Làmia

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Làmia
Carcharhinus longimanus
Classificacion classica
Renhe Animalia
Embrancament Chordata
Sosembr : Vertebrata
Classa Chondrichthyes
Sosclassa Elasmobranchii
Superòrdre Euselachii
Òrdre Carcharhiniformes

Heterodontiformes
Hexanchiformes
Lamniformes
Orectolobiformes
Pristiophoriformes
Squaliformes
Squatiniformes

Taxons de reng inferior
Sistematica :
  • Galeomorphii
    • Heterodontiformes
    • Orectolobiformes
    • Lamniformes
    • Carcharhiniformes
  • Squalea
    • Hexanchiformes
    • Squaliformes
    • Hypnosquales
      • Squatiniformes
      • Pristiophoriformes
      • Batoidea
        • Pristiformes
        • Torpediniformes
        • Rajiformes

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La làmia o lo verdon o lo peis-can (reg. peis-chan, peish-can) (superòrdre Selachimorpha) es lo nom d'un ensems de peisses dotats d'una esqueleta completament cartilaginosa e d'un còs streamlined. Pòdon alenar gràcias a entre cinc e sèt gaunhas. Las làmias possedisson una pellicula de denticles dermals que protegís sa pèl dels aleps e dels parasits e que renfòrça son idrodinamicitat.[1] Tenon de dents remplaçablas. Son de predators fòrça mal coneguts, vist qu'atacan rarament los umans a mens que foguèssen intimidats.

Las làmias comprenon d'espècias que van de la làmia pigmèa de la talha de la man, Euprotomicrus bispinatus, una espècia de mar prigonda que sonque mesura 22 cm, a la làmia balena, Rhincodon typus, lo pèis lo mai gròs, que pòt aténher una longor d'aperaquí 12 mètres e que, coma las grandas balenas, manja pas que plancton through filter feeding. La làmia buòu, Carcharhinus leucas, es l'espècia mai coneguda e pòt nadar dins d'aiga salada o doça (se pòt trapar dins lo Lac Nicaragua, en America Centrala) e dins los deltas.

Somari

[Modificar] Caracteristicas fisicas

Modèl:Main

[Modificar] Esqueleta

L'esqueleta d'una làmia es completament diferenta de la dels peisses ossoses coma la merluça; es facha d'un cartilatge fòrça leugièr e flexible, e mai lo cartilatge de las làmias mai vièlhas pòsca èsser a còps calcificat, e doncas mai dur e mai regde. La maissa de la làmia es variabla e se pensa qu'a evolucionat a partir del primièr arc de brànquias. Es pas estacada al cran e a de depausses minerals suplementaris que li donan una fòrça mai granda.[2]

[Modificar] Respiracion

Caracteristicas principalas de las làmias

Coma los autres peisses, las làmias tiran d'oxigèn de l'aiga de mar quand passa over their gills. Qualques làmias possedisson a modified slit sonat a spiracle que se situa just darrièr l'uèlh, qu'es emplegat per la respiracion.[3] Per encausa de sa talha e la nature de son metabolisme, fòrça làmias an un besonh d'oxigèn mai important que los peisses ossoses e pòdon pas dependre dels corrents d'aiga ambients per fornir an adequate supply d'aiga oxigenada. Se per cas aquelas làmias s'arrestèssen de nadar, la circulacion de l'aiga davalariá enjós del nivèl necessari per poder alenar e l'animal s'escanariá. Aqueste foncionar de ensuring un flux adequat de sas gills a partir de movements en avant se coneis coma la ram ventilacion. Qualques làmias, coma la nurse shark, Ginglymostoma cirratum, pòdon pompar d'aiga over sas gills mentre que son a se pausar.

