The Great White Shark is considered to be the largest predatory fish in the world. It has an amazing ability to adapt, which gives it significant advantages when it comes to feeding. Despite his imposing presence, he is much more to be feared in our imagination than in reality, since his image as a ferocious killing machine is not such. Find out all the White Shark Information here.
Great White Shark Information
The white shark belongs to that class of aquatic vertebrates called chondrichthyes (Chondrichthyes, from the Greek khóndros, "cartilage" and ikhthýs, "fish") or cartilaginous fish, whose skeleton is made up of cartilage instead of bone. It inhabits the warm and temperate waters of most of the oceans. This species is the only one of the Carcharodon genus that has survived to this day, and at a global level it is classified as Vulnerable according to the International Union for Conservation of Nature (IUCN) and in Mexico it is estimated as Threatened.
Taxonomy
Carcharodon Carcharias was the scientific identification with which it was initially cataloged by Carlos Linnaeus in 1758. It was in 1833 when Andrew Smith gave it the generic name Carcharodon, and in 1873 said name was equated with that denoted by Linnaeus and as it is scientifically called in the Currently, Carcharodon carcharias. The word Carcharodon comes from the Greek words karcharías, 'sharp' or 'toothed', and odous, which means 'tooth'.
The great white shark is also part of the Chondrichthyes class, which is one of the oldest vertebrate races dating back more than four hundred million years. Sharks, in particular, are part of the approximately 45% of known varieties of Elasmobranchii, which include numerous mid-level and higher oceanic carnivores.
Ancestry and Fossil Record
The great white shark dates back to Miocene times, where its oldest fossils are from approximately sixteen million years ago. However, the evolutionary development of the great white shark remains controversial. As part of the original theory about the origins of the white shark, it is pointed out that it had a common ancestor with a prehistoric shark, similar to the megalodon.
The similarities between the fossil remains and the large size of both led many scientists to consider that these species were closely related, the latter being assigned the name Carcharodon megalodon. However, a new conjecture assumes that C. megalodon and the white shark are distant relatives (also sharing the family Lamnidae).
The great white shark is also much more closely linked to an ancient variety of shark, the mako shark, than it is to C. megalodon, a thesis that appears to be supported by the finding of an intact set of jaws with 222 teeth and all 45 vertebrae. Carcharodon hubbelli in 1988, and which was made public on November 14, 2012. Additionally, recent hypotheses associate C. megalodon to the genus Carcharocles, of which other sharks such as Megalodon are also part. Otodus obliquus is the oldest representative of the extinct genus Carcharocles.
Common name
Different names are assigned to this species depending on the areas where it is distributed. In Spanish, it is usually known as white shark and great white shark (the latter taken from how they are called in English, great white shark). The "white" is due to the fact that certain old specimens, with the advance of the years, have clarified the blackish tone of their backs to become a light gray, which together with the whitishness of the belly makes them look like whites. And given their nature as sharks, they continue to grow throughout their lives, and the older they get, the bigger; hence the "great white."
In Spain, since the Middle Ages, it has traditionally been called jaquetón (increasing check, threat), a name that, together with different adjectives, is also given to numerous other varieties of the Carcharhinidae family. The name white shark is also known, coming from the union between the previous name and the white shark, which is more popular today. The name mako, as it is sometimes referred to, can lead to confusion with other varieties of sharks.
Evolution
It is considered that the great white shark emerged on the planet during the Miocene, conforming to the oldest fossil found with about 16 million years. According to biologists, its ancestor is Carcharodon megalodon, a colossal shark. prehistoric. However, other researchers estimate that, despite the undeniable belonging of the two to the order of the Lamniformes, the white shark is certainly more closely related to the mako, of the genus Isurus.
According to paleontologists Shelton Applegate, Maisey John, Robert Purdy, and biologist Leonard Compagno, the megalodon and the great white shark come from the Cretolamna carcharodon, and therefore must be considered as members of both the same genus, Carcharodon, and the same family, Lamnidae. Henri Cappetta, John Long, Mikael Siverson, and David Ward, on their side, determined that the great white shark comes from a different lineage than Megalodon, which in turn comes from Cretolamna and Otodus, two prehistoric sharks that have now disappeared.
There are also scholars who think that it descends from Carcharodon orientalis, which is considered to be part of a missing link in evolution. The similarity between the teeth of the megalodon and the great white shark shows the evolutionary confluence between the two, but not a direct genetic link. However, researchers today still dispute the exact origin of the great white shark. Fossil residues of Carcharodon have been obtained on the coasts of southeastern Argentina (Miramar, Mar del Sud) thanks to the collaboration of tourists and sport fishermen.
General Characteristics
White sharks are recognized by their elongated and very stocky body, unlike the flattened figures that other sharks usually present. The nose is like a cone, short and bulging. The mouth, large and round, similar to an arch. It keeps it constantly ajar, allowing at least one line of teeth from the upper jaw and one or two from the lower jaw to be seen, while water enters it and constantly emerges through the gills.
If this flow were to stop, the shark would drown since it lacks opercula to regulate the correct passage of water, and it would go to the bottom of the sea, since not having a swim bladder it is forced to be in constant movement to avoid let this happen. At the time of attack, the jaws open in such a way that the shape of the head is disfigured by projecting the jaw, and then close with a force that exceeds 300 times that of a man's jaw (12-24 tons) .
The teeth are huge, with saws, in the form of triangles and very wide. In contrast to other sharks, there is no separation between its teeth or reduction of any of them, but its entire jaw is equipped with aligned teeth and also with the ability to grab, cut and tear. On the back of the two main lines of teeth, white sharks have two or three more constantly growing that replace the continuous loss of teeth with new ones and are replaced by new lines over the years.
The seat of the tooth does not have a root and is bifurcated, giving it an unmistakable appearance similar to an arrowhead. The nostrils (nostrils) are not very wide, while the eyes are small, circular and totally black. On its sides there are five gill openings, two well-developed pectoral fins in the shape of a triangle and another pair, close to the caudal fin, much smaller.
The caudal is highly developed, as well as the large dorsal fin on its back, distinctive for those who observe it. Another pair of small fins (second dorsal and anal) near the tail complete the physique of this animal. Despite its name, the silky shark is only white on its underside, while the back is gray or bluish.
