Shark - SpeedyLook encyclopedia

Denomination

The origin of the term is discussed, can be is this a deformation of quin (dog), within the meaning of or dogfish Requiem. The term “squale”, of identical direction, which derives from Latin Squalus refers to the rough skin of these animals because of the dentils present on their body. There exists also one named Squalus of which one of the vernacular names is Aiguillat. Several species of shark comprise the shark term in one their vernacular names, such as for example: Hammerhead, Tiger shark, Basking shark, but it is not a general information, it in the case of exists also vernacular names not including/understanding the shark term like Maraîche, Roussette, Mako etc

Here two lists of sharks. First is classified according to the vernacular names, the second following the scientific names. As often in fish, the vernacular names are not always very precise. The same species can receive several names and the same name can indicate different species from where the contradictory aspect of these lists.

List of the vernacular names of shark
List of the species of shark

Description

The shark is particularly characterized by its tapered silhouette, hydrodynamic, and its pectoral fins and dorsal, like its caudal Nageoire Hétérocerque (of asymmetrical form). It is equipped with a Squelette entirely cartilagineux and with five to seven side slits branchiales according to the species.

The size of the shark varies according to the species, from 15 to 20 cm for smallest, like the dwarf Requin ( Squaliolus laticaudus ) and the Requin Pygmy ( Euprotomicrus bispinatus ), with more than 18 meters for largest, the Requin whale ( Rhincodon typus ).

Its Peau rough, is covered with innumerable Denticule S cutaneous, of the placoid scale S osseous of dermic origin and épidermique, which protects it from the parasitic and improves its penetration in water.

The jaws of the shark present single characteristics in the animal world. They entirely mobile, independent, and are furnished with several hundreds of Dent S distributed on several lines whose only last is functional, the others being teeth of replacement. The teeth, whose form varies according to the species, are renewed permanently throughout the life of the shark, and are spontaneously replaced by a tooth of the following line when they fall or are damaged. Fixed on a very solid fabric fibrous, they are rectified towards outside when the shark opens the mouth, which enables him to bite more easily a Proie and to firmly maintain it thanks to the Concavité teeth.

Its liver, which can represent up to 25% of its weight, is made up to 90% of Squalène, and its absence of swim Bladder is mainly used to him to compensate for to stabilize itself, but also energy reserve.

Diagram of identification

The order S of sharks of the superorder Euselachii of the traditional Classification are:

Carcharhiniformes (Shark-hammer, Dogfish…)
Heterodontiformes (Shark sleeper.)
Hexanchiformes Compagno, 1973 (Basking shark…)
Lamniformes (Megalodon, Large white shark…)
Orectolobiformes (Shark whale…)
Pristiophoriformes (Shark-saw)
Squaliformes Compagno, 1973 (Dog-fish…)
Squatiniformes (Angel of sea…)

For this reason, certain authors separated Euselachii into two:

superorder Selachimorpha corresponding to the orders of the sharks
superorder Rajomorphii corresponding to the order S of the Line S, torpedo S, sawfishes and fish guitar.

Distribution

The sharks are present in all the Mer S and all the Océan S of the sphere, except for the the Antarctic. Some species, like the Shark bulldog ( carcharhinus leucas ), are able to live in Fresh water or little salted (rivers, rivers, estuaries, lakes). It sometimes happens to them to go up certain rivers until more 3 000 km inside the grounds, such as for example in the Zambezi and the Lake Victoria, in Africa. Members of a species (Pristiophoridés) even will reproduce in the Lac Titicaca, in South America.

Certain species are pelagic, others coastal; one finds sharks from surface until 2 500 meters of depth approximately.

Locomotion

The sharks use to them caudal Nageoire to be propelled and to change direction brutally, the pectoral fins act as Gouvernail according to the same principle as the ailerons of plane, the dorsal fins are used as stabilizers. To be able to breathe, they are obliged to swim permanently, even at low speed, in order to maintain current of water sufficient bringing oxygen to their gills. It happens however that certain sharks, more particularly those alive near reefs, rest on the bottom while putting themselves vis-a-vis the current, which is sufficient so that they capture oxygen necessary to their metabolism.

Certain species, like the Shark mako ( Isurus oxyrinchus ), are able to reach top speeds of at least 50 km/h. The Denticule S present on the skin of the sharks cause microphone-disturbances which facilitate the hydrodynamic flow and the output of the stroke by creating a boundary layer of permanent water against the skin, with the result that they slip into water easily.

Contrary to the majority of other fish, they do not have a swim Bladder to stabilize itself in-depth but use the Squalène, oil present in their liver, of density less than water to correct their negative buoyancy.

The pelagic sharks are able to traverse considerable distances, and for certain species like the Blue shark ( prionace glauca ) to have sometimes a migratory circuit, but few data are available. However, a tracing by satellite showed that a Grand white shark, called “Nicole”, carried out a migration of South Africa towards the Australia. The distance of approximately 11000 km was covered in 99 days is a mean velocity of 4,6 km/h.

