Shark Fossil range: Late Devonian - Recent
Grey reef shark, Carcharhinus amblyrhynchos
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Chondrichthyes Subclass: Elasmobranchii Superorder: Selachimorpha
Orders
Carcharhiniformes Heterodontiformes Hexanchiformes Lamniformes Orectolobiformes Pristiophoriformes Squaliformes Squatiniformes † Symmoriida

Sharks (superorder Selachimorpha) are a type of fish with a full cartilaginous skeleton and a streamlined body. The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago. The gray reef shark, Carcharhinus amblyrhynchos, is one of the most common Sharks in Indo-Pacific waters from the Red Sea to Easter Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Chondrichthyes or cartilaginous fishes are jawed Fish with paired fins paired nostrils scales two-chambered hearts and skeletons made of Cartilage rather Elasmobranchii is the subclass of Cartilaginous fish that includes Skates rays (batoidea, and sharks (selachii. This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used The ground sharks, order Carcharhiniformes, are the largest order of Sharks they are also called whaler sharks. The bullhead sharks are a small order ( Heterodontiformes) of very basal (primitive modern Sharks ( Neoselachii) Hexanchiformes is the order consisting of the most primitive types of Sharks and numbering just five extant species Lamniformes is an order of Sharks also known as mackerel sharks (which may also be used to refer to the sub-group of Lamniformes Lamnidae) The order Orectolobiformes, also collectively known as the carpet sharks because many members have carpet-like patterned markings includes a number of familiar types of Squaliformes is an order of Sharks that includes about 80 species in seven families The angel sharks are an unusual genus of Sharks with flattened bodies and broad Pectoral fins that give them a strong resemblance to skates and Symmoriida is an extinct order of sharks that contains three families This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Cartilage is a type of dense Connective tissue. It is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix Fluid flow is described in general by a Vector field in three (for steady flows or four (for non-steady flows including time dimensions They respire with the use of five to seven gill slits. A gill is an anatomical structure found in many aquatic organisms Sharks have a covering of dermal denticles that protect their skin from damage and parasites and improve fluid dynamics; they also have replaceable teeth. Denticles are body surface structures found on some fish and insects Parasitism is a type of symbiotic relationship between Organisms of different Species. Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion ^[1] Shark teeth are prized by collectors for their beauty, and because they are surviving relics of ancient sharks that are now extinct. Shark teeth are relics of Shark Evolution and Biology. Shark skeletons are composed entirely of Cartilage. Sharks range in size from the small pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimetres (9 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, like baleen whales, feeds only on plankton, squid, and small fish through filter feeding. The pygmy shark, Euprotomicrus bispinatus, the second-smallest of all the shark species after the Dwarf lanternshark, is a sleeper shark of the Dalatiidae The whale shark, Rhincodon typus, is a slow filter feeding Shark that is the largest living Fish Species. The baleen whales, also called whalebone whales or great whales, form the Mysticeti, one of two suborders of the Cetacea (whales dolphins and Plankton consist of any drifting Organisms ( Animals Plants Archaea, or Bacteria) that inhabit the Pelagic zone of Squid are marine Cephalopods of the order Teuthida, which comprises around 300 species Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Filter feeders (also known as suspension feeders) are Animals that feed by straining suspended matter and food particles from water typically by passing the water The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water and in deltas. The bull shark, Carcharhinus leucas, also known as the bull whaler, Zambezi shark or unofficially known as Zambi in Africa and Nicaragua A delta is a Landform where the mouth of a River flows into an Ocean, Sea, Estuary, Lake or another river ^[2]

Contents 1 Physical characteristics 1.1 Skeleton 1.2 Respiration 1.3 Buoyancy 1.4 Osmoregulation 1.5 Teeth 1.6 Tails 1.7 Dermal denticles 1.8 Body temperature 1.9 Lifespan 2 Etymology 3 Evolution 4 Classification 5 Reproduction 5.1 Asexual reproduction 6 Shark senses 6.1 Sense of smell 6.2 Sense of sight 6.3 Sense of hearing 6.4 Electroreception 6.5 Lateral line 7 Behavior 7.1 Fear of dolphins 8 Shark intelligence 9 Shark sleep 10 Habitat 11 Shark attacks 12 Sharks in captivity 13 Conservation 14 Shark fishery 15 Sharks in mythology 16 Sharks in cultural tradition 17 In popular culture 17.1 Films 17.2 Television 17.3 Books 18 See also 19 References 20 External links

Physical characteristics

Main article: Physical characteristics of sharks

Skeleton

The skeleton of a shark is very different from that of bony fish and terrestrial vertebrates. The physical characteristics of Sharks are different from those of Bony fish, but the large number of species and the diversity of shark habitats means that there are Osteichthyes (ˌɒstiːˈɪkθiːz also called bony fish, are a taxonomic Class of Fish that includes the ray-finned fish ( Actinopterygii Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals Sharks and other cartilaginous fish (skates and rays) have skeletons made from rubbery cartilage, a tissue lighter and more flexible than bone. Chondrichthyes or cartilaginous fishes are jawed Fish with paired fins paired nostrils scales two-chambered hearts and skeletons made of Cartilage rather Cartilage is a type of dense Connective tissue. It is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix ^[1]

Like its relatives many rays and skates, the shark's jaw is not attached to the cranium. The jaw is either of the two opposable structures forming or near the entrance to the Mouth. The jaw's surface, which like the vertebrae and gill arches is a skeletal element that needs extra support due to its heavier exposure to physical stress and need for extra strength, has 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.

The general rule is that 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 both two and three layers, and even more, depending on the body size. The bull shark, Carcharhinus leucas, also known as the bull whaler, Zambezi shark or unofficially known as Zambi in Africa and Nicaragua The tiger shark, Galeocerdo cuvier, the fourth largest predatory Shark (after the Great white shark, Greenland shark, and Pacific The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform The jaws of a large white shark even had 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.

The inner parts of the males' pelvic fins have been modified to a pair of cigar- or sausage-shaped sex organs known as "claspers," used for internal fertilization.