Los procèsses de respiracion e de circulacion començan quand la sang desoxigenada viatja cap al còr, que possedís dos compartiments, de la làmia. Ailà la sang es pompadas to las gills de la làmia a travèrs l'artèria ventrala aòrta ont it branches off into afferent artèrias braquialas. La reoxigenacion se fa dins the gills e la sang reoxigenada flows dins las artèrias efferent brachial, que se reunisson per formar l'aòrta dorsala. La sang raja a partir de l'aòrta dorsala dins tot lo còs. La sang desoxigenada del còs puèi circula a travèrs de las venas cardinalas posterioras e dintra dins los sinuses cardinals posteriors. A partir d'aquel ponch la sang dintra dins lo ventricul del còr e lo cicle se repetís. Aqueste tipe de respiracion es pas gaire eficaç e se per cas la làmia se deviá arrestar de bolegar, la sang seriá pas en condicions de circular dins tot lo còs per encausa de la manca de fòrça de l'atrium del còr.Modèl:Fact

[Modificar] Buoyancy

A la diferéncia dels peisses ossoses, las làmias tenon pas de bofigas de natacion plenas de gas, mas al contrari rely sus son fetge ample plen d'òli que conten de squalene. Aqueste fetge pòt arribar a constituir fins a 25% de sa massa corporala[4] for buoyancy. Son eficacitat es limitada e doncas las làmias fan servir dynamic lift per mantenir depth e sink tre que quitan de nadar. D'unas làmias, if inverted, dintran dins un estat natural d'immobilitat tonica - los cercaires fan servir aqueste estat per tal de poder gerir e manipular las làmias amb seguretat.[5]

[Modificar] Osmoregulacion

Contràriament als peisses, las làmias bevon pas d'aiga de mar; al contrari they retain de grandas concentracions de waste chemicals dins son còs per cambiar the diffusion gradient per tal de poder absorbir l'aiga dirèctament de la mar. Aquesta adaptacion empacha fòrça làmias de subreviure dins d'aiga fresca, e doncas son confinadas a una environa marina. Existisson qualques excepcions a aquesta règla, coma la làmia taure, qu'a desvolopat un biais de modificar sa foncion renala per crear una excrecion de grandas quantitats d'urèa.[4]

[Modificar] Las dents

Las dents d'una làmia tigre
Las dents d'una làmia tigre

Las dents de las làmias carnivòras son pas ligadas a la maissa, mas embedded dins la carn, e dins fòrça espècias son constantament remplaçadas long de la vida de la làmia; d'unas làmias arriban a pèrdre 30.000 dents dins sa vida. Totas las làmias an de rengs multiples de dents along the edges de sas maissas superiora e inferiora. De dents novèlas creissan de longa dins a groove just dins la boca and move forward from dins la boca on a "conveyor belt" formed by the skin in which they are anchored. Per qualques làmias rows de dents son remplaçadas cada 8–10 jorns, mentre que dins d'autras espècias pòdon durar qualques mesadas. Las dents inferioras son emplegadas essencialament per agantar las prey, del temps que las dents superioras son a cutting into it.[3] Las dents range from thin, dents coma d'agulhas per tal de gripping lo peis a de large, de dents flat adaptadas per crushing shellfish.

[Modificar] Coas

The range de formas de coa de làmia shark tail shapes

Las coas (aletas caudalas) de las làmias varian considerablament en foncion de las espècias e son adaptadas a l'estil de vida de la làmia. La coa fornís thrust e sa velocitat e l'acceleracion dependon de la forma de la coa. Different formas de coas an evolved in làmias adapted a d'environas diferentas. La coa de la làmia tigre ten un large upper lobe que delivers the maximum amount of power for slow cruising o de sudden bursts de velocitat. La làmia tigre a una dieta variada, e per aquesta rason cal que siá capabla de twist e de virar dins l'aiga aisidament quand es a caçar, mentre que lo porbeagle, caçaire de schooling peisses coma los vairons e herring possedís un large lower lobe que li permet d'aténher una velocitat mai importanta e aital l'ajudar a gardar ritme amb sas prey que nadan lèu. Tanben se pensa que las làmias emplegan lo lobe superiora de sas coas per contrarrestar the lift generat per sas aletas pectoralas. [6]

Some adaptacions de coas an de tòcas autras que de provesir thrust. La cookiecutter shark a una coa amb broad lower e upper lobes of similar shape which are luminescent and may help to lure prey cap a la làmia. La thresher se noirís de peis e de squid, which it is believed to herd, e los ensuca puèi amb son potenta e elongated upper lobe.