This pattern, common in numerous marine animals, is useful for blending in with sunlight (when viewed from below) or with the gloomy sea waters (if viewed from above), forming a camouflage that is as simple as it is effective. The tip of the ventral part of the scapular fins and the area of the axils are shown stained black. The skin, very rough, is composed of rigid scales called dermal denticles due to their pointed shape.
However, the name "white shark" could make sense in the case of seeing albino specimens of this variety, which, despite being very rare, exist. In 1996, it was possible to fish off the coast of the Eastern Cape (South Africa) a juvenile female of only 145 centimeters that presented this curious characteristic.
Senses
The nerve receptors of the front end, referred to above, perceive even the slightest vibration that occurs in the water and lead the animal to the probable prey that is causing said disturbance. Other endings (known as ampullae of Lorenzini, specialized cells that look like tiny "bottles") located around the nostrils enable it to detect electrical fields of varying frequency, which it may use to guide its long-distance migrations.
In addition to all of the above, his sense of smell is so powerful that he can detect the existence of a couple of blood molecules among a million water molecules from kilometers away, which attracts his attention while becoming much more violent. Additionally, they have the ability to differentiate between the different concentrations in which a specific odor particle can be obtained, which enables them to better orient themselves towards the food.
Species with a keen sense of smell generally possess abundant loci or loci for OF olfactory receptor genes. Thanks to its great ability to recognize odors, that was what was expected when its genome was sequenced, however, that was not what happened. Given the above, it has been suggested that instead of what is indicated, they have highly preserved sequences (of positive selection by evolution) or enriched, of genes linked to the detection of odors, or that there is a family of optional genes that play a important role in this function.
The vomeronasal organ is an olfactory receiving structure that assists the sense of smell found in certain vertebrates. By sequencing the DNA of the white shark, it has been determined that they have 14 genes for the vomeronasal receptor, which complies with the thesis of gene enrichment, which indicates a greater regularization of the process. Additionally, a preserved gene sequence has been achieved whose purpose would be to compensate for the few sequences of the OF gene.
The Bbs5 protein is a molecule linked to the structure of the cell Cilio. Imperfections in this protein have been reported in Bardet-Biedl Syndrome which, among other things, can cause insufficiencies in odor recognition or anosmia. In the great white shark it has been observed that the sequence of the aforementioned protein is highly conserved, and could be constituted as another tactic for the development of a penetrating odor detection.
The sense of sight is also well developed and plays a very important role at the time of the final approach to the prey and its particular pattern of stalking and attacking below it. The Great White Shark's vision is entirely green, with their eyes looking sideways, and they cannot see straight ahead like humans.
Size
The length that adult white sharks most frequently have is between 5 and 7,5 meters (where females are larger than males), despite the fact that cases have been reported of exceptional specimens that greatly exceeded these measurements. Today it is not possible to say what the largest size of this species is, which has been reinforced by the existence of old and unreliable documents about truly colossal animals. Some of these cases are studied in the book The Great White Shark (1991), by Richard Ellis and John E. McCosker, both of great experience in sharks.
For decades, numerous reference texts in the discipline of ichthyology, as well as the Guinness Book of World Records, listed two great white sharks as the largest ever caught. One of which was a 9 meter specimen allegedly caught in the waters off South Australia, near Port Fairy, in the 1870s and the other was an 11,3 meter individual that was caught in a herring net. in New Brunswick, Canada in the 1930s.
Taking these maximum lengths as references, observations of white sharks of 7 to 10 meters in length were considered frequent to a certain extent and admitted without much controversy. However, several scholars doubted the reliability of the Port Fairy report, noting the huge difference in size between this specimen and any of the other white sharks caught.
A century after its capture, the jaws of the animal, still preserved, were analyzed, and it was determined that its genuine body size was about 6 meters long. The confusion could have been the result of a typographical error, a mistake due to the change from Anglo-Saxon units to international ones (6 meters is about 20.5 feet), or a mere exaggeration. In relation to the specimen from New Brunswick, connoisseurs today consider that it must have been a basking shark (Cetorhinus maximus), a variety with a body similar to that of the great white shark and that is frequent in Canadian waters.
Returning with Ellis and McCosker, they stated in their book that the largest white sharks are about 6 meters in length, and that reports of specimens of 7 meters or more, although predominant in the popular literature, do not exist in the scientific. They ironically highlight the fact that, like the supposedly colossal anacondas and pythons, "these enormous [sharks] usually disappear when approached by a sensible observer with a tape measure."
The greatest length that Ellis and McCosker estimate to be certain is that of a 64-meter white shark caught in Cuban waters in 1945, despite the fact that it has been pointed out by other scholars that its size was surely somewhat smaller. The weight attributed (but not confirmed) to this specimen was 3.270 kilograms. Since then, news of greater white sharks have been reported, however Ellis and McCosker warn that the measurements are frequently deficient and, once corroborated, their results are usually between 6,1 and 6,4 meters.
For example, a large number of publications report a 7-meter female great white shark caught by Alfredo Cutajar off the island of Malta in 1987. In their text, Ellis and McCosker admit that this specimen was apparently above average size, but they do not estimate as true the length of 7,3 meters. In the following years, other specialists have also found reasons to suspect this data, due to the discrepancy between Cutajar and other witnesses when referring to the measurements.
Finally, a BBC photographic technician determined, taking into account the mistake that perspective can lead to in photographing the animal, that the true size of the specimen would be around 5,6 meters. By April 2014 officials of the Australian Ministry of Fisheries managed to catch and tag a huge female white shark of about 30 years of age whose measurements were 5,3 meters in length and weighing 1,6 tons. This capture took place in the vicinity of Mistaken Island, 400 kilometers from Perth.
By August 2015, a colossal female was recorded that became known as Deep Blue on Guadalupe Island in the Mexican Pacific, which exceeded six meters long (20 feet) and was estimated to be approximately 50 years old. Today, most experts agree that the largest white shark can reach is approximately 6 meters in length and about 1,9 tons in weight.
