297 lines
12 KiB
Markdown
297 lines
12 KiB
Markdown
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white shark ( Carcharodon
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carcharias )
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white shark ( Carcharodon
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carcharias )
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### TABLE OF CONTENTS
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Introduction
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Distribution
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Body structure
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Behaviour
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Reproduction
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Ecology
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Evolution
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```
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# white shark
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**white shark** , ( _Carcharodon
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carcharias_ ), also called **great
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white shark** or **white pointer** ,
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any member of the largest living
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species of the mackerel sharks (Lamnidae) and one of the most
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powerful and dangerous predatory sharks in the world. Starring as the
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villain of movies such as _Jaws_ (1975), the white shark is much
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maligned and publicly feared. However, surprisingly little is
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understood of its life and behaviour.
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## Distribution
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```
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white shark ( Carcharodon
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carcharias )
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```
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```
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White shark ( Carcharodon
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carcharias )
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```
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White shark populations are
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frequently centred in highly
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productive temperate coastal
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waters (that is, waters
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characterized by an abundance of
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fishes and marine mammals),
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such as off the coasts of the
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northeastern and western United
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States, Chile, northern Japan, southern Australia, New Zealand,
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southern Africa, and the Mediterranean. Some individual white sharks
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may travel far out to sea or into tropical waters, but field studies show
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that most return to these temperate feeding areas each year.
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## Body structure
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White sharks are large bulky
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fishes with a body shaped like a
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blunt torpedo. They have a
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sharply pointed conical snout,
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large pectoral and dorsal fins,
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and a strong crescent-shaped tail.
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Only the belly of white sharks is
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whitish. They have a contrasting
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pattern of dark blue, gray, or brown on their back and sides. They are
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amazing hunters armed with strong muscles, good eyesight, and a
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keen sense of smell. In addition, their massive jaws are armed with
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```
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white shark
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```
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large sharply pointed, coarsely serrated teeth. Each tooth is designed
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to cut flesh and can easily puncture and shatter bone. The largest fully
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grown white sharks do not exceed 6.4 metres (21 feet) in length. Most
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weigh between 680 and 1,800 kg (1,500 and 4,000 pounds), but some
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weighing more than 2,270 kg (about 5,000 pounds) have been
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documented.
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Most fish are ectothermic, or cold-blooded, but white sharks have a
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complex circulatory system that conserves heat generated through the
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contraction of swimming muscles. This heat is distributed throughout
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the body to warm its critical regions, giving the white shark a body
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temperature higher than the temperature of the surrounding water.
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This adaptation, called regional endothermy (which is a type of warm-
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bloodedness), allows the animal to be active in water that may be too
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cold for other species of predatory sharks.
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## Behaviour
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## Feeding habits
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```
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Newborn white sharks feed on
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fishes and other sharks. As they
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reach adulthood, their prey
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includes sea turtles, seals, sea
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lions, porpoises, dolphins, and
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small whales. Prey is usually
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hunted by ambush, where the
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```
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shark will attempt to rush the animal by surprise and inflict a sudden
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and massive fatal bite. Often this initial rush is so strong that the
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intense impact may send the prey out of the water or will send the
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shark into the air if it misses the target. The sharks will retire and wait
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for the prey to quickly die, giving rise to the terms _bite and spit_ or
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_bite and wait_ for this method of attack. White sharks are also
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opportunistic scavengers and will feed on the carcasses of whales and
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basking sharks; however, they are not indiscriminate.
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## Attacks on humans
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In the areas where they are most common, white sharks are
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responsible for numerous unprovoked, and sometimes fatal, attacks on
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swimmers, divers, surfers, kayakers, and even small boats. A white
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shark tends to inflict a single bite on its human victim and then
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retreat. In many instances, however, the shark does not return for a
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second bite. If the victim suffers a moderate bite, he or she may have
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time to seek safety. In situations where a large bite occurs, however,
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serious tissue and organ damage may result in death. A review of
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white shark attacks off the western United States showed that about 7
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percent of attacks were fatal, but data from other localities, such as
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South Africa, show fatality rates of more than 20 percent. Fatality
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rates as high as 60 percent have been recorded from attacks in the
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waters off Australia.
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Many researchers maintain that attacks on humans stem from the
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shark’s curiosity. In contrast, other authorities contend that these
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attacks may be the result of the shark mistaking humans for its natural
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prey, such as seals and sea lions. It is also possible that white sharks
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intend to attack humans where their normal prey may be scarce.
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## Social behaviour
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Little is known about the social behaviour and natural history of the
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white shark. There appears to be no apparent social structure;
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however, there is evidence that some sharks may be territorial and
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assume dominance hierarchies around feeding areas. White sharks are
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largely solitary, but some pairs have been seen to travel together and
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associate for long periods of time. Some individuals may reside
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within feeding areas throughout the year, whereas other individuals
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may leave the feeding area and migrate widely. For example, some
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white sharks off California have been tracked to Hawaii, and some
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South African white sharks have been tracked to southern Australia
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and back.
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## Reproduction
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Mating has yet to be fully documented in white sharks, but it is
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assumed to be similar to internal fertilization in most sharks—that is,
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the male inserts his claspers into the cloaca of the female. Courtship
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behaviour, if there is any, is unknown. Male white sharks reach sexual
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maturity at 3.5 to 4 metres (about 11.5 to 13 feet) in length and about
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10 years of age, whereas females reach sexual maturity at 4.5 to 5
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metres (about 15 to 16 feet) in length and 12 to 18 years of age.