Reproduction

The majority of the sharks reproduce in the ocean; however certain sharks about the Pristiophoriformes choose the lakes (Central America). Contrary to the others Poisson S, the sharks have a not very effective mechanism of reproduction; and seldom observed. The sexual maturity is reached tardily (several years), the number of individuals per range is very weak (of an individual to a few hundreds according to the species) and the duration of the Gestation is particularly long (7 months to 2 years).

The male has two Ptérygopode S but only one is used during the coupling. The Sperme is deposited in the Cloaque female.

The development of the embryos is not identical according to the species considered; it can be:

oviparous animal: bridge egg S,
viviparous: development in the Uterus thanks to a ovoviviparous Placenta,
: the eggs develop and hatch inside even of the abdomen of the mother.

In all the cases with its birth the shark is autonomous.

Several cases of reproduction without coupling, are documented and let suppose that the shark would be capable of Parthénogenèse.

Threats and conservation

The sharks are intensively fished, sometimes for their meat but generally - only - for their ailerons which constitute the principal ingredient of mets (soup and mouthfuls) appreciated in Asia. The number of sharks killed annually in the world was evaluated in the years 1980 to at least 100 million individuals. However, the intensification of fishing and the increase in demand for the ailerons of shark leave think that this number is strongly underestimated today. A late sexual maturity and a particularly long duration of the Gestation, as well as a weak production of embryos make the sharks particularly vulnerable to the Surexploitation.

Nearly 10% of the species of élasmobranche S (sharks and Line S) is reproduced on the red list of IUCN and is threatened of extinction to differing degree.
the the Mediterranean holds according to the UICN the record of the number of cartilagineux fish species threatened of disappearance, with in 2007 42% of the species of sharks and lines threatened of extinction;

Thirty species threatened of disappearance, of which;

- 13 considered in critical danger of extinction , of which the Line of Malta (endemic, of which population dropped of 80% because of the Fisheries of deep seas, the Shark-mole blue and the Shark-mole commun run

- 8 species in danger

- 9 vulnerable .

In this area, the causes are:

- the Surpêche induced by the development and the use of the Trawl S,

- accidental catches (fishing with the Trawl line or the net),

- the Pollution (mercury and Méthylmercure in particular, with rates exceeding 0.50mg/kg, in particular at the common Dog-fish);

- the degradation of their habitats. The countries which fish some more are the Turkey, the Tunisia, the Greece, the Italy and the Spain.

the UICN alerts on the fact that the drifting net although prohibited at sea the Mediterranean, continues to be used and to capture many sharks.

In 2007, only the White shark and the Basking shark are protected in Water from the European Community (and in Croatia). The UICN noted in November 2007 that although eight species of sharks and lines were listed by four international conventions on the conservation of the Mediterranean wildlife, only three species were protected. The UICN thus requires a moratorium on the Pêche out of deep water, which the drifting nets are prohibited, the removal of the only fins of sharks can. The UICN requests also a real application of the laws, quotas and limits of catch of fishing for the sharks (and the lines) in the Mediterranean.

Various studies, show an alarming fall of the populations of sharks, going in the Gulf of Mexico up to 99% for the Requin longimane over one period of only 50 years. The size and the average mass of the pelagic poisons and the fished sharks are in very strong fall what lets think that many sharks are fished before being able to reach sexual maturity and thus to reproduce.

Phylogeny

The fossils of well preserved sharks are very rare taking into account the cartilagineuse nature of the skeleton, generally only the teeth resist the deterioration of time. The phylogenesis of the shark is thus particularly delicate. The oldest skeletons were discovered at the end of the 19th century in the state of the Ohio to the the United States are kind Cladoselache dating from the higher Dévonien (360 My). Of a size of approximately 2 meters this shark is far from being in position of Superprédateur but rather of prey in particular of the Placoderme S like the Dunkleosteus . The disappearance of Placodermes towards 354 My will support the development of the chondrichtyens, in particular as regards diversity. At the end of the Permien a extinction of mass occurs making disappear 90 % of the marine species of which chondrichtyens. A second extinction at the end of the Trias operates a selection again and eliminates, for example, the Xénacanthe S which had lived during 200 My. With the Mesozoic the Hybodonte S are characterized by their big size (at least 3 meters) and a jaw able to crush any Carapace. With the Jurassic the Néosélacien S are in competition with the hybodontes but the Extinction of the Cretaceous there are 65 My caused the end of the hybodontes like that of much of other species to be started with the Dinosaure S.

These neoselacians like, can be, the Mcmurdodus have the majority of the characteristics of the modern shark. Carcharocles megalodon was probably the superpredator of the tropical oceans starting from the Miocène, of a supposed size of 13 meters one finds in abundance his fossilized teeth, this shark probably died out there are 1,6 My.