Reports of sizes even larger than this are usually considered dubious, and according to the Canadian Shark Research Center, the largest properly measured great white shark was a female caught in August 1988 off the island. of Prince Edward, which reached 6.1 meters. The shark was caught by David McKendrick, a local from Alberton, West Prince. McKendrick and a man named David Livingstone preserve the first and second largest teeth of said shark.
Regarding the weight, a new inconvenience is added, since it can fluctuate slightly according to what the shark has eaten and how recently it has eaten. An adult animal can put up to 14 kilograms of meat in its mouth with a single bite, and accumulate some more in its stomach until it finishes digesting them. For this reason, Ellis and McConker estimate it likely that white sharks can achieve weights of up to 2 tons, despite the fact that the largest of those they have analyzed weighed "only" 1,75 tons.
The heaviest white shark ever recognized by the International Game Fishing Association (IGFA) is a 1.208-kilogram specimen caught by Alf Dean in 1959 off South Australia. Many other older individuals have been known, but the IGFA does not recognize them for having been caught without due respect for the rules required by this organization.
Distribution
The white shark inhabits the areas of the continental shelf, close to the coast, where the water is shallower. In these areas, the abundant light and the profusion of sea currents cause a greater number of animals to concentrate, which for this creature means a greater influx of food. However, they are absent from the frigid Arctic and Antarctic oceans, despite their enormous wealth of plankton, fish and marine mammals.
White sharks have an advanced metabolism that allows them to stay warmer than the water that surrounds them, but not enough to inhabit these extreme regions. These metabolic traits allow them to occupy the most superficial sectors of salt water, but also to submerge up to 1.000 meters deep, in which, added to the high pressure and lack of nutrients, the low temperature plays an essential role in the exclusion of species, thus being able to invade an alternate thermal niche.
Regions with a regular presence of white sharks are the waters of the Lesser Antilles, certain areas of the Greater Antilles, the Gulf of Mexico to Florida and Cuba, and the East Coast of the United States from there to Newfoundland; the coastal strip from Rio Grande do Sul to Patagonia, the North American Pacific (from Baja California to southern Alaska, where they arrive in irregularly warm years) and the South (from Panama to Chile); Pacific archipelagos such as Hawaii, Fiji and New Caledonia.
They are also frequent in Australia (excluding its north coast, abounding in the rest), Tasmania and New Zealand, being very common in the Great Barrier Reef area; northern Philippines and the entire Asian coast from Hainan to Japan and the island of Sakhalin; Seychelles, Maldives, South Africa (where it is very profuse) and the areas near the delta of the Congo and Volta rivers; and the coastal area from Senegal to England, with appreciable groups in the Cape Verde Islands and the Canary Islands, also entering the Mediterranean and Red Seas.
However, in the Mediterranean Sea, due to overfishing, the virtual disappearance of the monk seal in the western Mediterranean and water pollution, the distribution of this specimen has decreased considerably. In any case, it seems that a certain breeding area is maintained, such as the Strait of Messina or the Turkish coast of the Aegean Sea.
Therefore, the way in which it is distributed coincides with the migratory path of bluefin tuna and swordfish, the existence of monk seal or sea turtle territories, as well as the availability of shallow waters near the coast, there that the typical tuna trap regions are linked to the historical presence of the white shark.
Based on this, there are appropriate areas for a probable sighting, in the central Mediterranean region (primarily in the Sea of Sicily, the Gulf of Trieste and the Istrian peninsula), in the north of the western region (essentially in the Ligurian Sea , Gulf of León and Strait of Bonifacio) as well as in the Aegean Sea; to a lesser extent, in the Tyrrhenian Sea (around Naples), southwestern Sardinia, the rest of the Adriatic Sea, the Cyclades, the Thracian coast or the Bosphorus Strait.
In relation to the coast of Spain, historically it has also been common, in the Spanish Levant (Gulf of Valencia, in Castellón, an individual caught in 1962 and recorded by Asensi in 1977, Columbretes Islands, with a capture that was documented in 1878, or Vinaroz, in Alicante, particularly on the island of Tabarca with captures recorded in 1879, 1887 and 1946 according to the Alicante municipal archive, and the Mar Menor coast), the Balearic Islands (in Mallorca in the Tramuntana, Ses Salines cape, Cabrera and Cabo d'es Pinar, in Menorca its northern region, and in the Pitiusas Islands in the area of Es Freus).
As well as in the north of Catalonia, within the area of influence of the Gulf of León, specifically one specimen ended up stranded on the Mar Menuda beach in Tossa de Mar in 1992, as well as another specimen trapped in 1912 in Vilasar de Mar and whose teeth They were donated to the Zoology Museum of Barcelona, and finally in Andalusia, primarily in the Bay of Almería and in the Strait of Gibraltar, particularly on the coast of Cádiz and specifically Barbate.
In the Mediterranean, the date on which the bluefin tuna begins to migrate coincides with the entry of adult tuna between spring and summer, coming from the northwestern coast of the United States, and with their exit from the Mediterranean in autumn. The movements of young people gather in the western Mediterranean and the Adriatic Sea, centralizing the breeding area in the Balearic Islands and in the Tyrrhenian Sea.
In relation to Spain, as of 2011 the white shark is a species under protection, according to Royal Decree 139/2011, which means that this variety is returning to the Spanish coasts, with sightings on the coast of the southeastern peninsula, in particular on the coast of Cabo de Gata, in Almería, in the Columbretes Islands, Castellón, and in Cabo de Formentor, in Mallorca. Similarly, in recent years remains of tuna, dolphins and sea turtles with white shark bites have been found, which corroborates their reestablishment in the Spanish Mediterranean.
Sometimes, this species can also reach the waters of Indonesia, Malaysia, the Sea of Okhotsk. It regularly stays at a relative distance from the coastline, only approaching those areas with a particular concentration of tuna, seals, penguins or other coastal animals. Also, it usually stays close to the surface, although it eventually goes down to about a kilometer deep.
In a recent investigation, it was shown that the great white sharks of California migrate to a region between Baja California and Hawaii which is called "the Café of the White Shark", in which they spend at least a hundred days a year before to return to Baja California. During the crossing, they swim slowly and dive to a depth of about 900 meters. After their return, they modify their behavior and make short dives to about 300 meters for about 10 minutes. Another tagged specimen from the coast of South Africa reached the coast of South Australia and returned within a year.