[Modificar] Velocitat

En general, las làmias nadan ("cruise") a una velocitat mejana de 8 km/h (5 mph), pasmens quand se devon noirir o atacar, una làmia mejana average se pòt sarrar d'una velocitat upwards of 19 km/h (12 mph). The shortfin mako may range upwards of 50 km/h (31 mph)[7] e es considerat coma la làmia e a l'encòp un dels peisses mai rapids. La granda làmia blanca tanben es capabla de considerable bursts d'aviadesa. Aquestas exceptions se devon probablament a la natura "warm-blooded", o omeotermica de la fisiologia d'aquelas làmias.

[Modificar] Los denticles dermals

Modèl:Main Contràriament als peisses ossoses, las làmias an un complex dermal corset teissut de fibras collagenosas flexiblas, dispausadas coma una ret helical qu'envira lo còs. Aquò fonciona coma una esqueleta extèrna, providing attachment per sos muscles natatòris e que permeton aital d'estalviar d'energia. sas dents dermalas lor donan d'avantatges idrodinamics ja que demesisson las turbuléncias quand son a nadar.

[Modificar] Temperatura corporala

A few de las espècias mai gròssas, coma lo shortfin mako, Isurus oxyrinchus, e la granda làmia blanca, son mildly omeotermics[6] - capables de servar la temperatura corporala ensús de la temperatura de l'aiga de l'environa. This is possible gràcias a la preséncia de rete mirabile, a counter current exchange mecanisme que reduces la pèrdia de calor corporala. La contraccion musculara genera tanben a mild amount de calor corporala. Pr'aquò, es pro diferent d'un biais significatiu de l'omeotermia vertadièra, coma se pòt observar en çò dels mamifèrs e los aucèls, que sa calor es generada, mantenguda, e regulada per l'activitat metabolica.

[Modificar] Etimologia

Fins al [sègle XVI]],[8] sharks were known to mariners as "sea dogs".[9] According to the OED the name "shark" first came into use after Sir John Hawkins' sailors exhibited one in London in 1569 to refer to the large sharks of the Caribbean Sea, and later as a general term for all sharks. The name may have been derived from the Mayan word for fish, xoc, pronounced "shock" or "shawk".

[Modificar] Evolucion

A collection of fossilised shark teeth
A collection of fossilised shark teeth

The fossil record de las làmias extends back over 450 milions d'annadas - plan abans que los vertebrats terrèstres existèssen e abans que fòrça plantas comencèssen sa colonizacion dels continents.[10] Las primièras làmias èran fòrça diferents de las làmias modèrnas.[11] La part màger de las làmias modèrnas can be traced back to around 100 million years ago.[12]

Mostly only the fossilized dents fossilizadas de las làmias are found, although often in large numbers. In some cases pieces de l'esqueleta intèrna o even complete làmias fossilizadas have been discobèrtas. Estimates suggerisson que over a span of a few annadas una làmia may grow tens de milierats de dents, which explica l'abondància de fossils. Vist que las dents consistisson d'apatite minerala (calci phosphate), se fossilizan aisidament.

Puslèu que d'òsses, las làmias an d'esqueletas cartilagenous, amb a bonelike layer broken up en milierats of isolated apatite prismes. Quand una làmia se morís, l'esqueleta decomposing breaks up e los prismes apatite scatter. Se presèrvan d'esqueletas de làmias sonque quand un enterrament brusc dins de bottom sediments se produsís.

