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The great white shark (Carcharodon carcharias), also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark which can be found in the coastal surface waters of all the major oceans.

The English name 'white shark' and its Australian variant 'white pointer' is thought to have come from the shark's stark white underside, a characteristic feature most noticeable in beached sharks lying upside down with their bellies exposed.

Distribution and habitat

Great white sharks live in almost all coastal and offshore waters which have water temperature between 12 and 24 °C (54 and 75 °F). It is most common in the United States ( Northeast and California), South Africa, Japan, Oceania, Chile, and the Mediterranean including the Sea of Marmara and Bosphorus. One of the densest-known populations is found around Dyer Island, South Africa. Juvenile great white sharks inhabit a more narrow band of temperatures, between 14 and 24 °C (57 and 75 °F), in shallow coastal nurseries. Increased observation of young sharks in areas they were not previously common, such as Monterey Bay on the Central California coast, suggest climate change may be reducing the range of juvenile great white sharks and shifting it toward the poles.

In the Northwest Atlantic, the white shark populations off the New England coast were nearly eradicated due to over-fishing. In recent years, the populations have grown greatly, largely due to the increase in seal populations on Cape Cod, Massachusetts since the enactment of the Marine Mammal Protection Act in 1972.

A 2018 study indicated that white sharks prefer to congregate deep in anticyclonic eddies in the North Atlantic Ocean. The sharks studied tended to favour the warm-water eddies, spending the daytime hours at 450 meters and coming to the surface at night.

Description

The great white shark has a robust, large, conical snout. The upper and lower lobes on the tail fin are approximately the same size which is similar to some mackerel sharks. A great white displays countershading, by having a white underside and a grey dorsal area (sometimes in a brown or blue shade) that gives an overall mottled appearance.

Great white sharks, like many other sharks, have rows of serrated teeth behind the main ones, ready to replace any that break off. When the shark bites, it shakes its head side-to-side, helping the teeth saw off large chunks of flesh.

Great white sharks, like other mackerel sharks, have larger eyes than other shark species in proportion to their body size. The iris of the eye is a deep blue instead of black.

The great white shark is notable for its size, with the largest preserved female specimen measuring 5.83 m (19.1 ft) in length and around 2,000 kg (4,410 lb) in weight at maturity. However, most are smaller; males measure 11 to 13 ft (3.4 to 4.0 m), and females measure 15 to 16 ft (4.6 to 4.9 m) on average.

In great white sharks, sexual dimorphism is present, and females are generally larger than males. Adults of this species weigh 522-771 kg (1,151-1,700 lb) on average; however, mature females can have an average mass of 680-1,110 kg (1,500-2,450 lb).

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Lifespan and reproduction

According to a 2014 study, the lifespan of great white sharks is estimated to be as long as 70 years or more, well above previous estimates, making it one of the longest lived cartilaginous fishes currently known. According to the same study, male great white sharks take 26 years to reach sexual maturity, while the females take 33 years to be ready to produce offspring.

The great white has an 11-month gestation period. The shark pup's powerful jaws begin to develop in the first month. The unborn sharks participate in oophagy, in which they feed on ova produced by the mother. Delivery is in spring and summer. The largest number of pups recorded for this species is 14 pups from a single mother measuring 4.5 m (15 ft)

Great white sharks are carnivorous and prey upon fish (e.g. tuna, rays, other sharks), cetaceans (i.e., dolphins, porpoises, whales), pinnipeds (e.g. seals, fur seals, and sea lions), sea turtles, sea otters ( Enhydra lutris) and seabirds. Great whites have also been known to eat objects that they are unable to digest. Juvenile white sharks predominantly prey on fish, including other elasmobranchs, as their jaws are not strong enough to withstand the forces required to attack larger prey such as pinnipeds and cetaceans until they reach a length of 3 m (9.8 ft) or more, at which point their jaw cartilage mineralizes enough to withstand the impact of biting into larger prey species. Upon approaching a length of nearly 4 m (13 ft), great white sharks begin to target predominantly marine mammals for food, though individual sharks seem to specialize in different types of prey depending on their preferences.

The great white shark has only one recorded natural predator, the orca.

Adaptations

Electromagnetic detection

Great white sharks, like all other sharks, have an extra sense given by the ampullae of Lorenzini which enables them to detect the electromagnetic field emitted by the movement of living animals. Great whites are so sensitive they can detect variations of half a billionth of a volt. At close range, this allows the shark to locate even immobile animals by detecting their heartbeat. Most fish have a less-developed but similar sense using their body's lateral line.

Camouflage

In 2022, research in South Africa suggested that the great white shark has the ability to change colours to camouflage itself depending on the hormones it gives off. Different hormones would change the colour of the skin from white to grey. Skin dosed with adrenaline would turn lighter, with melanocyte-stimulating hormone causing melanocyte cells to dissipate thus making the shark's skin a darker colour, although hormone mediated color change is not fully validated due to the limited number of test subjects ( i.e. great whites). The camo shark hypothesis is supported by the fact that zebra sharks can change their colour as they age, and rainbow sharks can lose colour due to stress and aging.

Ecology and behaviour

This shark's behaviour and social structure are complex. In South Africa, white sharks have a dominance hierarchy depending on the size, sex and squatter's rights. Females dominate males, larger sharks dominate smaller sharks, and residents dominate newcomers.

When hunting, great whites tend to separate and resolve conflicts with rituals and displays. White sharks rarely resort to combat although some individuals have been found with bite marks that match those of other white sharks. This suggests that when a great white approaches too closely to another, they react with a warning bite. Another possibility is that white sharks bite to show their dominance.

White sharks are generally very curious animals, display intelligence and may also turn to socializing if the situation demands it.

Breaching behaviour

A breach is the result of a high-speed approach to the surface with the resulting momentum taking the shark partially or completely clear of the water. This is a hunting technique employed by great white sharks whilst hunting seals. This technique is often used on cape fur seals at Seal Island in False Bay, South Africa. Because the behaviour is unpredictable, it is very hard to document. It was first photographed by Chris Fallows and Rob Lawrence who developed the technique of towing a slow-moving seal decoy to trick the sharks to breach. Great white sharks can reach speeds of up to 40 km/h (25 mph) and can at times launch themselves more than 10 ft (3 m) into the air. Just under half of observed breach attacks are successful.

Relationship with humans

Shark culling

Shark culling is the deliberate killing of sharks by a government in an attempt to reduce shark attacks; shark culling is often called "shark control". These programs have been criticized by environmentalists and scientists-they say these programs harm the marine ecosystem; they also say such programs are "outdated, cruel, and ineffective".

Attacks on boats

Great white sharks infrequently bite and sometimes even sink boats. Only five of the 108 authenticated unprovoked shark bite incidents reported from the Pacific Coast during the 20th century involved kayakers. In a few cases they have bitten boats up to 10 m (33 ft) in length. They have bumped or knocked people overboard, usually biting the boat from the stern. In one case in 1936, a large shark leapt completely into the South African fishing boat Lucky Jim, knocking a crewman into the sea. Tricas and McCosker's underwater observations suggest that sharks are attracted to boats by the electrical fields they generate, which are picked up by the ampullae of Lorenzini and confuse the shark about whether or not wounded prey might be nearby.

Shark tourism

Cage diving is most common at sites where great whites are frequent including the coast of South Africa, the Neptune Islands in South Australia, and Guadalupe Island in Baja California. The popularity of cage diving and swimming with sharks is at the focus of a booming tourist industry. A common practice is to chum the water with pieces of fish to attract the sharks. These practices may make sharks more accustomed to people in their environment and to associate human activity with food; a potentially dangerous situation. By drawing bait on a wire towards the cage, tour operators lure the shark to the cage, possibly striking it, exacerbating this problem. Other operators draw the bait away from the cage, causing the shark to swim past the divers.

At present, hang baits are illegal off Isla Guadalupe and reputable dive operators do not use them. Operators in South Africa and Australia continue to use hang baits and pinniped decoys. In South Australia, playing rock music recordings underwater, including the AC/DC album Back in Black has also been used experimentally to attract sharks.

Companies object to being blamed for shark bite incidents, pointing out that lightning tends to strike humans more often than sharks bite humans. Their position is that further research needs to be done before banning practices such as chumming, which may alter natural behaviour. One compromise is to only use chum in areas where whites actively patrol anyway, well away from human leisure areas. Also, responsible dive operators do not feed sharks. Only sharks that are willing to scavenge follow the chum trail and if they find no food at the end then the shark soon swims off and does not associate chum with a meal. It has been suggested that government licensing strategies may help enforce these responsible tourism.

Conservation

Fishermen target many sharks for their jaws, teeth, and fins, and as game fish in general. The great white shark, however, is rarely an object of commercial fishing, although its flesh is considered valuable.

The species faces numerous ecological challenges which has resulted in international protection. The International Union for Conservation of Nature lists the great white shark as a vulnerable species, and it is included in Appendix II of CITES. It is also protected by several national governments, such as Australia (as of 2018). Due to their need to travel long distances for seasonal migration and extremely demanding diet, it is not logistically feasible to keep great white sharks in captivity; because of this, while attempts have been made to do so in the past, there are no known aquariums in the world believed to house a live specimen.