This refuted the traditional theses that indicated that white sharks are coastal territorial predators and leaves open the possibility that there is an interaction between groups of white sharks that were previously considered as independent. The reason for their migration is still unknown, attributing it to seasonal feeding or the availability of mating areas. In similar research, a South African great white shark was tracked swimming to the northwest coast of Australia and back to the same location in South Africa, a journey of 20.000 kilometers, in just under nine months.
Food
White sharks are extremely different from simple "killing machines", which is the popular representation that they have and has become a legend. In order to catch the huge marine mammals that make up the feeding base of adults, white sharks carry out their typical ambush. They are located a few meters below the prey, which swims on the surface or close to it, showing the dark color of its back to blend in with the background and thus become invisible to its victims.
When the moment to attack arrives, they move at high speed upwards with powerful movements of the tail and their jaws open. The impact is felt by the victim in its belly, to which the shark clings tightly: if it is modest prey like a sea lion, it kills it immediately and then swallows it whole. If its size is larger, it tears off a large piece of it that it swallows completely, since its teeth do not allow it to chew.
The prey may then be dead or dying, and the shark will return to feed on it, tearing off one piece after another. Stimulated by the appearance of blood, the area is soon filled with other sharks. In certain regions of the Pacific, white sharks charge seals and sea lions so powerfully that they rise a couple of meters above the water level with their prey in their jaws, before diving back down.
The diet of the white shark in the Mediterranean Sea is based primarily on bluefin tuna, emperors, sea turtles, cetaceans and the monk seal, the latter being almost extinct from the western Mediterranean. Indeed, in Spain, its annihilation took place at the same time as tourism development. At the beginning of the XNUMXth century, it was not feasible to offer sun and beach tourism while simultaneously protecting the monk seal and controlling the number of white sharks.
White shark attacks on humans in the Mediterranean today are extremely rare, and distant from the coast and at certain depths, not happening years ago. Most of the attacks take place at dawn or dusk, since both times are when the depths cannot be seen adequately. The surface is barely visible, since the sun's rays at that time are still weak to reach the depths, which gives the shark an advantage to attack its prey without being noticed.
This species also feeds on carrion, particularly that which comes from drifting whale carcasses, from which they extract huge pieces. Close to shore, white sharks mistakenly swallow large numbers of floating objects. Even car license plates have even been found in their stomachs. As well as at hunting time, the rest of his life the great white shark is usually alone. Sometimes pairs or small groups are seen moving in search of food, a task that leads them to travel hundreds of kilometers.
Although mainly nomadic, certain specimens choose to feed in certain coastal areas, as is the case in certain regions of California, South Africa and particularly Australia. Young white sharks primarily feed on fish such as rays and other sharks, but as adults they eat marine mammals such as seals, sea lions and sea lions, mainly on Californian coasts, but in areas where there are no pinnipeds they catch dolphins, porpoises and occasionally beaked whales.
They charge their prey from behind, above or below to prevent being located by their echolocation, eventually attacking other cetaceans such as pygmy sperm whales and pilot whales. They also hunt penguins, sea turtles and sea otters have been found with shark bites in California.
Natural Enemies
For white sharks, the killer whale can be a threat. On October 4, 1997, in the waters surrounding the Farallon Islands, a 6,50-meter female killer whale, known to scientists as Ca2, carried out an attack on a great white shark, in which the shark perished. The true size of that specimen is actually unknown since it was completely destroyed, yet some experts conjecture that it was a young shark.
Contrary to what many people believe, adult great white sharks do not suffer attacks from killer whales, which go primarily for young individuals because they are easier to capture. It is estimated that the attack occurred due to rivalry for prey since the two species have the same eating habits, in such a way that the sharks were relegated by the killer whales to areas where there are no more of these cetaceans.
One region where the two species overlap is the entire Californian coastline, but there is also rivalry in the western Pacific, probably in Japan where both species are abundant, the southwestern Atlantic, parts of Australia and the Mediterranean, and also in offshore waters. from New Zealand. In addition to killer whales, young specimens can be preyed upon by tiger sharks, bull sharks and saltwater crocodiles off the Australian coast, since cannibalism is not uncommon for this species.
Reproduction
Although there are only a few cases of trapped gravid females, it can be confirmed that this species prefers to reproduce in warm waters, in spring or summer, and is ovoviviparous. It has a slow reproductive cycle with embryos called oophages: the eggs have to remain from 4 to 10 or perhaps up to 14 weeks in the uterus until hatching.
Then intrauterine cannibalism or Oophagia takes place (the brothers with greater force devour the most fragile offspring and the eggs not yet opened) as occurs with other species of lamnids. It is believed that the gestation process of these animals lasts a year. Three to four offspring, 12 decimeters long and with serrated teeth, reach the outside during childbirth and immediately distance themselves from their mother to prevent her from devouring them. From then on they live a solitary existence, developing at an extremely rapid pace.
They reach two meters in length in their first year of life. The males, although smaller than the females, reach sexual maturity before the latter when they reach a length of 3.8 meters (at four years), despite the fact that according to Compagno (1984), certain specimens could mature exceptionally when they are still barely two and a half meters tall. They are differentiated by extensions of the pelvic fins that function as copulatory organs.
The females do not have the capacity to reproduce until they are 4,5 to 5 meters long and it is estimated that they are fertile for a short period of time, which causes their reproductive rate to be small. Much is unknown about the intraspecific linkages that occur in this species, and what has to do with mating is no exception.
It is likely that this occurs more frequently after several specimens share a large feast, such as a whale carcass. The average lifespan of these animals is not exactly known, but it may vary from 15 to 30 years. In January 2014, a group of scholars from the Woods Holle Oceanographic Institution on Cape Cod, Massachusetts, led by Dr. Li Ling Hamady, revealed a study based on carbon 14 dating of the vertebrae of different specimens (4 males and 4 females) from the Northwest Atlantic in the scientific publication PLOS ONE.
In the aforementioned investigation, it was concluded that the life expectancy of the white shark exceeded 70 years, three times higher than what was previously calculated, since the oldest specimen, a male, was 73 years old, meanwhile that the most mature female was about 40 years old.
