superorder of predaceous cartilaginous pisces

Sharks are a group of elasmobranch fish characterized by a cartilaginous skeletal system, five to seven gill slits on the sides of the fountainhead, and pectoral fins that are not fused to the head. advanced sharks are classified within the clade Selachimorpha ( or Selachii ) and are the sister group to the rays. however, the term “ shark ” has besides been ( incorrectly [ 2 ] ) used to refer to extinct members of the subclass Elasmobranchii, which are technically outside the Selachimorpha clade. luminary examples of improper categorization include Cladoselache, Xenacanthus, and diverse early members of the Chondrichthyes class like the holocephalid eugenedontidans. Under this broader definition, the earliest known sharks date back to more than 420 million years ago. [ 3 ] Acanthodians are often referred to as “ spinous sharks ” ; though they are not part of Chondrichthyes proper, they are a paraphyletic collection leading to cartilaginous pisces as a wholly. Since then, sharks have diversified into over 500 species. They range in size from the small shadow lanternshark ( Etmopterus perryi ), a deep sea species that is alone 17 centimetres ( 6.7 in ) in length, to the whale shark ( Rhincodon typus ), the largest fish in the worldly concern, which reaches approximately 12 metres ( 40 foot ) in distance. [ 4 ] Sharks are found in all seas and are common to depths up to 2,000 metres ( 6,600 foot ). They by and large do not live in fresh water, although there are a few know exceptions, such as the bull shark and the river shark, which can be found in both seawater and fresh water. [ 5 ] Sharks have a covering of cutaneous denticles that protects their skin from damage and parasites in addition to improving their fluent dynamics. They have numerous sets of replaceable teeth. [ 6 ]

respective species are vertex predators, which are organisms that are at the top of their food chain. choose examples include the tiger shark, bluing shark, great white shark, mako shark, thresher shark, and dunce shark. Sharks are caught by humans for shark meat or shark fin soup. many shark populations are threatened by human activities. Since 1970, shark populations have been reduced by 71 %, by and large from overfishing. [ 7 ]

etymology

Until the sixteenth century, [ 8 ] sharks were known to mariners as “ sea dogs ”. [ 9 ] This is however evidential in several species termed “ dogfish, ” or the porbeagle. The etymology of the password shark is uncertain, the most likely etymology states that the original sense of the discussion was that of “ predator, one who preys on others ” from the Dutch schurk, meaning ‘villain, villain ‘ ( cf. card shark, loan shark, etc. ), which was late applied to the pisces due to its predatory behavior. [ 10 ] A now disproven [ original research? ] hypothesis is that it derives from the Yucatec Maya word xook ( pronounced [ ʃoːk ] ), meaning ‘shark ‘. [ 11 ] evidence for this etymology came from the Oxford English Dictionary, which notes shark first came into function after Sir John Hawkins ‘ sailors exhibited one in London in 1569 and posted “ sharke “ to refer to the large sharks of the Caribbean Sea. however, the Middle English Dictionary records an isolate happening of the give voice shark ( referring to a ocean pisces ) in a letter written by Thomas Beckington in 1442, which rules out a New World etymology. [ 12 ] [ original research? ]

evolutionary history

Fossil shark tooth ( size over 9 cm or 3.5 inches ) with crown, shoulder, root and etymon lobe

fossil read

evidence for the universe of shark-like chondrichthyans dates from the ordovician period, 450–420 million years ago, before land vertebrates existed and before a kind of plants had colonized the continents. [ 3 ] only scales have been recovered from the first supposed elasmobranchians and not all paleontologists agree that these are from true sharks, suspecting that these scales are actually those of thelodont agnathans. [ 13 ] The oldest by and large accepted “ shark ” scales are from about 420 million years ago, in the silurian period. [ 13 ] Those animals looked very different from modern sharks. [ 14 ] At this time the most coarse shark tooth is the cladodont, a manner of thin tooth with three tines like a trident, obviously to help catch fish. The majority of modern sharks can be traced back to around 100 million years ago. [ 15 ] Most fossils are of teeth, frequently in big numbers. overtone skeletons and even complete fossilized remains have been discovered. Estimates suggest that sharks grow tens of thousands of teeth over a life, which explains the abundant fossils. The dentition dwell of well fossilized calcium phosphate, an apatite. When a shark dies, the decomposing skeleton breaks up, scattering the apatite prism. Preservation requires rapid burying in buttocks sediments. Among the most ancient and primitive shark-like pisces is Cladoselache, from about 370 million years ago, [ 14 ] which has been found within Paleozoic level in Ohio, Kentucky, and Tennessee. At that decimal point in Earth ‘s history these rocks made up the cushy bottom sediments of a large, shallow ocean, which stretched across much of North America. Cladoselache was only about 1 metre ( 3.3 foot ) farseeing with starchy trilateral fins and slender chew the fat. [ 14 ] Its teeth had several pointed cusp, which wore toss off from function. From the belittled number of teeth found together, it is most likely that Cladoselache did not replace its teeth angstrom regularly as modern sharks. Its caudal fins had a exchangeable supreme headquarters allied powers europe to the great white sharks and the oceanic shortfin and longfin mako. The presence of unharmed fish arranged tail-first in their stomach suggest that they were fast swimmers with great agility. Most fossil shark-like fish from approximately 300 to 150 million years ago can be assigned to one of two groups. The Xenacanthida was about exclusive to freshwater environments. [ 16 ] [ 17 ] By the time this group became extinct about 220 million years ago, they had spread cosmopolitan. The other group, the hybodonts, appeared about 320 million years ago and lived by and large in the oceans, but besides in fresh water. [ citation needed ] The results of a 2014 study of the gill social organization of an unusually well preserved 325-million-year-old dodo suggested that sharks are not “ living fossils ”, but rather have evolved more extensively than previously thought over the hundreds of millions of years they have been about. [ 18 ] Drawing comparing sizes of megalodon, great white shark and a man, megalodon is 18 m long and great white 6 m. Megalodon (top two, estimated maximum and conservative sizes) with the whale shark, great white shark, and a human for scale It appears Selachiimorpha and Batoidea divide in the Triassic. [ 2 ] Modern sharks began to appear about 100 million years ago. [ 15 ] Fossil mackerel shark tooth date to the early Cretaceous. One of the most recently evolved families is the hammerhead shark ( family Sphyrnidae ), which emerged in the Eocene. [ 19 ] The oldest white shark tooth date from 60 to 66 million years ago, around the prison term of the extinction of the dinosaurs. In early white shark development there are at least two lineages : one descent is of white sharks with coarsely serrated tooth and it credibly gave rise to the modern great white shark, and another lineage is of white sharks with finely serrated tooth. These sharks attained gigantic proportions and include the extinct megatoothed shark, C. megalodon. Like most extinct sharks, C. megalodon is besides primarily known from its fossil teeth and vertebra. This giant shark reached a total duration ( TL ) of more than 16 metres ( 52 foot ). [ 20 ] [ 21 ] C. megalodon may have approached a maximum of 20.3 metres ( 67 foot ) in total distance and 103 metric tons ( 114 short tons ) in batch. [ 22 ] Paleontological testify suggests that this shark was an active marauder of large cetaceans. [ 22 ]