In popular culture

The great white shark is depicted in popular culture as a ferocious man-eater, largely as a result of the novel by Peter Benchley and its subsequent film adaptation by Steven Spielberg. Humans are not a preferred prey, but nevertheless it is responsible for the largest number of reported and identified fatal unprovoked shark attacks on humans. However, attacks are rare, typically occurring fewer than 10 times per year globally.

Interesting facts about the great white shark

It is the only known surviving species of its genus Carcharodon.

Great white sharks can swim at speeds of 25 km/h (16 mph) for short bursts and to depths of 1,200 m (3,900 ft).

The great white shark is arguably the world's largest-known extant macropredatory fish.

A complete female great white shark specimen in the Museum of Zoology in Lausanne, and claimed by De Maddalena et al. (2003) as the largest preserved specimen, measured 5.83 m (19.1 ft) in total body length with the caudal fin in its depressed position, and is estimated to have weighed 2,000 kg (4,410 lb).

The largest great white recognized by the International Game Fish Association (IGFA) is one caught by Alf Dean in southern Australian waters in 1959, weighing 1,208 kg (2,663 lb).

In 2008, a team of scientists led by Stephen Wroe conducted an experiment to determine the great white shark's jaw power and findings indicated that a specimen massing 3,324 kg (7,328 lb) could exert a bite force of 18,216 newtons (4,095 lbf).

Great white sharks rely on the fat and oils stored within their livers for long-distance migrations across nutrient-poor areas of the oceans.

The great white shark is one of only a few sharks known to regularly lift its head above the sea surface to gaze at other objects such as prey.

Of all shark species, the great white shark is responsible for by far the largest number of recorded shark bite incidents on humans, with 272 documented unprovoked bite incidents on humans as of 2012.

A 2014 study estimated the population of great white sharks along the California coastline to be approximately 2,400.

Images for kids

In Spanish: Carcharodon carcharias para niños

List of sharks

List of threatened sharks

Outline of sharks

Shark culling

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The genus is the only one in its family, Squatinidae, and order Squatiniformes. They are worldwide in temperate and tropical seas. Most species are in shallow temperate or tropical seas, but one species is found in deeper water, down to 1,300 metres. Angel sharks are specialised for a kind of predation which is unusual for sharks.

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The Nurse Shark is a common inshore bottom-dwelling shark, found in tropical and subtropical waters on the continental and insular shelves. The Nurse Shark is frequently found at depths of one metre or less but may occur down to 12 metres. Its common habitats are reefs, channels between mangrove islands and sand flats.

The Nurse Shark occurs in the Western Atlantic from Rhode Island down to southern Brazil, in the Eastern Atlantic from Cameroon to Gabon, in the Eastern Pacific from the southern Baja California to Peru and around the islands of the Caribbean.

Nurse Shark Characteristics

Nurse sharks are light yellowish brown to dark brown, with or without small dark spots. The Nurse shark has a flattened body and a broad, rounded head with two conspicuous barbells between the nostrils which are used to help find food. Their mouth is filled with rows of small, serrated teeth for crushing hard-shelled prey. Female nurse sharks, average 7.5 to 9 feet (2.2 to 2.7 metres) in length and weigh 165 to 230 pounds (75 to 105 kilograms) and are slightly larger than male nurse sharks.

The estimated age of maturity for the Nurse Shark is 18 years for males and 20 to 22 years for females.

Nurse Shark Diet

Nurse sharks are nocturnal animals, spending the day in large inactive groups of up to 40 individuals. Hidden under submerged ledges or in crevices within the reef, the Nurse sharks seem to prefer specific resting sites and will return to them each day after the nights hunting. By night, the sharks are largely solitary. Nurse sharks spend most of their time foraging through the bottom sediments in search of food. Their diet consists primarily of crustaceans, molluscs, tunicates and other fish such as spiny lobsters, crabs, shrimps, sea urchins, octopuses, squid, marine snails and bivalves and in particularly, stingrays.

Nurse sharks are thought to take advantage of dormant fish which would otherwise be too fast for the sharks to catch, although their small mouths limit the size of prey items, the sharks have large throat cavities which are used as a sort of bellows valve. In this way, Nurse sharks are able to suck in their prey. Nurse sharks are also known to graze algae and coral.

Nurse Shark Reproduction

The mating season runs from late June to the end of July. Nurse sharks are ovoviviparous, meaning the eggs develop and hatch within the body of the female where the hatchlings develop further until live birth occurs. The gestation period is 6 months, with a typical litter of 21 - 28 pups. The mating cycle is biennial, as it takes 18 months for the females ovaries to produce another batch of eggs. The young Nurse sharks are born fully developed at about 30 centimetres long. They possess a spotted colouration which fades with age.

Nurse Shark Behaviour

Generally slow and sluggish, Nurse sharks spend much of their time resting on the bottom of the ocean. Nurse sharks have been observed resting on the bottom with their bodies supported on their fins, possibly providing a false shelter for crustaceans which they then ambush and eat. If it must move, the Nurse shark may even use its large front (or pectoral) fins to 'walk' along the ocean floor.

Because the Nurse shark can pump water over its gills, it does not need to swim in order to breathe.

Unlike many sharks, the Nurse shark is non-migratory. The Nurse shark adapts to cold by becoming even less active.

Nurse Shark Conservation

The Nurse shark is not widely commercially fished, but because of its sluggish behaviour it is an easy target for local fisheries. Its skin is exceptionally tough and is prized for leather. Its flesh is consumed fresh and salted and its liver utilised for oil. It is not taken as a game fish. It has been reported in some unprovoked attacks on humans but is not generally perceived as a threat.

Nurse sharks are common throughout their range but are still considered 'Near Threatened'.

No species is known to regularly prey on Nurse sharks, although they have been found in the stomach contents of lemon sharks, tiger sharks, bull sharks and great hammerhead sharks.

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Nurse Shark - Facts, Information & Habitat

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The Nurse Shark is a common inshore bottom-dwelling shark, found in tropical and subtropical waters on the continental and insular shelves. The Nurse Shark is frequently found at depths of one metre or less but may occur down to 12 metres. Its common habitats are reefs, channels between mangrove islands and sand flats.

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The blue shark (Prionace glauca) is a large, indigo-colored shark. It is a sleek shark with long, pointed fins, a pointed snout, and large eyes. It is indigo-blue on top and off-white on its belly.

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Blacktip Reef Shark (Carcharhinus melanopterus)

The Blacktip Reef Shark is a shark of tropical and warm temperate seas. It is often confused with the Blacktip Shark (Carcharhinus limbatus).

The Blacktip Reef Shark is one of the most common sharks found in shallow water, sometimes as shallow as 30 centimetres, around coral reefs of Indo-Pacific waters.

The water temperature they swim in is usually between 20 and 27° Centigrade (70 to 80º Fahrenheit). Blacktip Reef sharks do not venture into tropical lakes and rivers far from the ocean.

Blacktip Reef Shark Characteristics

As its name suggests, the tips of the sharks pectoral fins and dorsal fin are black, with a white underside. The Blacktip Reef Sharks skin is brownish in colour on the top half of its body. It has been recorded to measure upto 190 centimetres (6 feet) in length. The Blacktip Reef Sharks snout is blunt and rounded. Blacktip Reef sharks are not considered a real threat because they are usually quite small.

Blacktip Reef Shark Diet

A Blacktip Reef sharks diet consists mainly of reef fish, however, they will also feed on sturgeon and mullet.

Blacktip Reef Shark Reproduction

Reproduction is viviparous (the embryo develops inside the body of the mother, as opposed to outside in an egg), with 2 to 4 pups in a litter. Before giving birth, female Blacktip Reef sharks will incubate their young for 16 months. The pups' length at birth ranges from 33 to 52 centimetres.

Blacktip Reef Shark Behaviour

The Blacktip Reef Shark is not considered social, however, it can been seen in small groups. While generally shy, they are often curious about snorkelers and scuba divers. As with most sharks, the body is bent into a sort of 'S' shape when the shark feels threatened. Blacktip Reef sharks are harmless unless provoked. Incidents generally involve hand feeding or spear fishing, possibly in combination with low visibility.

The Blacktip Reef shark is one of only a few sharks that can jump fully out of the water, a behaviour called 'breaching'. They have also been observed surfacing to look around an action called 'spy-hopping'.

Blacktip Reef Shark Conservation Status

The status of the Blacktip Reef shark is 'Near Threatened'. Blacktip reef sharks are often the by catch from other fisheries and are often wasted. Their populations are declining and so are the population of many other shark species. Their fins are used for shark fin soup which is a major factor in the population decline in recent years.

Not to be confused with the Blacktip Shark.

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Blacktip Reef Shark - Facts, Information & Pictures

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Blacktip Reef Shark (Carcharhinus melanopterus) The Blacktip Reef Shark is a shark of tropical and warm temperate seas. It is often confused with the Blacktip Shark (Carcharhinus limbatus). The Blacktip Reef Shark is one of the most common sharks found in shallow water, sometimes as shallow as 30 centimetres, around coral reefs of Indo-Pacific waters.