Respiration

Like other fish, sharks extract oxygen from seawater as it passes over their gills. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the A gill is an anatomical structure found in many aquatic organisms 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. Spiracles are small openings on the surface of some Animals that usually lead to Respiratory systems In Elasmobranchs ( Sharks and Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain Aquatic respiration is the process whereby an Aquatic animal obtains Oxygen from Water. ^[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. Any water in the sea that is not close to the bottom is in the pelagic zone. 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. Afferent is an Anatomical term with the following meanings Conveying towards a center for example the Afferent arterioles conveying blood Reoxygenation takes place in the gills and the reoxygenated blood flows into the efferent brachial arteries, which come together to form the dorsal aorta. Each Primitive aorta receives anteriorly a vein—the Vitelline vein —from the Yolk-sac, and is prolonged backward on the lateral aspect of the Notochord 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. During development of the Veins, the first indication of a Parietal system consists in the appearance of two short transverse veins the Ducts of Cuvier, which open 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. gas bladder (also fish maw, less accurately swim bladder or air bladder) is an internal organ that contributes to the ability of a Fish Instead, sharks rely on a large liver, filled with oil that contains squalene. Squalene is a natural Organic compound originally obtained for commercial purposes primarily from Shark liver oil, though there are botanic sources as well including 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. The prevailing type of fish locomotion is Swimming in Water. In addition some fish can "walk" i 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 can't 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 for stationary rest on the ocean bottom. The nurse shark, Ginglymostoma cirratum, is a shark in the Nurse sharks family the only member of its Genus Ginglymostoma. ^[7]

Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility. Many Animals, such as Sharks, Beetles, Snakes and the Virginia opossum, are capable of appearing to be dead to an observer while 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 oxide, 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. Marine is an Umbrella term. As an adjective it is usually applicable to things relating to the Sea or Ocean, such as Marine biology, Marine 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. The bull shark, Carcharhinus leucas, also known as the bull whaler, Zambezi shark or unofficially known as Zambi in Africa and Nicaragua ^[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. ^[9][10]

Teeth

Main article: Shark 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. Shark teeth are relics of Shark Evolution and Biology. Shark skeletons are composed entirely of Cartilage. The tiger shark, Galeocerdo cuvier, the fourth largest predatory Shark (after the Great white shark, Greenland shark, and Pacific The jaw is either of the two opposable structures forming or near the entrance to the Mouth. All sharks have multiple rows of teeth along the edges of their upper and lower jaws. 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.

Tails

The tails (caudal fins) of sharks vary considerably between species and are adapted to the lifestyle of the shark. The tail is the section at the rear end of an Animal 's Body; in general the term refers to a distinct flexible Appendage to the Torso. 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. In Biomechanics, animal locomotion is the study of how Animals move. This is in contrast to the bony fishes, class osteichthyes, which possess a homocercal caudal fin. Osteichthyes (ˌɒstiːˈɪkθiːz also called bony fish, are a taxonomic Class of Fish that includes the ray-finned fish ( Actinopterygii

The tiger shark's tail has a large upper lobe which delivers the maximum amount of power for slow cruising or sudden bursts of speed. The tiger shark has a varied diet, and because of this it must be able to twist and turn in the water easily when hunting, whereas the porbeagle, which hunts schooling fish such as mackerel and herring has a large lower lobe to provide greater speed to help it keep pace with its fast-swimming prey. The porbeagle, Lamna nasus, is a Pelagic predatory Shark of the family Lamnidae. Mackerel is a common name applied to a number of different species of Fish, mostly but not exclusively from the family Scombridae. Herring are small Oily fish of the genus Clupea found in the shallow temperate waters of the North Atlantic, the Baltic Sea, the North It is also believed that sharks use the upper lobe of their tails to counter the lift generated by their pectoral fins. ^[11]

Some tail adaptations have purposes other than providing thrust. The cookiecutter shark has a tail with broad lower and upper lobes of similar shape which are luminescent and may help to lure prey towards the shark. The thresher feeds on fish and squid, which it is believed to herd, then stun with its powerful and elongated upper lobe. Thresher sharks are large Lamniform Sharks of the family Alopiidae.

Dermal denticles

Main article: Dermal denticle

Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibres and arranged as a helical network surrounding their body. Denticles are body surface structures found on some fish and insects This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy. In past days the sharks skin has been used as sandpaper.

Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming. ^[12]

Body temperature

A few of the larger species, such as the shortfin mako, Isurus oxyrinchus, and the great white, are mildly homeothermic^[11]; that is: they are able to maintain their body temperature above the surrounding water temperature. The shortfin mako shark, Isurus oxyrinchus ("sharp nose" is a large Shark of the Lamnidae family The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant 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.

Lifespan

Maximum shark ages vary by species. Most sharks live for 20 to 30 years, while the spiny dogfish lives a record lifespan of more than 100 years. The spiny dogfish, spurdog, or piked dogfish, Squalus acanthias, is one of the best known of the Dogfish, members of the family ^[13] Whale sharks (Rhincodon typus) have been hypothesized to also live over 100 years. The whale shark, Rhincodon typus, is a slow filter feeding Shark that is the largest living Fish Species. ^[14]

Etymology

Until the 16th century,^[15] sharks were known to mariners as "sea dogs". ^[16] 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 Oxford English Dictionary ( OED) published by the Oxford University Press (OUP is a comprehensive Dictionary of the English Admiral Sir John Hawkins (also spelled as John Hawkyns) ( Plymouth 1532 &ndash November 12 1595) was an English shipbuilder For the region see Caribbean. The Caribbean Sea (kəˈrɪbiən or /ˌkærɨˈbiːən/ is a tropical Sea in the Western Hemisphere The name may have been derived from the Yucatec Maya word for shark, xook, pronounced [ʃoːk].

