sharks

Shark

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Sharks Temporal range: Silurian–Recent PreЄ Є O S D C P T J K Pg N
Grey reef shark (Carcharhinus amblyrhynchos)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Superorder:	Selachimorpha
Orders
Carcharhiniformes Heterodontiformes Hexanchiformes Lamniformes Orectolobiformes Pristiophoriformes Squaliformes Squatiniformes

Sharks are a group of fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii), and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus. Under this broader definition, the earliest known sharks date from more than 420 million years ago.^[1]
Since that time, sharks have diversified into over 400 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (39 ft). Despite its size, the whale shark feeds only on plankton, squid, and small fish by filter feeding. Sharks are found in all seas and are common down to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark that can survive in both seawater and freshwater.^[2] They breathe through five to seven gill slits. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They also have several sets of replaceable teeth.^[3]
Well-known species such as the great white shark, tiger shark, blue shark, mako shark, and the hammerhead shark are apex predators—organisms at the top of their underwater food chain. Their predatory skill fascinates and frightens humans, even though their survival is threatened by human-related activities.

Contents [hide] 1 Etymology 2 Evolution 2.1 Taxonomy 3 Anatomy 3.1 Teeth 3.2 Skeleton 3.3 Jaw 3.4 Fins 3.5 Dermal denticles 3.6 Tails 4 Physiology 4.1 Buoyancy 4.2 Respiration 4.3 Thermoregulation 4.4 Osmoregulation 4.5 Digestion 5 Senses 5.1 Smell 5.2 Sight 5.3 Hearing 5.4 Electroreception 5.5 Lateral line 6 Life history 6.1 Reproduction 6.1.1 Sexual 6.1.2 Asexual 6.2 Brooding 6.2.1 Ovoviviparity 6.2.2 Oviparity 6.2.3 Viviparity 7 Behavior 7.1 Speed 7.2 Intelligence 7.3 Sleep 8 Ecology 8.1 Feeding 8.2 Range and habitat 9 Relationship with humans 9.1 Attacks 9.2 In captivity 9.3 In Hawaii 9.4 Popular misconceptions 10 Conservation 10.1 Fishery 10.2 Other threats 10.3 Protection 11 See also 12 References 13 External links

Etymology

Until the 16th century,^[4] sharks were known to mariners as "sea dogs".^[5] The etymology of the word "shark" is uncertain. One theory is that it derives from the Yucatec Maya word xok, pronounced 'shok'.^[6] Evidence for this etymology comes from the OED, which notes the name "shark" first came into use after Sir John Hawkins' sailors exhibited one in London in 1569 and used the word "sharke" to refer to the large sharks of the Caribbean Sea.
An alternate etymology states that the original sense of the word was that of "predator, one who preys on others" from the German Schorck, a variant of Schurke "villain, scoundrel" (cf. card shark, loan shark, etc.), which was later applied to the fish due to its predatory behaviour.^[7]

Evolution

A collection of Cretaceous shark teeth

Evidence for the existence of sharks dates from the Ordovician period, over 450–420 million years ago, before land vertebrates existed and before many plants had colonized the continents.^[1] Only scales have been recovered from the first sharks and not all paleontologists agree that these are from true sharks.^[8] The oldest generally accepted shark scales are from about 420 million years ago, in the Silurian period.^[8] The first sharks looked very different from modern sharks.^[9] The majority of modern sharks can be traced back to around 100 million years ago.^[10] Most fossils are of teeth, often in large numbers. Partial skeletons and even complete fossilized remains have been discovered. Estimates suggest that sharks grow tens of thousands of teeth over a lifetime, which explains the abundant fossils. The teeth consist of easily fossilized calcium phosphate, an apatite. When a shark dies, the decomposing skeleton breaks up, scattering the apatite prisms. Preservation requires rapid burial in bottom sediments.
Among the most ancient and primitive sharks is Cladoselache, from about 370 million years ago,^[9] which has been found within Paleozoic strata in Ohio, Kentucky and Tennessee. At that point in Earth's history these rocks made up the soft bottom sediments of a large, shallow ocean, which stretched across much of North America. Cladoselache was only about 1 metre (3.3 ft) long with stiff triangular fins and slender jaws.^[9] Its teeth had several pointed cusps, which wore down from use. From the small number of teeth found together, 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 presence of whole fish arranged tail-first in their stomachs suggest that they were fast swimmers with great agility.
Most fossil sharks from about 300 to 150 million years ago can be assigned to one of two groups. The Xenacanthida was almost exclusive to freshwater environments.^[11][12] By the time this group became extinct about 220 million years ago, they had spread worldwide. The other group, the hybodonts, appeared about 320 million years ago and lived mostly in the oceans, but also in freshwater.

Megalodon with the whale shark, great white shark, and a human for scale

Modern sharks began to appear about 100 million years ago.^[10] Fossil mackerel shark teeth date to the Early Cretaceous. One of the most recently evolved families is the hammerhead shark (family Sphyrnidae), which emerged in the Eocene.^[13] 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 lineage is of white sharks with coarsely serrated teeth and it probably gave rise to the modern great white shark, and another lineage is of white sharks with finely serrated teeth. These sharks attained gigantic proportions and include the extinct megatoothed shark, C. megalodon. Like most extinct sharks, C. megalodon is also primarily known from its fossil teeth and vertebrae. This giant shark reached a total length (TL) of more than 16 metres (52 ft).^[14][15] C. megalodon may have approached a maxima of 20.3 metres (67 ft) in total length and 103 metric tons (114 short tons) in mass.^[16] Paleontological evidence suggests that this shark was an active predator of large cetaceans.^[16]

Taxonomy

Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. It is currently thought that the sharks form a polyphyletic group: some sharks are more closely related to rays than they are to some other sharks.^[17]
The superorder Selachimorpha is divided into Galea (or Galeomorphii), and Squalea. The Galeans are the Heterodontiformes, Orectolobiformes, Lamniformes, and Carcharhiniformes. Lamnoids and Carcharhinoids are usually placed in one clade, but recent studies show the Lamnoids and Orectoloboids are a clade. Some scientists now think that Heterodontoids may be Squalean. The Squalea is divided into Hexanchoidei and Squalomorpha. The Hexanchoidei includes the Hexanchiformes and Chlamydoselachiformes. The Squalomorpha contains the Squaliformes and the Hypnosqualea. The Hypnosqualea may be invalid. It includes the Squatiniformes, and the Pristorajea, which may also be invalid, but includes the Pristiophoriformes and the Batoidea.^[17][18]
More than 440 species of sharks split across eight orders, listed below in roughly their evolutionary relationship from ancient to modern:^[18]

• Hexanchiformes: Examples from this group include the cow sharks and frilled shark, which somewhat resembles a marine snake.
• Squaliformes: This group includes the bramble sharks, dogfish and roughsharks, and prickly shark.
• Pristiophoriformes: These are the sawsharks, with an elongated, toothed snout that they use for slashing their prey.
• Squatiniformes: Also known as angel sharks, they are flattened sharks with a strong resemblance to stingrays and skates.
• Heterodontiformes: They are generally referred to as the bullhead or horn sharks.
• Orectolobiformes: They are commonly referred to as the carpet sharks, including zebra sharks, nurse sharks, wobbegongs and the whale shark.
• Carcharhiniformes: Commonly known as groundsharks, 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. 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. They include the goblin shark, basking shark, megamouth shark, the thresher sharks, shortfin and longfin mako sharks, and great white shark. They are distinguished by their large jaws and ovoviviparous reproduction. The Lamniformes include the extinct megalodon, Carcharodon megalodon.