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The Lemon shark gets its name from the fact that it is yellow in colour. The underside is usually white or a lighter yellowish colour. Besides yellow, the Lemon shark is also brown and olive grey in colour. The Lemon shark is stocky, blunt-nosed, and has two dorsal fins of similar size and shape.

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A hammerhead shark uses its wide head to trap stingrays by pinning them to the seafloor. The shark's eye placement, on each end of its very wide head, allows it to scan more area more quickly than other sharks can. The hammerhead also has special sensors across its head that helps it scan for food in the ocean. Living creatures' bodies give off electrical signals, which are picked up by sensors on the prowling hammerhead.

The shark hunts alone, and can find stingrays that hide under the sand on the seafloor. Hammerheads also eat bony fishes, crabs, squid, lobsters, and other sea creatures. The upper sides of these fish are grayish-brown or olive-green and they have white bellies. They have very impressive triangular, serrated teeth-like the edge of a saw's blade. Hammerheads' mouths are on the underside of their heads.

Unlike many fish, hammerheads do not lay eggs. A female gives birth to live young. One litter can range from six to about 50 pups. When a hammerhead pup is born, its head is more rounded than its parents'.

There have been very few recorded attacks on people by the great hammerhead.

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This shark's unusual name comes from the unusual shape of its head, an amazing piece of anatomy built to maximize the fish's ability to find its favorite meal: stingrays. A hammerhead shark uses its wide head to trap stingrays by pinning them to the seafloor.

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The Bull shark mainly feeds on bony fish and small sharks. In the western Atlantic they commonly feed on mullet, tarpon, catfish, menhaden, gar, snook, jacks, mackerel, snappers, and other schooling fish. They also regularly feed on stingrays and young sharks including small individuals of their own species in their inshore nursery habitats.

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Tiger Shark facts for kids (and adults), with pictures, information and video.

Tiger Shark Facts

The Tiger Shark is one of the most feared ocean predators. With explosive speed, powerful jaws, and excellent eyesight, the Tiger Shark's bad reputation is well-deserved. Some people consider it to be even more dangerous than the Great White Shark! It certainly looks the part, with its menacing tiger-like stripes. Let's find out more about this underwater hunting machine ...

(Scroll down to the end of the article for the top ten Tiger Shark facts, or read on for in-depth information.)

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Tiger Shark Scientific Name and Family

The Tiger Shark's scientific name is Galeocerdo cuvier. It is a member of the requiem shark family Carcharhinidae.

Other requiem sharks include the Spinner Shark, the Blacknose Shark, the Blacktip Shark, the Blacktail Reef Shark, and the Blacktip Reef Shark.

Tiger Shark Size & Appearance

The Tiger Shark gets its name from the tiger-like stripes and spots on the sides of its body. These markings fade as the shark matures, and are barely visible on older individuals.

The Tiger Shark is a bulky, powerful-looking shark, with a blunt, wide nose that allows it to make quick turns. It has two dorsal fins (fins on its back), and a pointed tail fin which is longer on the top than the bottom.

The Tiger Shark has five gill slits. Like many sharks, it has nictitating membranes that slide over its eyes. These are clear covers that protect the eyes.

Like many sharks, the Tiger Shark has dark upperparts and pale undersides. This is known as ' countershading'. Because natural light generally comes from above, the shark's lighter undersides can confuse observers and break up its outline. This conceals the shark from potential predators and prey.

The Tiger Shark's sides and back are grey-blue or green and its underparts are almost white.

Tiger Shark Video

Get up close and personal to the Tiger Shark in this amazing video ...

Tiger Shark Facts For Kids: How Big Is A Tiger Shark?

Length

The Tiger Shark is the world's fourth-largest shark. Only the Whale Shark, Basking Shark and Great White Shark are bigger.

(Sharks such as the Greenland Shark are a similar size, but have not been studied in as much depth as the Tiger Shark.)

Most tiger sharks are between 3 and 4.5 m (10 to 14 ft.) in length. Female Tiger Sharks are larger than males.

Weight

Tiger sharks weigh between 385 and 635 kg (850 and 1,400 lb)

Largest Tiger Shark

Occasionally, bigger Tiger Sharks are recorded. The Tiger Shark can attain a length of over 5.5 m (18 feet), and a weight of over 900 kg (2,000 lb).

One of the largest tiger sharks ever reported was caught near Australia. It weighed 1,524 kg (3,360 lb), and was around 5.5 m (18 feet) long.

Where Do Tiger Sharks Live?

The Tiger Shark is found in tropical and subtropical waters. It is present in the Atlantic, Pacific and Indian oceans. The Tiger Shark is most often found in coastal waters, and is present around the United States, South America, Australia and Africa.

Tagging studies have found that some Tiger Sharks stay in the same area, whereas others are more nomadic. The largest distance a tagged Tiger Shark has been found to cover was 3,430 km (2,130 miles).

The deepest a Tiger Shark has been recorded swimming at was 350 m (1,150 ft.).

What Do Tiger Sharks Eat? Tiger Shark Diet & Hunting

The Tiger Shark is an apex predator (it has no natural predators), and is top of the food chain.

The Tiger Shark comes inshore to eat, usually at night. Its diet is extremely varied, and includes fish (including other sharks), birds, sea turtles, dolphins, squids, sea snakes, rays, seals and many other animals.

The Tiger Shark will snap out at and swallow almost anything that falls within the range of its powerful jaws. Its stomach has been found to contain license plates, tyres, clothing and other man-made objects. Because of this the Tiger Shark is known as 'The Wastebucket of the Sea'.

Due to its camouflage and slow swimming speed, the Tiger Shark is often only seen by its prey at the last minute. The Tiger Shark is capable of a powerful burst of acceleration, which it uses to capture its prey.

Reproduction

Tiger Sharks are mature at around 2.75 m (9 ft.). They attain this size after around 5-10 years.

Unlike all other requiem sharks, the Tiger Shark is ovoviviparous; its eggs develop inside the female's body, and it gives birth to live young.

The female Tiger Shark gives birth to an average of 30 to 35 pups. New-born Tiger Sharks are between 51 and 76 cm (20 and 30 in) in length. They are extremely vulnerable at this stage, and many are predated by other sharks, including other Tiger Sharks.

Are Tiger Sharks Endangered?

Tiger sharks are rated Near Threatened on the IUCN Red List.

Tiger Sharks are targeted by fishermen, and are also caught as bycatch when fishermen are targeting other species. (Bycatch is when a species is caught by mistake.)

Tiger Sharks are caught for their flesh, fins, skin and liver oil.

Because Tiger Sharks can be dangerous to humans, their populations are sometimes controlled in tourist areas. This is achieved with netting and other methods.

Tiger Sharks are occasionally preyed upon by Killer Whales.

Tiger Shark Facts for Kids: Top Ten Facts

1. The Tiger Shark's scientific name is Galeocerdo cuvier.

2. It is a member of the requiem shark family Carcharhinidae.

3. The Tiger Shark gets its name from the tiger-like stripes along its sides. These stripes fade as the shark gets older.

4. The Tiger Shark is the fourth-largest shark species in the world.

5. The tiger shark is considered by some to be even more dangerous than the Great White Shark.

6. The Tiger Shark exhibits 'countershading'. This is where an animal's upperparts are dark and the undersides are pale. This provides camouflage from predators and prey.

7. Most tiger sharks are between 3 and 4.5 m (10 to 14 ft.) in length, and weigh between 385 and 635 kg (850 and 1,400 lb).

8. One of the largest tiger sharks ever reported weighed 1,524 kg (3,360 lb), and was around 5.5 m (18 feet) long.

9. The Tiger Shark has an extremely varied diet, which includes, fish, dolphins, and jellyfish.

10. The Tiger Shark is an apex predator.

Tiger Shark Facts For Kids: Conclusion

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Tiger Shark facts for kids (and adults), with pictures, information and video. The Tiger Shark is one of the most feared ocean predators. With explosive speed, powerful jaws, and excellent eyesight, the Tiger Shark's bad reputation is well-deserved. Some people consider it to be even more dangerous than the Great White Shark!

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The leopard shark ( Triakis semifasciata) is a species of houndshark, in the family Triakidae. It is found along the Pacific coast of North America, from the U.S. state of Oregon to Mazatlán in Mexico. Typically measuring 1.2-1.5 m (3.9-4.9 ft) long, this slender-bodied shark is immediately identifiable by the striking pattern of black saddle-like markings and large spots over its back, from which it derives its common name. Large schools of leopard sharks are a common sight in bays and estuaries, swimming over sandy or muddy flats or rock-strewn areas near kelp beds and reefs. They are most common near the coast, in water less than 4 m (13 ft) deep.

Active-swimming predators, groups of leopard sharks often follow the tide onto intertidal mudflats to forage for food, mainly clams, spoon worms, crabs, shrimp, bony fish, and fish eggs. Most leopard sharks tend to remain within a particular area rather than undertaking long movements elsewhere, which has led to genetic divergence between populations of sharks living in different regions. This species is aplacental viviparous, meaning that the young hatch inside the uterus and are nourished by yolk. From March to June, the female gives birth to as many as 37 young after a gestation period of 10-12 months. It is relatively slow-growing and takes many years to mature.