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```
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marine food chain
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```
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Reproduction is viviparous (that is, fertilized eggs are retained within
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the body). Prior to birth, the young in the womb may feed on
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undeveloped eggs and possibly their unborn siblings. Litters consist of
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2 to 10 pups; the newborns are more than 1 metre (about 3.3 feet) in
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length. Gestation is thought to take about 12 months, and females are
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assumed to give birth in warm temperate and subtropical waters, but
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specific nursery areas are unknown.
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## Ecology
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## Role in marine food chains
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As top predators in marine food
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chains, white sharks have few
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natural enemies. While it is true
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that young white sharks are
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sometimes eaten by larger sharks
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(including other white sharks),
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they have fewer potential
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enemies as they grow. Adult white sharks fear few other animals;
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however, in at least one documented instance, an adult killer whale
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( _Orcinus orca_ ) attacked and killed an adult white shark. The most
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profound enemies of the white shark are human beings.
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## Conservation
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The white shark has been classified as a vulnerable species by the
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International Union for Conservation of Nature (IUCN) since 1996.
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Its wide distribution throughout many areas of the ocean has made
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comprehensive population surveys difficult; however, catch-rate data
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collected by fishery officials worldwide suggest that the species may
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be undergoing a decline, but the white shark has only been assessed in
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selected regions, such as the Mediterranean Sea, where it is
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considered critically endangered.
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Humans hunt white sharks for a variety of reasons. They are a good
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food fish, and they are caught and sold commercially in many
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countries. Because of their impressive size and fabled ferocity, they
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are also highly prized sport fish, and their teeth are often treasured as
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jewelry. In addition, the jaws of large individuals can fetch thousands
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of dollars.
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Sharks of all types are also victims of finning, the practice of
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harvesting the lateral and dorsal fins and the lower tail fin from a
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shark by commercial fishing operations and others worldwide.
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Although the United States and several other industrialized countries
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have enacted laws that prohibit many shark-finning practices, white
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sharks continue to be hunted for their fins. In addition, many white
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sharks are caught accidentally in commercial fishing nets each year.
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Some of these sharks die in the nets; however, survivors may be killed
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intentionally for their fins and other parts by commercial anglers.
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White sharks are widespread. However, they are not common. They
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fill an important niche as a top predator and may help to keep
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populations of marine mammals in balance. Since they are positioned
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```
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great white shark
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```
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at the top of the food chain, they
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are never abundant. As a result,
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the removal of a few individuals
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can have a profound effect on
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the population. Since they grow
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slowly and produce few young,
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it takes a long time for
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populations to rebound, and harvesting has depleted populations of
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these sharks in many areas. Consequently, white sharks are legally
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protected in several places (such as Australia, South Africa, and
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California) despite their bad reputation. The protection of white
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sharks may even have economic benefits. For example, in waters that
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contain white sharks, boaters and dive operators earn tens of
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thousands of dollars yearly by featuring popular “shark dives” where
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guests can see white sharks from the safety of steel cages suspended
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in the water. Such a change in image from wanton killer to majestic
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predator may assure the future survival of white sharks.
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## Evolution
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According to the fossil record, modern white sharks evolved
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sometime between 10 million and 4 million years ago, from the
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middle of the Miocene Epoch (23 million to 5.3 million years ago)
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through the first half of the Pliocene Epoch (5.3 million to 2.6 million
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years ago), but their ancestors may date back to at least the Eocene
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Epoch (about 56 million to 34 million years ago). Early authorities
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maintained that white sharks were descended from the extinct
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megalodon ( _Carcharocles megalodon_ , formerly _Carcharodon
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megalodon_ )—the largest shark in the fossil record and now
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considered to be a member of the megatooth shark family
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Otodontidae.
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Newer paleontological interpretation is contentious, however, and two
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competing hypotheses have developed. In the first hypothesis, modern
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white sharks branched off from megatooth sharks to evolve alongside
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megalodon and other similar megatooth species. In contrast, the
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second hypothesis, based largely on 21st-century fossil finds and
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tooth analyses, suggests that modern white sharks descended from a
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line of ancient broad-toothed mako sharks—starting with
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_Carcharodon hastalis_. _C. hastalis_ had teeth similar in size and shape
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to those of modern white sharks but without serrations. These first
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white sharks likely first appeared during the middle of the Miocene
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Epoch. (However, some studies suggest that they may have evolved
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during the Oligocene Epoch [33.9 million to 23 million years ago].)
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Descendent species do not appear to have branched off from _C.
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hastalis_. Instead, white sharks are thought to have gradually
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transitioned from _C. hastalis_ to _C. hubbelli_ (between 8 million and 6
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million years ago) and then later to _C. carcharias_ (that is, modern
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white sharks) in a single evolutionary lineage, or chronospecies.
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Fossil discoveries suggest that tooth serrations characteristic of
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modern white sharks appeared gradually in the chronospecies,
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showing as small serrations in _C. hubbelli_ before becoming fully
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developed in _C. carcharias_.
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Douglas Long The Editors of Encyclopaedia Britannica
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```
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Citation Information
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Article Title: white shark
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Website Name: Encyclopaedia Britannica
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Publisher: Encyclopaedia Britannica, Inc.
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Date Published: 05 December 2022
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URL: https://www.britannica.comhttps://www.britannica.com/animal/white-shark
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Access Date: January 23, 2023
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