Anatomy

General anatomical features of sharks

Main article: Physical characteristics of sharks

Teeth

Main article: Shark tooth

The teeth of tiger sharks are oblique and serrated to saw through flesh

Shark teeth are embedded in the gums rather than directly affixed to the jaw, and are constantly replaced throughout life. Multiple rows of replacement teeth grow in a groove on the inside of the jaw and steadily move forward in comparison to a conveyor belt; some sharks lose 30,000 or more teeth in their lifetime. The rate of tooth replacement varies from once every 8 to 10 days to several months. In most species, teeth are replaced one at a time as opposed to the simultaneous replacement of an entire row, which is observed in the cookiecutter shark.^[19]
Tooth shape depends on the shark's diet: those that feed on mollusks and crustaceans have dense and flattened teeth used 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. The teeth of plankton-feeders such as the basking shark are small and non-functional.^[20]

Skeleton

Shark skeletons are very different from those of bony fish and terrestrial vertebrates. Sharks and other cartilaginous fish (skates and rays) have skeletons made of cartilage and connective tissue. Cartilage is flexible and durable, yet is about half the normal density of bone. This reduces the skeleton’s weight, saving energy.^[21] Because sharks do not have rib cages, they can easily be crushed under their own weight on land.^[22]

Jaw

Jaws of sharks, like those of rays and skates, are not attached to the cranium. The jaw's surface (in comparison to the shark's vertebrae and gill arches) needs extra support due to its heavy exposure to physical stress and its need for strength. It has a layer of tiny hexagonal plates called "tesserae", which are crystal blocks of calcium salts arranged as a mosaic.^[23] This gives these areas much of the same strength found in the bony tissue found in other animals.
Generally sharks have only one layer of tesserae, but the jaws of large specimens, such as the bull shark, tiger shark, and the great white shark, have two to three layers or more, depending on body size. The jaws of a large great white shark may have up to five layers.^[21] In the rostrum (snout), the cartilage can be spongy and flexible to absorb the power of impacts.

Fins

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.^[24] Most sharks have eight fins. Sharks can only drift away from objects directly in front of them because their fins do not allow them to move in the tail-first direction.^[22]

Dermal denticles

Main article: Dermal denticle

Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body. This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy.^[25] Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming.^[19]

Tails

Tails provide thrust, making speed and acceleration dependent on tail shape. Caudal fin shapes vary considerably between shark species, due to their evolution in separate environments. Sharks possess a heterocercal caudal fin in which the dorsal portion is usually noticeably larger than the ventral portion. This is because the shark's vertebral column extends into that dorsal portion, providing a greater surface area for muscle attachment. This allows more efficient locomotion among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a homocercal caudal fin.^[26]
Tiger sharks have a large upper lobe, which allows for slow cruising and sudden bursts of speed. The tiger shark must be able to twist and turn in the water easily when hunting to support its varied diet, whereas the porbeagle shark, which hunts schooling fish such as mackerel and herring, has a large lower lobe to help it keep pace with its fast-swimming prey.^[27] Other tail adaptations help sharks catch prey more directly, such as the thresher shark's usage of its powerful, elongated upper lobe to stun fish and squid.

Physiology

Buoyancy

Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver filled with oil that contains squalene, and their cartilage, which is about half the normal density of bone.^[25] Their liver constitutes up to 30% of their total body mass.^[28] The liver's effectiveness is limited, so sharks employ dynamic lift to maintain depth when not swimming. Sand tiger sharks store air in their stomachs, using it as a form of swim bladder. Most sharks need to constantly swim in order to breathe and cannot sleep very long without sinking (if at all). However, certain species, like the nurse shark, are capable of pumping water across their gills, allowing them to rest on the ocean bottom.^[29]
Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility. Researchers use this condition to handle sharks safely.^[30]

Respiration

Like other fish, sharks extract oxygen from seawater as it passes over their gills. Unlike other fish, shark gill slits are not covered, but lie in a row behind the head. A modified slit called a spiracle lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active pelagic sharks.^[20] While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species.^[31]
The respiration and circulation process begins when deoxygenated blood travels to the shark's two-chambered heart. Here the shark pumps blood to its gills via the ventral aorta artery where it branches into afferent brachial arteries. Reoxygenation takes place in the gills and the reoxygenated blood flows into the efferent brachial arteries, which come together to form the dorsal aorta. The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from the body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses^{[disambiguation needed]}. From there blood enters the heart ventricle and the cycle repeats.^[32]

Thermoregulation

Most sharks are "cold-blooded" or, more precisely, poikilothermic, meaning that their internal body temperature matches that of their ambient environment. Members of the family Lamnidae (such as the shortfin mako shark and the great white shark) are homeothermic and maintain a higher body temperature than the surrounding water. In these sharks, a strip of aerobic red muscle located near the center of the body generates the heat, which the body retains via a countercurrent exchange mechanism by a system of blood vessels called the rete mirabile ("miraculous net"). The common thresher shark has a similar mechanism for maintaining an elevated body temperature, which is thought to have evolved independently^{[not in citation given]}.^[33]

Osmoregulation

In contrast to bony fish, with the exception of the coelacanth,^[34] the blood and other tissue of sharks and Chondrichthyes is generally isotonic to their marine environments because of the high concentration of urea and trimethylamine N-oxide (TMAO), allowing them to be in osmotic balance with the seawater. This adaptation prevents most sharks from surviving in freshwater, and they are therefore confined to marine environments. A few exceptions exist, such as the bull shark, which has developed a way to change its kidney function to excrete large amounts of urea.^[28] When a shark dies, the urea is broken down to ammonia by bacteria, causing the dead body to gradually smell strongly of ammonia.^[35][36]

Digestion

Digestion can take a long time. The food moves from the mouth to a J-shaped stomach, where it is stored and initial digestion occurs.^[37] Unwanted items may never get past the stomach, and instead the shark either vomits or turns its stomachs inside out and ejects unwanted items from its mouth.
One of the biggest differences between the digestive systems of sharks and mammals is that sharks have much shorter intestines. This short length is achieved by the spiral valve with multiple turns within a single short section instead of a long tube-like intestine. The valve provides a long surface area, requiring food to circulate inside the short gut until fully digested, when remaining waste products pass into the cloaca.^[37]

Senses

Smell

The shape of the hammerhead shark's head may enhance olfaction by spacing the nostrils further apart.