Harmless to humans, the leopard shark is caught by commercial and recreational fisheries for food and the aquarium trade. This species is mostly fished in the waters off California where, after a period of population decline in the 1980s, new fishing regulations in the early 1990s reduced harvesting to sustainable levels. The International Union for Conservation of Nature has assessed this species as of Least Concern, while noting that local stocks may easily become overfished because of the shark's slow growth and limited migratory habits.

The first scientific name applied to the leopard shark was Triakis californica, coined by British zoologist John Edward Gray in the 1851 List of the specimens of fish in the collection of the British Museum. However, Gray did not furnish the name with a proper description, rendering it a nomen nudum. In December 1854, American ichthyologist William Orville Ayres gave a lecture describing the species as Mustelus felis, which included the first scientific description of the species. His lecture was reprinted first in The Pacific, a San Francisco newspaper, and then in the journal Proceedings of the California Academy of Natural Sciences. In April 1855, French biologist Charles Frédéric Girard published another description of this species, naming it Triakis semifasciata.

Despite M. felis being the senior synonym, an error in recording the dates of publication resulted in the widespread use of T. semifasciata as the leopard shark's scientific name. As a result of this long-standing error, Triakis semifasciata came to be recognized as the valid name (as a nomen protectum) and Mustelis felis was invalidated (as a nomen oblitum). The specific epithet semifasciata comes from the Latin words semi ("half") and fasciatus ("banded"), describing this shark's dorsal pattern of saddle-like markings. In older literature, this species may be referred to as " tiger shark" or " catshark".

Phylogenetic relationships of houndsharks, based on protein-coding gene sequences.

The genus Triakis contains two subgenera, Triakis and Cazon. The leopard shark is placed within the subgenus Triakis along with the banded houndshark ( T. (Triakis) scyllium). A 2006 phylogenetic analysis by J. Andrés López and colleagues, based on protein-coding genes, revealed that Triakis and Cazon are in fact not closely related, and additionally that the leopard shark may be the most basal member of its family.

The leopard shark occurs in the Northeastern Pacific Ocean, from the temperate continental waters of Coos Bay, Oregon to the tropical waters of Mazatlán, Mexico, including the Gulf of California. It favors muddy or sandy flats within enclosed bays and estuaries, and may also be encountered near kelp beds and rocky reefs, or along the open coast. Numbers have been known to gather near discharges of warm effluent from power plants. Leopard sharks generally swim close to the bottom and are most abundant from the intertidal zone to a depth of 4 m (13 ft), though they may be found as deep as 91 m (299 ft). Many leopard sharks, particularly in the north, leave their coastal habitats in winter and return in early spring. A study in Tomales Bay in northern California determined that they depart when the water temperature drops below 10-12 °C (50-54 °F); one tagged shark was found to have swum some 140 km (87 mi) south.

While a few leopard sharks have been documented traveling hundreds of kilometers, most individuals tend to remain in a localized area for much of their lives. This low level of dispersal has led to genetic divergence across its range. Seven discrete gene pools have been identified along the Californian coast between Humboldt Bay and San Diego. Of these, the Humboldt Bay subpopulation is perhaps the most isolated, with the sharks there maturing at a larger size and producing fewer offspring than those from other areas. By contrast, the area around Los Angeles represents a genetic transitional zone between subpopulations whose boundaries are more diffuse. Off Baja California, the leopard sharks on the Pacific side are probably distinct from those in the northern Gulf of California. Although there is equivocal evidence for natal philopatry (returning to one's birthplace to breed) in this species, proximity to established breeding grounds likely contributes to the structuring of these different subpopulations.

The leopard shark has a moderately stout body, with a short, rounded snout. There are well-developed, triangular flaps of skin in front of the nares. The eyes are large and oval, with a nictitating membrane (a protective third eyelid). The line of the mouth is strongly curved. There are furrows at the corners of the mouth extending onto both jaws, with those on the lower jaw almost long enough to meet at the midline. The tooth rows number 41-55 in the upper jaw and 34-45 in the lower jaw; each tooth has a slightly oblique, smooth-edged cusp in the center and 1-2 small cusplets on either side. These teeth are arranged into a flat, "pavement"-like surface with overlapping ridges.

The large first dorsal fin is positioned about halfway between the pectoral and pelvic fins; the second is almost as large as the first and much larger than the anal fin. The pectoral fins are wide and triangular. The lower lobe of the caudal fin is well-developed in adults but less than half the length of the upper lobe, which has a strong ventral notch near the tip. The coloration is unique, consisting of prominent black "saddles" and large black spots running along the back, on a silvery to bronzy gray background. Adult sharks often have more spots and saddles with lighter centers compared to juveniles. The underside is whitish and plain. The average length of a leopard shark is 1.2-1.5 m (3.9-4.9 ft). Rarely males may grow to 1.5 m (4.9 ft) and females 1.8 m (5.9 ft), and there is a record of an exceptional female that measured 2.1 m (6.9 ft) long. The heaviest known leopard shark weighed 18.4 kg (41 lb).

The dorsal color pattern of the leopard shark gives it its common name

An active species that swims with a strong undulating motion, the leopard shark is commonly spotted cruising in or just beyond the surf zone. It is more active at night than during the day, and sometimes lies still on the bottom. In Tomales Bay and elsewhere, the leopard shark follows the tide onto mudflats to forage for food, retreating just fast enough to prevent being stranded or trapped as the water recedes. At Santa Catalina Island, resident sharks spend the day together in the shallows and at night disperse into deeper water, ranging up to 10 km (6.2 mi) away.

From birth, leopard sharks form large schools generally segregated by age and sex, which may intermingle with grey or brown smoothhounds ( Mustelus californicus and M. henlei) or spiny dogfish ( Squalus acanthias). These schools are apparently nomadic, often appearing suddenly in an area for a few hours and then vanishing just as quickly. In captivity, larger sharks have been observed establishing their dominance over smaller individuals via light nips to the pectoral fins. During summer days, large aggregations of mature females assemble in shallow bays and estuaries, dispersing at night. As these females follow the warmest patches of water, allowing them to raise their internal body temperatures by up to 3 °C (5.4 °F), they are speculated to be taking advantage of the heat to speed their growth and that of their gestating young. The membership of these aggregations is inconstant, with individual females periodically switching between different sites scattered over several kilometers.

Compared to the related grey and brown smoothhounds that share its range, the leopard shark has smaller and more numerous red blood cells, allowing it to process oxygen more efficiently. This may be an adaptation for foraging in deoxygenated estuary environments. Their eyes contain very few cone cells, likely due to the murky water they inhabit. Small leopard sharks fall prey to larger sharks such as the great white shark ( Carcharodon carcharias) and the broadnose sevengill shark ( Notorynchus cepedianus). On one occasion, a sevengill shark was seen ambushing a leopard shark on a tidal mudflat in Humboldt Bay, striking with such momentum that the larger predator momentarily beached itself. Known parasites of this species include the tapeworms Phyllobothrium riseri, Lacistorhynchus dollfusi and Paraorygmatobothrium barber, as well as the copepods Echthrogaleus eoleoptratus and Achtheinus oblongatus.

The diet of the leopard shark consists of small benthic and littoral animals, most significantly crabs ( Cancridae, Grapsidae, and Hippoidea), shrimp, bony fish (including anchovies, herring, topsmelt, croakers, surfperch, gobies, rockfish, sculpins, flatfish, and midshipmen), fish eggs, clams, and the echiurid fat innkeeper worm ( Urechis caupo). This opportunistic hunter has also been known to eat ghost shrimp, polychaete worms, and the young of smoothhounds, shovelnose guitarfish ( Rhinobatos productus), and bat rays ( Myliobatis californicus). Eelgrass ( Zostera) and algae may be swallowed incidentally.

The leopard shark captures prey by expanding its buccal cavity to create a suction force, which is facilitated by its labial cartilages swinging forward to form the mouth into a tube. Simultaneously, the shark protrudes its jaws forward to grip the prey between its teeth. As with other sharks, the teeth of the leopard shark are periodically shed and replaced; it takes 9-12 days for a replacement tooth to move into position. Leopard sharks have been caught with stomachs filled with clam siphons, which the sharks seize before the clams can retract and break off with a levering motion of their bodies. On occasion, the shark tears the entire clam body out of its shell this way. Other sharks examined have had stomachs containing whole innkeeper worms with no bite marks, suggesting that the sharks sucked them out of their burrows. Under a hollow bridge support in San Francisco Bay, a group of leopard sharks and spiny dogfish have been observed feeding on a dense school of anchovies by slowly swimming counterclockwise through the clockwise-swimming school, and swallowing any anchovies that accidentally entered their open mouths.

In some places, this species feeds only on a few prey types and little else (e.g. innkeeper worms and cancrid crabs in Tomales Bay, jack silverside ( Atherinopsis californiensis) eggs and the crabs Romaleon antennarium and Metacarcinus magister in Humboldt Bay). The predominant prey taken depends on location, time of year, and age. For example, in the Elkhorn Slough at Monterey Bay, cancrid crabs and innkeeper worms are mostly eaten in winter and spring, fish eggs from winter to early summer, bony fish in summer, and grapsid crabs and clams in fall. Young sharks feed mostly on crabs and transition to clam siphons, fish eggs, and innkeeper worms once they reach 70-80 cm (2.3-2.6 ft) long. The largest sharks are the ones that consume the most fish.