Danger of extinction
Due to the vast range of distribution of this animal, it is not possible to know the number of white sharks that exist, although it is a mere approximation. However, its low population concentration, coupled with its low reproductive rate, its long infancy and its low life expectancy mean that the white shark is not necessarily an abundant animal.
The sport fishing of this species, without economic interest involved, has intensified in the last three decades due, to a large extent, to the popularity of films such as Jaws (Steven Spielberg, 1975) so much so that it is classified as threatened. or endangered in various places. The IUCN Red List included the white shark for the first time in 1990 as a species not fully known, and as of 1996 it is classified as vulnerable. Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) refers to it as a vulnerable species if it is not exploited rationally.
The measures for its preservation must be applied in a compulsory way on the populations in the wild, since the breeding in captivity of the white shark is not possible, possibly due to the nomadic nature of the species (data have been collected from specimens visiting alternative beaches in South Africa and Australia, 22.000 kilometers away). The only creature that could be exhibited alive in a building was a young female named Sandy, who came to live for only three days in August 1980 at the Steinhart Aquarium in San Francisco.
After just 72 hours in captivity, Sandy had to be released after she stopped feeding and caused severe injuries by repeatedly crashing into one of the walls of her aquarium. A posteriori it was discovered that what caused the attraction of Sandy to that particular place was a tiny difference of 125 microvolts (millionths of a volt) of electrical potential between that wall and the other walls of the aquarium.
The magnitude of the electric field that Sandy recognized was so minute that it could not be perceived by any of the other animals in the same water tank, including different sharks of other species. To date there is no international legal extension on white shark fishing, despite the fact that it is prohibited in certain areas of its distribution.
The great white shark is a protected species in California, the East Coast of the United States, the Gulf of Mexico, Namibia, South Africa, the Maldives, Israel, and parts of Australia (South Australia, New South Wales, Tasmania, and Queensland). The Barcelona Convention classifies it as a threatened species in the Mediterranean, but almost no nation with access to this sea has established any measure for its preservation.
Genome and Cancer
The shark genome has a number of chromosomes 2N=82, with a total length of 3,92 Gpb and 24.500 predicted genes. 58% of the sequences make up repetition sequences. It has similar dimensions compared to other vertebrates, such as humans, with a genome of 3,2 Gpb and 20.000 genes listed, although organized in a chromosome number of 2N=23 and with a lower number of repeated sequences.
In the shark genome, about 3 million SNPs or variants of a single nucleotide were considered, which, compared to the human being, which can have up to 5 million SNPs, makes up a more or less small number. This may be due to the strong genomic consistency that identifies the white shark. There are specific reports about the ability of Elasmobranchs to prevent the development of tumors in their cells.
However, it is an unsubstantiated fact due to the lack of systematic studies on the matter. One of the main characteristics of cancer, which afflicts both the initiation and the development of the tumor, is the lack of genomic stability that malignant cells have. Throughout an organism's lifespan, its genome is threatened by exogenous, endogenous, and cellular processes that can cause DNA damage, thereby compromising genome integrity.
The consequence of this group of continuous selective pressures has been the development of defense mechanisms to neutralize the detrimental effects of these events and safeguard genetic information. Deficiencies in these mechanisms, in addition to unbalancing genomic sequences, can trigger neurodegenerative diseases and early aging.
Mass sequencing analyzes of DNA samples from various great white shark specimens have shown that, throughout their evolutionary trajectory, various subsets of genes linked to genome stability have been positively chosen. Most of the chosen genes are directly linked to the reaction to DNA damage and its repair.
Second, the positive selection of another subset of genes, linked to protein ubiquitination, has been confirmed. Protein ubiquitination is part of a wide spectrum of processes, such as protein degradation, but there is also ample evidence of the relevance of ubiquitination and deubiquitination in the environment of genome stability.
To the preservation of their sequences in genes linked to repair mechanisms, we must add that, when compared to other vertebrates such as humans, Elasmobranchs have a higher proportion of genes linked to DNA repair, control of apoptosis and the negative control of cell proliferative processes, in which proteins of the wtn and Tp53 signaling pathway are involved, transcendental in the control of the cell cycle. This sequence enrichment indicates the difficult regulation of such processes.
The enrichment and preservation of sequences of histone alterations deserve a separate reference, since they are characteristic of the white shark and have not been recognized to date in any other Elasmobranch. Histones play a fundamental role in genomic packaging. Although less is known, they are an active part of maintaining genomic stability.
Certain histone alterations, such as phosphorylation of H2AX 21 or acetylation of H3K56 22, play an essential role in the reaction to DNA damage. The proteins that carry out such functions, and consequently, these alterations, are enriched and preserved in this organism, facilitating the genomic conservation of the great white shark.
Anecdotally, culture media generated based on the epigonal tissue of Elasmobranchs have been reported with the capacity to display cytotoxic activity against tumor cells of human origin, unleashing programmed cell death or apoptosis in these target cells. Many more analyzes are necessary on the protection of Elasmobranchs in order to protect their low influence against tumor processes, however, these aforementioned data encourage us to continue with this line of research, with the aim of developing probable anticancer treatments in the future.
Skin and Wound Healing
Shark skin is an extraordinary adaptive attribute in the aquatic world for various reasons. It is a very rough skin when compared to other vertebrates, due to the high degree of keratinization of this layer. This constitutes an advantage when producing superficial wounds.
Additionally, the scales that constitute the skin have a tooth shape and are arranged in an overlapping manner, in such a way that they represent a hydrodynamic benefit by reducing the fluidity of the water on its surface, which makes it easier for them to reduce the friction of the organism with the environment. , the consequence of which is a lower energy expenditure and a greater speed at the time of swimming.
The appearance of these scales gives them another adaptive advantage: the development of nanoconformations of ridges and valleys that cause an exaggerated energy expenditure for the bacteria that settle on their surface. The variation in surface tension is such that many bacteria cannot survive in this environment because they cannot cope with the energy expenditure involved, making this system a kind of stupendous immune barrier.
As DNA sequencing methods, processes of positive selection and improvement of genes linked to wound healing have been recognized. The FFG, EXTL-2 and KRT18 gene sets are highly preserved in this species. The FFG gene encodes for the protein Fibrinogen that is involved in the formation of blood clots.