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.^[38]
Sharks have the ability to determine the direction of a given scent based on the timing of scent detection in each nostril.^[39] This is similar to the method mammals use to determine direction of sound.
They are more attracted to the chemicals found in the intestines 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.

Sight

Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas, though their eyesight is well adapted to the marine environment with the help of a tissue called tapetum lucidum. This means that sharks can contract and dilate their pupils, like humans, something no teleost fish can do. This tissue is behind the retina and reflects light back to it, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes. This membrane covers the eyes while hunting and when the shark is being attacked. However, some species, including the great white shark (Carcharodon carcharias), do not have this membrane, but instead roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunting behavior is debated. Some believe that electro- and chemoreception are more significant, while others point to the nictating membrane as evidence that sight is important. Presumably, the shark would not protect its eyes were they unimportant. The use of sight probably varies with species and water conditions. The shark's field of vision can swap between monocular and stereoscopic at any time.^[40] A micro-spectrophotometry study of 17 species of shark found 10 had only rod photoreceptors and no cone cells in their retinas giving them good night vision while making them colorblind. The remaining seven species had in addition to rods a single type of cone photoreceptor sensitive to green and, seeing only in shades of grey and green, are believed to be effectively colorblind. The study indicates that an object's contrast against the background, rather than colour, may be more important for object detection.^{[41] [42][43]}

Hearing

Although it is hard to test sharks' hearing, they may have a sharp sense of hearing and can possibly hear prey many miles away.^[44] A small opening on each side of their heads (not the spiracle) leads directly into the inner ear through a thin channel. The lateral line shows a similar arrangement, and is open to the environment via a series of openings called lateral line pores. This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fish and tetrapods the external opening into the inner ear has been lost.

Electroreception

Main article: Electroreception

Electromagnetic field receptors (ampullae of Lorenzini) and motion detecting canals in the head of a shark

The ampullae of Lorenzini are the electroreceptor organs. They number in the hundreds to thousands. Sharks use the ampullae of Lorenzini to detect the electromagnetic fields that all living things produce.^[45] This helps sharks (particularly the hammerhead shark) find prey. The shark has the greatest electrical sensitivity of any animal. Sharks find prey hidden in sand by detecting the electric fields they produce. Ocean currents moving in the magnetic field of the Earth also generate electric fields that sharks can use for orientation and possibly navigation.^[46]

Lateral line

Main article: Lateral line

This system is found in most fish, including sharks. It detects motion or vibrations in water. The shark can sense frequencies in the range of 25 to 50 Hz.^[47]

Life history

The claspers of male spotted wobbegong

Shark lifespans vary by species. Most live 20 to 30 years. The spiny dogfish has the longest lifespan at more than 100 years.^[48] Whale sharks (Rhincodon typus) may also live over 100 years.^[49]

Reproduction

Unlike most bony fish, sharks are K-selected reproducers, meaning that they produce a small number of well-developed young as opposed to a large number of poorly developed young. Fecundity in sharks ranges from 2 to over 100 young per reproductive cycle.^[50] Sharks mature slowly relative to many other fish. For example, lemon sharks reach sexual maturity at around age 13–15.^[51]

Sexual

Sharks practice internal fertilization. The posterior part of a male shark's pelvic fins are modified into a pair of intromittent organs called claspers, analogous to a mammalian penis, of which one is used to deliver sperm into the female.^[52]
Mating has rarely been observed in sharks. The smaller catsharks often mate with the male curling around the female. In less flexible species the two sharks swim parallel to each other while the male inserts a clasper into the female's oviduct. Females in many of the larger species have bite marks that appear to be a result of a male grasping them to maintain position during mating. The bite marks may also come from courtship behavior: the male may bite the female to show his interest. In some species, females have evolved thicker skin to withstand these bites.^[52]

Asexual

There are two documented cases in which a female shark who has not been in contact with a male has conceived a pup on her own through parthenogenesis.^[53][54] The details of this process are not well understood, but genetic fingerprinting showed that the pups had no paternal genetic contribution, ruling out sperm storage. The extent of this behavior in the wild is unknown, as is whether other species have this capability. Mammals are now the only major vertebrate group in which asexual reproduction has not been observed.
Scientists assert that asexual reproduction in the wild is rare, and probably a last-ditch effort to reproduce when a mate is not present. Asexual reproduction diminishes genetic diversity, which helps build defenses against threats to the species. Species that rely solely on it risk extinction. Asexual reproduction may have contributed to the blue shark's decline off the Irish coast.^[55]

Brooding

Sharks display three ways to bear their young, varying by species, oviparity, viviparity and ovoviviparity.^[56]

Ovoviviparity

Most sharks are ovoviviparous, meaning that the eggs hatch in the oviduct within the mother's body and that the egg's yolk and fluids secreted by glands in the walls of the oviduct nourishes the embryos. 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. Lamniforme sharks practice oophagy, where the first embryos to hatch eat the remaining eggs. Taking this a step further, sand tiger shark pups cannibalistically consume neighboring embryos. The survival strategy for ovoviviparous species is to brood the young to a comparatively large size before birth. The whale shark is now classified as ovoviviparous rather than oviparous, because extrauterine eggs are now thought to have been aborted. Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs. They choose such areas for protection from predators (mainly other sharks) and the abundance of food. Dogfish have the longest known gestation period of any shark, at 18 to 24 months. Basking sharks and frilled sharks appear to have even longer gestation periods, but accurate data are lacking.^[56]

Oviparity

The spiral egg case of a Port Jackson shark

Some species are oviparous like most other fish, laying their eggs in the water. In most oviparous shark species, an egg case with the consistency of leather protects the developing embryo(s). These cases may be corkscrewed into crevices for protection. Once empty, the egg case is known as the mermaid's purse, and can wash up on shore. Oviparous sharks include the horn shark, catshark, Port Jackson shark, and swellshark.^[56][57]

Viviparity

Finally some sharks maintain a placental link to the developing young, this method is called viviparity. This is more analogous to mammalian gestation than that of other fishes. The young are born alive and fully functional. Hammerheads, the requiem sharks (such as the bull and blue sharks), and smoothhounds are viviparous.^[50][56]