Life history

The leopard shark is aplacental viviparous, with the developing embryos sustained by a yolk sac until birth. In northern areas, females use bays and sloughs as nursery areas, while to the south they give birth in more open areas. Known breeding grounds along the coast of California include Humboldt Bay, Tomales Bay, Bodega Bay, San Francisco Bay, Elkhorn Slough, Morro Bay, Santa Monica Bay (Los Angeles), Catalina Harbor (Santa Catalina Island), and San Diego Bay.

Females give birth to 1-37 young annually from March and July (most in April or May), with the number of pups increasing with female size. Multiple males may father a litter from a single mother In Humboldt and San Francisco Bays, females drop their pups in beds of eelgrass that provide both shelter and food. In Catalina Harbor, females give birth on flats in 1 m (3.3 ft) of water, their backs and dorsal fins exposed; the pups stay in even shallower water less than 30 cm (12 in) deep. Mating occurs in early summer following birth; the only known observation of this in the wild was in 2004 off La Jolla, amongst nine sharks gathered 19 m (62 ft) from shore in water 0.3-3 m (0.98-9.84 ft) deep.

Newborn leopard sharks measure around 20 cm (7.9 in) long. Relatively slow-growing after the first 3-4 years of life, male leopard sharks grow an average of 2.0 cm (0.79 in) per year, reaching maturity at an age of 7-13 years and a length of 0.7-1.2 m (2.3-3.9 ft), while females grow an average of 2.3 cm (0.91 in) per year, reaching maturity at an age of 10-15 years and a length of 1.1-1.3 m (3.6-4.3 ft). Individuals of the same age can vary significantly in size and large sharks are especially slow-growing: one specimen was documented to have gained only 4 cm (1.6 in) in length over 12 years. The maximum lifespan of this species is estimated to be 30 years.

Wary and quick to flee, leopard sharks pose almost no danger to humans. There is a single record from 1955 of a leopard shark harassing a skin diver with a nosebleed, though no injuries resulted. This species is caught by commercial fisheries using gillnets and longlines, and by recreational anglers and spearfishers; it is also caught as bycatch in bottom trawls. The meat is considered excellent eating and is sold fresh or frozen. However, leopard sharks living alongside human development may accumulate pollutants such as mercury, pesticides, and polychlorinated biphenyls (PCBs) within their bodies, and the California Department of Fish and Wildlife warns against eating them regularly. The leopard shark is prized by the aquarium trade for its attractive appearance and hardiness; this led to many newborn pups being captured with hook-and-line off southern California in the late 1980s and early 1990s. It may live for over 20 years in captivity.

Most of the fishing for leopard sharks occurs in the waters off California, where commercial landings peaked at 45,953 kg (101,309 lb) in 1983 and has averaged 14,060 kg (31,000 lb) annually since 1991. These figures are believed to be underestimates, as an unknown portion of the leopard shark catch is recorded simply as "shark". In recent decades the number of sharks taken recreationally has exceeded those taken commercially, with sport fishers catching an average of 52,000 sharks per year from 1980-1988, and 45,000 sharks per year since 1993. This species contributes negligibly to fishery landings off Oregon. The status of leopard sharks off Mexico is uncertain, although Mexican shark fisheries tend to focus more on larger species.

The International Union for Conservation of Nature (IUCN) has assessed the leopard shark as of Least Concern. It is highly susceptible to local depletion due to its slow growth rate and low level of exchange between regional stocks. It was considered for, but is not managed under, the U.S. Pacific Fishery Management Council's (PMC) 1982 Groundfish Management Plan. In 1992, the State of California imposed a recreational minimum size limit of 91 cm (36 in) and a possession limit of three fish, a move that was strongly supported and promoted by the sport fishing community. In 1993, the State also instituted a minimum size limit of 46 cm (18 in) for the commercial harvesting of all sharks and rays, including for the aquarium trade. In addition, Californian restrictions on the use of certain types of fishing gear in near-shore waters confer good protection to this shark's core population. These management measures seem to have successfully reduced fishing mortality and halted the population decline from the 1980s; the status of the leopard shark off California is regarded as secure, with demographic models estimating an annual population increase of 3-6% with sustainable fishing.

1. Carlisle, A. & S.E. Smith (2004). "Triakis semifasciata". IUCN Red List of Threatened Species. 2004.

2. ^ Girard, C.F. (April 13, 1855). "Characteristics of some cartilaginous fishes of the Pacific coast of North America". Proceedings of the Academy of Natural Sciences of Philadelphia. 7: 196-197.

3. ^ Compagno, L.J.V. (1984). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date. Rome: Food and Agricultural Organization. pp. 433-434. ISBN 978-92-5-101384-7.

4. Pietsch, T.W.; Orr, J.W.; Eschmeyer, W.N. (2012). "Mustelus felis Ayres, 1854, a Senior Synonym of the Leopard Shark, Triakis semifasciata Girard, 1855 (Carchariniformes: Triakidae), Invalidated by "Reversal of Precedence"". Copeia. 2012: 98-99. doi:10.1643/ci-11-089. S2CID 85623853.

5. ^ Ebert, D.A. (2003). Sharks, Rays, and Chimaeras of California. University of California Press. pp. 144-147. ISBN 978-0-520-22265-6.

6. López, J.A.; J.A. Ryburn; O. Fedrigo; G.J.P. Naylor (2006). "Phylogeny of sharks of the family Triakidae (Carcharhiniformes) and its implications for the evolution of carcharhiniform placental viviparity". Molecular Phylogenetics and Evolution. 40 (1): 50-60. doi:10.1016/j.ympev.2006.02.011. PMID 16564708.

7. ^ Fowler, S.L.; R.D. Cavanagh; M. Camhi; G.H. Burgess; G.M. Cailliet; S.V. Fordham; C.A. Simpfendorfer & J.A. Musick (2005). Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes. International Union for Conservation of Nature and Natural Resources. pp. 281-283. ISBN 978-2-8317-0700-6.

8. ^ Hopkins, T.E.; J.J. Cech (Jr.) (2003). "The influence of environmental variables on the distribution and abundance of three elasmobranchs in Tomales Bay, California". Environmental Biology of Fishes. 66 (3): 279-291. doi:10.1023/A:1023907121605. S2CID 1799958.

9. ^ Delius, B. Biological Profiles: Leopard Shark. Florida Museum of Natural History Ichthyology Department. Retrieved on August 9, 2009.

10. Froese, Rainer and Pauly, Daniel, eds. (2009). ^ "Triakis semifasciata" in FishBase. August 2009 version.

11. Manley, J.F. (1995). Diel movement patterns of leopard sharks, Triakis semifasciata, at Santa Catalina Island, California. MS Thesis. California State University, Long Beach, CA.

12. ^ Hight, B.V.; C.G. Lowe (2007). "Elevated body temperatures of adult female leopard sharks, Triakis semifasciata, while aggregating in shallow nearshore embayments: Evidence for behavioral thermoregulation?". Journal of Experimental Marine Biology and Ecology. 352: 114-128. doi:10.1016/j.jembe.2007.07.021.

13. Martin, R.A. Estuaries: Leopard Shark. ReefQuest Centre for Shark Research. Retrieved on August 9, 2009.

14. ^ Sillman, A.J.; G.A. Letsinger; S. Patel; E.R. Loew & A.P. Klimley (1998). "Visual pigments and photoreceptors in two species of shark, Triakis semifasciata and Mustelus henlei". Journal of Experimental Zoology Part A: Comparative Experimental Biology. 276 (1): 1-10. doi:10.1002/(SICI)1097-010X(19960901)276:1<1::AID-JEZ1>3.0.CO;2-T.

15. ^ Leet, W.S.; Dewees, C.M.; Klingbeil, R.; Larson, E.J., eds. (2001). "Leopard Shark". California's Living Resources: A Status Report (fourth ed.). ANR Publications. pp. 252-254. ISBN 978-1-879906-57-0.

16. Martin, R.A. ^ Sandy Plains: Broadnose Sevengill Shark. ReefQuest Centre for Shark Research. Retrieved on August 9, 2009.

17. ^ Ruhnke, T.R. (January 1996). "Taxonomic resolution of Phyllobothrium van Beneden (Cestoda: Tetraphyllidea) and a description of a new species from the leopard shark Triakis semifasciata". Systematic Parasitology. 33 (1): 1-12. doi:10.1007/bf00009715. S2CID 22881890.

18. ^ Russo, R.A. (1975). "Notes on the external parasites of California inshore sharks". California Fish and Game. 61: 228-232.

19. ^ Causey, D. (July 1960). "Parasitic Copepoda from Mexican Coastal Fishes". Bulletin of Marine Science. 10 (3): 323-337.

20. ^ Ferry-Graham, L.A. (1998). "Effects of prey size and mobility on prey-capture kinematics in leopard sharks Triakis semifasciata" (PDF). Journal of Experimental Biology. 201 (16): 2433-2444. PMID 9679105.