EXTL-2 performs the same process for the exostosin-1 protein, a glycosyl-transferase found in the biosynthesis of heparan sulfate, a key element in the formation of blood vessels. KRT-18 codes for collagen XVIII, a protein from the keratin family that provides mechanical support against the development of wounds in addition to playing an important role in wound healing.
Additionally, other enriched series have been sequenced in relation to the conformation of blood vessels. Angiogenesis is a process by which blood vessels are formed based on an existing vascular network. It forms an essential fact for wound healing processes by providing oxygen and nutrients to the cells that are in this area, in addition to disposing of their waste substances.
For this purpose, there is a series of growth factors produced by the cells of that environment that promote the formation of said blood vessels, becoming the cells of the adjacent endothelial wall that receive such factors, responsible for initiating this process. of conformation.
In the white shark, the series of vascular endothelial growth factors VEGF and its receptor VEGFR-2 have been enriched. Likewise, series that code for FGF (fibroblast growth) and EGFR, which forms a membrane receptor for the epidermal growth factor EGF, have been enriched.
Relationship with Humans
The interaction of the white shark with humans is long-standing, not only in relation to when it has been a victim of fishing but also when humans have been prey to their attacks not only on the same people but also on their boats. Likewise, and despite not being entirely true, we have represented it at the media level as an extremely aggressive creature that stops at nothing.
Attacks against Humans
Although it is not easy to believe due to the persistent urban legend against it, shark attacks on people are extremely rare. As part of them, those of the white shark can be considered anecdotal when compared to those of the tiger shark (Galeocerdo cuvier) or the bull shark (Carcharhinus leucas), the latter being a species that can even go up large rivers (Mississippi, Amazon, Zambezi, etc.) and attack people a few kilometers from the sea.
However, the deaths caused by these three varieties of shark together are less than those caused by sea snakes and crocodiles throughout a year, and even less than the deaths attributed to apparently harmless animals such as bees, wasps and hippos It is estimated that you are more likely to perish from a heart attack on the high seas than from a shark attack.
As biologist Douglas Long put it, in the United States (where a significant concentration of silky sharks reside on the West Coast) "many more people die each year from dog attacks than have died from great white sharks in the last century." In those areas where the presence of the great white is not so profuse, the attacks show truly derisory numbers: for example, in the entire Mediterranean only 31 shark attacks against people have been confirmed in the last two centuries, in its greatest number. part without fatal consequences.
In Spain, the number is four attacks since the second part of the 314th century (despite the fact that the ISAF International File of Shark Attacks only recognizes two as amply proven) without any of them being fatal. For these last two cases, such figures do not even refer to white shark attacks specifically, but to all varieties of sharks as a whole. ISAF itself calculates a total of 1580 white shark attacks globally, from XNUMX to the present day.
According to some American scientists, the number of white shark attacks worldwide between 1926 and 1991 would be 115, with California, Australia and South Africa being the places with the highest records. It is highly illustrative that in South African waters, plagued by sharks, the number of white shark attacks since 1940 is only 29, in contrast to the 89 attacks perpetrated by bull sharks. In California, it is estimated that there is about one fatality due to a white shark attack every five years.
This lack of particularly deadly attacks is due to the fact that most sharks in general and whites in particular do not have humans as genuine potential prey. Indeed, it is probable that the taste of human meat is even somewhat repugnant to them, and of course it is much less nutritious and more difficult to digest than that of whale or seal, endowed with a large amount of fat.
A large part of the white shark's attacks are based on a single bite, after which the animal moves away, seldom taking a piece of the unfortunate victim (mainly feet and legs). These attacks can be due to three possible reasons:
- The shark does not attack the victim with the intention of eating it, but because it considers it as an intruder in its daily actions, whom it deduces as a potential threat. Therefore, the bite and subsequent withdrawal would be nothing more than a simple although exaggerated «warning».
- The animal is confused by something it has never seen before and does not know if it can be eaten or not. Therefore, the brief lunge is a kind of "bite-test" with which he tries to recognize if it is convenient for him to feed on this new component of his world in the future. The probable unpleasant taste and subsequent digestive disorders will prevent the shark from hunting humans after this experience.
- The shark could mistake the victim for its normal food. The above would explain a large part of the attacks against bathers and surfers in California, for example, since when seen from below they would be quite similar to a sea lion that emerges to breathe air or that moves very quickly near the surface of the water. . The reported attacks against modest fishing and pleasure boats could be explained as the shark mistaking them for the bodies of medium-sized cetaceans or drifting carcasses of elephant seals.
Due to the nature of the attack, the person who is the victim perishes very rarely during the attack. When this happens, most of the time it is due to massive blood loss, which must be prevented as soon as possible. When blood is released into the water, other sharks and carnivorous fish of various species may also be attracted and may be provoked into making their own "test bites", much to the victim's misfortune.
Given the above, the risk of attack will always exist, however remote it may seem. It is interesting that 80% of the deaths caused by white sharks took place in very warm waters, almost equatorial, when most of these animals live in temperate zones. This may possibly be due to the fact that a large proportion of white sharks are young and pups, which require warm waters for their development, while in warmer areas only larger and older individuals venture, which show greater violence and danger.
Various methods have been designed and tested to prevent white shark bite wounds in the event of a sudden attack, including chemical repellents, metal mesh armor that overlaps diving suits, and equipment that produces an electric field around the diver or surfer to disorient any shark that approaches, since they alter the information they receive through their ampullae of Lorenzini that serve to capture electrical variations.
However, and no matter how effective these methods may be, it is obvious that the best thing to do when it comes to preventing attacks is not to incur in recklessness such as staying far from the coast, swimming alone or in the first and last hours of the day, swimming in areas with a high profusion of pinnipeds (the staple food of adult white sharks) or, obviously, intentionally approaching a specimen, particularly if it is large.
While diving in the vicinity of the Cape Verde Islands, the oceanographer Jacques-Yves Cousteau and his companion accidentally came across a huge white shark. "[Her] response from him was the least we could have imagined," Cousteau notes. Terrified, the monster expelled a cloud of excrement and moved away with incredible speed. He concluded as follows: "In reflecting on all the experiences we have experienced with the white shark, I have always been drawn to the great chasm that exists between what the public figures and what we confirm that it really is."