Evolution

Evidence for the existence of sharks extends back over 450–420 million years, into the Ordovician period, before land vertebrates existed and before many plants had colonised the continents. Shark teeth are relics of Shark Evolution and Biology. Shark skeletons are composed entirely of Cartilage. The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Plants are living Organisms belonging to the kingdom Plantae. ^[17] All that has been recovered from the first sharks are some scales. The oldest shark teeth are from 400 million years ago. The first sharks looked very different from modern sharks. ^[18] The majority of the modern sharks can be traced back to around 100 million years ago. ^[19]

Mostly only the fossilized teeth of sharks are found, although often in large numbers. In some cases pieces of the internal skeleton or even complete fossilized sharks have been discovered. Estimates suggest that over a span of a few years a shark may grow tens of thousands of teeth, which explains the abundance of fossils. As the teeth consist of calcium phosphate, an apatite, they are easily fossilized. Calcium phosphate is the name given to a family of Minerals containing Calcium Ions (Ca2+ together with orthophosphates (PO43-

Instead of bones, sharks have cartilagenous skeletons, with a bone-like layer broken up into thousands of isolated apatite prisms. Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce Cartilage is a type of dense Connective tissue. It is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix When a shark dies, the decomposing skeleton breaks up and the apatite prisms scatter. Complete shark skeletons are only preserved when rapid burial in bottom sediments occurs.

Among the most ancient and primitive sharks is Cladoselache, from about 370 million years ago,^[18] which has been found within the Paleozoic strata of Ohio, Kentucky and Tennessee. Cladoselache is a Genus of extinct Shark. It appeared in the Devonian period The Paleozoic or Palaeozoic Era (from the Greek palaio (παλαιο "old" and zoe (ζωη "life" meaning "ancient life" Ohio ( is a Midwestern state of the United States. As part of the Great Lakes region, Ohio has long been a cultural and geographical crossroads The Commonwealth of Kentucky ( is a state located in the East Central United States of America. Tennessee ( is a state located in the Southern United States. At this point in the Earth's history these rocks made up the soft sediment of the bottom of a large, shallow ocean, which stretched across much of North America. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Cladoselache was only about 1 m long with stiff triangular fins and slender jaws. ^[18] Its teeth had several pointed cusps, which would have been worn down by use. From the number of teeth found in any one place it is most likely that Cladoselache did not replace its teeth as regularly as modern sharks. Its caudal fins had a similar shape to the great white sharks and the pelagic shortfin and longfin makos. The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform The shortfin mako shark, Isurus oxyrinchus ("sharp nose" is a large Shark of the Lamnidae family The longfin mako, Isurus paucus, is a large Shark of the Lamnidae family found in Temperate and Tropical seas worldwide The discovery of whole fish found tail first in their stomachs suggest that they were fast swimmers with great agility.

From about 300 to 150 million years ago, most fossil sharks can be assigned to one of two groups. One of these, the Acanthodii, was almost exclusive to freshwater environments. Acanthodii (sometimes called spiny sharks) is a class of extinct Fishes having features of both bony fish ( Osteichthyes) and cartilaginous fish ( ^[20][21] By the time this group became extinct (about 220 million years ago) they had achieved worldwide distribution. The other group, the hybodonts, appeared about 320 million years ago and was mostly found in the oceans, but also in freshwater.

Modern sharks began to appear about 100 million years ago. ^[19] Fossil mackerel shark teeth occurred in the Lower Cretaceous. The Early Cretaceous ( timestratigraphic name or the Lower Cretaceous ( logstratigraphic name is the earlier of the two major divisions of the Cretaceous One of the most recent families of sharks that evolved is the hammerhead sharks (family Sphyrnidae), which emerged in Eocene. Hammerhead sharks of the Genus Sphyrna are members of the family Sphyrnidiae. Hammerhead sharks of the Genus Sphyrna are members of the family Sphyrnidiae. The Eocene epoch (558 ± 02 - 339 ± 01 Ma) is a major division of the Geologic timescale and the second epoch of the Palaeogene period in ^[22] The oldest white shark teeth date from 60 to 65 million years ago, around the time of the extinction of the dinosaurs. In early white shark evolution there are at least two lineages: one with coarsely serrated teeth that probably gave rise to the modern great white shark, and another with finely serrated teeth and a tendency to attain gigantic proportions. This group includes the extinct Megalodon, Carcharodon megalodon, which like most extinct sharks is only known from its teeth and a few vertebrae. The megalodon (ˡmɛgələˌdɒn or MEG -a-la-don meaning "big tooth" or in Greek as μέγας 'οδόντος was a giant Shark This shark could grow to more than 16 metres (52 ft) long and is recognized as the biggest known carnivorous fish to have ever existed. Fossil records reveal that this shark preyed upon whales and other large marine mammals. Whales are marine mammals which are neither Dolphins (ie members of the families Delphinidae or Platanistoidae) nor Porpoises Orcas Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands

It is believed that the immense size of predatory sharks such as the great white may have arisen from the extinction of the dinosaurs and the diversification of mammals. The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform It is known that at the same time these sharks were evolving some early mammalian groups evolved into aquatic forms. Certainly, wherever the teeth of large sharks have been found, there has also been an abundance of marine mammal bones, including seals, porpoises and whales. Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising Porpoises are Small Cetaceans of the Family Phocoenidae; they are related to Whales and Dolphins They are distinct from dolphins These bones frequently show signs of shark attack. There are hypotheses that suggest that large sharks evolved to better take advantage of larger prey.

Classification

Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. Elasmobranchii is the subclass of Cartilaginous fish that includes Skates rays (batoidea, and sharks (selachii. Chondrichthyes or cartilaginous fishes are jawed Fish with paired fins paired nostrils scales two-chambered hearts and skeletons made of Cartilage rather The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. Batoidea is a Superorder of cartilaginous fish containing more than 500 described species in thirteen families Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays Chimaeras are cartilaginous fish in the order Chimaeriformes. It is currently thought that the sharks form a polyphyletic group: in particular, some sharks are more closely related to rays than they are to some other sharks. In Phylogenetics, a Taxon is polyphyletic ( Greek for "of many races" if the trait its members have in common evolved separately in different

There are more than 360 described species of sharks split across are eight orders of sharks, listed below in roughly their evolutionary relationship from more primitive to more modern species:

• Hexanchiformes: Examples from this group include the cow sharks, frilled shark and even a shark that looks on first inspection to be a marine snake. This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used Hexanchiformes is the order consisting of the most primitive types of Sharks and numbering just five extant species Cow sharks, or the Hexanchidae, are a family of Sharks characterized by extra pairs of Gill slits There are probably only two seven-gilled genera The frilled shark, Chlamydoselachus anguineus, is a primitive Shark species of the family Chlamydoselachidae in the order
• Squaliformes: This group includes the bramble sharks, dogfish and roughsharks, and prickly shark. Squaliformes is an order of Sharks that includes about 80 species in seven families The bramble shark, Echinorhinus brucus, is covered with large thorn-like Denticles and hence the name "bramble" shark In freshwater lakes and rivers "Dogfish" refers to a member of the Bowfin family Squalidae is the family of dogfish sharks. These sharks are characterized by smooth Dorsal fin spines teeth in upper and lower jaws similar in size Caudal The prickly shark, Echinorhinus cookei, is a species of large bottom dwelling Shark from the Pacific Ocean.
• Pristiophoriformes: These are the sawsharks, with an elongated, toothed snout that they use for slashing the fish that they eat.
• Squatiniformes: Also known as angel sharks, they are flattened sharks with a strong resemblance to stingrays and skates. The angel sharks are an unusual genus of Sharks with flattened bodies and broad Pectoral fins that give them a strong resemblance to skates and The angel sharks are an unusual genus of Sharks with flattened bodies and broad Pectoral fins that give them a strong resemblance to skates and Dasyatidae is a family of rays, cartilaginous marine Fishes related to Skates and Sharks Dasyatids are common in tropical Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays
• Heterodontiformes: They are generally referred to as the bullhead or horn sharks. The bullhead sharks are a small order ( Heterodontiformes) of very basal (primitive modern Sharks ( Neoselachii) The bullhead sharks are a small order ( Heterodontiformes) of very basal (primitive modern Sharks ( Neoselachii) The horn shark, Heterodontus francisci, is a Bullhead shark. It can reach a size of 121 cm (4 ft) and weigh 10 kg (22 lb
• Orectolobiformes: They are commonly referred to as the carpet sharks, including zebra sharks, nurse sharks, wobbegongs and the whale shark. The order Orectolobiformes, also collectively known as the carpet sharks because many members have carpet-like patterned markings includes a number of familiar types of The order Orectolobiformes, also collectively known as the carpet sharks because many members have carpet-like patterned markings includes a number of familiar types of The zebra shark, Stegostoma fasciatum, is a common Carpet shark of inshore Indo-Pacific waters notable for its very long Caudal fin The nurse shark, Ginglymostoma cirratum, is a shark in the Nurse sharks family the only member of its Genus Ginglymostoma. The whale shark, Rhincodon typus, is a slow filter feeding Shark that is the largest living Fish Species.
• Carcharhiniformes: These are commonly referred to as the groundsharks, and some of the species include the blue, tiger, bull, grey reef, blacktip reef, Caribbean reef, blacktail reef, whitetip reef and oceanic whitetip sharks (collectively called the requiem sharks) along with the houndsharks, catsharks and hammerhead sharks. The ground sharks, order Carcharhiniformes, are the largest order of Sharks they are also called whaler sharks. The ground sharks, order Carcharhiniformes, are the largest order of Sharks they are also called whaler sharks. The blue shark, Prionace glauca, is a Carcharhinid Shark which is found in the deep waters of the world's Temperate and Tropical The tiger shark, Galeocerdo cuvier, the fourth largest predatory Shark (after the Great white shark, Greenland shark, and Pacific The bull shark, Carcharhinus leucas, also known as the bull whaler, Zambezi shark or unofficially known as Zambi in Africa and Nicaragua The gray reef shark, Carcharhinus amblyrhynchos, is one of the most common Sharks in Indo-Pacific waters from the Red Sea to Easter The blacktip reef shark, Carcharhinus melanopterus, is a Shark of tropical and warm temperate seas The Caribbean reef shark or reef shark, Carcharhinus perezii, discovered by Alonso Garza, is a Requiem shark of the family The whitetip reef shark, Triaenodon obesus, is a Requiem shark of the family Carcharhinidae, the only member of the Genus The oceanic whitetip shark, Carcharhinus longimanus, is a large pelagic Shark of tropical and warm temperate seas The requiem sharks refer to all members of the Carcharhinidae family that includes a family of migratory live-bearing Sharks of warm seas sometimes also found in The cat sharks or catsharks are a family ( Scyliorhinidae) of Sharks with over 110 Species recorded Hammerhead sharks of the Genus Sphyrna are members of the family Sphyrnidiae. They are distinguished by an elongated snout and a nictitating membrane which protects the eyes during an attack.
• Lamniformes: They are commonly known as the mackerel sharks. Lamniformes is an order of Sharks also known as mackerel sharks (which may also be used to refer to the sub-group of Lamniformes Lamnidae) Lamniformes is an order of Sharks also known as mackerel sharks (which may also be used to refer to the sub-group of Lamniformes Lamnidae) They include the goblin shark, basking shark, megamouth shark, the thresher sharks, shortfin and longfin mako sharks, and great white shark. The goblin shark, Mitsukurina owstoni, is a deep-sea Shark, the sole living species in the family Mitsukurinidae. The basking shark, Cetorhinus maximus, is the second largest Fish, after the Whale shark. The megamouth shark, Megachasma pelagios, is an extremely rare and unusual species of deepwater Shark. Thresher sharks are large Lamniform Sharks of the family Alopiidae. The shortfin mako shark, Isurus oxyrinchus ("sharp nose" is a large Shark of the Lamnidae family The longfin mako, Isurus paucus, is a large Shark of the Lamnidae family found in Temperate and Tropical seas worldwide The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform They are distinguished by their large jaws and ovoviviparous reproduction. The Lamniformes include the extinct megalodon, Carcharodon megalodon. The megalodon (ˡmɛgələˌdɒn or MEG -a-la-don meaning "big tooth" or in Greek as μέγας 'οδόντος was a giant Shark

Reproduction

The sex of a shark can be easily determined. The Evolution of sexual reproduction is a major puzzle The first Fossilized evidence of sexually reproducing Organisms is from Eukaryotes of the Stenian The males have modified pelvic fins which have become a pair of claspers. The pelvis (pl pelvises or pelves) or pelvic girdle is the irregular bony structure located at the base of the spine (properly known In Biology, a clasper or valva (plural valvae) is a body part of certain male animals used in mating The name is somewhat misleading as they are not used to hold on to the female, but fulfill the role of the mammalian penis. The penis (plural penises, penes

Mating has rarely been observed in sharks. In Biology, mating is the pairing of opposite- Sex or hermaphroditic Organisms for copulation and in Social animals also to raise their 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. Oviduct is also another name for Fallopian tube In Oviparous Animals (those that lay eggs, the passage from the ovaries 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 behaviour: 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). The blue shark, Prionace glauca, is a Carcharhinid Shark which is found in the deep waters of the world's Temperate and Tropical ^[23] These pups are either protected by egg cases or born live.