21. ^ Reif, W.E.; D. McGill & P. Motta (1978). "Tooth replacement rates of the sharks Triakis semifasciata and Ginglymostoma cirratum". Zoologische Jahrbücher (Anat.). 99: 151-156.

22. Ebert, D.A.; T.B. Ebert (2005). "Reproduction, diet and habitat use of leopard sharks, Triakis semifasciata (Girard), in Humboldt Bay, California, USA". Marine and Freshwater Research. 56 (8): 1089-1098. doi:10.1071/MF05069.

23. ^ Webber, J.D.; J.J. Cech (Jr.) (1998). "Nondestructive diet analysis of the leopard shark from two sites in Tomales Bay, California". California Fish and Game. 84 (1): 18-24.

24. ^ https://www.nbcnews.com/sciencemain/one-female-sharks-litter-may-have-many-dads-study-finds-6C10848675

25. Smith, S.E. (2004). ^ "Leopard Shark (Triakis semifasciata) Mating Activity Observed off La Jolla, California". Southwest Fisheries Science Center, San Diego. Note.

# data[].attributes.attachment_link.description
The leopard shark ( Triakis semifasciata) is a species of houndshark, in the family Triakidae. It is found along the Pacific coast of North America, from the U.S. state of Oregon to Mazatlán in Mexico.

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Nurse SHARK - Enchanted Learning Software

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The nurse shark (Ginglymostoma cirratum) is a large, sluggish, bottom-dwelling shark that is generally harmless unless provoked. It has very strong jaws, a stout body, and a wide head with obvious barbels (thin, fleshy, whisker-like organs on the lower jaw that sense touch and taste)..

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There are more than 465 known species of sharks living in our oceans today. Sharks are an apex predator at or near the top of their marine food chains, and they regulate the populations of species below them. Research has shown that massive depletion of sharks has cascading effects throughout the ocean's ecosystems.

© Ridlon Kiphart

Sharks belong to a family of fish that have skeletons made of cartilage, a tissue more flexible and lighter than bone. They breathe through a series of five to seven gill slits located on either side of their bodies. All sharks have multiple rows of teeth, and while they lose teeth on a regular basis, new teeth continue to grow in and replace those they lose.

Shark 'skin' is made up of a series of scales that act as an outer skeleton for easy movement and for saving energy in the water. The upper side of a shark is generally dark to blend in with the water from above and their undersides are white or lighter colored to blend in with the lighter surface of the sea from below. This helps to camouflage them from predators and prey.

Diet

Most species of shark eat things like fish, crustaceans, mollusks, plankton, krill, marine mammals and other sharks. Sharks also have a very acute sense of smell that allows them to detect blood in the water from miles away.

Population

It is difficult to estimate population numbers since there are many different species spanning a large geographic area. However, overall shark numbers are on the decline due to the many threats they face in the wild.
Did You Know?
Sharks predate the dinosaurs by 200 million years. The largest known species of shark, C. megalodon, might have reached a maximum length of 67 feet.

Habitat & Range

Sharks have adapted to living in a wide range of aquatic habitats at various temperatures. While some species inhabit shallow, coastal regions, others live in deep waters, on the ocean floor and in the open ocean. Some species, like the bull shark, are even known to swim in salt, fresh and brackish waters.

Behavior

Most sharks are especially active in the evening and night when they hunt. Some sharks migrate over great distances to feed and breed. This can take them over entire ocean basins. While some shark species are solitary, others display social behavior at various levels. Hammerhead sharks, for instance, school during mating season around seamounts and islands.

Some shark species, like the great white shark, attack and surprise their prey, usually seals and sea lions, from below. Species that dwell on the ocean floor have developed the ability to bottom-feed. Others attack schooling fish in a feeding frenzy, while large sharks like the whale and basking sharks filter feed by swimming through the ocean with their mouths open wide, filtering large quantities of plankton and krill.

Reproduction

Sharks mature slowly, and reach reproductive age anywhere from 12 to 15 years. This, combined with the fact that many species only give birth to one or two pups at a time, means that sharks have great difficulty recovering after their populations have declined.

Soon after birth, sharks pups swim away to fend for themselves. They are born with fully-fledged sets of teeth and are able to feed and live on their own.

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There are more than 465 known species of sharks living in our oceans today. Sharks are an apex predator at or near the top of their marine food chains, and they regulate the populations of species below them.

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A hammerhead shark uses its wide head to trap stingrays by pinning them to the seafloor. The shark's eye placement, on each end of its very wide head, allows it to scan more area more quickly than other sharks can. The hammerhead also has special sensors across its head that helps it scan for food in the ocean. Living creatures' bodies give off electrical signals, which are picked up by sensors on the prowling hammerhead.

The shark hunts alone, and can find stingrays that hide under the sand on the seafloor. Hammerheads also eat bony fishes, crabs, squid, lobsters, and other sea creatures. The upper sides of these fish are grayish-brown or olive-green and they have white bellies. They have very impressive triangular, serrated teeth-like the edge of a saw's blade. Hammerheads' mouths are on the underside of their heads.

Unlike many fish, hammerheads do not lay eggs. A female gives birth to live young. One litter can range from six to about 50 pups. When a hammerhead pup is born, its head is more rounded than its parents'.

There have been very few recorded attacks on people by the great hammerhead.

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This shark's unusual name comes from the unusual shape of its head, an amazing piece of anatomy built to maximize the fish's ability to find its favorite meal: stingrays. A hammerhead shark uses its wide head to trap stingrays by pinning them to the seafloor.

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Fun shark facts for kids including photos and printable activity worksheets; suitable for Kindergarten through Grade 6.

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Your destination for news, pictures, facts, and videos about fish.

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When a great white shark is born, along with up to a dozen siblings, it immediately swims away from its mother. Born on the east and west coasts of North America, the south of Africa and southwest Australia, baby sharks are on their own right from the start. Their mother may see them only as prey.

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When a great white shark is born, along with up to a dozen siblings, it immediately swims away from its mother. Born on the east and west coasts of North America, the south of Africa and southwest Australia, baby sharks are on their own right from the start.

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Sharks

Temporal range: Early Jurassic - Present

Clockwise from top left: spiny dogfish, Australian angelshark, whale shark, great white shark, horn shark, frilled shark, scalloped hammerhead and Japanese sawshark representing the orders Squaliformes, Squatiniformes, Orectolobiformes, Lamniformes, Heterodontiformes, Hexanchiformes, Carcharhiniformes and Pristiophoriformes respectively.

Scientific classification

Clade:

Neoselachii

Orders

Synonyms

Pleurotremata

Selachii

Sharks are a group of elasmobranch 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 Batoidea ( rays and kin). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts. Shark-like chondrichthyans such as Cladoselache and first appeared in the Devonian Period (419-359 million years), though some fossilized chondrichthyan-like scales are as old as the Late Ordovician (458-444 million years ago). The oldest modern sharks (selachimorphs) are known from the Early Jurassic, about 200 million years ago.[citation needed ]

Sharks range in size from the small dwarf lanternshark ( Etmopterus perryi), a deep sea species that is 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 (40 ft) in length. They are found in all seas and are common to depths up to 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, which can be found in both seawater and freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.

Several species are apex predators, which are organisms that are at the top of their food chain. Select examples include the tiger shark, blue shark, great white shark, mako shark, thresher shark, and hammerhead shark.

Until the 16th century, sharks were known to mariners as "sea dogs". This is still evidential in several species termed " dogfish," or the porbeagle.

The etymology of the word shark is uncertain, the most likely etymology states that the original sense of the word was that of "predator, one who preys on others" from the Dutch schurk, meaning 'villain, scoundrel' ( cf. , , etc.), which was later applied to the fish due to its predatory behaviour.

A now disproven[original research? ] theory is that it derives from the Yucatec Maya word xook (pronounced ), meaning 'shark'. Evidence for this etymology came from the Oxford English Dictionary, which notes shark first came into use 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 isolated occurrence of the word shark (referring to a sea fish) in a letter written by Thomas Beckington in 1442, which rules out a New World etymology.[original research? ]

Evolutionary history

Fossil record

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

The oldest total-group chondrichthyans, known as acanthodians or "spiny sharks", appeared during the Early Silurian, around 439 million years ago. The oldest confirmed members of Elasmobranchii sensu lato (the group containing all cartilaginous fish more closely related to modern sharks and rays than to chimaeras) appeared during the Devonian. The oldest representatives of Neoselachii, the group containing modern sharks (Selachii) and rays (Batoidea) to the exclusion of most extinct elasmobranch groups, date to the Permian. Selachiimorpha and Batoidea are suggested to have diverged during the Triassic. The oldest modern sharks date to the Early Jurassic, with most modern orders appearing by the end of the Jurassic. Selachians largely replaced the hybodonts, which had previously been dominant group of shark-like fish during the Triassic and Early Jurassic. A study in 2023 showed that sharks such as the epaulette shark has a low mutation rate which is consistent with their evolutionary history. This means that sharks have low cancer rate and are considered a slow evolving linage.

Shark fossil, Lebachacanthus senckenbergianus, at Permian period

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 was thought that the sharks form a polyphyletic group: some sharks are more closely related to rays than they are to some other sharks, but current molecular studies support monophyly of both groups of sharks and batoids.