early Miocene extinction consequence

A study published in 2021 provided attest for a major shark extinction event that occurred 19 million years ago. This is 5 million years before the established Middle Miocene disruption. The campaign of this extinction event is not yet known, however, the study suggests that oceanic shark diversity decreased by over 70 % and abundance by over 90 %, and that advanced sharks never recovered from this consequence. The authors besides state that anterior to the extinction event, “ sharks played a much larger role in the open-ocean ecosystem than they do today. ” In show times, alone 53 open-ocean shark species remains. [ 23 ] [ 24 ] [ 25 ]

taxonomy

Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii besides include rays and skates ; the Chondrichthyes besides include Chimaeras. It was thought that the sharks form a polyphyletic group : some sharks are more closely related to rays than they are to some early sharks, [ 26 ] but current molecular studies support monophyly of both groups of sharks and batoids. [ 27 ] [ 28 ] The superorder Selachimorpha is divided into Galea ( or Galeomorphii ), and Squalea ( or Squalomorphii ). The Galeans are the Heterodontiformes, Orectolobiformes, Lamniformes, and Carcharhiniformes. Lamnoids and Carcharhinoids are normally placed in one clade, but late studies show the Lamnoids and Orectoloboids are a clade. Some scientists now think that Heterodontoids may be Squalean. The Squaleans are divided into Hexanchiformes and Squalomorpha. The former includes cow shark and frilled shark, though some authors propose both families to be moved to separate orders. The Squalomorpha contains the Squaliformes and the Hypnosqualea. The Hypnosqualea may be invalid. It includes the Squatiniformes, and the Pristorajea, which may besides be invalid, but includes the Pristiophoriformes and the Batoidea. [ 26 ] [ 29 ] There are more than 500 species of sharks split across thirteen orders, including four orders of sharks that have gone extinct : [ 29 ] [ 30 ]

anatomy

Drawing of a shark labeling major anatomical features, including mouth, snout, nostril, eye, spiracle, dorsal fin spine, caudal keel, clasper, labial furrows, gill openings, precaudal pit and fins: first and second dorsal, anal, pectoral, caudal and pelvic General anatomic features of sharks

Teeth

The serrated teeth of a tiger shark, used for sawing through flesh The tooth of tiger sharks are oblique and serrated to saw through flesh Shark teeth are embedded in the gums rather than directly affixed to the chew the fat, and are constantly replaced throughout liveliness. multiple rows of substitute teeth grow in a rut on the inside of the chew and steadily move ahead in comparison to a conveyer belt out ; some sharks lose 30,000 or more teeth in their life. The rate of tooth refilling 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 coincident substitution of an entire row, which is observed in the cookiecutter shark. [ 32 ] Tooth form depends on the shark ‘s diet : those that feed on mollusks and crustaceans have dense and flattened teeth used for jam, those that feed on fish have needle-like teeth for fascinate, and those that feed on larger prey such as mammals have pointed lower dentition for gripping and triangular upper berth tooth with serrate edges for cutting. The tooth of plankton-feeders such as the enjoy shark are small and non-functional. [ 33 ]

skeleton

Shark skeletons are very unlike from those of bony fish and tellurian vertebrates. Sharks and other cartilaginous pisces ( 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 system of weights, saving energy. [ 34 ] Because sharks do not have ridicule cages, they can easily be crushed under their own weight on land. [ 35 ]

yack

The chew of sharks, like those of rays and skates, are not attached to the cranium. The yack ‘s surface ( in comparison to the shark ‘s vertebra and gill arches ) needs excess support due to its heavy exposure to physical stress and its motivation for military capability. It has a layer of bantam hexangular plates called “ tessera “, which are crystal blocks of calcium salts arranged as a mosaic. [ 36 ] This gives these areas much of the same intensity found in the osseous tissue found in early animals. by and large sharks have lone one layer of tessera, but the jaw of large specimens, such as the bull shark, tiger shark, and the great egg white shark, have two to three layers or more, depending on body size. The call on the carpet of a bombastic great whiten shark may have up to five layers. [ 34 ] In the snout ( beak ), 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. [ 37 ] Most sharks have eight fins. Sharks can alone drift away from objects immediately in front of them because their fins do not allow them to move in the tail-first direction. [ 35 ]

cutaneous denticles

Unlike bony fish, sharks have a complex cutaneous corset made of compromising collagenous fibers and arranged as a coiling network surrounding their body. This works as an out skeleton, providing attachment for their swim muscles and thus saving energy. [ 38 ] Their cuticular teeth give them hydrodynamic advantages as they reduce turbulence when liquid. [ 39 ] Some species of shark have pigmented out skin layers under the denticles that form complex patterns like spots ( e.g. Zebra shark ) and stripes ( e.g. Tiger shark ). These markings are crucial for camouflage and help sharks blend in with their environment, a well as making them unmanageable for prey to detect. [ 40 ] For some species, patterning returns to the healed dermis evening after areas have been removed by injury. [ 41 ]

