Introduction
The great white shark is found in all major oceans around the world and is also known as the great white or white death. The great white shark belongs to the species of lamniform shark and are widely distributed all over the globe. The taxonomic name for white shark is Carolus Linnaeus. White sharks are famous for their massive size and voracious eating habits. A mature male white shark could grow up to 6.5m in length. Researches have published work stating that great white sharks grow up to 8m in length. A mature white shark would weigh around 3,300 kg. Sharks are known to live for more than 15 years but researchers claim that they survive for more than 30 years. It is a known fat that sharks are the only cartilaginous fish that live for such a long time. Great white sharks can swim at high speeds to nearly 56 km/hour.
In the food pyramid, the great white shark is at the apex and has no evidence for natural predators. Great white sharks are one of the main predators in the marine ecosystem and is claimed to be the largest known macropredatory fish. White sharks feed on smaller fish and seabirds. In the genus Carcharodon, the great white shark is the only surviving species. It is known as the only species to have attacked humans in deep sea.
Taxonomy
Squaluscarcharias, the scientific name for shark was first given by Carolus Linnaeus in 1758. In 1833, Carcharodon was given as the generic name by Sir Andrew Smith. In 1873, the sappropriate scientific name Carcarodoncarcharias was given by Sir Andrew. Carcharodon is derived from the Greek wordsodous, which means tooth and karcharos, which means sharp or jagged.
Distribution and Habitat
Great white sharks survive in deep water at temperatures ranging from 12⁰c to 25⁰c and is found in most offshore and coastal water. Its abundance is greatly observed in the United States. Great white sharks are also found in Japan, South Africa and Chile. They are also found in some parts of Chile and the Mediterranean. Research on sharks is mainly conducted in Dyer Island and South Africa. These two places have the highestnumber of great white sharks.
The great white is found to be present among other fish species. It is also found among sea lions, fur seal and other sharks. It was also observed that great white sharks live among large bony fishes and cetaceans. Marine biologists challenge that great white sharks are observed at the depth of 2,500 to 3,500 ft.as predicted by other researchers who claim that sharks are found in coastal areas.
Marinebiologists have found out that great white sharks migrate from place to place. One such incident was observed in California white sharks. Sharks have been found to migrate from Baja California to Hawaii. They spend nearly 100 days in Hawaii which is also known as White shark café. The behavior in such white sharks is significant. They swim at depths of around 3,000 ft.
Biologists also observed that great whites change their behavior on way back to Baja California. They swim at depths of around 1000 ft. for near 10 minutes. They take short dives of around 300 m en-route the journey. Another study reported a white shark that swam from South Africa to Australia and back then. The entire journey was completed within a year.
These studies contradict the theories that hypothesize sharks as coastal territorial predators. There are no studies that reveal the reason of migration and behavior in sharks. Some suggest that their change in behavior may be linked to reproduction and survival.
Anatomy and appearance
The main characteristics of white sharks is their large, robust and conical snout. They are similar to mackerel sharks in terms of upper and lower lobes on the tail fin.
Countershading is observed in great white sharks. They have a mottled appearance by having a grey dorsal area and a white underside. In some cases, brown or blue shades are also observed. The coloration seen in white sharks prevents them being visible from prey. The underside coloration breaks up the shark’s outline which makes sharks difficult to spot by other fish. The darker side on shark depicts the ocean while the lower grey underside depicts the sunlight. This color pattern on sharks make them likely visible by prey in deep sea ocean.
Like many other sharks, great white sharks have rows of serrated teeth. These teeth are present behind the main ones. They are replaced during break off of old ones. Biting in sharks is unique. They shake their head from side to side, tearing apart the flesh of the prey.
Size
Great white sharks are known for their huge body structure. On an average a male white shark on maturity would reach 4m in length. Females are larger compared to males and reach 5m in length. An adult male would be around 5.5m in length with a mass of 650kg to 1,200kg. An adult female would grow to 6.5m in length and weigh around 3,500kg. The maximum size of a great white shark is controversial since no full-proof studies on the size of sharks were published.
Many large specimens of great white sharks have been recorded. According to the Guinness book of world records, 2 great white sharks were captured. In Southern Australia, a 10.9m great white shark was captured in 1870. In Canada, a great white shark was captured which was 11.3m in length.
According to the International Game Fish association (IGFA), the largest great white shark was caught by Alf Dean. The shark weighed around 1,200kg. The shark was caught in 1959 and was 6m in length.
Adaptations
The Ampullae of Lorenzini is present in most fishes. It enables fish to detect electromagnetic waves which is emitted by the movements of other fishes. Great white sharks also have Ampullae of Lorenzini.
Great white sharks have the capability of detecting half a billionth of a volt emitted by the movement of other fish in deep sea. Studies have reported that great white sharks can even detect electric waves emitted due to heart beats in other fishes. This makes great white sharks a competitive predator.
Great white sharks have adapted to survive in deep sea by maintaining their body temperature. They are warmer than the surrounding water which helps them in preying on larger animals like sea lions. They also maintain different temperatures for specific organs. Temperature in the stomach is maintained at 14⁰C above the surrounding water. Heart and gills of great white sharks have temperatures similar to the surrounding water.
Temperature changes in great white sharks change drastically depending on the surrounding water temperature. They are also known as endothermic poikilotherm, which simply means that they do not have a fixed body temperature.