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 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 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 also be invalid, but includes the Pristiophoriformes and the Batoidea.

There are more than 500 species of sharks split across thirteen orders, including several orders of sharks that have gone extinct:

Carcharhiniformes: Commonly known as ground sharks, the order includes 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.

Heterodontiformes: They are generally referred to as the bullhead or horn sharks.

Hexanchiformes: Examples from this group include the cow sharks and frilled sharks, which somewhat resembles a marine snake.

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 also include the extinct megalodon, Otodus megalodon.

Orectolobiformes: They are commonly referred to as the carpet sharks, including zebra sharks, nurse sharks, wobbegongs, and the whale shark.

Pristiophoriformes: These are the sawsharks, with an elongated, toothed snout that they use for slashing their prey.

Squaliformes: This group includes the dogfish sharks and roughsharks.

Squatiniformes: Also known as angel sharks, they are flattened sharks with a strong resemblance to stingrays and skates.

Echinorhiniformes: This group includes the prickly shark and bramble shark. Phylogenetic placement of this group has been ambiguous in scientific studies. They are sometimes given their own order, Echinorhiniformes.

General anatomical features of sharks

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

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.

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. Because sharks do not have rib cages, they can easily be crushed under their own weight on land.

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. In the rostrum (snout), the cartilage can be spongy and flexible to absorb the power of impacts.

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. 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.

Dermal denticles

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. Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming. Some species of shark have pigmented denticles that form complex patterns like spots (e.g. Zebra shark) and stripes (e.g. Tiger shark). These markings are important for camouflage and help sharks blend in with their environment, as well as making them difficult for prey to detect. For some species, dermal patterning returns to healed denticles even after they have been removed by injury.

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.

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. 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

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. Their liver constitutes up to 30% of their total body mass. The liver's effectiveness is limited, so sharks employ dynamic lift to maintain depth while swimming. Sand tiger sharks store air in their stomachs, using it as a form of swim bladder. Bottom-dwelling sharks, like the nurse shark, have negative buoyancy, allowing them to rest on the ocean floor.

Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility. Researchers use this condition to handle sharks safely.

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. 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.

The respiratory and circulatory process begins when deoxygenated venous blood travels to the shark's two-chambered heart. Here the shark pumps blood to its gills via the ventral aorta where it branches into afferent branchial arteries. Gas exchange takes place in the gills and the reoxygenated blood flows into the efferent branchial arteries, which come together to form the dorsal aorta. The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from the body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses. From there venous blood re-enters the heart ventricle and the cycle repeats.

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 and bigeye thresher sharks have a similar mechanism for maintaining an elevated body temperature.

Larger species, like the whale shark, are able to conserve their body heat through sheer size when they dive to colder depths, and the scalloped hammerhead close its mouth and gills when they dives to depths of around 800 metres, holding its breath till it reach warmer waters again.

Osmoregulation

In contrast to bony fish, with the exception of the coelacanth, the blood and other tissue of sharks and Chondrichthyes is generally isotonic to their marine environments because of the high concentration of urea (up to 2.5%) 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. When a shark dies, the urea is broken down to ammonia by bacteria, causing the dead body to gradually smell strongly of ammonia.

Research in 1930 by Homer W. Smith showed that sharks' urine does not contain sufficient sodium to avoid hypernatremia, and it was postulated that there must be an additional 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 function is the secretion of chlorides.

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. 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.

Fluorescence

A few sharks appear fluorescent under blue light, such as the swell shark and the chain catshark, where the fluorophore derives from a metabolite of kynurenic acid.

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. The size of the olfactory bulb varies across different shark species, with size dependent on how much a given species relies on smell or vision to find their prey. In environments with low visibility, shark species generally have larger olfactory bulbs. In reefs, where visibility is high, species of sharks from the family Carcharhinidae have smaller olfactory bulbs. Sharks found in deeper waters also have larger olfactory bulbs.

Sharks have the ability to determine the direction of a given scent based on the timing of scent detection in each nostril. 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.

Eye of a bigeyed sixgill shark (Hexanchus nakamurai)

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 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. Many sharks can contract and dilate their pupils, like humans, something no teleost fish can do. 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, since 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. 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.

Although it is hard to test the hearing of sharks, they may have a sharp sense of hearing and can possibly hear prey from many miles away. The hearing sensitivity for most shark species lies between 20 and 1000 Hz. 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

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. 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.

Lateral line

This system is found in most fish, including sharks. It is a tactile sensory system which allows the organism to detect water speed and pressure changes near by. The main component of the system is the neuromast, a cell similar to hair cells present in the vertebrate ear 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 visual view. The shark can sense frequencies in the range of 25 to 50 Hz.

Life history

Shark lifespans vary by species. Most live 20 to 30 years. The spiny dogfish has one of the longest lifespans at more than 100 years. Whale sharks ( Rhincodon typus) may also live over 100 years. Earlier estimates suggested the Greenland shark ( Somniosus microcephalus) could reach about 200 years, but a recent study found that a 5.02-metre-long (16.5 ft) specimen was 392 ± 120 years old (i.e., at least 272 years old), making it the longest-lived vertebrate known.

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. Sharks mature slowly relative to many other fish. For example, lemon sharks reach sexual maturity at around age 13-15.

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.

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.

There have been a number of 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. 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. Mammals are now the only major vertebrate group in which asexual reproduction has not been observed.

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

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 , 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.

Some species are oviparous, laying their fertilized 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. The egg case is commonly called a mermaid's purse. Oviparous sharks include the horn shark, catshark, Port Jackson shark, and swellshark.

Viviparity

Viviparity is the gestation of young without the use of a traditional egg, and results in live birth. Viviparity in sharks can be placental or aplacental. Young are born fully formed and self-sufficient. Hammerheads, the requiem sharks (such as the bull and blue sharks), and smoothhounds are viviparous.

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 social, sedentary, benthic lives, and appear likely to have their own distinct personalities. Even solitary sharks meet for breeding or at rich hunting grounds, which may lead them to cover thousands of miles in a year. 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. Cross-species social hierarchies exist. For example, oceanic whitetip sharks dominate silky sharks of comparable size during feeding.

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.

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). 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. Sharks can travel 70 to 80 km in a day.

Intelligence

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

There is evidence that juvenile lemon sharks can use observational learning in their investigation of novel objects in their environment.

All sharks need to keep water flowing over their gills in order for them to breathe; however, not all species need to be moving to do this. Those that are able to breathe while not swimming do so by using their spiracles to force water over their gills, thereby allowing them to extract oxygen from the water. It has been recorded that their eyes remain open while in this state and actively follow the movements of divers swimming around them and as such they are not truly asleep.

Species that do need to swim continuously to breathe go through a process known as sleep swimming, in which the shark is essentially unconscious. It is known from experiments conducted on the spiny dogfish that its spinal cord, rather than its brain, coordinates swimming, so spiny dogfish can continue to swim while sleeping, and this also may be the case in larger shark species. In 2016 a great white shark was captured on video for the first time in a state researchers believed was sleep swimming.

Most sharks are carnivorous. Basking sharks, whale sharks, and megamouth sharks have independently evolved different strategies for filter feeding plankton: basking sharks practice ram feeding, whale sharks use suction to take in plankton and small fishes, and megamouth sharks make suction feeding more efficient by using the luminescent tissue inside of their mouths to attract prey in the deep ocean. 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.

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.

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. 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.

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. 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).

Relationship with humans

Snorkeler swims near a 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.

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.

Contrary to popular belief, 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, unprovoked attacks on humans: the great white, oceanic whitetip, tiger, and bull sharks. 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.

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 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.

To help avoid an unprovoked attack, humans should not wear jewelry or metal that is shiny and refrain from splashing around too much.

In general, sharks show little pattern 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. This was further proven in a recent study conducted by researchers at the California State University's Shark Lab. According to footage caught by the Lab's drones, juveniles swam right up to humans in the water without any bites incidents. The lab stated that the results showed that humans and sharks can co-exist in the water.

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, along with safer transportation techniques that have enabled long-distance transportation. The great white shark had never been successfully held in captivity for long periods of time until September 2004, when the Monterey Bay Aquarium successfully kept a young female for 198 days before releasing her.

Most species are not suitable for home aquaria, and not every species sold by pet stores are appropriate. Some species can flourish in home saltwater aquaria. Uninformed or unscrupulous dealers sometimes sell juvenile sharks like the nurse shark, which upon reaching adulthood is far too large for typical home aquaria. Public aquaria generally do not accept donated specimens that have outgrown their housing. Some owners have been tempted to release them. Species appropriate to home aquaria represent considerable spatial and financial investments as they generally approach adult lengths of 3 feet (90 cm) and can live up to 25 years.

Sharks figure prominently in Hawaiian mythology. Stories tell of men with shark jaws on their back who could change between shark and human form. 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.

Kamohoali'i is the best known and revered of the shark gods, he was the older and favored brother of Pele, 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 (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. In Fijian mythology, Dakuwaqa was a shark god 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 location called Turtle and Shark ( Laumei ma Malie) which is important in Samoan culture-the location is the site of a legend 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. 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 song intended to summon the legendary animals to the ocean surface, and visitors are frequently amazed to see one or both of these creatures emerge from the sea in apparent response to this call."