There are three ways in which shark pups are born:

• Oviparity - Some sharks lay eggs. The Port Jackson shark, Heterodontus portusjacksoni, is a type of bullhead Shark of the family Heterodontidae, found in the coastal The Jervis Bay Territory is a territory of the Commonwealth of Australia. For a topic outline on this subject see List of basic Australia topics. Oviparous animals are animals that lay eggs, with little or no other Embryonic development within the mother In most of these species, the developing embryo is protected by an egg case with the consistency of leather. Sometimes these cases are corkscrewed into crevices for protection. The mermaid's purse, found washed-up on beaches, is an empty egg case. Mermaid's purses (also known as Devil's Purses are the normally empty egg cases of Skates Sharks and rays. Oviparous sharks include the horn shark, catshark, Port Jackson shark, and swellshark. The horn shark, Heterodontus francisci, is a Bullhead shark. It can reach a size of 121 cm (4 ft) and weigh 10 kg (22 lb The cat sharks or catsharks are a family ( Scyliorhinidae) of Sharks with over 110 Species recorded The Port Jackson shark, Heterodontus portusjacksoni, is a type of bullhead Shark of the family Heterodontidae, found in the coastal ^[24]
• Viviparity - These sharks maintain a placental link to the developing young, more analogous to mammalian gestation than that of other fishes. A viviparous Animal is an animal employing vivipary: the embryo develops inside the body of the mother as opposed to outside in an egg ( Ovipary Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands The young are born alive and fully functional. Hammerheads, the requiem sharks (such as the bull and tiger sharks), the basking shark and the smooth dogfish fall into this category. Hammerhead sharks of the Genus Sphyrna are members of the family Sphyrnidiae. The requiem sharks refer to all members of the Carcharhinidae family that includes a family of migratory live-bearing Sharks of warm seas sometimes also found in The bull shark, Carcharhinus leucas, also known as the bull whaler, Zambezi shark or unofficially known as Zambi in Africa and Nicaragua The tiger shark, Galeocerdo cuvier, the fourth largest predatory Shark (after the Great white shark, Greenland shark, and Pacific The basking shark, Cetorhinus maximus, is the second largest Fish, after the Whale shark. In freshwater lakes and rivers "Dogfish" refers to a member of the Bowfin family Dogfish have the longest known gestation period of any shark, at 18 to 24 months. Basking sharks and frilled sharks are likely to have even longer gestation periods, but accurate data is lacking. ^[23]
• Ovoviviparity - Most sharks utilize this method. Ovoviviparous Animals develop within eggs that remain within the mother's body up until they hatch or are about to hatch The young are nourished by the yolk of their egg and by fluids secreted by glands in the walls of the oviduct. The eggs hatch within the oviduct, and the young continue to be nourished by the remnants of the yolk and the oviduct's fluids. As in viviparity, the young are born alive and fully functional. Some species practice oophagy, where the first embryos to hatch eat the remaining eggs in the oviduct. Oophagy (egg eating is the practice of Embryos feeding on eggs produced by the Ovary while still inside the mother's Uterus. This practice is believed to be present in all lamniforme sharks, while the developing pups of the grey nurse shark take this a stage further and consume other developing embryos (intrauterine cannibalism). The grey nurse shark (Australia spotted ragged-tooth shark (Africa or sand tiger shark (US and UK Carcharias taurus, is a large Shark Cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food The survival strategy for the species that are ovoviviparous is that the young are able to grow to a comparatively larger size before being born. The whale shark is now considered to be in this category after long having been classified as oviparous. Whale shark eggs found are now thought to have been aborted. The whale shark, Rhincodon typus, is a slow filter feeding Shark that is the largest living Fish Species. Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs. They choose such areas because of the protection from predators (mainly other sharks) and the abundance of food.

Asexual reproduction

In December 2001, a pup was born from a female hammerhead shark who had not been in contact with a male shark for over three years. This has led scientists to believe that sharks can reproduce without the mating process.

After three years of research, this hypothesis was confirmed on May 23, 2007, after determining the shark born had no paternal DNA, ruling out sperm-storage as an alternative hypothesis. Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. It is unknown as to the extent of this behaviour in the wild, and how many species of shark are capable of parthenogenesis. Parthenogenesis (from the Greek παρθένος parthenos, "virgin" + γένεσις genesis, "creation" is an asexual form This observation in sharks made mammals the only remaining major vertebrate group in which the phenomenon of asexual reproduction has not been observed.

Scientists warned that this type of behaviour in the wild is rare, and probably a last ditch effort of a species to reproduce when a mate isn't present. This leads to a lack of genetic diversity, required to build defences against natural threats, and if a species of shark were to rely solely on asexual reproduction, it would probably be a road to extinction, and may have contributed to the decline of blue sharks off the Irish coast. Genetic diversity is a level of Biodiversity that refers to the total number of genetic characteristics in the genetic makeup of a species ^{[25] [26]}

Shark senses

Sense of smell

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. Olfaction (also known as olfactics or smell) refers to the Sense of smell. "Parts-per" notation is used especially in Science and Engineering, to denote Ratios (relative proportions in measured quantities particularly They are 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. The nurse shark, Ginglymostoma cirratum, is a shark in the Nurse sharks family the only member of its Genus Ginglymostoma. A barbel on a Fish is a slender whiskerlike tactile organ near the Mouth.