; Simplified tree ─o Euselachii ├─o several let us tax extinct or alive of which dreams └─o ├─o several let us tax extinct of which the Xenacanthiformes └─o ├─o several let us tax extinct of which the Hybodontoidei └─o mixed Neoselachii, taxon ├─o Galeomorphii, taxon of shark │ ├─o Orectolobiformes │ └─o │ └─o Lamniformes and Carcharhiniformes └─o mixed Squalea, taxon └─o Squalimorpha ├─o several families of shark of which the Hexanchidae, Echinorhinidae, Chlamydoselachidae └─o Batoidea or Batidoidimorpha, of which rays, fish guitars, sawfishes, fish angels, which are not regarded as sharks ├─o Torpediniformes of which the Torpedo S ├─o Myliobatiformes └─o Rajiformes

Danger to the man

Myths and realities

Reputation

The quadrilogy Teeth of the sea (American original title: Jaws ) contributed much to the bad reputation which the sharks near the public have. Although there is no glaring error size behavior, the accumulation of the scenes wanted for the scenario is on the other hand noncredible and could not be the fact of only one shark. However as of the Moyen-âge this reputation was not any more to make:

Paradoxically the reputation of the shark is due especially to the exceptional and rare aspect of an attack. Indeed, the Hippopotamus or the Cobra kills out of the thousands of people each year in the world without for all this that is médiatisé, on the other hand an attack or even the only presence of a shark in water gives place in an article in good place in the newspapers. In fact, the reason of this fear is especially related to the even psychoanalytical psychological perception dark and unknown depths of the oceans which feed all the phantasms.

“Man-eater”

The shark is a predatory , in particular specialized in the cleaning of corpses and the attack of sick animals. To qualify a shark of man-eater is unsuitable because its mode includes/understands only exceptionally human beings. The majority of the rare attacks of sharks are of the type bite-slackened (or bite of exploration) without another continuation that the consequences of the single bite (which can be mutilating and fatal due to Hémorragie).

Generally an attack is related to a misidentifying or can be moved by curiosity; this last assumption becoming increasingly credible with the eyes of specialists in the Large white shark like R. Aidan Martin.

An event as spectacular as an attack of shark often has a broad press coverage, supplied with the research of the sensational one. It is what brought George Burgess, specialist in the sharks of the natural history museum of natural history of Florida and person in charge of the world database of the attacks of sharks, to recall that statistically there was much more risk to be killed while going to bathe in Florida by a Coconut which falls on the head than by a shark. The risk is also much greater to be made crush by a car while crossing the street.

Cancer and shark

Contrary to a generally received idea the sharks can develop a cancer. However, they lay out of particular biological mechanisms which seem to be very effective to prevent the Angiogenèse, i.e. the formation of small vessels which irrigate the cancer cells. The drugs containing cartilages of shark are very subjects to deposit in the scientific circle. The Squalamine, substance extracted the stomach of the shark, could be effective in the treatment of the cancerous tumors. The squalamine would starve the cancer cells by inhibiting the angiogenèse.

Use of the sharks

In addition to the use of its flesh and its ailerons for the food, the shark is entirely exploitable. One can quote in particular the Huile of his liver which is exploited in the drug company or for the lubrication of machines, his skin which after tanning is employed in Maroquinerie, his cartilages which can be transformed into Gélatine, etc However, the disproportion of the purchase price between the ailerons and the other parts of the body makes that in practice the shark is exploited almost only for its ailerons, the remainder being turned over to the sea not to encumber the holds.

For a few years the plunged without cage with sharks in tropical medium has developed. The sharks, sometimes, are then accustomed to be nourished, an activity commonly called feeding (of “ to feed ”, “ nourrir ” in English). Hundreds of divings are organized each day in the world in company primarily of sharks of reef but also on the occasion in the presence of tiger sharks, of large shark-hammers or of sharks bulldogs. This activity, makes it possible to demystify the shark near the plungers and to observe it in natural environment. This ecotourism meets a real success and takes part for a big part in the saving in country like the Egypt, the Maldives or the French Polynésie. This is why measures prohibiting or limiting the taking away of ailerons of sharks were taken under the pressure of tourism industry and the plungers.

Fossil teeth of sharks

The fossil teeth of sharks were a enigma a long time. See the article Glossopètre.

Symbolic system

In the Symbolic system Tahiti enne, the shark is associated with the Sagesse.
In the Symbolic system Hawaii enne, the shark is associated with protection (Aumakua).
In the Symbolic system Māori, the shark is associated with a guide benefactor of the stray sailor.
In the Symbolic system Japan ease, the shark is associated with terror.
In the Symbolic system Polynesia nne, the shark is associated with the ultimate incarnation of the heart.

Notes and references of the article

See too

Poisson
cartilagineux Poisson
the various hammerheads

And also:

Bay of the Angels

External bonds

shark|shark

Natural history museum of natural history, press kit of the exposure “Sharks, between fear and knowledge”, (document consulted with some technical difficulties on August 21st, 2007), Press kit
Natural history museum of natural history of Florida, department of ichtyology, (site consulted on May 20th, 2007), very up to date Gate on the sharks, also maintains the statistics of attacks (ISAF)
Underwater Times, (site consulted on May 20th, 2007) Current events concerning the sharks
Gilles Cuny, Futura sciences, 2004, (consulted page on May 20th, 2007), the long story of the sharks
Association Longitude 181, (consulted site May 20th, 2007), very active Association for the protection of the sharks

Zh-yue: 鯊魚

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