Behavior

The classic view describes a solitary hunter, ranging the oceans in search of food. However, this applies to only a few species. Most live far more sedentary, benthic lives. Even solitary sharks meet for breeding or at rich hunting grounds, which may lead them to cover thousands of miles in a year.^[58] Shark migration patterns may be even more complex than in birds, with many sharks covering entire ocean basins.
Sharks can be highly social, remaining in large schools. Sometimes more than 100 scalloped hammerheads congregate around seamounts and islands, e.g., in the Gulf of California.^[28] Cross-species social hierarchies exist. For example, oceanic whitetip sharks dominate silky sharks of comparable size during feeding.^[50]
When approached too closely some sharks perform a threat display. This usually consists of exaggerated swimming movements, and can vary in intensity according to the threat level.^[59]

Speed

In general, sharks swim ("cruise") at an average speed of 8 kilometres per hour (5.0 mph) but when feeding or attacking, the average shark can reach speeds upwards of 19 kilometres per hour (12 mph). The shortfin mako shark, the fastest shark and one of the fastest fish, can burst at speeds up to 50 kilometres per hour (31 mph).^[60] The great white shark is also capable of speed bursts. These exceptions may be due to the warm-blooded, or homeothermic, nature of these sharks' physiology.

Intelligence

Sharks possess brain-to-body mass ratios that are similar to mammals and birds,^[61] and have exhibited apparent curiosity and behavior resembling play in the wild.^[62][63]

Sleep

Some sharks can lie on the bottom while actively pumping water over their gills, but their eyes remain open and actively follow divers.^[64] When a shark is resting, it does not use its nares, but rather its spiracles. If a shark tried to use its nares while resting on the ocean floor, it would "inhale" 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 spiny dogfish can continue to swim while sleeping.^[64] It is also possible that sharks sleep in a manner similar to dolphins,^[64] one cerebral hemisphere at a time, thus maintaining some consciousness and cerebral activity at all times.

Ecology

Feeding

This section is about shark feeding. For the sport of shark feeding, see Shark baiting.

Most sharks are carnivorous.^[65] Basking sharks, whale sharks, and megamouth sharks 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. 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.^[65]

Like many sharks, the great white shark is an apex predator in its environment.

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.^[28]
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 flat molariform teeth.
Other sharks feed on squid or fish, which they swallow whole. 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.
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.^[67]

Range and habitat

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). The deepest confirmed report of a shark is a Portuguese dogfish at 3,700 metres (12,100 ft).^[69]

Relationship with humans

Attacks

A sign warning about the presence of sharks in Salt Rock, South Africa

Snorkeler swims near blacktip reef shark. In rare circumstances involving poor visibility, blacktips may bite a human, mistaking it for prey. Under normal conditions they are harmless and shy.

Main article: Shark attack

In 2006 the International Shark Attack File (ISAF) undertook an investigation into 96 alleged shark attacks, confirming 62 of them as unprovoked attacks and 16 as provoked attacks. The average number of fatalities worldwide per year between 2001 and 2006 from unprovoked shark attacks is 4.3.^[70]
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.^{[71] [72]} 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 Jaws film series. Jaws author Peter Benchley, as well as Jaws director Steven Spielberg later attempted to dispel the image of sharks as man-eating monsters.^[74]

In captivity

Main article: Sharks in captivity

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. 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] 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.

A whale shark in Georgia Aquarium

Most species are not suitable for home aquaria and not every species sold by pet stores are appropriate. Some species can flourish in home saltwater aquaria.^[76] Uninformed or unscrupulous dealers sometimes sell juvenile sharks like the nurse 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] 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.^[76]

In Hawaii

Sharks figure prominently in Hawaiian mythology. Stories tell of men with shark jaws on their back who could change between shark and human form. 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. Kamaku describes 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. 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. 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.^[79][80] In Fijian mytholog, Dakuwanga was a shark god who was the eater of lost souls.

Popular misconceptions

A popular myth is that sharks are immune to disease and cancer; this is not scientifically supported. Sharks may get cancer.^[81][82] Both diseases and parasites affect sharks. 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 show sharks to have heightened immunity to disease.^[83] Other apparently false claims are that fins prevent cancer^[84] and treat osteoarthritis.^[85] No scientific proof supports these claims; at least one study has shown shark cartilage of no value in cancer treatment.^[86]

Conservation

Further information: Shark sanctuary

The value of shark fins for shark fin soup has led to an increase in shark catches. Usually only the fins are taken, while the rest of the shark is discarded, usually into the sea.

The annual shark catch has increased rapidly over the last 50 years.

A 14-foot (4.3 m), 1,200-pound (540 kg) tiger shark caught in Kāne‘ohe Bay, Oahu in 1966

Fishery

It is estimated that 100 million sharks are killed by people every year, due to commercial and recreational fishing.^[87][88] 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. 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. They are considered a delicacy in coastal Tamil Nadu. Icelanders ferment Greenland sharks to produce hákarl, which is widely regarded as a national dish.^{[citation needed]}
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.^[89] Shark fin has become a major trade within black markets all over the world. Fins sell for about $300/lb in 2009.^[90] 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.^[91]
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.^[92] However, the U.S. FDA lists sharks as one of four fish (with swordfish, king mackerel, and tilefish) whose high mercury content is hazardous to children and pregnant women.
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.^[30] 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.^[93] Many governments and the UN have acknowledged the need for shark fisheries management, but little progress has been made due to their low economic value, the small volumes of products produced and sharks' poor public image.^{[citation needed]}

Other threats

Other threats include habitat alteration, damage and loss from coastal development, pollution and the impact of fisheries on the seabed and prey species.^[94] The 2007 documentary, Sharkwater exposed how sharks are being hunted to extinction.^[95]

Protection

In 1991 South Africa was the first country in the world to declare Great White sharks a legally protected species.^[96]
Intending to ban the practice of shark finning while at sea, the United States Congress passed the Shark Finning Prohibition Act in 2000.^[97] Two years later the Act saw its first legal challenge in United States v. Approximately 64,695 Pounds of Shark Fins. 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.^[98] 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.^[99][100]
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.^[101][102]
In 2010, the Convention on International Trade in Endangered Species (CITES) rejected proposals from the United States and Palau that 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. China, by far the world’s largest shark market, and Japan, which battles all attempts to extend the convention to marine species, led the opposition.^[103][104]
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.^[105] Advocacy group Shark Trust campaigns to limit shark fishing. Advocacy group Seafood Watch directs American consumers to not eat sharks.^[106]
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. 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.