Ship Attacks
Great white sharks rarely charge, although sometimes they even sink ships. Only five of the 108 shark attacks, without apparent provocation, that were reported on the Pacific coast throughout the 10th century, have been on people who were kayaking. In certain cases they have rammed boats of up to 33 meters ( 1936 feet) long. They have collided or knocked people overboard, even though they usually attack the ship from the stern. There was a case, in XNUMX, of a large shark attacking the fishing boat Lucky Jim off the South African coast, knocking one of the sailors out to sea.
The White Shark in Fiction
White sharks are presented as the embodiment of danger in certain cultures and are given the name "man-eaters" in different languages, particularly in the Caribbean region. However, the current popular representation of the great white shark as the exterminator of the sea par excellence would not make sense (or would not be so widespread) were it not for the commercial success of the film Jaws in 1975.
The film was based on the 1974 novel of the same name by American author Peter Benchley, which loosely referred to a historical event: the deaths of four people and the amputations of others that occurred during the wave of New York shark attacks. Jersey of 1916. However, it is now considered more likely that those who caused these attacks were several sharks and not the product of a specific serial killer.
Apparently it is also not clear that the shark (or sharks) was white, indicating the species Carcharhinus plumbeus and Carcharhinus leucas as probable culprits. This film caused great psychosis around the white shark.
In the film, certain references were added in the mouth of Captain Quint to the misfortune of the USS Indianapolis, a ship that was sunk in 1945 in the Pacific after being hit by a Japanese torpedo, and whose survivors had to remain in the water for five days in the meantime. They were punished by the heat, the lack of water and the attacks of the sharks, which on this occasion were not identified as white sharks, but as the Carcharhinus longimanus species.
The book and later the film implanted a series of clichés that since then have been reiterated in the cinema of "killer monsters", both of land and water, and that on numerous occasions do not match the real attributes of the primordial species. harmed, the white shark. This has served to establish a series of notions and inaccurate beliefs around this species, which Benchley himself, who wrote the novel, has assured that he would never have written if he had known what the habits of white sharks were really like.
Jaws was a resounding commercial success, so much so that it became the first film to exceed 100 million dollars at the box office, replacing The Godfather (The Godfather 1972) as the film that had collected the most money in history. This position was not taken from him until the debut of Star Wars (1977) and his shock on the public was of such magnitude that cases of aquaphobia and fear of sharks increased throughout the planet.
The level of tourist flow to the beaches was even reduced during a good season. On the other hand, some people began to fish intensively for white sharks, eager to emulate Martin Brody and Captain Quint, which caused a considerable drop in the populations of this creature. The legend of Tiburón was eternalized in the media, and its influence can be seen in television series, comic strips and even video games such as Tomb Raider or Jaws: Unleashed.
A large number of other films reiterated the formula that led to the success of its predecessor, among which we have the following:
- Jaws 2 (Jaws 2, 1978): An unknown colossal white shark meets Martin Brody again in his native town.
- The Last Shark (1981): resounding Italian copy of Jaws, with a story almost identical to it. It was distributed in Spain under the false name of Shark 3.
- Jaws 3 (also known as Jaws 3-D, El Gran Tiburón, Jaws 3-D): was the forerunner in using 3-D technology, reproducing the attack of a colossal mother shark on a Florida water park in which it has her offspring has been locked up (a case that would never happen in reality). The main character is Brody's oldest son.
- Jaws, La Venganza (Jaws: The Revenge, 1987): after actor Roy Scheider refused to play the character of Martin Brody again (he already had to do it in Jaws 2 unwillingly and forced by the contract), he was "killed » with a heart attack and the leading role was transferred to his widow, who was also harassed by a great white shark.
- Shark Attack (1999): television production that reproduces a succession of attacks in a village in Africa.
- Shark Attack 2 (2001) - Continuation of Shark Attack.
- 12 Days Of Terror (2004): recounts the 12 days during which the inhabitants of the New Jersey coast were under constant attack by a great white shark.
The new animated films "Finding Nemo" (Finding Nemo, 2003) and "The Shark Tale" (Shark Tale, 2004) incorporate comic characters represented by great white sharks. In the first, Bruce the shark (obvious allusion to the mechanical shark from Jaws) is a vegetarian and attends a reunion class for ex-carnivores in which he seeks to get rid of his addiction to eating animals, but suffers a relapse when he perceives the smell of blood in the water.
In the second film, the sharks are a class of gangsters from the oceans headed by their particular White Godfather, Don Lino, with whom the main fish, Óscar, is confronted. This, in turn, has the help of the shark Lenny, son of Don Lino and also a vegetarian. Although obviously based on Jaws, other films have been made with a similar plot but replacing the white shark with other varieties of sharks (tiger sharks, bull sharks or mako sharks, as in the film Deep Blue Sea) or other marine creatures (orcas, barracudas, etc.) or rivers (piranhas or crocodiles) to enchant the public.
The Dreaded White Shark and its Surprising Diet
Initial study of the feeding of great white sharks off the eastern seaboard of Australia found that this feared predator spends more time eating deep below the seafloor than previously expected.
“In the stomachs of sharks we find remnants of a diversity of marine species that usually live on the ocean floor or are buried in the sand. This tells us that sharks certainly spend a good deal of their time eating just above the seafloor," said lead author Richard Grainger, a doctoral candidate in the School of Life and Environmental Sciences at the University of from Sydney.
"The image of a shark's dorsal fin breaking the surface of the sea while hunting may not be a very accurate representation," he noted. The research, published on World Oceans Day in the journal Frontiers in Marine Science, is an important contribution to understanding the feeding and migratory habits of sharks.
Dr Vic Peddemors, who co-wrote the study and is part of the NSW Department of Primary Industries (Fisheries), explained: 'We found that although midwater fish, particularly salmon from eastern Australia, They were the preponderant prey for young white sharks, the contents of their stomachs have revealed that these sharks also feed on or near the seafloor.
Grainger also noted: "The findings are consistent with data from tagged great white sharks that have shown they spend considerable time at great depths." The research looked at the stomach contents of 40 juvenile great white sharks (Carcharodon carcharias) caught in the NSW Shark Meshing Programme. The scientists matched this with data reported elsewhere in the world, primarily South Africa, to form a nutritional picture for the species.