Demest l'ensems de las làmias mai ancianas e primitivas cal citar ka Cladoselache, from about fa 370 milion d'ans years ago,[11] qu'es estada trobada dins the Paleozoic strata dels estats americans de l'Ohio, Kentucky e Tennessee. At this point in l'istòria de la Tèrra these rocks made up the soft sediment of the bottom of a large, shallow ocean, que s'espandissiá a travèrs una part bèla de l'America del nòrd. Cladoselache was only about 1 m long with stiff triangular fins and slender jaws.[11] Sas dents possedissián several pointed cusps, which would have been worn down by use. A partir del nombre de dents found in any one place es plan probable que Cladoselache remplaçava pas sas dents d'un biais tan regular coma las làmias modèrnas. Sas aletas caudalas avián una forma que sembla la del pelagic makos e las grandas làmias blancas. La descobèrta de peisses entièrs trobats la coa primièra dins los estomacs suggerís qu'èran de nadaires rapids de granda agility.

From about 300 a 150 milions d'annadas ago, una part importanta de las làmias fossilas can be assigned a un o dos grops. Un d'aquestes, los xenacantas, was almost exclusive to freshwater environments.[13],[14] By the time aqueste grop became extinct (about 220 million years ago) they had achieved distribucion dins tot lo mond. L'autre grop, los hybodonts, appeared about 320 million years ago and was mostly found dins los oceans, mas tanben dins los flums.

Las làmias modèrnas faguèron son aparicion fa aperaquí 100 milion d'annadas.[12] Fossil mackerel shark teeth occurred in the Lower Cretaceous. Las dents oldest làmia blanca date from 60 to 65 million years ago, a l'entorn del temps que se faguèt l'extincion dels dinosaures. Dins l'evolucion early de la làmia blanca shark existisson almens dos lineages: one with coarsely dents serrated que probablament foguèron la naissença de la granda làmia blanca modèrna, e another amb de dents finament serrated e una tendéncia to attain de proporcions gigantescas. Aqueste grop compren lo extinct megalodon, Carcharodon megalodon, que coma la part màger de totas las làmias desapareguda se coneis sonque per encausa de sas dents. Un reproduccion de sas maissas se faguèt a partir on some de las dents mai largest which up to almost 17 cm (7 in) long and suggested a fish that could grow to a length of 25 to 30.5 m (80 to 100 ft). La reconstruccion foguèt considerada puèi coma inexacta, e las darrièras ipotèsis revised downwards to around 13 to 15.9 m (43 to 52 ft).

Se pensa que la talha immensa de las làmias predatory coma la Granda làmia blanca may have arisen a partir de l'extincion del dinosaures e la diversificacion dels mamifèrs. Se sap que pendent aquel quite moment aquestas làmias èran evolving some early mammalian groups evolved into aquatic forms. Certainly, wherever las dents de las làmias large have been found, there has also been an abundance d'òsses de mamifèrs marins, including seals, porpoises and whales. These bones frequently show de marcas d'atacas de làmias. De teorias existisson que suggerisson que las làmias large evolucionèron per tal de better take advantage of larger prey.

[Modificar] Classificacion

Identificacion dels 8 extant shark orders

Las làmias apartenon al superorder Selachimorpha dins la subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii tanben include rays e skates; the Chondrichthyes also include Chimaeras. It is currently thought que las làmias forman un grop polyphyletic: particularament, qualques làmias son mai closely related to rays que o son a d'autras làmias.

Existisson mai de 360 espècias descrichas de làmias.