In popular culture

In contrast to the complex portrayals by Hawaiians and other Pacific Islanders, the European and Western view of sharks has historically been mostly of fear and malevolence. Sharks are used in popular culture commonly as eating machines, notably in the novel and the film of the same name, along with its sequels. Sharks are threats in other films such as Deep Blue Sea, , 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, , and other shows produced by Hanna-Barbera. They also are used commonly as a clichéd means of killing off a character that is held up by a rope or some similar object as the sharks swim right below them, or the character may be standing on a plank above shark infested 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. 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. Other apparently false claims are that fins prevent cancer and treat osteoarthritis. No scientific proof supports these claims; at least one study has shown shark cartilage of no value in cancer treatment.

Threats to sharks

The annual shark catch has increased rapidly over the last 60 years.

A 4.3-metre (14 ft), 540-kilogram (1,200 lb) tiger shark caught in Kāne'ohe Bay, Oahu in 1966

In 2008, it was estimated that nearly 100 million sharks were being killed by people every year, due to commercial and recreational fishing. In 2021, it was estimated that the population of oceanic sharks and rays had dropped by 71% over the previous half-century.

Shark finning yields are estimated at 1.44 million metric tons (1.59 million short tons) for 2000, and 1.41 million metric tons (1.55 million short tons) for 2010. Based on an analysis of average shark weights, this translates into a total annual mortality estimate of about 100 million sharks in 2000, and about 97 million sharks in 2010, with a total range of possible values between 63 and 273 million sharks per year. Sharks are a common seafood in many places, including Japan and Australia. In southern Australia, shark is commonly used 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 a delicacy called hákarl. During a four-year period from 1996 to 2000, an estimated 26 to 73 million sharks were killed and traded annually in commercial markets.

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. The resulting immobile shark soon dies from suffocation or predators. Shark fin has become a major trade within black markets all over the world. Fins sell for about $300/lb in 2009. Poachers illegally fin millions each year. Few governments enforce laws that protect them. In 2010 Hawaii became the first U.S. state to prohibit the possession, sale, trade or distribution of shark fins. From 1996 to 2000, an estimated 38 million sharks had been killed per year for harvesting shark fins. It is estimated by TRAFFIC that over 14,000 tonnes of shark fins were exported into Singapore between 2005-2007 and 2012-2014.

Shark fin soup is a status symbol in Asian countries and is erroneously considered healthy and full of nutrients. Scientific research has revealed, however, that high concentrations of BMAA are present in shark fins. Because BMAA is a neurotoxin, consumption of shark fin soup and cartilage pills, therefore, may pose a health risk. BMAA is under study for its pathological role in neurodegegerative diseases such as ALS, Alzheimer's disease, and Parkinson's disease.

Sharks are also killed for meat. European diners consume dogfishes, smoothhounds, catsharks, makos, porbeagle and also skates and rays. 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. Capture induced premature birth and abortion (collectively called capture-induced parturition) occurs frequently in sharks/rays when fished. Capture-induced parturition is rarely considered in fisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).

The majority of shark fisheries have little monitoring or management. The rise in demand for shark products increases pressure on fisheries. 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. A study by the International Union for Conservation of Nature suggests that one quarter of all known species of sharks and rays are threatened by extinction and 25 species were classified as critically endangered.

Shark culling

In 2014, a shark cull in Western Australia killed dozens of sharks (mostly tiger sharks) using drum lines, until it was cancelled after public protests and a decision by the Western Australia EPA; from 2014 to 2017, there was an "imminent threat" policy in Western Australia in which sharks that "threatened" humans in the ocean were shot and killed. This "imminent threat" policy was criticized by senator Rachel Siewart for killing endangered sharks. The "imminent threat" policy was cancelled in March 2017. In August 2018, the Western Australia government announced a plan to re-introduce drum lines (though, this time the drum lines are "SMART" drum lines).

From 1962 to the present, the government of Queensland has targeted and killed sharks in large numbers by using drum lines, under a "shark control" program-this program has also inadvertently killed large numbers of other animals such as dolphins; it has also killed endangered hammerhead sharks. Queensland's drum line program has been called "outdated, cruel and ineffective". From 2001 to 2018, a total of 10,480 sharks were killed on lethal drum lines in Queensland, including in the Great Barrier Reef. From 1962 to 2018, roughly 50,000 sharks were killed by Queensland authorities.

The government of New South Wales has a program that deliberately kills sharks using nets. The current net program in New South Wales has been described as being "extremely destructive" to marine life, including sharks. Between 1950 and 2008, 352 tiger sharks and 577 great white sharks were killed in the nets in New South Wales-also during this period, a total of 15,135 marine animals were killed in the nets, including dolphins, whales, turtles, dugongs, and critically endangered grey nurse sharks. There has been a very large decrease in the number of sharks in eastern Australia, and the shark-killing programs in Queensland and New South Wales are partly responsible for this decrease.

Kwazulu-Natal, an area 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. During a 30-year period, more than 33,000 sharks have been killed in KwaZulu-Natal's shark-killing program-during the same 30-year period, 2,211 turtles, 8,448 rays, and 2,310 dolphins were killed in KwaZulu-Natal. Authorities on the French island of Réunion kill about 100 sharks per year.

Killing sharks negatively affects the marine ecosystem. Jessica Morris of Humane Society International calls shark culling a "knee-jerk reaction" and says, "sharks are top order predators that play an important role in the functioning of marine ecosystems. We need them for healthy oceans."

George H. Burgess, the former director of the International Shark Attack File, "describes [shark] culling as a form of revenge, satisfying a public demand for blood and little else"; he also said shark culling is a "retro-type move reminiscent of what people would have done in the 1940s and 50s, back when we didn't have an ecological conscience and before we knew the consequences of our actions." Jane Williamson, an associate professor in marine ecology at Macquarie University, says "There is no scientific support for the concept that culling sharks in a particular area will lead to a decrease in shark attacks and increase ocean safety."

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. The 2007 documentary Sharkwater exposed how sharks are being hunted to extinction.

Conservation

In 1991, South Africa was the first country in the world to declare Great White sharks a legally protected species (however, the KwaZulu-Natal Sharks Board is allowed to kill great white sharks in its " shark control" program in eastern South Africa).

Intending to ban the practice of shark finning while at sea, the United States Congress passed the Shark Finning Prohibition Act in 2000. 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. 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.

In 2003, the European Union introduced a general shark finning ban for all vessels of all nationalities in Union waters and for all vessels flying a flag of one of its member states. This prohibition was amended in June 2013 to close remaining loopholes.

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 risk of extinction due to fishing and shark finning.

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. 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 licensing and regulation.

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. Advocacy group Shark Trust campaigns to limit shark fishing. Advocacy group Seafood Watch directs American consumers to not eat sharks.

Under the auspices of the Convention on the Conservation of 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 in 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.

In July 2013, New York state, a major market and entry point 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 protection to sharks.

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.

Several regions now 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.

In April 2020 researchers reported to have traced the origins of shark fins of endangered hammerhead sharks from a retail market in Hong Kong back to their source populations and therefore the approximate locations where the sharks were first caught using DNA analysis.

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 almost 20% of the surveyed reefs and shark depletion was strongly associated with both socio-economic conditions and conservation measures. Sharks are considered to be a vital part of the ocean ecosystem.

According to a 2021 study in , overfishing has resulted in a 71% global decline in the number of oceanic sharks and rays over the preceding 50 years. The oceanic whitetip, and both the scalloped hammerhead and great hammerheads are now classified as critically endangered. Sharks in tropical waters have declined more rapidly than those in temperate zones during the period studied. A 2021 study published in Current Biology found that overfishing is currently driving over one-third of sharks and rays to extinction.

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General and cited references

Further reading

Calma, Justine (16 August 2021). "How drones are changing our view of sharks". The Verge.

Sharks 'critical' to restoring damaged ecosystems, finds study. The Guardian, 22 March 2021

Musick, John A and Musick, Susanna (2011) "Sharks" Archived 2016-03-03 at the Wayback Machine In: Review of the state of world marine fishery resources, pages 245-254, FAO Fisheries technical paper 569, FAO, Rome. ISBN 978-92-5-107023-9.

"Sharks Falling Prey To Humans' Appetites". National Geographic, 28 October 2010.

External links

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Sharks Temporal range: Early Jurassic - Present Clockwise from top left: spiny dogfish, Australian angelshark, whale shark, great white shark, horn shark, frilled shark, scalloped hammerhead and Japanese sawshark representing the orders Squaliformes, Squatiniformes, Orectolobiformes, Lamniformes, Heterodontiformes, Hexanchiformes, Carcharhiniformes and Pristiophoriformes respectively.

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Sharks - What is a Shark?- Enchanted Learning Software

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Zoom Sharks is a comprehensive on-line hypertext book about sharks. It is designed for people of all ages and levels of comprehension. It has an easy-to-use structure that allows readers to start at a basic level on each topic, and then to progress to much more advanced information as desired, simply by clicking on links.

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Fun shark facts for kids including photos and printable activity worksheets; suitable for Kindergarten through Grade 6.

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