Great whites are also known for their special adaptations in specific organs. They use stored fats and oils during long distance migrations. According to a scientific study published by Stanford University in July 2013, the liver of sharks depend on the pattern of migration.
Ecology and behavior
Ecology and behavior in great white sharks has not been studied well. In a South African study, dominance in great white sharks was observed. Dominance was found on the basis of size, sex and squatter’s rights. Females dominated males, while resident sharks would dominate newcomers. Hunting in sharks is mainly individualized. It was observed that great whites on meeting, greet each other by a bite. Great white sharks also show their dominance by a bite.
Spy-hopping is observed in great white sharks. They lift their head out of the water to gaze at possible prey. A similar observation was seen in reef sharks. A theory suggests that great white sharks lift their head above water to enhance smell reception. It is a known fact that smell travels faster in air than water.
Great whites are known for their curious behavior. They are also said to have higher intelligence levels compared to fish in the cartilaginous group. A study in Sea Island reported socializing in sharks. These sharks moved in clans of 4 or 6 individuals. Unique interaction patterns were observed when two different clans met each other. Further studies are being conducted to reveal ecological behavior of sharks.
Diet
Great white sharks are carnivorous and their diet consist mainly of fish. They feed on dolphins, porpoises and whales. Some deep sea sharks also feed on sea otters cetaceans. They are also known to prey on sea-birds and sea lions. Marine biologists have reported that shark feed on objects that cannot be digested.
When a mature shark grows up to 4m, they begin to prey on large marine mammals. These sharks feed on fish that are fat and energy rich. Sharks are known for their ferocious behavior. They are also termed as ‘Eating machines’ by marine biologists. They attack prey from beneath by a sudden attack. Hence they are known as ambush hunters.
Reproduction
There are not many studies that talk about the reproduction of white sharks. Almost nothing on reproduction in great white sharks have been reported. According to the Woods Hole oceanographic institute, great white males survive up to 30 years of age while females survive up to 40 years of age.
Mating habits in sharks are still not known. Birth in great whites have never been observed. Pregnant females have been examined. They are ovoviviparous. Eggs develop and hatch in the uterus itself. Gestation period in great whites is near 11 months. In the first month, jaws in shark pups are observed. Unborn sharks feed on ova produced by the mother. Not many studies have been published in the gestation and development of sharks.
Threats to great white sharks
The great white shark is known for its lethal attacks on humans. It has gained negative attention among humans. The species of white shark is threatened for its commercial use. White sharks are targeted for sports-fishing. Humans attack sharks for their jaws, teeth and preserved specimens.
It is a known fact that white sharks face trauma after being captured. White sharks kept in captivity do not survive for a long time. Exploitation of white sharks is observed in sports-fishing, shark fin-trade. Nowadays, sharks are kept in public aquariums which increases their rate of exploitation. Mortality rates among regional populations has increased over the years due to such exploitation. Beach meshing and indirect fishery captures have led to the decline of white sharks. Removal of white sharks from discrete location increases their vulnerability to exploitation.
Habitual degradation has had direct impacts on white shark population. Development, pollution and overfishing are some of the key factors that diminish the population of white sharks.
As mentioned earlier, great white sharks are known for their teeth and jaws. In South Africa, shark jaws and teeth have become rare and famous over the last 3 years. For a great white shark, around $20,000 US is paid for single jaw while around $600 is paid for a single tooth.
Great white sharks are also famous for their fins and curios. The fins and curios draw great economic value to traders. A fin-set of a great white would cost around $1,000. Similar to rhino horns and elephant tusks, there is an increasing demand of great white teeth and jaws. This demand has had negative impact on white shark population.
A classic example of white shark population decline can be seen in south-east Australia. The rate of fishing since 1960 has increased to ten-fold in these areas. The demand of shark fin and teeth has increased fishing. Over fishing has left the great white shark to decline at drastic levels.
Thus, great white sharks are on the verge of being extinct and stringent rules need to be implied. Great white shark are at the top of the pyramid in deep sea ecosystem. The decrease in the species could have significant impacts on the natural ecosystem.
References
Gottfried, Fordyce, R. E. (2001). "An associated specimen of Carcharodon angustidens (Chondrichthyes, Lamnidae) from the Late Oligocene of New Zealand, with comments on Carcharodon interrelationships". Journal of Vertebrate Paleontology 21 (4): 730–739.
Taylor, Leighton R. (1993). Sharks of Hawaii: Their Biology and Cultural Significance. University of Hawaii Press. p. 65.
Martin, R. Aidan. (2013)m "Pacific Sleeper Shark". Reef Quest Centre for Shark Research. Biology of Sharks and Rays.
Ellis,Richard and John E. McCosker. 1995. Great White Shark. Stanford University Press,
Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats.
"The physiology of the ampullae of Lorenzini in sharks". Biology Dept., Davidson College. Biology @ Davidson.
Government of Australia Department of Sustainability, Environment, Water, Population and Communities (2013).Recovery Plan for the White Shark (Carcharodon carcharias) (Report).
Mollet, H. F. (2008) White Shark Summary Carcharodon carcharias (Linnaeus, 1758). Home Page of Henry F. Mollet, Research Affiliate, Moss Landing Marine Laboratories.