There are uèch orders de làmias, listed below in roughly their evolutionary relationship from more primitive to more modern espècias mai modèrnas:

  • Hexanchiformes: Examples d'aqueste grop include the cow sharks, frilled shark and even a shark that looks on first inspection to be a marine snake.
  • Squaliformes: Aqueste grop includes the bramble sharks, dogfish and roughsharks, e prickly shark.
  • Pristiophoriformes: These are the sawsharks, qu'a un morre alongat, toothed snout that they use for slashing the fish that they eat.
  • Squatiniformes: Que se coneis tanben coma angel sharks, son de làmias flattened with a strong semblança granda amb las stingrays e los skates.
  • Heterodontiformes: They are generally referred to as the bullhead o horn sharks.
  • Orectolobiformes: Son sonats comunament carpet sharks, including zebra sharks, nurse sharks, wobbegongs e la làmia balena.
  • Carcharhiniformes: These are commonly referred to as the groundsharks, and some of the espècias include la blue, tiger, bull, reef e oceanic whitetip sharks (collectively called the requiem sharks) along with the houndsharks, catsharks e hammerhead sharks. They are distinguished by an elongated snout and a nictitating membrana que protegís los uèlhs durint una ataca.
  • Lamniformes: Son commonly coneguts as the mackerel sharks. They include the goblin shark, basking shark, megamouth shark, the thresher sharks, shortfin and longfin mako sharks, and great white shark. They are distinguished by sas maissas grandas e ovoviviparous reproduccion. The Lamniformes include the extinct megalodon, Carcharodon megalodon.

[Modificar] Reproduccion

Claspers of male spotted wobbegong, Orectolobus maculatus
Claspers of male spotted wobbegong, Orectolobus maculatus

Se pòt determinar aisidament lo sèxe d'una làmia. Los mascles an d'aletas pelvicas modificadas que son vengudas un parelh de claspers. The name is somewhat misleading as they are not used to hold on to the femèla, las fulfill lo ròtle del penis dels mamifèrs.

Mating has rarely been observed in sharks. The smaller catsharks often mate with the mascle curling around the female. In less flexible species the doas làmias nadan parallelament to each other while lo mascle inserts a clasper dins l'oviducte de la femèla. Las femèlas in many of the larger espècias have bite marks that appear to be a result of a male grasping them to maintain posicion del temps de mating. The bite marks may also come from courtship behaviour: the male may bite the female per tal de manifestar son interés. Dins qualques espècias, las femèlas an evolved una pèl mai thicker per endurar aquelas bites.

Las làmias have a different estrategia reproductiva qu'una part màger dels peisses. Instead of producing huge numbers d'uòus e fry (99.9% of which never reach sexual maturity in fishes which use this strategy), las làmias normally produce around a dozen pups (blue sharks have been recorded as producing 135 and some espècias produce as few as dos).[15] These pups are either protected by egg cases or born live. No shark species are known to provide post-natal parental proteccion per their young, pasmens las femèlas tenon una ormona que is released into la sang pendent the pupping season que las empacha aparentament de se noirir de sos youngModèl:Fact.

Clòsca d'uòu de làmia de Port Jackson - trobada sus la platja Vincentia, Jervis Bay Territory, Austràlia
Clòsca d'uòu de làmia de Port Jackson - trobada sus la platja Vincentia, Jervis Bay Territory, Austràlia

Existisson tres ways in which pups làmias are born:

  • Oviparity - Some làmias pondon d'uòus. In most of d'aquelas espècias, the developing embrion es protegit per una clòsca d'uòi que ten la consisténcia del cuèr. De còps que i a aquelas clòscas son corkscrewed into crevices per proteccion. The mermaid's purse, found washed-up on platjas, es una clòsca d'uòu vuèja. Las làmias oviparas include the horn shark, catshark, Port Jackson shark, and swellshark.[16]
  • Viviparity - These sharks maintain a placental link to the developing young, more analogous a la gestacion mammalian que that of other fishes. The young are born alive and fully functional. Hammerheads, the requiem sharks (such as the bull and tiger sharks), the basking shark and the smooth dogfish fall into this category. Dogfish have the longest known gestation period of any shark, at 18 to 24 months. Basking sharks and frilled sharks are likely to have even longer gestation periods, but accurate data is lacking.[15]
  • Ovoviviparity - Most sharks utilize this method. The young are nourished by the yolk of their egg and by fluids secreted by glands in the walls of the oviduct. The eggs hatch within the oviduct, and the young continue to be nourished by the remnants of the yolk and the oviduct's fluids. As in viviparity, the young are born alive and fully functional. Some species practice oophagy, where the first embryos to hatch eat the remaining eggs in the oviduct. This practice is believed to be present in all lamniforme sharks, while the developing pups of the grey nurse shark take this a stage further and consume other developing embryos (intrauterine cannibalism). The survival strategy for the species that are ovoviviparous is that the young are able to grow to a comparatively larger size before being born. The whale shark is now considered to be in this category after long having been classified as oviparous. Whale shark eggs found are now thought to have been aborted. Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs. They choose such areas because of the protection from predators (mainly other sharks) and the abundance of food.