See also

• CMS Migratory Sharks Memorandum of Understanding
• List of sharks
• List of prehistoric cartilaginous fish
• Marine vertebrate
• Outline of sharks
• Shark Week

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100. ^ Shark Conservation Act of 2009 | The Humane Society of the United States^{[dead link]}. Hsus.org. Retrieved on 2010-09-16.
101. ^ Camhi, M.D; Valenti, S.V.; Fordham, S.V.; Fowler, S.L.; Gibson, C., ed. (February 2007). "The Conservation Status of Pelagic Sharks and Rays" (PDF). Pelagic Shark Red List Workshop. Oxford, England: IUCN Shark Specialist Group. ISBN 978-0-9561063-1-5. http://cmsdata.iucn.org/downloads/ssg_pelagic_report_final.pdf. Retrieved April 03, 2012.
102. ^ Jha, Alok (2009-06-25). "Fishing puts a third of all oceanic shark species at risk of extinction". The Guardian. http://www.guardian.co.uk/science/2009/jun/25/sharks-extinction-iucn-red-list. Retrieved 2009-07-16.
103. ^ Jolly, David (March 23, 2010). "U.N. Group Rejects Shark Protections". The New York Times.
104. ^ "Qatar. UN body flip-flops on shark protection". Tawa News, Canwest News Service. March 26, 2010. http://www.ottawacitizen.com/business/Qatar+body+flip+flops+shark+protection/2727330/story.html. ^{[dead link]}
105. ^ "Greenpeace International Seafood Red list". Greenpeace.org. 2003-03-17. Archived from the original on 2010-08-20. http://web.archive.org/web/20100820034707/http://www.greenpeace.org/international/seafood/red-list-of-species. Retrieved 2010-09-23.
106. ^ "Seafod WATCH, National Sustainable Seafood Guide July 2009". July 2009. http://www.montereybayaquarium.org/cr/cr_seafoodwatch/content/media/MBA_SeafoodWatch_NationalGuide.pdf. Retrieved 2009-08-29.

General references

• Castro, Jose (1983). The Sharks of North American Waters. College Station: Texas A&M University Press. ISBN 0-89096-143-3. OCLC 183037060.
• Stevens, John D. (1987). Sharks. New York: NY Facts on File Publications. ISBN 0-8160-1800-6. OCLC 15163749.
• Pough, F. H.; Janis, C. M. & Heiser, J. B. (2005). Vertebrate Life. 7th Ed.. New Jersey: Pearson Education Ltd.. ISBN 0-13-127836-3. OCLC 54822028.
• Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 0-09-189780-7
• Owen, David, Shark: In Peril in the Sea, New South Wales, Allen and Unwin, 2009. ISBN 978-1-74175-032-4
• Moss, Jillian. 2010. "The Invention of Sharks, AKA: I Read It On the Internet". University of North Carolina Publishing, Raleigh, USA. (Publishing Pending)

External links

Find more about Shark on Wikipedia's sister projects:
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Wikispecies has information related to: Selachimorpha

The Wikibook Dichotomous Key has a page on the topic of: Selachimorpha

• CMS Migratory Sharks Memorandum of Understanding
• WikiAnswers: questions and answers about Sharks
• Oceana's International Shark Campaign
• 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
• Shark pictures by Wolfgang Leander
• Shark Diversity by The Smithsonian Institution: Ocean Portal
• Sharks.org.za A detailed study
• BBC Nature: Shark news & video clips from BBC programmes past & present
• South African Marine Predator Lab a research institute studying marine top predators

[show] v t e Sharks Topics Outline of sharks Physical characteristics Shark teeth Threat display Taxonomy Hexanchiformes Squaliformes Pristiophoriformes (Sawsharks) Squatiniformes (Angel sharks) Heterodontiformes (Bullhead sharks) Orectolobiformes (Carpet sharks) Carcharhiniformes (Ground sharks) Lamniformes (Mackerel sharks) List of sharks Human interaction Shark attack Shark net Shark proof cage Shark tourism Drum lines Jersey Shore shark attacks of 1916 Category Portal

[show] v t e Extant cartilaginous fish orders Kingdom Animalia Phylum Chordata Subphylum Vertebrata Infraphylum Gnathostomata Elasmobranchii Selachii (sharks) Hexanchiformes (frilled and cow sharks) Echinorhiniformes (bramble sharks) Squaliformes (dogfish sharks) Pristiophoriformes (sawsharks) Squatiniformes (angel sharks) Heterodontiformes (bullhead sharks) Orectolobiformes (carpet sharks) Carcharhiniformes (ground sharks) Lamniformes (mackerel sharks) Batoidea (rays) Torpediniformes (electric rays) Pristiformes (sawfishes) Rajiformes (skates and guitarfishes) Myliobatiformes (stingrays and relatives) Holocephali Chimaeriformes (chimaeras)

