All sharks need to keep water flowing

All sharks need to keep water flowing over their gills in order for them to breathe, however not all species need to be moving to do this. Sony VGP-BPS15/B Battery Those that are able to breathe whilst not swimming breathe by using their spiracles to force water over their gills, thereby allowing them to extract oxygen from the water. It has been recorded that their eyes remain open whilst in this state and actively follow the movements of divers swimming around them^[64] and as such they are not truly asleep. Sony VGP-BPL15/S Battery Species that do need to swim continuously to breathe go through a process known as sleep swimming, in which the shark is essentially unconscious. It is known from experiments conducted on the spiny dogfish that its spinal cord, rather than its brain, coordinates swimming, so spiny dogfish can continue to swim while sleeping, and this also may be the case in larger shark species.Sony VGP-BPS15/S Battery Most sharks are carnivorous.^[65] Basking sharks, whale sharks, and megamouth sharks have independently evolved different strategies for filter feeding plankton: basking sharks practice ram feeding, whale sharks use suction to take in plankton and small fishes, and megamouth sharks make suction feeding more efficient by using the luminescent tissue inside of their mouths to attract prey in the deep ocean. Sony VGP-BPS15 Battery This type of feeding requires gill rakers—long, slender filaments that form a very efficient sieve—analogous to the baleen plates of the great whales. The shark traps the plankton in these filaments and swallows from time to time in huge mouthfuls. Teeth in these species are comparatively small because they are not needed for feeding. Sony VGP-BPL15 Battery Other highly specialized feeders include cookiecutter sharks, which feed on flesh sliced out of other larger fish and marine mammals. Cookiecutter teeth are enormous compared to the animal's size. The lower teeth are particularly sharp. Although they have never been observed feeding, they are believed to latch onto their prey and use their thick lips to make a seal, twisting their bodies to rip off flesh. Sony VGN-P series Battery Some seabed–dwelling species are highly effective ambush predators. Angel sharks and wobbegongs use camouflage to lie in wait and suck prey into their mouths.^[66] Many benthic sharks feed solely on crustaceans which they crush with their flatmolariform teeth. Other sharks feed on squid or fish, which they swallow whole. Sony VGN-P11Z/Q Battery The viper dogfish has teeth it can point outwards to strike and capture prey that it then swallows intact. The great white and other large predators either swallow small prey whole or take huge bites out of large animals. Thresher sharks use their long tails to stun shoaling fishes, and sawsharks either stir prey from the seabed or slash at swimming prey with their tooth-studded rostra. Sony VGN-P11Z/R Battery Many sharks, including the whitetip reef shark are cooperative feeders and hunt in packs to herd and capture elusive prey. These social sharks are often migratory, traveling huge distances around ocean basins in large schools. These migrations may be partly necessary to find new food sources. Sony VGN-P11Z/W Battery Sharks are found in all seas. They generally do not live in fresh water, with a few exceptions such as the bull shark and the river shark which can swim both in seawater and freshwater.^[68] 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). Sony VGN-P21S/W Battery The deepest confirmed report of a shark is a Portuguese dogfish at 3,700 metres (12,100 ft). 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. Sony VGN-P21Z/G Battery The average number of fatalities worldwide per year between 2001 and 2006 from unprovoked shark attacks is 4.3.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.^{Sony PCG-31211T Battery} These sharks are large, powerful predators, and may sometimes attack and kill people. Despite being responsible for attacks on humans they have all been filmed without using a protective cage.^[73] 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 Jawsfilm series. ^{Sony PCG-31311T Battery} Jaws author Peter Benchley, as well as Jaws director Steven Spielberg later attempted to dispel the image of sharks as man-eating monsters. Until recently only a few benthic species of shark, such as hornsharks, leopard sharks and catsharks had survived in aquarium conditions for a year or more. ^{Sony PCG-51111T Battery} This gave rise to the belief that sharks, as well as being difficult to capture and transport, were difficult to care for. More knowledge has led to more species (including the large pelagic sharks) living far longer in captivity. At the same time, safer transportation techniques have enabled long distance movement.