Tails

Tails provide thrust, making speed and acceleration dependant on tail determine. Caudal fin shapes vary well between shark species, ascribable to their evolution in separate environments. Sharks possess a heterocercal caudal fin in which the dorsal share is normally perceptibly larger than the ventral fortune. This is because the shark ‘s vertebral column extends into that abaxial part, providing a greater surface sphere for muscle attachment. This allows more effective locomotion among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a homocercal caudal tail fin. [ 42 ] tiger sharks have a big upper berth lobe, which allows for boring cruise and sudden bursts of travel rapidly. The tiger shark must be able to twist and turn in the water well when hunting to support its varied diet, whereas the porbeagle shark, which hunts schooling fish such as mackerel and herring, has a bombastic lower lobe to help it keep footstep with its fast-swimming prey. [ 43 ] early fag end adaptations help sharks catch prey more directly, such as the thresher shark ‘s custom of its herculean, elongated upper lobe to stun fish and squid .

physiology

buoyancy

Unlike osseous fish, sharks do not have gas-filled swim bladders for buoyancy. rather, sharks rely on a large liver-colored filled with oil that contains squalene, and their cartilage, which is about half the normal density of bone. [ 38 ] Their liver-colored constitutes up to 30 % of their total body mass. [ 44 ] The liver ‘s effectiveness is limited, then shark employ moral force pilfer to maintain depth while swimming. Sand tiger sharks store air in their stomach, using it as a kind of float bladder. bottom-dwelling sharks, like the breastfeed shark, have negative airiness, allowing them to rest on the ocean floor. Some sharks, if inverted or stroked on the nozzle, enter a natural state of tonic immobility. Researchers use this condition to handle sharks safely. [ 45 ]

breathing

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 question. A modified cunt called a spiracle lies good behind the eye, which assists the shark with taking in body of water during respiration and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active oceanic sharks. [ 33 ] While the shark is moving, water system passes through the mouth and over the gills in a procedure known as “ aries ventilation ”. While at rest, most sharks pump water over their gills to ensure a changeless add of oxygenate water system. A little issue of species have lost the ability to pump body of water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate aries ventilation is besides true of some oceanic bony pisces species. [ 46 ] [ 47 ] The breathing and circulation procedure begins when deoxygenate blood travels to the shark ‘s bicameral heart. here the shark pumps blood to its gills via the adaxial aorta artery where it branches into afferent brachial arteries. Reoxygenation takes locate in the gills and the reoxygenated blood flows into the motor nerve brachial arteries, which come together to form the abaxial aorta. The blood flows from the dorsal aorta throughout the body. The deoxygenate blood from the body then flows through the later cardinal number veins and enters the posterior cardinal number sinuses. From there blood enters the center ventricle and the cycle repeats. [ 48 ]

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 homoiothermic and maintain a higher body temperature than the wall water. In these sharks, a strip of aerobic crimson muscleman located near the center of the body generates the heat, which the body retains via a countercurrent change mechanism by a system of blood vessels called the plexus mirabile ( “ marvelous net ” ). The common thresher and bigeye thresher sharks have a similar mechanism for maintaining an elevated body temperature. [ 49 ]

Osmoregulation

In contrast to bony fish, with the exception of the coelacanth, [ 50 ] the blood and early tissue of sharks and Chondrichthyes is generally isotonic to their marine environments because of the high concentration of urea ( up to 2.5 % [ 51 ] ) and trimethylamine N-oxide ( TMAO ), allowing them to be in osmotic balance with the seawater. This adaptation prevents most sharks from surviving in fresh water, and they are therefore confined to marine environments. A few exceptions exist, such as the bull shark, which has developed a manner to change its kidney function to excrete large amounts of urea. [ 44 ] When a shark dies, the urea is broken depressed to ammonia by bacteria, causing the dead consistency to gradually smell powerfully of ammonia. [ 52 ] [ 53 ] research in 1930 by Homer W. Smith showed that sharks ‘ urine does n’t contain sufficient sodium to avoid hypernatremia, and it was postulated that there must be an extra mechanism for salt secretion. In 1960 it was discovered at the Mount Desert Island Biological Laboratory in Salsbury Cove, Maine that sharks have a type of salt gland located at the end of the intestine, known as the “ rectal gland ”, whose officiate is the secretion of chlorides. [ 54 ]

digestion

digestion can take a retentive time. The food moves from the talk to a J-shaped digest, where it is stored and initial digestion occurs. [ 55 ] Unwanted items may never get past the stomach, and alternatively the shark either vomits or turns its digest inside out and ejects undesirable items from its mouth. [ 56 ] One of the biggest differences between the digestive systems of sharks and mammals is that sharks have a lot shorter intestines. This abruptly length is achieved by the spiral valve with multiple turns within a individual short section alternatively of a long tube-like intestine. The valve provides a long open area, requiring food to circulate inside the unretentive gut until fully digested, when remaining thriftlessness products pass into the sewer. [ 55 ]

fluorescence

A few sharks appear fluorescent under bluing unhorse, such as the swell shark and the chain catshark, where the fluorophore derives from a metabolite of kynurenic acid. [ 57 ]