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. In Fish, the lateral line is a Sense organ used to detect movement and vibration in the surrounding water The ampullae of Lorenzini are special sensing organs forming a network of jelly-filled canals found on Elasmobranchs ( Sharks and rays) and

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. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes The lens is a transparent biconvex structure in the Eye that along with the Cornea, helps to Refract Light to be focused The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. 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. As an Animal behavior, nocturnality describes sleeping during the Daytime and being active at Night - the opposite of the diurnal Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some have nictitating membranes. The nictitating membrane is a transparent or Translucent third Eyelid present in some animals that can be drawn across the Eye for protection and to moisten 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 great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform The importance of sight in shark hunting behaviour 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. ^[27] 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. Spiracles are small openings on the surface of some Animals that usually lead to Respiratory systems In Elasmobranchs ( Sharks and The lateral line shows a similar arrangement, as it is open to the environment via a series of openings called lateral line pores. In Fish, the lateral line is a Sense organ used to detect movement and vibration in the surrounding water 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. Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals

Electroreception

Main article: Electroreception

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. The ampullae of Lorenzini are special sensing organs forming a network of jelly-filled canals found on Elasmobranchs ( Sharks and rays) and Sharks use the Ampullae of Lorenzini to detect the electromagnetic fields that all living things produce. This helps sharks find its prey (mostly the hammer head). The shark has the greatest electricity 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. It is this sense that sometimes confuses a shark into attacking a boat: when the metal interacts with salt water, the electrochemical potentials generated by the rusting metal are similar to the weak fields of prey, or in some cases, much stronger than the prey's electrical fields: strong enough to attract sharks from miles away. The oceanic currents moving in the magnetic field of the Earth also generate electric fields that can be used by the sharks for orientation and navigation. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001

Lateral line

Main article: Lateral line

This system is found in most fish, including sharks. In Fish, the lateral line is a Sense organ used to detect movement and vibration in the surrounding water It is used to detect motion or vibrations in the water. The shark uses this to detect the movements of other organisms, especially wounded fish. The shark can sense frequencies in the range of 25 to 50 Hz. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. ^[28]

Behavior

Studies on the behaviour of sharks have only recently been carried out leading to little information on the subject, although this is changing. The classic view of the shark is that of a solitary hunter, ranging the oceans in search of food; however, this is only true for a few species, with most living far more sedentary, benthic lives. Even solitary sharks meet for breeding or on rich hunting grounds, which may lead them to cover thousands of miles in a year. ^[29] Migration patterns in sharks may be even more complex than in birds, with many sharks covering entire ocean basins. Hydrologically an oceanic basin may be anywhere on Earth that is covered by Seawater, but geologically ocean basins are large geologic basins

Some sharks can be highly social, remaining in large schools, sometimes up to over 100 individuals of scalloped hammerheads congregating around seamounts and islands e. The scalloped hammerhead, Sphyrna lewini, is a Hammerhead shark of the family Sphyrnidae. A seamount is a Mountain rising from the Ocean Seafloor that does not reach to the water's surface ( Sea level) and thus is not an Island g. in the Gulf of California. " Sea of Cortez " redirects here For the book by John Steinbeck, see The Log from the Sea of Cortez. ^[6] Cross-species social hierarchies exist with oceanic whitetip sharks dominating silky sharks of comparable size when feeding. The oceanic whitetip shark, Carcharhinus longimanus, is a large pelagic Shark of tropical and warm temperate seas The silky shark, Carcharhinus falciformis, is a large Pelagic Shark of Tropical and warm temperate seas

When approached too closely some sharks will perform a threat display to warn off the prospective predators. Shark threat display, a type of Agonistic display, is a behaviour observed in some Sharks when they feel threatened or protective This usually consists of exaggerated swimming movements, and can vary in intensity according to the level of threat. ^[30]

Fear of dolphins

There are many stories that tell of dolphins protecting humans from shark attacks. Dolphins are Marine mammals that are closely related to Whales and Porpoises There are almost forty species of dolphin in seventeen genera. This phenomenon was investigated in an episode of Discovery Channel's Mythbusters, where in a feeding great white shark did not attack either a seal cutout or raw bait when a mechanical dolphin was placed in the water nearby. Discovery Channel is an American Satellite and Cable TV channel (also delivered via IPTV, Terrestrial television and The cast of the television series MythBusters perform experiments to verify or debunk Urban legends Old wives' tales and the like It has been the subject of scientific study for many years now, however there has been no conclusive answer as to what is the reason for this behavior.

Shark intelligence

Despite the common myth that sharks are instinct-driven "eating machines", recent studies have indicated that many species possess powerful problem-solving skills, social complexity and curiosity. The brain-mass-to-body-mass ratios of sharks are similar to those of mammals and other higher vertebrate species. ^[31]

In 1987, near Smitswinkle Bay, South Africa, a group of up to seven great white sharks worked together to relocate the partially beached body of a dead whale to deeper waters to feed. The Republic of South Africa (also known by other official names) is a country located at the southern tip of the continent of Africa The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform ^[32]

Sharks have even been known to engage in playful activities (a trait also observed in cetaceans and primates). The Order Cetacea (sɪˈteɪʃiə L cetus, whale includes Whales Dolphins and Porpoises Cetus is A primate is a member of the biological order Primates ( Latin: "prime first rank" the group that contains Lemurs the Aye-aye Porbeagle sharks have been seen repeatedly rolling in kelp and have even been observed chasing an individual trailing a piece behind them. The porbeagle, Lamna nasus, is a Pelagic predatory Shark of the family Lamnidae. ^[33]

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. Spiracles are small openings on the surface of some Animals that usually lead to Respiratory systems In Elasmobranchs ( Sharks and 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. The spiny dogfish, spurdog, or piked dogfish, Squalus acanthias, is one of the best known of the Dogfish, members of the family The spinal cord is a long thin tubular bundle of Nerves that is an extension of the Central nervous system from the brain and is enclosed in and protected The spiny dogfish, spurdog, or piked dogfish, Squalus acanthias, is one of the best known of the Dogfish, members of the family

It is also possible that a shark can sleep in a manner similar to dolphins. Dolphins are Marine mammals that are closely related to Whales and Porpoises There are almost forty species of dolphin in seventeen genera. ^[34] In this situation, one half of the brain sleeps at a time, thereby allowing the shark to be half conscious while sleeping.