^{[75] Sony PCG-81111T Battery} One shark that never had been successfully held in captivity for long was the great white. But in September 2004 the Monterey Bay Aquarium successfully kept a young female for 198 days before releasing her. Most species are not suitable for home aquaria and not every species sold by pet stores are appropriate. ^{Sony PCG-81311T Battery} Some species can flourish in home saltwater aquaria.^[76] Uninformed or unscrupulous dealers sometimes sell juvenile sharks like thenurse shark, which upon reaching adulthood is far too large for typical home aquaria.^[76] Public aquaria generally do not accept donated specimens that have outgrown their housing. Some owners have been tempted to release them.^{[76] Sony VPCF138FC Battery} Species appropriate to home aquaria represent considerable spatial and financial investments as they generally approach adult lengths of 3 feet and can live up to 25 years. Sharks figure prominently in Hawaiian mythology. Stories tell of men with shark jaws on their back who could change between shark and human form. ^{Sony VPCF219FC Battery} A common theme was that a shark-man would warn beach-goers of sharks in the waters. The beach-goers would laugh and ignore the warnings and get eaten by the shark-man who warned them. Hawaiian mythology also includes many shark gods. Among a fishing people, the most popular of all aumakua, or deified ancestor guardians, are shark aumakua. ^{Sony VPCS135EC Battery} Kamakudescribes in detail how to offer a corpse to become a shark. The body transforms gradually until the kahuna can point the awe-struck family to the markings on the shark's body that correspond to the clothing in which the beloved's body had been wrapped. Such a shark aumakua becomes the family pet, receiving food, and driving fish into the family net and warding off danger. ^{Sony VPCS136EC Battery} Like all aumakua it had evil uses such as helping kill enemies. The ruling chiefs typically forbade such sorcery. Many Native Hawaiian families claim such an aumakua, who is known by name to the whole community.^[77] Kamohoali'i is the best known and revered of the shark gods, he was the older and favored brother of Pele,^[78] and helped and journeyed with her to Hawaii. ^{Sony VPCS138EC Battery} He was able to assume all human and fish forms. A summit cliff on the crater of Kilauea is one of his most sacred spots. At one point he had a heiau (temple or shrine) dedicated to him on every piece of land that jutted into the ocean on the island of Molokai. Kamohoali'i was an ancestral god, not a human who became a shark and banned the eating of humans after eating one herself.^{Sony VPCS139GC Battery} In Fijian mytholog, Dakuwanga was a shark god who was the eater of lost souls. A popular myth is that sharks are immune to disease and cancer; this is not scientifically supported. Sharks may get cancer.Both diseases and parasitesaffect sharks. The evidence that sharks are at least resistant to cancer and disease is mostly anecdotal and there have been few, ^{Sony VPCYA15EC Battery} if any, scientific orstatistical studies that show sharks to have heightened immunity to disease.^[83] Other apparently false claims are that fins prevent cancer^[84] and treatosteoarthritis.^[85] No scientific proof supports these claims; at least one study has shown shark cartilage of no value in cancer treatment. ^{Sony VPCYA16EC Battery} It is estimated that 100 million sharks are killed by people every year, due to commercial and recreational fishing.^[87][88]Shark finning yields are estimated at 1.44 million metric tons for 2000, and 1.41 million tons for 2010. Based on an analysis of average shark weights, this translates into a total annual mortality estimate of about 100 million sharks in 2000, ^{Sony VPCYA25EC Battery} and about 97 million sharks in 2010, with a total range of possible values between 63 and 273 million sharks per year.^[89] Sharks are a common seafood in many places, 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. ^{Sony VPCYA26EC Battery} In fish and chip shops, shark is called flake. In India, small sharks or baby sharks (called sora in Tamil language, Telugu language) are sold in local markets. Since the flesh is not developed, cooking the flesh breaks it into powder, which is then fried in oil and spices (called sora puttu/sora poratu). The soft bones can be easily chewed. ^{Sony VPCYB15JC Battery} They are considered a delicacy in coastal Tamil Nadu. Icelanders ferment Greenland sharks to produce hákarl, which is widely regarded as a national dish.During a four-year period from 1996 to 2000, an estimated 26 to 73 million sharks were killed and traded annually in commercial markets^{Sony VPCYA17GH/R Battery} Sharks are often killed for shark fin soup. Fishermen capture live sharks, fin them, and dump the finless animal back into the water. Shark finning involves removing the fin with a hot metal blade.^[88] The resulting immobile shark soon dies from suffocation or predators.