Senses

smell

Eyelevel photo of hammerhead from the front The determine of the dunce shark ‘s head may enhance smell by spacing the nostrils further apart. Sharks have lament olfactory senses, located in the short duct ( which is not fused, unlike bony pisces ) between the front tooth and back tooth adenoidal openings, with some species able to detect equally fiddling as one partially per million of blood in seawater. [ 58 ] The size of the olfactory medulla oblongata varies across different shark species, with size pendent on how much a given species relies on smell or vision to find their prey. [ 59 ] In environments with first gear visibility, shark species broadly have larger olfactory light bulb. [ 59 ] In witwatersrand, where visibility is high, species of sharks from the kin Carcharhinidae have smaller olfactory light bulb. [ 59 ] Sharks found in deep waters besides have larger olfactory bulb. [ 60 ] Sharks have the ability to determine the direction of a given aroma based on the clock of perfume detection in each nostril. [ 61 ] This is exchangeable to the method acting mammals use to determine steering of fathom. They are more attract to the chemicals found in the intestines of many species, and as a result often linger dear or in sewage outfalls. Some species, such as nurse sharks, have external barbels that greatly increase their ability to sense raven .

sight

Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retina, though their eyesight is well adapted to the marine environment with the help of a tissue called tapetum lucidum. This tissue is behind the retina and reflects abstemious back to it, thereby increasing visibility in the dark waters. The potency of the tissue varies, with some sharks having stronger nocturnal adaptations. many sharks can condense and dilate their pupils, like humans, something no teleost fish fish can do. Sharks have eyelids, but they do not blink because the wall 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 alternatively roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunt behavior is debated. Some believe that electro- and chemoreception are more significant, while others point to the nictating membrane as attest that spy is significant. presumably, the shark would not protect its eyes were they unimportant. The habit of spy credibly varies with species and water system conditions. The shark ‘s field of vision can swap between monocular and stereoscopic at any time. [ 62 ] A micro-spectrophotometry discipline of 17 species of shark found 10 had lone rod photoreceptors and no cone cells in their retina giving them good night vision while making them colorblind. The remaining seven species had in addition to rods a unmarried type of cone photoreceptor sensitive to greens 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 setting, rather than colour, may be more important for object signal detection. [ 63 ] [ 64 ] [ 65 ]

Hearing

Although it is hard to test the listening of sharks, they may have a sharp sense of hearing and can possibly hear prey from many miles away. [ 66 ] The hear sensitivity for most shark species lies between 20 and 1000 Hz. [ 67 ] A small open on each english of their heads ( not the spiracle ) leads immediately into the inner ear through a thin groove. The lateral line shows a similar arrangement, and is capable to the environment via a series of openings called lateral pass 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 possibility into the inner auricle has been lost .
Drawing of shark head. electromagnetic sphere receptors ( ampulla of Lorenzini ) and apparent motion detection canals in the head of a shark

Electroreception

The ampulla of Lorenzini are the electroreceptor organs. They number in the hundreds to thousands. Sharks use the ampulla of Lorenzini to detect the electromagnetic fields that all live things produce. [ 68 ] This helps sharks ( particularly the hammerhead shark ) find raven. The shark has the greatest electric sensitivity of any animal. Sharks find prey hidden in sandpaper by detecting the electric fields they produce. Ocean currents moving in the magnetic field of the Earth besides generate electric fields that sharks can use for orientation and possibly seafaring. [ 69 ]

lateral line

This system is found in most fish, including sharks. It is a haptic sensational organization which allows the organism to detect body of water travel rapidly and pressure changes near by. [ 70 ] The main component of the system is the neuromast, a cell like to hair cells stage in the vertebrate auricle that interact with the surrounding aquatic environment. This helps sharks distinguish between the currents around them, obstacles off on their periphery, and struggling prey out of ocular opinion. The shark can sense frequencies in the scope of 25 to 50 Hz. [ 71 ]

Life history

Shark egg Shark lifespans vary by species. Most live 20 to 30 years. The barbed bowfin has one of the longest lifespans at more than 100 years. [ 72 ] Whale sharks ( Rhincodon typus ) may besides live over 100 years. [ 73 ] Earlier estimates suggested the Greenland shark ( Somniosus microcephalus ) could reach about 200 years, but a holocene study found that a 5.02-metre-long ( 16.5 foot ) specimen was 392 ± 120 years old ( i.e., at least 272 years old ), making it the longest-lived vertebrate known. [ 74 ] [ 75 ]

reproduction

Unlike most bony fish, sharks are K-selected reproducers, meaning that they produce a belittled numeral of well-developed young as opposed to a large number of ailing developed young. fruitfulness in sharks ranges from 2 to over 100 young per generative cycle. [ 76 ] Sharks mature lento relative to many other pisces. For example, lemon sharks reach sexual maturity at around senesce 13–15. [ 77 ]

sexual

Sharks practice internal fertilization. [ 78 ] The later separate 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. [ 79 ] coupling has rarely been observed in sharks. [ 80 ] The smaller catsharks much mate with the male curling around the female. In less flexible species the two sharks swim analogue to each other while the male inserts a clasper into the female ‘s fallopian tube. Females in many of the larger species have bite marks that appear to be a solution of a male grasping them to maintain position during copulate. The bite marks may besides come from courtship behavior : the male may bite the female to show his interest. In some species, females have evolved thick hide to withstand these bites. [ 79 ]

asexual

There have been a number of attested cases in which a female shark who has not been in touch with a male has conceived a whelp on her own through parthenogenesis. [ 81 ] [ 82 ] The details of this procedure are not well silent, but familial fingerprint showed that the pups had no paternal genic contribution, ruling out sperm memory. The extent of this behavior in the crazy is unknown. Mammals are now the lone major vertebrate group in which asexual reproduction has not been observed. Scientists say that asexual replica in the rampantly is rare, and probably a last-ditch attempt to reproduce when a mate is not confront. asexual replica diminishes genic diversity, which helps build defenses against threats to the species. Species that rely entirely on it risk extinction. asexual reproduction may have contributed to the blue shark ‘s decline off the Irish coast. [ 83 ]

Brooding

Sharks display three ways to bear their young, varying by species, oviparity, viviparity and ovoviviparity. [ 84 ] [ 85 ]