Habitat

A December 10, 2006 report by the Census of Marine Life group reveals that 70% of the world's oceans are shark-free. Events 1041 - Empress Zoe of Byzantium elevates her adoptive son to the throne of the Eastern Roman Empire as Michael V Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. The Census of Marine Life (CoML is an ambitious 10-year program with the aim of answering three basic questions "what lives in the oceans" (current and near-current data They have discovered that although many sharks live up to depths as low as 1,500 metres (5,000 ft), they fail to colonize deeper, putting them more easily within reach of fisheries and thus endangered status. ^[35]

Shark attacks

Main article: Shark attack

Sharks rarely attack humans unless provoked. A shark attack is an attack on a human by a Shark. Every year a number of people are attacked by sharks although death is quite unusual 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 International Shark Attack File is a global database of shark attacks It began as an attempt to catalogue shark attacks on servicemen during World War II. The average number of fatalities per year between 2001 and 2006 from unprovoked shark attacks is 4. 3. ^[36]

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. The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform The oceanic whitetip shark, Carcharhinus longimanus, is a large pelagic Shark of tropical and warm temperate seas The tiger shark, Galeocerdo cuvier, the fourth largest predatory Shark (after the Great white shark, Greenland shark, and Pacific The bull shark, Carcharhinus leucas, also known as the bull whaler, Zambezi shark or unofficially known as Zambi in Africa and Nicaragua ^{[37] [38]} These sharks, being large, powerful predators, may sometimes attack and kill people, but all of these sharks have been filmed in open water, without the use of a protective cage. ^[39]

The perception of sharks as dangerous animals has been popularised 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 Jersey Shore shark attacks of 1916 were a series of shark attacks along the coast of New Jersey between July 1 and July 12 1916 in which four people were killed Jaws is a 1975 thriller / horror Film directed by Steven Spielberg and based on Peter Benchley 's best-selling The author of Jaws, Peter Benchley, had in his later years attempted to dispel the image of sharks as man-eating monsters. Peter Bradford Benchley ( May 8, 1940 -11 February 2006 was an American author best known for writing the novel Jaws and co-writing the

Sharks in captivity

Until recently only a few benthic species of shark, such as hornsharks, leopard sharks and catsharks could survive in aquarium conditions for up to a year or more. The whale shark, Rhincodon typus, is a slow filter feeding Shark that is the largest living Fish Species. The, located in Okinawa Japan, is the world's second largest Aquarium behind the Georgia Aquarium in Atlanta. The benthic zone is the ecological region at the lowest level of a Body of water such as an Ocean or a Lake, including the sediment surface and some sub-surface The horn shark, Heterodontus francisci, is a Bullhead shark. It can reach a size of 121 cm (4 ft) and weigh 10 kg (22 lb The leopard shark, Triakis semifasciata, is a Hound shark found in the coastal waters of the eastern Pacific Ocean, along the coast The cat sharks or catsharks are a family ( Scyliorhinidae) of Sharks with over 110 Species recorded This gave rise to the belief that sharks, as well as being difficult to capture and transport, were difficult to care for. A better knowledge of sharks has led to more species (including the large pelagic sharks) being able to be kept for far longer. Any water in the sea that is not close to the bottom is in the pelagic zone. At the same time, transportation techniques have improved and now provide a way for the long distance movement of sharks. ^[40] The only species of shark to have never been successfully held in captivity was the great white, until September 2004 when the Monterey Bay Aquarium successfully kept a young female great white shark for 198 days before releasing her back into the wild.

Despite being considered critical for the health of the shark, very few studies on feeding have been carried out. Since food is the reward for appropriate behaviour, trainers must rely on control of feeding motivation.

Conservation

The majority of shark fisheries around the globe have little monitoring or management. With the rise in demand of shark products there is a greater pressure on fisheries. ^[41] Stocks decline and collapse because sharks are long-lived apex predators with comparatively small populations, which makes it difficult for them breed rapidly enough to maintain population levels. Major declines in shark stocks have been recorded in recent years - some species have been depleted by over 90% over the past 20-30 years with a population decline of 70% not being unusual. ^[42] Many governments and the UN have acknowledged the need for shark fisheries management, but due to the low economic value of shark fisheries, the small volumes of products produced and the poor public image of sharks, little progress has been made. The United Nations ( UN) is an International organization whose stated aims are to facilitate cooperation in International law, International security

Many other threats to sharks include habitat alteration, damage and loss from coastal developments, pollution and the impact of fisheries on the seabed and prey species.

A Canadian-made documentary, Sharkwater is raising awareness of the depletion of the world's shark population. Sharkwater is a 2007 Canadian film written and directed by Rob Stewart, who also plays the lead role

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. The tiger shark, Galeocerdo cuvier, the fourth largest predatory Shark (after the Great white shark, Greenland shark, and Pacific Kāneohe Bay, at 45 km² is the largest sheltered body of water in the main Hawaiian Islands. Oahu (usually Oahu outside Hawaiian and Hawaiian English) known as ''"The Gathering Place", is the third largest of the ^[43] 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. ^[44]

Sharks are a common seafood in many places around the world, including Japan and Australia. For a topic outline on this subject see List of basic Japan topics. For a topic outline on this subject see List of basic Australia topics. 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. Fish and chips (sometimes written " fish ’n’ chips " is a popular Take-away food originating from the United Kingdom. When served in fish and chip shops, it is called flake. Flake is a term used in Australia to indicate the flesh of any of several Species of small Shark, particularly Gummy shark. In India small sharks or baby sharks (called sora in Tamil language) are caught by fishermen routinely and are sold in the local markets. India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country Tamil (ta தமிழ்; t̪əmɨɻ is a Dravidian language spoken predominantly by Tamil people of the Indian subcontinent. 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. Tamil Nadu ( Tamil:, Country of the Tamils, t̪ɐmɨɻ n̪aːɽɯ is one of the 28 states of India.