^[91] Shark fin has become a major trade within black markets all over the world. Fins sell for about $300/lb in 2009.^{[92] Sony VPCCW2S8E/W Battery} Poachers illegally fin millions each year. Few governments enforce laws that protect them.^{[citation needed]} In 2010 Hawaii became the first U.S. state to prohibit the possession, sale, trade or distribution of shark fins.^[93] From 1996 to 2000, an estimated 38 million sharks had been killed per year for harvesting shark fins.^{[90] Sony VPCCW2Z1E/B Battery} Shark fin soup is a status symbol in Asian countries, and is considered healthy and full of nutrients. Sharks are also killed for meat. European diners consume dogfishes, smoothhounds, catsharks, makos, porbeagle and also skates and rays.^[94] However, the U.S. FDA lists sharks as one of four fish (withswordfish, king mackerel, and tilefish) whose high mercury content is hazardous to children and pregnant women. ^{Sony VPCY11S1E Battery} Sharks generally reach sexual maturity only after many years and produce few offspring in comparison to other harvested fish. Harvesting sharks before they reproduce severely impacts future populations. The majority of shark fisheries have little monitoring or management. The rise in demand for shark products increases pressure on fisheries.^{[30Sony VPCY11S1E/S Battery} Major declines in shark stocks have been recorded—some species have been depleted by over 90% over the past 20–30 years with population declines of 70% not unusual. Other threats include habitat alteration, damage and loss from coastal development, pollution and the impact of fisheries on the seabed and prey species.^[96] The 2007 documentary, Sharkwater exposed how sharks are being hunted to extinction. ^{Sony VPCW1 Battery} In 1991 South Africa was the first country in the world to declare Great White sharks a legally protected species.Intending to ban the practice of shark finning while at sea, the United States Congress passed the Shark Finning Prohibition Act in 2000.^[99] Two years later the Act saw its first legal challenge in United States v. Approximately 64,695 Pounds of Shark Fins. ^{Sony VPCW1E8R/BU Battery} In 2008 a Federal Appeals Court ruled that a loophole in the law allowed non-fishing vessels to purchase shark fins from fishing vessels while on the high seas.^[100] Seeking to close the loophole, the Shark Conservation Act was passed by Congress in December 2010, and it was signed into law in January 2011.^{[101][102] Sony VPCY11AGJ Battery} In 2009, the International Union for Conservation of Nature IUCN Red List of Endangered Species named 64 species, one-third of all oceanic shark species, as being at risk of extinction due to fishing and shark finning. In 2010, the Convention on International Trade in Endangered Species (CITES) ^{Sony VPCY11AHJ Battery} rejected proposals from the United States and Palauthat would have required countries to strictly regulate trade in several species of scalloped hammerhead, oceanic whitetip and spiny dogfish sharks. The majority, but not the required two-thirds of voting delegates, approved the proposal. ^{Sony VPCY11AVJ Battery} China, by far the world’s largest shark market, andJapan, which battles all attempts to extend the convention to marine species, led the opposition.^[105][106] In 2010, Greenpeace International added the school shark, shortfin mako shark, mackerel shark, tiger shark and spiny dogfish to its seafood red list, a list of common supermarket fish that are often sourced from unsustainable fisheries.^{[107] Sony VPCY11M1E Battery} Advocacy group Shark Trust campaigns to limit shark fishing. Advocacy groupSeafood Watch directs American consumers to not eat sharks.^[108] Under the auspices of the Convention on Migratory Species of Wild Animals (CMS), also known as the Bonn Convention, the Memorandum of Understanding on the Conservation of Migratory Sharks was concluded and came into effect on 1 March 2010.^{Sony VPCY11S1E Battery} It was the first global instrument concluded under CMS and aims at facilitating international coordination for the protection, conservation and management of migratory sharks, through multilateral, intergovernmental discussion and scientific research. A shark tooth is one of the numerous teeth of a shark. Sharks continually shed their teeth, ^{Sony VPCY11V9E Battery} and some Carcharhiniformes shed approximately 35,000 teeth in a lifetime. In some geological formations, shark's teeth are a common fossil. These fossils can be analyzed for information on shark evolution and biology, especially because the teeth are often the only part of the shark to be fossilized, ^{Sony VPCY11V9E/S Battery} in fact fossil teeth comprise much of the fossil record of the Selachimorpha, extending back hundreds of millions of years. The most ancient types of sharks date back to 450 million years ago, during the Late Ordovician period, and they are mostly known from