Ovoviviparity

Most sharks are ovoviviparous, meaning that the eggs hatch in the fallopian tube within the mother ‘s body and that the egg ‘s yolk and fluids secreted by glands in the walls of the fallopian tube nourishes the embryo. The young retain to be nourished by the remnants of the yolk and the fallopian tube ‘s fluids. As in viviparity, the young are born alive and in full functional. Lamniforme sharks practice oophagy, where the beginning embryo to hatch eat the remaining eggs. Taking this a mistreat far, sandpaper tiger shark pups cannibalistically consume neighboring embryo. The survival scheme for ovoviviparous species is to brood the unseasoned to a relatively large size before birth. The whale shark is nowadays 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 ( chiefly other sharks ) and the abundance of food. Dogfish have the longest acknowledge gestation period of any shark, at 18 to 24 months. Basking sharks and frilled sharks appear to have even longer pregnancy periods, but accurate data are lacking. [ 84 ]

Oviparity

Some species are oviparous, laying their fertilized eggs in the water. In most oviparous shark species, an testis case with the consistency of leather protects the developing embryo ( mho ). These cases may be corkscrewed into crevices for protection. The egg event is normally called a mermaid’s purse. oviparous sharks include the horn shark, catshark, Port Jackson shark, and swellshark. [ 84 ] [ 86 ]

Viviparity

Viviparity is the pregnancy of new without the use of a traditional egg, and results in live birth. [ 87 ] Viviparity in sharks can be placental or aplacental. [ 87 ] Young are born amply formed and self-sufficient. [ 87 ] Hammerheads, the dirge sharks ( such as the bull and blue sharks ), and smoothhounds are viviparous. [ 76 ] [ 84 ]

behavior

The classical opinion describes a alone orion, ranging the oceans in search of food. however, this applies to entirely a few species. Most populate far more sociable, sedentary, benthic lives, and appear likely to have their own clear-cut personalities. [ 88 ] even lone sharks meet for breeding or at rich hunting grounds, which may lead them to cover thousands of miles in a class. [ 89 ] 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 big schools. sometimes more than 100 scalloped hammerheads congregate around seamounts and islands, for example, in the Gulf of California. [ 44 ] Cross-species sociable hierarchies exist. For exemplar, oceanic whitetip sharks dominate satiny sharks of comparable size during feeding. [ 76 ] When approached besides closely some sharks perform a menace display. This normally consists of exaggerated swim movements, and can vary in intensity according to the menace horizontal surface. [ 90 ]

speed

In general, shark swim ( “ cruise ” ) at an average speed of 8 kilometres per hour ( 5.0 miles per hour ), but when run or attack, the average shark can reach amphetamine upwards of 19 kilometres per hour ( 12 miles per hour ). The shortfin mako shark, the fastest shark and one of the fastest fish, can burst at speeds up to 50 kilometres per hour ( 31 miles per hour ). [ 91 ] The great white shark is besides adequate to of speed bursts. These exceptions may be due to the warm-blooded, or homoiothermic, nature of these sharks ‘ physiology. Sharks can travel 70 to 80 km in a day. [ 92 ]

intelligence

Sharks posse brain-to-body mass ratios that are similar to mammals and birds, [ 93 ] and have exhibited apparent curiosity and behavior resembling play in the wild. [ 94 ] [ 95 ] There is evidence that adolescent lemon sharks can use experimental determine in their probe of fresh objects in their environment. [ 96 ]

rest

All sharks need to keep water system flowing over their gills in arrange for them to breathe ; however, not all species need to be moving to do this. Those that are able to breathe while not swimming do indeed by using their spiracles to force water over their gills, thereby allowing them to extract oxygen from the water. It has been recorded that their eyes remain overt while in this country and actively follow the movements of divers swimming around them [ 97 ] and as such they are not rightfully asleep. Species that do need to swim continuously to breathe go through a procedure known as rest float, in which the shark is basically unconscious. It is known from experiments conducted on the spinous bowfin that its spinal cord, rather than its genius, coordinates swimming, so barbed bowfin can continue to swim while sleeping, and this besides may be the case in larger shark species. [ 97 ] In 2016 a great white shark was captured on video recording for the first clock time in a state researchers believed was sleep swim. [ 98 ]

ecology

Feeding

This section is about shark feed. For the fun of shark feed, see Shark bait Most sharks are carnivorous. [ 99 ] Basking sharks, whale sharks, and megamouth sharks have independently evolved different strategies for filter feeding plankton : enjoy 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 weave inside of their mouths to attract prey in the thick ocean. This type of feeding requires gill rakers —long, slender filaments that form a identical efficient sieve —analogous to the whalebone plates of the great whales. The shark traps the plankton in these filaments and swallows from prison term to clock time in huge taste. Teeth in these species are relatively small because they are not needed for feeding. [ 99 ] other highly speciate 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 peculiarly sharp. Although they have never been observed feed, they are believed to latch onto their raven and use their thick lips to make a seal, twisting their bodies to rip off human body. [ 44 ] 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. [ 100 ] Many benthic sharks feed entirely on crustaceans which they crush with their flat molariform teeth. other sharks feed on squid or fish, which they swallow hale. The viper bowfin has teeth it can point outwards to strike and capture prey that it then swallows intact. The bang-up white and other large predators either swallow little prey unharmed or take huge bites out of big animals. Thresher sharks use their long tails to stun shoaling fishes, and sawsharks either arouse prey from the ocean floor or convulse at swimming raven with their tooth-studded dais. many sharks, including the whitetip reef shark are cooperative feeders and hunt in packs to herd and capture baffling prey. These social sharks are often migratory, traveling huge distances around ocean basins in large schools. These migrations may be partially necessary to find new food sources. [ 101 ]