[show] v t e Extant shark species Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Chondrichthyes Subclass Elasmobranchii [show] Order Hexanchiformes Chlamydoselachidae Chlamydoselachus Frilled shark (C. anguineus) Southern African frilled shark (C. africana) Hexanchidae (Cow sharks) Heptranchias Sharpnose sevengill shark (H. perlo) Hexanchus Bluntnose sixgill shark (H. griseus) Bigeyed sixgill shark (H. nakamurai) Notorynchus Broadnose sevengill shark (N. cepedianus) [show] Order Squaliformes Centrophoridae (Gulper sharks) Centrophorus Needle dogfish (C. acus) Dwarf gulper shark (C. atromarginatus) Gulper shark (C. granulosus) Dumb gulper shark (C. harrissoni) Blackfin gulper shark (C. isodon) Lowfin gulper shark (C. lusitanicus) Smallfin gulper shark (C. moluccensis) Taiwan gulper shark (C. niaukang) Leafscale gulper shark (C. squamosus) Mosaic gulper shark (C. tessellatus) Little gulper shark (C. uyato) Deania Birdbeak dogfish (D. calcea) Rough longnose dogfish (D. hystricosa) Arrowhead dogfish (D. profundorum) Longsnout dogfish (D. quadrispinosum) Dalatiidae Euprotomicroides Taillight shark (E. zantedeschia) Heteroscymnoides Longnose pygmy shark (H. marleyi) Mollisquama Pocket shark (M. parini) Dalatias Kitefin shark (D. licha) Isistius Cookiecutter shark (I. brasiliensis) South China cookiecutter shark (I. labialis) Largetooth cookiecutter shark (I. plutodus) Euprotomicrus Pygmy shark (E. bispinatus) Squaliolus Smalleye pygmy shark (S. aliae) Spined pygmy shark (S. laticaudus) Echinorhinidae Echinorhinus Bramble shark (E. brucus) Prickly shark (E. cookei) Etmopteridae Aculeola Hooktooth dogfish (A. nigra) Centroscyllium Highfin dogfish (C. excelsum) Black dogfish (C. fabricii) Granular dogfish (C. granulatum) Bareskin dogfish (C. kamoharai) Combtooth dogfish (C. nigrum) Ornate dogfish (C. ornatum) Whitefin dogfish (C. ritteri) Etmopterus (Lantern sharks) New Zealand lanternshark (E. baxteri) Blurred lanternshark (E. bigelowi) Shorttail lanternshark (E. brachyurus) Lined lanternshark (E. bullisi) E. burgessi Cylindrical lanternshark (E. carteri) Tailspot lanternshark (E. caudistigmus) Combtooth lanternshark (E. decacuspidatus) Pink lanternshark (E. dianthus) E. dislineatus Blackmouth lanternshark (E. evansi) Pygmy lanternshark (E. fusus) Broadbanded lanternshark (E. gracilispinis) Southern lanternshark (E. granulosus) Caribbean lanternshark (E. hillianus) Smalleye lantern shark (E. litvinovi) Blackbelly lanternshark (E. lucifer) Slendertail lanternshark (E. molleri) Dwarf lanternshark (E. perryi) African lanternshark (E. polli) Great lanternshark (E. princeps) False lanternshark (E. pseudosqualiolus) Smooth lanternshark (E. pusillus) Dense-scale lantern shark (E. pycnolepis) West Indian lanternshark (E. robinsi) Fringefin lanternshark (E. schultzi) Thorny lanternshark (E. sentosus) Velvet belly lantern shark (E. spinax) Splendid lanternshark (E. splendidus) Tasmanian lanternshark (E. tasmaniensis) Brown lanternshark (E. unicolor) Hawaiian lanternshark (E. villosus) Green lanternshark (E. virens) Miroscyllium Rasptooth dogfish (M. sheikoi) Trigonognathus Viper dogfish (T. kabeyai) Oxynotidae (Rough sharks) Oxynotus Prickly dogfish (O. bruniensis) Caribbean roughshark (O. caribbaeus) Angular roughshark (O. centrina) Japanese roughshark (O. japonicus) Sailfin roughshark (O. paradoxus) Somniosidae (Sleeper sharks) Centroscymnus Portuguese dogfish (C. coelolepis) Shortnose velvet dogfish (C. cryptacanthus) Roughskin dogfish (C. owstoni) Centroselachus Longnose velvet dogfish (C. crepidater) Proscymnodon Largespine velvet dogfish (P. macracanthus) Plunket shark (P. plunketi) Scymnodalatias Whitetail dogfish (S. albicauda) Azores dogfish (S. garricki) Sparsetooth dogfish (S. oligodon) Sherwood dogfish (S. sherwoodi) Scymnodon Smallmouth velvet dogfish (S. obscurus) Knifetooth dogfish (S. ringens) Somniosus Southern sleeper shark (S. antarcticus) Frog shark (S. longus ) Greenland shark (S. microcephalus) Pacific sleeper shark (S. pacificus) Little sleeper shark (S. rostratus) Zameus Japanese velvet dogfish (Z. ichiharai) Velvet dogfish (Z. squamulosus) Squalidae (Dogfish sharks) Cirrhigaleus Roughskin spurdog (C. asper) Mandarin dogfish (C. barbifer) Squalus (Spurdogs) Spiny dogfish (S. acanthias) Eastern highfin spurdog (S. albifrons) S. acutirostris Western highfin spurdog (S. altipinnis) Longnose spurdog (S. blainville) Fatspine spurdog (S. crassispinus) Cuban dogfish (S. cubensis) Eastern longnose spurdog (S. grahami) Japanese spurdog (S. japonicus) Shortnose spurdog (S. megalops) Blacktailed spurdog (S. melanurus) Shortspine spurdog (S. mitsukurii) Bartail spurdog (S. notocaudatus) Western longnose spurdog (S. nasutus) Cyrano spurdog (S. rancureli) Squalus suckleyi [show] Order Pristiophoriformes (Sawsharks) Pristiophoridae Pliotrema Sixgill sawshark (P. warreni) Pristiophorus Longnose sawshark (P. cirratus) Tropical sawshark (P. delicatus) Japanese sawshark (P. japonicus) Shortnose sawshark (P. nudipinnis) Bahamas sawshark (P. schroederi) Eastern Australian sawshark (Pristiophorus peroniensis) Philippine sawshark (Pristiophorus sp. C) Dwarf sawshark (Pristiophorus sp. D) [show] Order Squatiniformes (Angel sharks) Squatinidae Squatina Sawback angelshark (S. aculeata) African angelshark (S. africana) Eastern Australian angelshark (Squatina albipunctata) Argentine angelshark (S. argentina) Chilean angelshark (S. armata) Australian angelshark (S. australis) Pacific angelshark (S. californica) Sand devil (S. dumeril) Taiwan angelshark (S. formosa) Angular angel shark (S. guggenheim) S. heteroptera Japanese angelshark (S. japonica) Indonesian angelshark (S. legnota) Cortez angelshark (S. mexicana) Clouded angelshark (S. nebulosa) Smoothback angelshark (S. oculata) S. punctata Western Australian angelshark (Squatina pseudocellata) Angelshark (S. squatina) Ornate angelshark (S. tergocellata) Ocellated angelshark (S. tergocellatoides) [show] Order Heterodontiformes (Bullhead sharks) Heterodontidae Heterodontus Horn shark (H. francisci) Crested bullhead shark (H. galeatus) Japanese bullhead shark (H. japonicus) Mexican