Their teeth are used on necklaces.

Shark senses
Sense of smell
Sharks, like this hammerhead, can use electroreception to detect changes in Earth's geomagnetic field.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. They are more attracted to the chemicals found in the guts of many species, and as a result often linger near or in sewage outfalls. Some species, such as nurse sharks, have external barbels that greatly increase their ability to sense prey.
Sharks generally rely on their superior sense of smell to find prey, but at closer range they also use the lateral lines running along their sides to sense movement in the water, and also employ special sensory pores on their heads (Ampullae of Lorenzini) to detect electrical fields created by prey and the ambient electric fields of the ocean.

Sense of sight
Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas, though their eyesight is well adapted to the marine environment with the help of a tissue called tapetum lucidum. This tissue is behind the retina and reflects light back to the retina, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some have nictitating membranes. This membrane covers the eyes during predation, and when the shark is being attacked. However, some species, including the great white shark (Carcharodon carcharias), do not have this membrane, but instead roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunting behavior is debated. Some believe that electro and chemoreception are more significant, while others point to the nictating membrane as evidence that sight is important. (Presumably, the shark would not protect its eyes were they unimportant.) The degree to which sight is used probably varies with species and water conditions. In effect the shark's field of vision can swap between monnocular and stereoscopic at any time.

Sense of hearing
Although it is hard to test the hearing of sharks, there are indications that suggest that they have a sharp sense of hearing and can possibly hear prey many miles away.[29] A small opening on each side of their heads (not to be confused with the spiracle) leads directly into the inner ear through a thin channel. The lateral line shows a similar arrangement, as it is open to the environment via a series of openings called lateral line pores. This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fish and tetrapods the external opening into the inner ear has been lost.

Shark sleep
It is unclear how sharks sleep. Some sharks can lie on the bottom while actively pumping water over their gills, but their eyes remain open and actively follow divers. When a shark is resting, it does not use its nares, but rather its spiracles. If a shark tried to use its nares while resting on the ocean floor, it would be sucking up sand rather than water. Many scientists believe this is one of the reasons sharks have spiracles. The spiny dogfish's spinal cord, rather than its brain, coordinates swimming, so it is possible for a spiny dogfish to continue to swim while sleeping.
It is also possible that sharks sleep in a manner similar to dolphins,[38] one cerebral hemisphere at a time, thus maintaining some consciousness and cerebral activity at all times.

Habitat
Sharks are found all around the globe from the north to the south in all seas, they generally do not live in freshwater except for a few exceptions like the bull shark and the river sharks which can swim both in seawater and freshwater. Sharks are common down to depths of 2,000 metres (7,000 ft), and some live even deeper, but they are almost entirely absent below 3,000 metres (10,000 ft). The deepest confirmed report of a shark is a Portuguese dogfish that was found at 3,700 metres (12,000 ft).

Shark fishery
An estimate states that, every year, 26 to 73 million (median value is at 38 million) sharks are killed by people in commercial and recreational fishing.[43] Over 11,000 sharks are killed each hour, amounting to near 100 million a year [44]. In the past, sharks were killed simply for the sport of landing a good fighting fish (such as the shortfin mako sharks). Shark skin is covered with dermal denticles, which are similar to tiny teeth, and was used for purposes similar to sandpaper. Other sharks are hunted for food (Atlantic thresher, shortfin mako and others), and some species for other products.[45]
Sharks are a common seafood in many places around the world, including Japan and Australia. In the Australian State of Victoria shark is the most commonly used fish in fish and chips, in which fillets are battered and deep-fried or crumbed and grilled and served alongside chips. When served in fish and chip shops, it is called flake. In India small sharks or baby sharks (called sora in Tamil language, Telugu language) are caught by fishermen routinely and are sold in the local markets. Since the flesh is not developed completely it just breaks into powder once boiled and this is then fried in oil and spices (called sora puttu). Even the bones are soft and these can be easily chewed and considered a delicacy in coastal Tamil Nadu. In Iceland, Greenland sharks are fished to produce hákarl or fermented shark, which is widely regarded as a national dish.
A 14-foot (4 m), 544 kg (1200 pound) Tiger shark caught in Kaneohe Bay, Oahu in 1966.Sharks are often killed for shark fin soup: the finning process involves the removal of the fin with a hot metal blade. Fishermen will capture live sharks, fin them, and release the finless animal back into the water. The immobile shark soon dies from suffocation or predators. Despite claims that this practice is rare, it has become a major trade within black markets all over the world with shark fins going at about $220/ lbs. Millions of sharks a year are being illegally poached for their fins and not many governments are enforcing the laws of protecting these apex predators. The dish is considered a status symbol in Asian countries, and is considered healthy and full of nutrients, with some even claiming they prevent cancer and other ailments.[46] There is no scientific proof that supports these claims; at least one study has shown shark cartilage of no value in cancer treatment.[47] The shark fin trade is a major problem and has gained international controversy.
Sharks are also killed for their meat. Conservationists have campaigned for changes in the law to make finning illegal in the U.S. The meat of dogfishes, smoothhounds, catsharks, makos, porbeagle and also skates and rays are in high demand by European consumers.[48] However, the U.S. FDA lists sharks as one of four fish (with swordfish, king mackerel, and tilefish,) that children and women who are or may be pregnant should refrain from eating. For details see mercury poisoning.
Shark cartilage has been advocated as effective against cancer and for treatment of osteoarthritis. (This is because many people believe that sharks cannot get cancer and that taking it will prevent people from getting these diseases, which is untrue.) However, a trial by Mayo Clinic found no effect in advanced cancer patients.
Sharks generally reach sexual maturity slowly and produce very few offspring in comparison to other fish that are harvested. This has caused concern among biologists regarding the increase in effort applied to catching sharks over time, and many species are considered to be threatened.
Some organizations, such as the Shark Trust, campaign to limit shark fishing. According to Seafood Watch, sharks are currently on the list of fish that American consumers, who are sustainability minded, should avoid.

Life of Sharks


Shark attacks
In 2006 the International Shark Attack File (ISAF) undertook an investigation into 96 alleged shark attacks, confirming 62 of them as unprovoked attacks and 16 as provoked attacks. The average number of fatalities per year between 2001 and 2006 from unprovoked shark attacks is 4.3.[49]
Contrary to popular belief, only a few sharks are dangerous to humans. Out of more than 360 species, only four have been involved in a significant number of fatal, unprovoked attacks on humans: the great white, oceanic whitetip, tiger, and bull sharks.[50] [51] These sharks, being large, powerful predators, may sometimes attack and kill people, but all of these sharks have been filmed without the use of a protective cage.[52]
The perception of sharks as dangerous animals has been popularized by publicity given to a few isolated unprovoked attacks, such as the Jersey Shore shark attacks of 1916, and through popular fictional works about shark attacks, such as the Jaws film series. The author of Jaws, Peter Benchley, had in his later years attempted to dispel the image of sharks as man-eating monsters.