Range and habitat

Sharks are found in all seas. They generally do not live in bracing water, with a few exceptions such as the taurus shark and the river shark which can swim both in seawater and fresh water. [ 102 ] Sharks are coarse down to depths of 2,000 metres ( 7,000 foot ), and some survive even deeper, but they are about entirely absent below 3,000 metres ( 10,000 foot ). The deepest confirmed report card of a shark is a portuguese dogfish at 3,700 metres ( 12,100 foot ). [ 103 ]

relationship with humans

Attacks

Photo of snorkeler with shark in shallow water. Snorkeler swims near a blacktip reef shark. In rare circumstances involving poor visibility, blacktips may bite a human, mistaking it for raven. Under convention conditions they are harmless and shy. In 2006 the International Shark Attack File ( ISAF ) undertook an probe into 96 allege shark attacks, confirming 62 of them as motiveless attacks and 16 as provoke attacks. The average count of fatalities worldwide per year between 2001 and 2006 from motiveless shark attacks is 4.3. [ 104 ] contrary to popular impression, only a few sharks are dangerous to humans. Out of more than 470 species, only four have been involved in a significant number of fatal, motiveless attacks on humans : the bang-up white, oceanic whitetip, tiger, and taurus sharks. [ 105 ] [ 106 ] These sharks are boastfully, brawny 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. [ 107 ] The perception of sharks as dangerous animals has been popularized by promotion given to a few sequester motiveless attacks, such as the Jersey Shore shark attacks of 1916, and through popular fabricated works about shark attacks, such as the Jaws film series. Jaws writer Peter Benchley, deoxyadenosine monophosphate well as Jaws film director Steven Spielberg, late attempted to dispel the image of sharks as man-eating monsters. [ 108 ] To help avoid an motiveless attack, humans should not wear jewelry or alloy that is glazed and abstain from splashing around excessively much. [ 109 ] In general, sharks show little design of attacking humans specifically. Research indicates that when humans do become the object of a shark attack, it is possible that the shark has mistaken the human for species that are its normal prey, such as seals. [ 110 ] [ 111 ]

In captivity

Until recently, entirely 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, deoxyadenosine monophosphate well as being unmanageable to capture and transport, were unmanageable to care for. More cognition has led to more species ( including the large oceanic sharks ) living far longer in enslavement, along with safer exile techniques that have enabled long-distance transportation system. [ 112 ] The great white shark had never been successfully held in enslavement for long periods of time until September 2004, when the Monterey Bay Aquarium successfully kept a new female for 198 days before releasing her .
Most species are not suitable for home aquarium, and not every species sold by darling stores are appropriate. Some species can flourish in base seawater aquarium. [ 113 ] Uninformed or unscrupulous dealers sometimes sell adolescent sharks like the nurse shark, which upon reaching adulthood is far excessively large for typical family aquarium. [ 113 ] Public aquarium generally do not accept donate specimens that have outgrown their housing. Some owners have been tempted to release them. [ 113 ] Species appropriate to home aquaria represent considerable spatial and fiscal investments as they generally approach adult lengths of 3 feet ( 90 curium ) and can live up to 25 years. [ 113 ]

In polish

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 phase. A coarse composition 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 besides includes many shark gods. Among a fish people, the most popular of all aumakua, or deified ancestor guardians, are shark aumakua. Kamaku describes in detail how to offer a cadaver 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 equate to the invest 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 regnant chiefs typically forbade such sorcery. many native hawaiian families claim such an aumakua, who is known by name to the unharmed community. [ 114 ] Kamohoali’i is the best know and idolize of the shark gods, he was the older and favored brother of Pele, [ 115 ] and helped and travel with her to Hawaii. He was able to assume all homo and pisces forms. A summit cliff on the crater of Kilauea is one of his most sacred spots. At one indicate he had a heiau ( temple or shrine ) dedicated to him on every assemble of bring 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 consume of humans after eating one herself. [ 116 ] [ 117 ] In fijian mythology, Dakuwaqa was a shark deity who was the eater of lost souls .

In American Samoa

On the island of Tutuila in American Samoa ( a U.S. territory ), there is a placement called Turtle and Shark ( Laumei ma Malie ) which is significant in Samoan culture — the placement is the locate of a caption called O Le Tala I Le Laumei Ma Le Malie, in which two humans are said to have transformed into a turtle and a shark. [ 118 ] [ 119 ] [ 120 ] According to the U.S. National Park Service, “ Villagers from nearby Vaitogi continue to reenact an important aspect of the legend at Turtle and Shark by performing a ritual birdcall intended to summon the fabled animals to the ocean open, and visitors are frequently amazed to see one or both of these creatures emerge from the sea in apparent answer to this call. ” [ 118 ]

In popular polish

In contrast to the complex portrayals by Hawaiians and other Pacific Islanders, the European and Western view of sharks has historically been by and large of fear and malevolence. [ 121 ] Sharks are used in democratic culture normally as eating machines, notably in the Jaws fresh and the film of the lapp identify, along with its sequels. [ 122 ] Sharks are threats in other films such as Deep Blue Sea, The Reef, and others, although they are sometimes used for comedic effect such as in Finding Nemo and the Austin Powers series. Sharks tend to be seen quite often in cartoons whenever a scene involves the ocean. such examples include the Tom and Jerry cartoons, Jabberjaw, and early shows produced by Hanna-Barbera. They besides are used normally as a clichéd means of killing off a character that is held up by a r-2 or some exchangeable object as the sharks swim right below them, or the quality may be standing on a plank above shark invade waters. [ citation needed ]

popular misconceptions

A popular myth is that sharks are immune to disease and cancer, but this is not scientifically supported. Sharks have been known to get cancer. [ 123 ] [ 124 ] Both diseases and parasites affect sharks. The testify that sharks are at least immune to cancer and disease is largely anecdotic and there have been few, if any, scientific or statistical studies that show sharks to have heightened exemption to disease. [ 125 ] other apparently false claims are that fins prevent cancer [ 126 ] and treat osteoarthritis. [ 127 ] No scientific proof supports these claims ; at least one learn has shown shark cartilage of no measure in cancer treatment. [ 128 ]