Sharks are often killed for shark fin soup: the finning process involves the removal of the fin with a hot metal blade. Shark fin soup (or shark's fin soup) is a Chinese cuisine Delicacy since Ming Dynasty, commonly served as part of a Chinese feast, 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, even to go as for to say they prevent cancer and other ailments. There is no scientific proof that supports these claims. 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. ^[45] 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. The United States of America —commonly referred to as the Swordfish ( Xiphias gladius) are large highly migratory Predatory Fish characterized by a long flat bill. The king mackerel ( Scomberomorus cavalla) is a migratory species of Mackerel that lives its entire life in the open waters of the western Atlantic Ocean Tilefishes, also known as blanquillo, are mostly small Perciform marine Fish comprising the family Malacanthidae. For details see mercury poisoning. Mercury poisoning (also known as mercurialism, hydrargyria, Hunter-Russell syndrome, or acrodynia when affecting children is a Disease

Shark cartilage has been advocated as effective against cancer and for treatment of osteoarthritis. Shark Cartilage, the tough material that a sharks' skeleton is composed of is dried and powdered to create this popular Dietary supplement. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled Osteoarthritis ( OA, also known as degenerative Arthritis, degenerative joint disease) is a clinical syndrome in which low-grade inflammation (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. Mayo Clinic is a Non-profit medical practice Its headquarters the Mayo Medical School and its research facilities are in Rochester Minnesota in

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. Shark Trust is a Charitable organization founded in the UK in 1997 "dedicated to promoting the study management and conservation of Sharks According to Seafood Watch, sharks are currently on the list of fish that American consumers, who are sustainability minded, should avoid. Seafood Watch is a program designed to raise consumer awareness about the importance of buying Seafood from sustainable sources

Sharks in mythology

Sharks figure prominently in the Hawaiian mythology. Hawaiian mythology is a variant of a more general Polynesian mythology. There are stories of shark men who have shark jaws on their back. They could change form between shark and human at any time they desired. A common theme in the stories was that the shark men would warn beach-goers that sharks were in the waters. The beach-goers would laugh and ignore the warnings and go swimming, subsequently being eaten by the same shark man who warned them not to enter the water.

Hawaiian mythology also contained many shark gods. God is the principal or sole Deity in Religions and other belief systems that worship one deity. They believed that sharks were guardians of the sea, and called them Aumakua:^[46]

• Kamohoali'i - The best known and revered of the shark gods, he was the older and favoured brother of Pele,^[47] and helped and journeyed with her to Hawaii. In Hawaiian mythology, Pele (ˈpɛlɛ PEH-leh not PAY-lay is the goddess of Fire, Lightning, The State of Hawaii ( or həˈwaɪʔiː Hawaiian: Mokuāina o Hawaii) is a state in the United States located on an Archipelago in the He was able to take on all human and fish forms. A summit cliff on the crater of Kilauea is considered to be one of his most sacred spots. At one point he had a he'iau (temple or shrine) dedicated to him on every piece of land that jutted into the ocean on the island of Moloka'i.
• Ka'ahupahau - This goddess was born human, with her defining characteristic being her red hair. She was later transformed into shark form and was believed to protect the people who lived on O'ahu from sharks. She was also believed to live near Pearl Harbor. Pearl Harbor is a Harbor on the Island of O{{okina}}ahu, Hawaii, west of Honolulu.
• Kaholia Kane - This was the shark god of the ali'i Kalaniopu'u and he was believed to live in a cave at Puhi, Kaua'i.
• Kane'ae - The shark goddess who transformed into a human in order to experience the joy of dancing.
• Kane'apua - Most commonly, he was the brother of Pele and Kamohoali'i. He was a trickster god who performed many heroic feats, including the calming of two legendary colliding hills that destroyed canoes trying to pass between.
• Kawelomahamahai'a - Another human, he was transformed into a shark.
• Keali'ikau 'o Ka'u - He was the cousin of Pele and son of Kua. He was called the protector of the Ka'u people. He had an affair with a human girl, who gave birth to a helpful green shark.
• Kua - This was the main shark god of the people of Ka'u, and believed to be their ancestor.
• Kuhaimoana - He was the brother of Pele and lived in the Ka'ula islet. He was said to be 30 fathoms (55 m) long and was the husband of Ka'ahupahau.
• Kauhuhu - He was a fierce king shark that lived in a cave in Kipahulu on the island of Maui. He sometimes moved to another cave on the windward side of island of Moloka'i.
• Kane-i-kokala - A kind shark god that saved shipwrecked people by taking them to shore. The people who worshipped him feared to eat, touch or cross the smoke of the kokala, his sacred fish.

In other Pacific Ocean cultures, Dakuwanga was a shark god who was the eater of lost souls.

Sharks in cultural tradition

In ancient Greece, it was forbidden to eat shark flesh at women's festivals.

A popular myth is that sharks are immune to disease and cancer; however, this is untrue. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled There are both diseases and parasites that affect sharks. Parasitism is a type of symbiotic relationship between Organisms of different Species. The evidence that sharks are at least resistant to cancer and disease is mostly anecdotal and there have been few, if any, scientific or statistical studies that have shown sharks to have heightened immunity to disease. The expression anecdotal evidence has two quite distinct meanings Statistics is a mathematical science pertaining to the collection analysis interpretation or explanation and presentation of Data. ^[48]

In popular culture

Films

Television

Books

See also

• List of sharks
• Marine vertebrates
• Whale Shark

References

General references

External links

• Shark Attack Survivors Shark Attack Education and Prevention
• South African Marine Predator Lab a research institute studying marine top predators.
• Shark Research Institute
• Greenland Shark and Elasmobranch Education and Research Group
• The International Shark Attack File
• Shark Trust Organization
• ReefQuest Centre for Shark Research
• ECOCEAN Whale Shark Photo-identification Library
• Updated list of all known shark species
• Global Shark Attack File
• Shark Research Committee
• Shark Pictures and Elasmobranch Field Guide
• Shark pictures on Morphbank

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