Shark : Information & Its related topics.

Shark : Information & Its related topics. The next topic in this blog will explicate about sharks life's. 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. Sharks range in size from the small dwarf lanternshark, 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.

Massively misunderstood and a source of fascination for many, the Shark is globally recognized and, quite often, feared. Many species of Shark are hunted for sport or for delicacies and medicine, meaning a worrying trend in worsening conservations statuses for many Shark species. There are about 368 species of Shark ranging from the tiny Spined Pygmy Shark to the massive Whale Shark.

Parts of Shark Physical characteristics.

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. 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.
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. 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. 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.

sharks do not have gas-filled swim bladders for buoyancy. sharks rely on a large liver, filled with oil that contains squalene. The buoyant liver may constitute up to 30% of their body mass, 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. 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. 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.

The tails (caudal fins) of sharks vary considerably between species and are adapted to the lifestyle of the shark. The tail provides thrust and so speed and acceleration are dependent on tail shape. Different tail shapes have evolved in sharks adapted for different environments. Sharks possess a heterocercal caudal fin in which the dorsal portion is usually noticeably larger than the ventral portion. This is due to the fact that the shark's vertebral column extends into that dorsal portion, allowing for a greater surface area for muscle attachment which would then be used for more efficient locomotion among the negatively buoyant cartilaginous fishes. This is in contrast to the bony fishes, class osteichthyes, which possess a homocercal caudal fin. Some tail adaptations have purposes other than providing thrust. sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body. This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy. In the past, sharks' skin has been used as sandpaper. Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming.

Shark able to maintain their body temperature above the surrounding water temperature. This is possible because of the presence of the suprahepatic rate, a counter current exchange mechanism that reduces the loss of body heat. Muscular contraction also generates a mild amount of body heat. However, this differs significantly from true homeothermy, as found in mammals and birds, in which heat is generated, maintained, and regulated by metabolic activity. The maximum lifespan of a shark varies from species to species. Most sharks live for 20 to 30 years. The sex of a shark can be easily determined. The males have modified pelvic fins which have become a pair of claspers. The name is somewhat misleading as they are not used to hold on to the female, but fulfill the role of the mammalian penis. Mating has rarely been observed in sharks. The smaller catsharks often mate with the male curling around the female. In less flexible species the two sharks swim parallel to each other while the male inserts a clasper into the female's oviduct. Females in many of the larger species have bite marks that appear to be a result of a male grasping them to maintain position during mating. The bite marks may also come from courtship behavior: the male may bite the female to show his interest. In some species, females have evolved thicker skin to withstand these bites. Sharks have a different reproductive strategy from most fish. Instead of producing huge numbers of eggs and fry (a strategy which can result in a survival rate of less than 0.01%), sharks normally produce around a dozen pups (blue sharks have been recorded as producing 135 and some species produce as few as two). These pups are either protected by egg cases or born live. There are two documented cases in which a female shark who has not been in contact with a male has conceived a pup on her own through a process known as parthenogenesis. The pups in these cases had no paternal contribution to their genome and were clones of their mothers, ruling out sperm-storage as an alternative hypothesis. It is unknown as to the extent of this behavior in the wild, and how many species of shark are capable of parthenogenesis. This observation in sharks made mammals the only remaining major vertebrate group in which the phenomenon of asexual reproduction has not been observed, and this case had known from the genetic fingerprinting .

Shark has many senses. they are sense of smell, sight, hearing, Electroreception which the Ampullae of Lorenzini are the electroreceptor organs of the shark, and they vary in number from a couple of hundred to thousands in an individual. Sharks use the Ampullae of Lorenzini to detect the electromagnetic fields that all living things produce. This helps sharks (mostly the hammer head) find its prey. The shark has the greatest electrical sensitivity known in all animals. This sense is used to find prey hidden in sand by detecting the electric fields inadvertently produced by all fish. Sharks have even been known to engage in playful activities (a trait also observed in cetaceans and primates). Porbeagle sharks have been seen repeatedly rolling in kelp and have even been observed chasing an individual trailing a piece behind them. How is a shark sleeps ? 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.


Sharks Habitat.