Threats to sharks

Graph of shark catch from 1950, linear growth from less than 200,000 tons per year in 1950 to about 500,000 in 2011 The annual shark catch has increased quickly over the last 60 years .Photo of shark fin soup in bowl with Chinese spoon The value of shark fins for shark louver soup has led to an addition in shark catches where normally only the fins are taken, while the rest of the shark is discarded, typically into the ocean ; health concerns about BMAA in the fins now exists regarding pulmonary tuberculosis of the soup

fishery

In 2008, it was estimated that about 100 million sharks were being killed by people every class, due to commercial and amateur fish. [ 129 ] [ 130 ] In 2021, it was estimated that the population of oceanic sharks and rays had dropped by 71 % over the former half-century. [ 7 ] Shark fin yields are estimated at 1.44 million system of measurement tons ( 1.59 million short-circuit tons ) for 2000, and 1.41 million measured tons ( 1.55 million inadequate tons ) for 2010. Based on an analysis of modal shark weights, this translates into a total annual mortality estimate of about 100 million sharks in 2000, and about 97 million sharks in 2010, with a total range of potential values between 63 and 273 million sharks per year. [ 131 ] [ 132 ] Sharks are a common seafood in many places, including Japan and Australia. In the australian state of Victoria, shark is the most normally use fish in pisces and chips, [ citation needed ] in which fillets are battered and french-fry or crumbed and grilled. In fish and chip shops, shark is called flake. In India, humble sharks or baby sharks ( called sora in Tamil language, Telugu linguistic process ) are sold in local markets. Since the flesh is not developed, cooking the human body breaks it into powder, which is then fried in vegetable oil and spices ( called sora puttu/sora poratu ). The voiced bones can be well chewed. They are considered a airiness in coastal Tamil Nadu. Icelanders ferment Greenland sharks to produce a delicacy called hákarl. [ 133 ] During a four-year time period from 1996 to 2000, an estimated 26 to 73 million sharks were killed and traded per annum in commercial markets. [ 134 ] Sharks are much 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 tail fin with a hot alloy blade. [ 130 ] The resulting immobile shark soon dies from suffocation or predators. [ 135 ] Shark fin has become a major trade within black markets all over the world. Fins sell for about $ 300/lb in 2009. [ 136 ] Poachers illegally fin millions each class. few governments enforce laws that protect them. [ 132 ] In 2010 Hawaii became the first U.S. country to prohibit the possession, sale, deal or distribution of shark fins. [ 137 ] From 1996 to 2000, an estimated 38 million sharks had been killed per year for harvesting shark fins. [ 134 ] It is estimated by TRAFFIC that over 14,000 tonnes of shark fins were exported into Singapore between 2005–2007 and 2012–2014. [ 138 ] Shark fin soup is a condition symbol in asian countries and is mistakenly considered healthy and full of nutrients. Scientific research has revealed, however, that high concentrations of BMAA are present in shark fins. [ 139 ] Because BMAA is a neurotoxin, consumption of shark fin soup and cartilage pills, consequently, may pose a health risk. [ 140 ] BMAA is under analyze for its pathological function in neurodegegerative diseases such as, ALS, Alzheimer ‘s disease, and Parkinson ‘s disease. Sharks are besides killed for kernel. european diners consume dogfishes, smoothhounds, catsharks, mako, porbeagle and besides skates and rays. [ 141 ] however, the U.S. FDA lists sharks as one of four fish ( with swordfish, king mackerel, and blanquillo ) whose high mercury contented is hazardous to children and meaning women. Sharks broadly reach sexual maturity only after many years and produce few offspring in comparison to early reap fish. Harvesting sharks before they reproduce hard impacts future populations. appropriate induce previous birth and abortion ( jointly called capture-induced parturition ) occurs frequently in sharks/rays when fished. [ 78 ] Capture-induced parturition is rarely considered in fisheries management despite being shown to occur in at least 12 % of alive bear sharks and rays ( 88 species to date ). [ 78 ] The majority of shark fisheries have little monitoring or management. The upgrade in demand for shark products increases pressure on fisheries. [ 45 ] 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. [ 142 ] A study by the International Union for Conservation of Nature suggests that one one-fourth of all known species of sharks and rays are threatened by extinction and 25 species were classified as critically endangered. [ 143 ] [ 144 ]

Shark cull

In 2014, a shark pick in western Australia killed dozens of sharks ( largely tiger sharks ) using drum lines, [ 145 ] until it was cancelled after public protests and a decision by the Western Australia EPA ; from 2014 to 2017, there was an “ at hand menace ” policy in western Australia in which sharks that “ threatened ” humans in the ocean were shot and killed. [ 146 ] This “ at hand terror ” policy was criticized by senator Rachel Siewart for killing endangered sharks. [ 147 ] The “ at hand threat ” policy was cancelled in March 2017. [ 148 ] In August 2018, the Western Australia politics announced a plan to re-introduce drum lines ( though, this time the cram lines are “ SMART ” barrel lines ). [ 149 ] From 1962 to the salute, [ 150 ] the government of Queensland has targeted and killed sharks in bombastic numbers by using drum lines, under a “ shark control condition ” program—this program has besides unwittingly killed large numbers of early animals such as dolphins ; it has besides killed endangered hammerhead sharks. [ 151 ] [ 152 ] [ 153 ] [ 154 ] Queensland ‘s drum channel program has been called “ outdated, barbarous and ineffective ”. [ 154 ] From 2001 to 2018, a total of 10,480 sharks were killed on deadly drum lines in Queensland, including in the Great Barrier Reef. [ 155 ] From 1962 to 2018, approximately 50,000 sharks were killed by Queensland authorities. [ 156 ] The government of New South Wales has a course of study that measuredly kills sharks using nets. [ 153 ] [ 157 ] The current final program in New South Wales has been described as being “ extremely destructive ” to marine animation, including sharks. [ 158 ] Between 1950 and 2008, 352 tiger sharks and 577 great white sharks were killed in the nets in New South Wales — besides during this period, a full of 15,135 marine animals were killed in the nets, including dolphins, whales, turtles, dugongs, and critically endangered grey nurse sharks. [ 159 ] There has been a very large decrease in the number of sharks in easterly Australia, and the shark-killing programs in Queensland and New South Wales are partially creditworthy for this decrease. [ 156 ] Kwazulu-Natal, an sphere of South Africa, has a shark-killing program using nets and drum lines—these nets and drum lines have killed turtles and dolphins, and have been criticized for killing wildlife. [ 160 ] During a 30-year period, more than 33,000 sharks have been killed in KwaZulu-Natal ‘s shark-killing course of study — during the lapp 30-year time period, 2,211 turtles, 8,448 rays, and 2,310 dolphins were killed in KwaZulu-Natal. [ 160 ] Authorities on the french island of Réunion kill about 100 sharks per class. [ 161 ] Killing sharks negatively affects the nautical ecosystem. [ 162 ] [ 163 ] Jessica Morris of Humane Society International calls shark culling a “ knee-jerk reaction ” and says, “ sharks are acme arrange predators that play an important function in the functioning of marine ecosystems. We need them for healthy oceans. ” [ 164 ] George H. Burgess, the erstwhile [ 165 ] film director of the International Shark Attack File, “ describes [ shark ] pick as a mannequin of retaliation, satisfying a populace necessitate for rake and little else ” ; [ 166 ] he besides said shark cull is a “ retro-type motivate evocative of what people would have done in the 1940s and 50s, back when we did n’t have an ecological conscience and before we knew the consequences of our actions. ” [ 166 ] Jane Williamson, an associate degree professor in marine ecology at Macquarie University, says “ There is no scientific corroborate for the concept that culling sharks in a finical area will lead to a decrease in shark attacks and increase ocean guard. ” [ 167 ]