[Modificar] Los senses de las làmias

[Modificar] Sens olfactiu

Las làmias tenon de senses keen olfactory, e some espècias son capablas de detectar as little as one part per million de sang dins l'aiga de mar. Son atirats pels chemicals found dins los budèls de mantas espècias, e as a result often linger near or in sewage outfalls. Some espècias, coma la nurse sharks, have external barbels that greatly increase their ability a sentir prey. The short duct between the anterior and posterior nasal openings are not fused as in peisses bony.

Sharks generally rely on their superior sense of smell per trobar sas prey, but at closer range they also use the lateral lines running along their sides per distinguir los movements dins l'aiga, e emplegan tanben special sensory pores on their heads (Ampullae of Lorenzini) to detectar los camps electrics created by prey and the ambient electric fields of the ocean.

[Modificar] Sens de sight

Los uèlhs de las làmias son similar als uèlhs dels autres vertebrats, including similar lenses, cornèas e retinas, though their eyesight is well adapted to the marine environment amb the help of a tissue called tapetum lucidum. This tissue es situat darrièr la retina e rebat la lutz back a la retina, thereby increasing la visibilitat dins las aigas foscas. The effectiveness del the tissue es variabla, with qualques làmias having stronger nocturnal adaptations. Las làmias an de parpèlas, pasmens they do not blink because the surrounding aiga neteja sos uèlhs. Pr'amor d'aver los uèlhs protegits some have membranas nictitating. Aquela membrana cobrís los uèlhs del temps de predation, and when the shark is being attacked. Pr'aquò, some espècias, including the great white shark (Carcharodon carcharias), possedisson pas una membrana aital, e doncas instead roll their eyes backwards pr'amor de los protegir quand son a atacar.

[Modificar] Sense of hearing

Sharks also have a sharp sense of hearing and can hear prey many miles away. A small opening on each side of their heads (not to be confused with the spiracle) leads directly into the inner ear through a thin channel. The lateral line shows a similar arrangement, as it is open to the environment via a series of openings called lateral line pores. This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fishes and tetrapods the external opening into the inner ear has been lost.

[Modificar] Ampullae of Lorenzini

Modèl:Main

Electroreceptors (Ampullae of Lorenzini) and lateral line canals in the head of a shark.
Electroreceptors (Ampullae of Lorenzini) and lateral line canals in the head of a shark.

The Ampullae of Lorenzini are the electroreceptor organs of the shark, and they vary in number from a couple of hundred to thousands in an individual. The shark has the greatest electricity sensitivity known in all animals. This sense is used to find prey hidden in sand by detecting the electric fields inadvertently produced by all fish. It is this sense that sometimes confuses a shark into attacking a boat: when the metal interacts with salt water, the electrochemical potentials generated by the rusting metal are similar to the weak fields of prey, or in some cases, much stronger than the prey's electrical fields: strong enough to attract sharks from miles away. The oceanic currents moving in the magnetic field of the Earth also generate electric fields that can be used by the sharks for orientation and navigation.