hornshark (H. mexicanus) Oman bullhead shark (H. omanensis) Port Jackson shark (H. portusjacksoni) Galapagos bullhead shark (H. quoyi) Whitespotted bullhead shark (H. ramalheira) Zebra bullhead shark (H. zebra) [show] Order Orectolobiformes (Carpet sharks) Brachaeluridae Brachaelurus Blind shark (B. waddi) Heteroscyllium Bluegrey carpetshark (H. colcloughi) Ginglymostomatidae (Nurse sharks) Ginglymostoma Nurse shark (G. cirratum) Nebrius Tawny nurse shark (N. ferrugineus) Pseudoginglymostoma Short-tail nurse shark (P. brevicaudatum) Hemiscylliidae (Bamboo sharks) Chiloscyllium Arabian carpetshark (C. arabicum) Burmese bamboo shark (C. burmensis) Bluespotted bamboo shark (C. caerulopunctatum) Grey bamboo shark (C. griseum) Hasselt's bamboo shark (C. hasseltii) Slender bamboo shark (C. indicum) Whitespotted bamboo shark (C. plagiosum) Brownbanded bamboo shark (C. punctatum) Hemiscyllium Indonesian speckled carpetshark (H. freycineti) H. galei Papuan epaulette shark (H. hallstromi) H. henryi Epaulette shark (H. ocellatum) Hooded carpetshark (H. strahani) Speckled carpetshark (H. trispeculare) Orectolobidae (Wobbegongs) Eucrossorhinus Tasselled wobbegong (E. dasypogon) Orectolobus Floral banded wobbegong (O. floridus) Banded wobbegong (O. halei) Western wobbegong (O. hutchinsi) Japanese wobbegong (O. japonicus) Spotted wobbegong (O. maculatus) Ornate wobbegong (O. ornatus) Dwarf spotted wobbegong (O. parvimaculatus) Network wobbegong (O. reticulatus) Northern wobbegong (O. wardi) Sutorectus Cobbler wobbegong (S. tentaculatus) Parascylliidae (Collared carpet sharks) Cirrhoscyllium Barbelthroat carpetshark (C. expolitum) Taiwan saddled carpetshark (C. formosanum) Saddle carpetshark (C. japonicum) Parascyllium Collared carpetshark (P. collare) Rusty carpetshark (P. ferrugineum) Ginger carpetshark (P. sparsimaculatum) Necklace carpetshark (P. variolatum) Rhincodontidae Rhincodon Whale shark (R. typus) Stegostomatidae Stegostoma Zebra shark (S. fasciatum) [show] Order Carcharhiniformes (Ground sharks) Hemigaleidae (Weasel sharks) Hemipristis Snaggletooth shark (H. elongata) Chaenogaleus Hooktooth shark (C. macrostoma) Hemigaleus Australian weasel shark (H. australiensis) Sicklefin weasel shark (H. microstoma) Paragaleus Whitetip weasel shark (P. leucolomatus) Atlantic weasel shark (P. pectoralis) Slender weasel shark (P. randalli) Straight-tooth weasel shark (P. tengi) Leptochariidae Leptocharias Barbeled houndshark (L. smithii) Proscylliidae (Finback sharks) Ctenacis Harlequin catshark (C. fehlmanni) Eridacnis Cuban ribbontail catshark (E. barbouri) Pygmy ribbontail catshark (E. radcliffei) African ribbontail catshark (E. sinuans) Proscyllium Graceful catshark (P. habereri) P. venustum Pseudotriakidae Gollum Slender smooth-hound (G. attenuatus) Pseudotriakis False catshark (P. microdon) Sphyrnidae (Hammerhead sharks) Eusphyra Winghead shark (E. blochii) Sphyrna Scalloped bonnethead (S. corona) Whitefin hammerhead (S. couardi) Scalloped hammerhead (S. lewini) Scoophead (S. media) Great hammerhead (S. mokarran) Bonnethead (S. tiburo) Smalleye hammerhead (S. tudes) Smooth hammerhead (S. zygaena) Triakidae (Houndsharks) Furgaleus Whiskery shark (F. macki) Galeorhinus School shark (G. galeus) Gogolia Sailback houndshark (G. filewoodi) Hemitriakis Deepwater sicklefin hound shark (H. abdita) Sicklefin hound shark (H. falcata) Japanese topeshark (H. japanica) Whitefin topeshark (H. leucoperiptera) Ocelate topeshark (Hemitriakis Sp.A) Hypogaleus Blacktip tope (H. hyugaensis) Iago Longnose houndshark (I. garricki) Bigeye houndshark (I. omanensis) Lowfin houndshark (Iago Sp.A) Mustelus (Smooth-hounds) M. albipinnis Gummy shark (M. antarcticus) Starry smooth-hound (M. asterias) Grey smooth-hound (M. californicus) Dusky smooth-hound (M. canis) Sharptooth smooth-hound (M. dorsalis) Striped smooth-hound (M. fasciatus) Spotless smooth-hound (M. griseus) Brown smooth-hound (M. henlei) Smalleye smooth-hound (M. higmani) Spotted estuary smooth-hound (M. lenticulatus) Sicklefin smooth-hound (M. lunulatus) Starspotted smooth-hound (M. manazo) Speckled smooth-hound (M. mento) M. minicanis Arabian smooth-hound (M. mosis) Common smooth-hound (M. mustelus) Narrowfin smooth-hound (M. norrisi) Whitespotted smooth-hound (M. palumbes) Blackspotted smooth-hound (M. punctulatus) M. ravidus Narrownose smooth-hound (M. schmitti) Gulf smoothhound (M. sinusmexicanus) Humpback smooth-hound (M. whitneyi) M. widodoi Scylliogaleus Flapnose houndshark (S. quecketti) Triakis Sharpfin houndshark (T. acutipinna) Spotted houndshark (T. maculata) Sharptooth houndshark (T. megalopterus) Banded houndshark (T. scyllium) Leopard shark (T. semifasciata) Carcharhinidae Large family listed below Scyliorhinidae Large family listed below [show] Family Carcharhinidae (Requiem sharks) Carcharhinus Blacknose shark (C. acronotus) Silvertip shark (C. albimarginatus) Bignose shark (C. altimus) Graceful shark (C. amblyrhynchoides) Grey reef shark (C. amblyrhynchos) Pigeye shark (C. amboinensis) Borneo shark (C. borneensis) Copper shark (C. brachyurus) Spinner shark (C. brevipinna) Nervous shark (C. cautus) Whitecheek shark (C. dussumieri) Silky shark (C. falciformis) Creek whaler (C. fitzroyensis) Galapagos shark (C. galapagenisis) Pondicherry shark (C. hemiodon) Finetooth shark (C. isodon) Smoothtooth blacktip shark (C. leiodon) Bull shark (C. leucas) Blacktip shark (C. limbatus) Oceanic whitetip shark (C. longimanus) Hardnose shark (C. macloti) Blacktip reef shark (C. melanopterus) Dusky shark (C. obscurus) Caribbean reef shark (C. perezii) Sandbar shark (C. plumbeus) Smalltail shark (C. porosus) Blackspot shark (C. sealei) Night shark (C. signatus) Spottail shark (C. sorrah) Australian blacktip shark (C. tilstoni) Galeocerdo Tiger shark (G. cuvier) Glyphis (River sharks) Ganges shark (G. gangeticus) Northern river shark (G. garricki) Speartooth shark (G. glyphis) Irrawaddy river shark (G. siamensis) Borneo river shark (Glyphis sp. B) Isogomphodon Daggernose shark (I. oxyrhynchus) Lamiopsis Broadfin shark (L. temminckii) Loxodon Sliteye shark (L. macrorhinus) Nasolamia