other threats

other threats include habitat revision, damage and loss from coastal development, pollution and the impact of fisheries on the ocean floor and prey species. [ 168 ] The 2007 documentary Sharkwater exposed how sharks are being hunted to extinction. [ 169 ]

conservation

In 1991, South Africa was the first country in the populace to declare Great White sharks a legally protected species [ 170 ] ( however, the KwaZulu-Natal Sharks Board is allowed to kill great flannel sharks in its “ shark dominance “ plan in eastern South Africa ). [ 160 ] Intending to ban the practice of shark finning while at sea, the United States Congress passed the Shark Finning Prohibition Act in 2000. [ 171 ] Two years late the Act saw its first base 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 police allowed non-fishing vessels to purchase shark fins from fishing vessels while on the high seas. [ 172 ] 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. [ 173 ] [ 174 ] In 2003, the European Union introduced a general shark fin ban for all vessels of all nationalities in Union waters and for all vessels flying a ease up of one of its member states. [ 175 ] This prohibition was amended in June 2013 to close remaining loopholes. [ 176 ] In 2009, the International Union for Conservation of Nature ‘s IUCN Red List of Endangered Species named 64 species, one-third of all oceanic shark species, as being at hazard of extinction ascribable to fishing and shark fin. [ 177 ] [ 178 ] 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 barter in several species of scallop hammerhead, oceanic whitetip and barbed bowfin sharks. The majority, but not the ask two-thirds of vote delegates, approved the proposal. China, by far the earth ‘s largest shark market, and Japan, which battles all attempts to extend the convention to marine species, led the opposition. [ 179 ] [ 180 ] In March 2013, three endangered commercially valuable sharks, the hammerheads, the oceanic whitetip and porbeagle were added to Appendix 2 of CITES, bringing shark fishing and commerce of these species under license and regulation. [ 181 ] In 2010, Greenpeace International added the school shark, shortfin mako shark, mackerel shark, tiger shark and spinous bowfin to its seafood red number, a number of coarse supermarket fish that are frequently sourced from unsustainable fisheries. [ 182 ] Advocacy group Shark Trust campaigns to limit shark fish. Advocacy group Seafood Watch directs american consumers to not eat sharks. [ 183 ] Under the auspices of the Convention on the Conservation of Migratory Species of Wild Animals ( CMS ), besides known as the Bonn Convention, the Memorandum of Understanding on the Conservation of Migratory Sharks was concluded and came into effect in March 2010. It was the beginning ball-shaped musical 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. In July 2013, New York state, a major market and entry degree for shark fins, banned the shark fin trade joining seven other states of the United States and the three Pacific U.S territories in providing legal protective covering to sharks. [ 184 ] In the United States, and as of January 16, 2019, 12 states including ( Massachusetts, Maryland, Delaware, California, Illinois, Hawaii, Oregon, Nevada, Rhode Island, Washington, New York and Texas ) along with 3 U.S. territories ( american Samoa, Guam and the Northern Mariana Islands ) have passed laws against the sale or possession of shark fins. [ 185 ] [ 186 ] respective regions immediately have shark sanctuaries or have banned shark fishing — these regions include american Samoa, the Bahamas, the Cook Islands, french Polynesia, Guam, the Maldives, the Marshall Islands, Micronesia, the Northern Mariana Islands, and Palau. [ 187 ] [ 188 ] [ 189 ] In April 2020 researchers reported to have traced the origins of shark fins of endangered hammerhead sharks from a retail commercialize in Hong Kong back to their source populations and therefore the approximate locations where the sharks were first caught using DNA analysis. [ 190 ] [ 191 ] In July 2020 scientists reported results of a survey of 371 reefs in 58 nations estimating the conservation status of reef sharks globally. No sharks have been observed on about 20 % of the surveyed reefs and shark depletion was powerfully associated with both socio-economic conditions and conservation measures. [ 192 ] [ 193 ] Sharks are considered to be a vital part of the ocean ecosystem. According to a 2021 study in Nature, [ 194 ] overfishing has resulted in a 71 % global worsen in the number of oceanic sharks and rays over the preceding 50 years. The oceanic whitetip, and both the scalloped hammerhead and bang-up hammerheads are now classified as critically endangered. [ 195 ] Sharks in tropical waters have declined more quickly than those in temperate zones during the period studied. [ 196 ] A 2021 study published in Current Biology found that overfishing is presently driving over one-third of sharks and rays to extinction. [ 197 ]

See besides

farther reading

References

General references

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