Until the 16th century, sharks were known to mariners as "sea dogs". According to the OED the name "shark" first came into use after Sir John Hawkins' sailors exhibited one in London in 1569 and used the word to refer to the large sharks of the Caribbean Sea, and later as a general term for all sharks. The name may have been derived from the Yucatec Maya word for shark, xook, pronounced, 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). The truth of the Shark is different - while many perceive a Shark to be a ruthless killing machine, only about 25 species are reported to have attacked people. While hard to quantify, you are supposedly more likely to be killed by a pig or a donkey than a Shark. The idea is that Shark attacks and fatalities are so ridiculously low that you are more likely to be kicked to death by your mule. Sharks are often fished for sport and this causes more damage than is realised. Sharks are part of the natural ecosystem and upsetting the balance can have knock on effects to other marine species, and consequently this can affect human life in the way of fishing catches and tourism. The ancestory of the modern Shark can be traced back to over 450 million years ago. So well evolved is the shark that the species has survived successive max extinctions, including the disaster at the end of the Permian period (245 million years ago) when 96% of other marine life was made extinct.

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. 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. 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. 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. 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.

Types of Sharks species

Courtesy : sharkinformation

Great White Shark. Its scientific name - Carcharodon carcharias

It is always made famous in the media and film, the Great White Shark is known and feared world wide. A product of 350 million years of evolution, the Great White is perfectly adapted to it's environment and should have no one to fear - apart from man. Largely misunderstood, this species has been over hunted and the future of the Great White on this planet is uncertain. Nobody can be certain of the typical lifespan of a Great White Shark. Various scientific evidence suggests around 30 to 40 years, although it is not unreasonable for a large marine animal to live longer. The Great White is often feared as a man eater, although the truth is that the shark confuses the victim with it's normal prey - this is backed up by the fact that victims are typically bitten and released, not eaten. The average length of a Great White shark is 4 to 5 metres, with females being generally larger than males. A Great White shark is able to reproduce when grown to a length of about 3.8 meters for a male and 4.5 meters for a female. Little is known of the mating habits and rituals.

The Great White Shark is ovoviviparous, meaning the eggs develop and hatch in the females uterus. When born the offspring are about 1.5m long and perfectly capable predators. A female Great White Shark will give typically give birth to 8 or 9 pups. Great white sharks have a top swimming speead of 25mph. When attacking prey a burst speed of 35mph is possible. A Great White shark can reach a weight of around 3180kg. Females will typically weigh more than males.

Mako Shark. Its scientific name - Isurus oxyrinchus

The mako sharks are an easily recognizable shark exhibiting all the traits of a Lamnid, they are an extremely robust and streamlined pelagic shark with well developed eyes (larger in the Longfin) and an endothermic circulatory system (warm bloodedness) that is known to maintain elevated muscle temperatures of up to 6°C above the ambient water temperature. Makos are heavily built with the trademark strong caudal keels that are a common feature among Lamnids such as Great Whites, Porbeagles and Salmon sharks.

Life Expectancy : 20 years

Dangerous to Man? Yes

Conservation Status : Near Threatened

Size : Up to 3.8m

Reproduction : 8-10 pups

Diet : swordfish, tunas, other sharks and squid

Other Names : atlantic mako, blue pointer, blue shark, dog shark, mackerel shark, snapper shark

Speed : 20 mph

Weight : Up to 570kg

Population : Unknown

Tiger Shark. Its scientific name - Galeocerdo cuvier

The tiger shark (Galeocerdo cuvier) is one of nature's largest sharks. A mature shark can average 3.25-4.25 meters (10-14 feet) long and weigh 325-425 kilograms (850-1400 pounds). It is found in many tropical and temperate regions of the world's oceans, and is especially common around islands in the central Pacific. The tiger shark hunts alone, usually at night. Its name is derived from the dark stripes down its body, which fade as the shark matures.

Life Expectancy : unknown

Dangerous to Man? Yes

Conservation Status : Vulnerable

Size : 7.4m

Reproduction : The female gives birth to between 10 and 80 pups.

Diet : Fish, turtles, crabs, clams, mammals, sea birds, reptiles and other sharks

Speed : 2.4mph

Weight : 850-1400 pounds

Population : unknown

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Sources : Wikipedia
sharkinformation