Whitenose shark (N. velox) Negaprion Sicklefin lemon shark (N. acutidens) Lemon shark (N. brevirostris) Prionace Blue shark (P. glauca) Rhizoprionodon Milk shark (R. acutus) Brazilian sharpnose shark (R. lalandii) Pacific sharpnose shark (R. longurio) Grey sharpnose shark (R. oligolinx) Caribbean sharpnose shark (R. porosus) Australian sharpnose shark (R. taylori) Atlantic sharpnose shark (R. terraenovae) Scoliodon Spadenose shark (S. laticaudus) Triaenodon Whitetip reef shark (T. obesus) [show] Family Scyliorhinidae (Catsharks) Apristurus Flatnose cat shark (A. acanutus) A. albisoma A. aphyodes Atlantic ghost catshark (A. atlanticus) Brown catshark (A. brunneus) Hoary catshark (A. canutus) Flaccid catshark (A. exsanguis) A. fedorovi Humpback cat shark (A. gibbosus) Longfin catshark (A. herklotsi) Smallbelly catshark (A. indicus) A. internatus Broadnose catshark (A. investigatoris) Japanese catshark (A. japonicus) Longnose catshark (A. kampae) Iceland catshark (A. laurussonii) Longhead catshark (A. longicephalus) Flathead catshark (A. macrorhynchus) Broadmouth cat shark (A. macrostomus) Ghost catshark (A. manis) Black roughscale catshark (A. melanoasper) Smalleye catshark (A. microps) Smalldorsal cat shark (A. micropterygeus) Largenose catshark (A. nasutus) Smallfin catshark (A. parvipinnis) A. pinguis Spatulasnout catshark (A. platyrhynchus) Deepwater catshark (A. profundorum) Broadgill catshark (A. riveri) Saldanha catshark (A. saldanha) Pale catshark (A. sibogae) South China catshark (A. sinensis) Spongehead catshark (A. spongiceps) Panama ghost catshark (A. stenseni) Asymbolus Australian spotted catshark (A. analis) A. funebris Western spotted catshark (A. occiduus) Pale spotted catshark (A. pallidus) A. parvus A. rubiginosus Variegated catshark (A. submaculatus) Gulf catshark (A. vincenti) Atelomycterus A. baliensis Banded sand catshark (A. fasciatus) Australian marbled catshark (A. macleayi) Coral catshark (A. marmoratus) Aulohalaelurus New Caledonia catshark (A. kanakorum) Australian blackspotted catshark (A. labiosus) Cephaloscyllium Whitefin swellshark (C. albipinnum) Circle-blotch pygmy swellshark (C. circulopullum) Cook's swellshark (C. cooki) Reticulated swellshark (C. fasciatum) Australian reticulate swellshark (C. hicosellum) Draughtsboard shark (C. isabellum) Australian swellshark (C. laticeps) Spotted swellshark (C. maculatum) Leopard-spotted swellshark (C. pardelotum) Painted swellshark (C. pictum) Sarawak pygmy swellshark (C. sarawakensis) Flagtail swellshark (C. signourum) Indian swellshark (C. silasi) Speckled swellshark (C. speccum) Balloon shark (C. sufflans) Blotchy swellshark (C. umbratile) Saddled swellshark (C. variegatum) Swellshark (C. ventriosum) Narrowbar swellshark (C. zebrum) Cephalurus Lollipop catshark (C. cephalus) Figaro Australian sawtail catshark (F. boardmani) Northern sawtail catshark (F. striatus) Galeus Antilles catshark (G. antillensis) Roughtail catshark (G. arae) Atlantic sawtail cat shark (G. atlanticus) Longfin sawtail cat shark (G. cadenati) Gecko catshark (G. eastmani) Slender sawtail catshark (G. gracilis) Longnose sawtail cat shark (G. longirostris) Blackmouth catshark (G. melastomus) Southern sawtail catshark (G. mincaronei) Mouse catshark (G. murinus) Broadfin sawtail catshark (G. nipponensis) Peppered catshark (G. piperatus) African sawtail catshark (G. polli) G. priapus Blacktip sawtail catshark (G. sauteri) Dwarf sawtail catshark (G. schultzi) Springer's sawtail cat shark (G. springeri) Halaelurus Arabian catshark (H. alcockii) Speckled catshark (H. boesemani) Blackspotted catshark (H. buergeri) Dusky catshark (H. canescens) Broadhead cat shark (H. clevai) New Zealand catshark (H. dawsoni) Bristly catshark (H. hispidus) Spotless catshark (H. immaculatus) Lined catshark (H. lineatus) Mud catshark (H. lutarius) Tiger catshark (H. natalensis) Quagga catshark (H. quagga) Haploblepharus Puffadder shyshark (H. edwardsii) Brown shyshark (H. fuscus) Natal shyshark (H. kistnasamyi) Dark shyshark (H. pictus) Holohalaelurus H. favus H. grennian Crying izak (H. melanostigma) African spotted catshark (H. punctatus) Izak catshark (H. regani) Parmaturus White-tip catshark (P. albimarginatus) White-clasper catshark (P. albipenis) Beige catshark (P. bigus) Campeche catshark (P. campechiensis) Velvet catshark (P. lanatus) McMillan's catshark (P. macmillani) Blackgill catshark (P. melanobranchus) Salamander shark (P. pilosus) Filetail catshark (P. xaniurus) Shorttail catshark (Parmaturus sp. A) Pentanchus Onefin catshark (P. profundicolus) Poroderma Pyjama catshark (P. africanum) Leopard catshark (P. pantherinum) Schroederichthys Narrowmouthed catshark (S. bivius) Redspotted catshark (S. chilensis) Narrowtail catshark (S. maculatus) Lizard catshark (S. saurisqualus) Slender catshark (S. tenuis) Scyliorhinus Polkadot catshark (S. besnardi) Boa catshark (S. boa) Small-spotted catshark (S. canicula) Yellowspotted catshark (S. capensis) West African catshark (S. cervigoni) Comoro cat shark (S. comoroensis) Brownspotted catshark (S. garmani) Freckled catshark (S. haeckelii) Whitesaddled catshark (S. hesperius) Blotched catshark (S. meadi) Chain catshark (S. retifer) Nursehound (S. stellaris) Izu cat shark (S. tokubee) Cloudy catshark (S. torazame) Dwarf catshark (S. torrei) [show] Order Lamniformes (Mackerel sharks) Alopiidae Alopias (Thresher sharks) Pelagic thresher (A. pelagicus) Bigeye thresher (A. superciliosus) Common thresher (A. vulpinus) Cetorhinidae Cetorhinus Basking shark (C. maximus) Lamnidae Carcharodon Great white shark (C. carcharias) Isurus Shortfin mako shark (I. oxyrinchus) Longfin mako shark (I. paucus) Lamna Salmon shark (L. ditropis) Porbeagle (L. nasus) Megachasmidae Megachasma Megamouth shark (M. pelagios) Mitsukurinidae Mitsukurina Goblin shark (M. owstoni) Odontaspididae Carcharias Grey nurse shark (C. taurus) Indian sand tiger (C. tricuspidatus) Odontaspis Smalltooth sand tiger (O. ferox) Bigeye sand tiger (O. noronhai) Pseudocarchariidae Pseudocarcharias Crocodile shark (P. kamoharai)

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