"Understanding the nutritional goals of these cryptic carnivores and how they are linked to migratory patterns will give us insight into what drives human-shark conflict and how this species can be better protected," said Dr. Gabriel Machovsky Capuska, a Senior Research Associate Expert at the Charles Perkins Center and co-author of the study.
Grainger said: "Great white sharks have a diverse diet. In addition to the salmon fish from eastern Australia, evidence could be obtained of other bony varieties, such as eels, whiting, mullet and turnips. Rays were also found to be an important part of their diet, including manta rays and electric rays.
"This is consistent with numerous other studies that have been done showing that wild creatures, including predators, choose precisely balanced diets to meet their nutrient requirements," added co-author Professor David Raubenheimer, President of Nutritional Ecology in the School of Life and Environmental Sciences. Monitoring of great white sharks shows that they migrate seasonally along the eastern seaboard of Australia from southern Queensland to northern Tasmania, with range increasing with age.
The Mediterranean White Shark in Danger of Extinction
Despite having controlled the Mediterranean Sea for about 3,2 million years, the white shark in this area is in danger of disappearing due to its low genetic diversity, according to research that has studied its DNA.
The white shark (Carcharodon carcharias) is the largest carnivorous fish on the planet, with evidence of specimens that could have exceeded six meters in length and managed to weigh around a ton. Such characteristics have led it to be present even in the small Mediterranean Sea, which it has populated for about 3,2 million years. However, and despite their trajectory, it is likely that these sharks will become just another part of the history of our sea.
According to a study published in the Journal of Biogeography, which has thoroughly studied the DNA of this creature, the great white shark of the Mediterranean Sea is at risk of disappearing. Mediterranean white sharks have usually been little studied since they suffered a considerable population reduction in the last century.
Therefore, the experts of this study tried to overcome this problem by going to museums and private collections that preserve historical artifacts made from white sharks, such as teeth, jaws and vertebrae from the last two centuries. Thanks to the latest technologies with the ability to analyze the ancient genome, it was possible to sequence the mitochondrial DNA of different white sharks in the Mediterranean and subsequently match it with other populations of sharks residing in other regions.
In this way, they were able to discover that the gradient of genetic variability between subjects of this species of white shark is extremely negligible and, therefore, they are in danger: “The group of white sharks in the Mediterranean is possibly a modest community in danger of disappearing. “, specified Agostino Leone, academic at the University of Bologna and initial author of the study.
"For their timely salvation, it is essential to proceed quickly: their disappearance would be harmful to the ecological balance of the Mediterranean Sea, as well as to the already highly unstable global situation of these magnificent marine predators," he suggested. By studying and comparing different specimens, the team was able to additionally obtain other important data, such as that Mediterranean white sharks began to evolve differently from other related populations approximately 3,2 million years ago.
"The foregoing basically shows that the theses about sharks occupying the Mediterranean some 450.000 years ago are wrong," said Agostino Leone. It can be concluded that this data made it possible to corroborate that these white sharks are more closely related to those that populate the Pacific Ocean than those that reside in the Atlantic Ocean, a similarity that can only be explained by following the predator's colonization route through the seas.
According to scholars, the Mediterranean white sharks had their origin from those from the Pacific Ocean, since the latter crossed the Atlantic through the Central American river route, prior to the formation of the Isthmus of Panama, and finally arrived to the Mediterranean Sea.
About 3,5 million years ago, the formation of the Isthmus of Panama obstructed the fluvial route between North America and South America, which brought about a succession of drastic changes in the climate of the Atlantic Ocean and, as a consequence, numerous species of fish disappeared. The great white shark may have been part of them. Thanks to this event, the Atlantic suffered a more or less recent repopulation of white sharks, perhaps due to the migratory waves of white sharks from South Africa, hence the genetic divergence between them and the white specimens of the Mediterranean.
The Ancestor of the Great White Shark
Barely one meter long, a team of Austrian researchers has established that it existed in the Middle Jurassic and that, despite its size, they estimate it as the ancestor of the white shark of the present due to the structure of its teeth, which is unique. Mackerel sharks (Lamniformes) are a group made up of some of the most representative specimens known, including the mako shark (the fastest on the planet), the great white shark and Megalodon, the largest predatory shark that has never crossed the oceans.
Currently, and as a review in the journal Scientific Reports, Patrick Jambura, from the University of Vienna, who acts as coordinator of an international team of experts, have located a unique feature in the teeth of these carnivores, which made it possible for them to trace the provenance of this group to a modest benthic shark from the Middle Jurassic. Similar to those of humans, shark teeth are made up of two mineralized structures: a rigid covering of tissue and a core of dentin. According to their structure, they are differentiated into two different types: orthodentine and osteodentine.
Orthodentine has a very compact appearance and is similar to the dentin that we can get in human teeth. In shark teeth, orthodentine is limited to the crown of the tooth. In contrast, the other kind of dentin is spongy in appearance and resembles true bone and is therefore called osteodentin. It can be found in the root, holding the tooth to the jaw and in certain species also in the dental crown in which it supports the orthodentine.
Using high-resolution computed tomography, Patrick Jambura and his team analyzed the constitution of the teeth of the great white shark and its relatives and found a unique condition of the teeth of the members of this group: the osteodentin of the roots intrudes into the crown and replaces orthodentine. This situation has not been seen in any other shark, all of which have orthodentine to a certain level and, therefore, are restricted to the members of this group.
Another species that was examined was the fossil shark Palaeocarcharias stromeri, which is well represented by intact skeletons from the famous Solnhofen Plattenkalk (Solnhofen clay tiles), from about 150 million years ago, in southern Germany. The oldest discovery of this species is from the Middle Jurassic period (around 165 million years ago) and it did not have much in common with today's mackerel sharks.
The great white shark's ancestor was a modest, very slow benthic shark, not exceeding a length of more than a meter and apparently feeding on small fish in shallow waters. Until now, their association has been a mystery to researchers, since the appearance of their body resembles that of a carpet shark, while their fang-like teeth are similar to those of mackerel sharks. The study of dental microstructure led to the determination of the same unique dental composition found only in great white sharks and their relatives.
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