their fossilised teeth. The most commonly found fossil shark's teeth are, however, from the Cenozoic (the last 65 million years). ^{Sony VPCY219FJ/S Battery} The shape of sharks' teeth vary according to their diet; those species that feed on mollusks and crustaceans have dense flattened teeth for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey such as mammals have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. ^{Sony VPCY21AFJ Battery} The teeth of plankton-feeders such as the basking shark are greatly reduced and non-functional. Shark teeth are arranged in lines. The lines can be described as "rows" that are parallel to the line of the jaw, or as "series" which are perpendicular to the line of the jaw. Intaxonomy, shark teeth are counted as follows: ^{Sony VPCY21AGJ Battery} rows of teeth are counted along the line of the jaw, while series of teeth are counted from the front of the jaw inward. A single tooth row includes one or more functional teeth at the front of the jaw, and multiple replacement teeth behind this.^[2] For example, the jaws of a bull shark can have 50 rows of teeth in 7 series, with the outermost series functional. ^{Sony VPCY21AHJ Battery} The small teeth at the symphysis, where the two halves of the jaw meet, are usually counted separately from the main teeth on either side. The oldest known records of fossilized shark teeth are by Pliny the Elder who believed that these triangular objects fell from the sky during lunar eclipses. ^{Sony VPCY21AVJ Battery} According to Renaissance accounts, large, triangular fossil teeth often found embedded in rocky formations were believed to be petrified tongues of dragons and snakes and so were referred to as "tongue stones" or "glossopetrae", Glossopetrae were commonly thought to be a remedy or cure for various poisons and toxins. They were used in the treatment of snake bites. ^{Sony VPCY21S1E/L Battery} Due to this ingrained belief, many noblemen and royalty wore these "tongue stones" pendants or kept them in their pockets as good-luck charms.This interpretation was corrected in 1611 by the Italian naturalist Fabio Colonna, who recognized them as ancient shark teeth, and, in 1667, by the Danish naturalist Nicolaus Steno, who discussed their composition and famously produced a depiction of a shark's head bearing such teeth.^{[3] Sony VPCY21S1E/P Battery} He mentioned his findings in a book, The Head of a Shark Dissected, which also contained an illustration of a C. megalodon tooth, previously considered to be a tongue stone. As one species evolves into another, its teeth may become difficult to classify, exhibiting characteristics of both species. ^{Sony VPCY21S1E/SI Battery} For example, teeth from Carcharocles auriculatus as it evolved into C. angustidens, are difficult to definitively identify as coming from either species. A commonly referred to transition is the evolution of Isurus hastalis, the Extinct Giant Mako, into the Great White shark,Carcharodon carcharias. There exist teeth which are believed to represent the transition between the two species. ^{Sony VPCCW1E8R/WU Battery} These teeth, from Carcharodon sp. are characterised by the wider, flatter crowns of the Extinct Giant Mako. However, they also exhibit partial, fading serrations which are more pronounced near the root, and disappear towards the tip of the tooth - serrations being found in Great Whites but not Extinct Giant Makos. ^{Sony VPCCW1S1E Battery} C. megalodon teeth are the largest of any shark, extinct or living, and are among the most sought after types of shark teeth in the world. This shark lived during the late Oligocene epoch and Neogene period, roughly about 25 to 1.5 million years ago. The smallest teeth are only 1.2 cm (0.5 in) in maximum height, while the largest teeth are in excess of 17.7 cm (7.0 in) in maximum height.Sony  VAIO VGN-FZ31M Battery These teeth are in extremely high demand by collectors and private investors, and they can fetch steep prices. Shark teeth cannot be collected from just any type of rock. Any fossils, including fossil shark teeth, are preserved insedimentary rocks. Shark teeth are most commonly found between Upper Cretaceous and Tertiary periods.^[5] Sony Vaio VGN-FZ19VN Battery Fossilized shark teeth can often be found in or near river bed banks, sand pits, and beaches. These teeth are typically worn, because they were frequently moved and redeposited in different areas repeatedly before settling down.^[5] Other locations, however, yield perfect teeth that were hardly moved during the ages. Sony Vaio VGN-FZ39VN Battery These teeth are typically fragile, and great care should be taken while excavating them.^[5] Phosphate pits, containing mostly fossil bones and teeth, or kaolin pits, are ideal places to look for fossil shark teeth. One of the most notable phosphate mines is in Central Florida, Polk County, and is known as Bone Valley. Sony Vaio VGN-FZ39VN Battery