[Modificar] Lateral line

Modèl:Main This system is found in most fish, including sharks. It is used to detect motion or vibrations in the water. The shark uses this to detect the movements of other organisms, especially wounded fish. The shark can sense frequencies in the range of 25 to 50 Hz.[17]

[Modificar] Behaviour

Studies on the behaviour of sharks have only recently been taken, leading to little information on the subject, although this is changing. The classic view of the shark is of a solitary hunter, ranging the oceans in search of food; this is only true for a few species, with most living far more sedentary, benthic lives. Even solitary sharks meet for breeding or on rich hunting grounds, which may lead them to cover thousands of miles in a year.[18] Migration patterns in sharks may be even more complex than in birds, with many sharks covering entire ocean basins.

Some sharks can be highly social, remaining in large schools, sometimes up to over 100 individuals for scalloped hammerheads congregating around seamounts and islands e.g. in the Sea of Cortez.[4] Cross-species social hierarchies exist with oceanic whitetip sharks dominating silky sharks of comparable size when feeding.

When approached too closely some sharks will perform a threat display to warn off the prospective predators. This usually consists of exaggerated swimming movements, and can vary in intensity according to the level of threat.[19]

[Modificar] Shark intelligence

Despite the common myth that sharks are instinct-driven "eating machines", recent studies have indicated that many species possess powerful problem-solving skills, social complexity and curiosity. The brain-mass-to-body-mass ratios of sharks are similar to those of mammals and other higher vertebrate species.[20]

In 1987, near Smitswinkle Bay, South Africa, a group of up to seven great white sharks worked together to relocate the partially beached body of a dead whale to deeper waters to feed.[21]

Sharks have even been known to engage in playful activities (a trait also observed in cetaceans and primates). Porbeagle sharks have been seen repeatedly rolling in kelp and have even been observed chasing an individual trailing a piece behind them.[22]

[Modificar] sleep de las làmias

It is unclear cossí dormisson las làmias. Qualques làmias can lie on the bottom mentre que pumping activament d'aiga over their gills, pasmens sos uèlhs demòran dobèrts e seguisson d'un biais actiu divers. Quand una làmia es a se pausar, fan pas servir sas nares, mas puslèu rather their spiracles. If a shark tried to use their nares while resting on the ocean floor, they would be sucking up la sabla puslèu que l'aiga. Un bon nombre de scientifics pensa qu'aquesta es una de las rasons que las làmias possedisson de spiracles. The spiny dogfish's spinal cord, rather que son cervèl, coordina swimming e doncas es possible per a spiny dogfish de contunhar a nadar mentre que fa sa dormida. It is also possible qu'una làmia pòsca dormir amb sonque qualques parts de son cervèl d'un biais similar als dalfins.[23]

[Modificar] Las atacas de làmias

Modèl:Main

Snorkeler with blacktip reef shark. In rare circumstances involving poor visibilitat, blacktips may bite un uman, mistaking it for prey. Under normal condicions normalas they are harmless e timids.
Snorkeler with blacktip reef shark. In rare circumstances involving poor visibilitat, blacktips may bite un uman, mistaking it for prey. Under normal condicions normalas they are harmless e timids.

Contràriament a las cresenças popularas, sonque un manat de làmias son perilhosas pels umans. Out of more than 360 species, only four have been involved in a significant number of fatal, unprovoked attacks on humans: the great white, tiger, oceanic whitetip and bull sharks.[24] These sharks, being large, powerful predators, may sometimes attack and kill people, but all of these sharks have been filmed in open water, without the use of a protective cage.[25]

The perception of sharks as dangerous animals has been popularised by publicity given to a few isolated unprovoked attacks, such as the Jersey Shore Shark Attacks of 1916, and through popular fictional works about shark attacks, such as the Jaws film series. The author of Jaws, Peter Benchley, had in his later years attempted to dispel the image of sharks as man-eating monsters. In 2005, according to the International Shark Attack File, there were a total of 58 unprovoked attacks recorded worldwide, of which four were fatal.[26]

In 2005 the International Shark Attack File (ISAF) took an investigation on 105 shark attacks. Out of those 105, 58 of the attacks were unprovoked. [27]


[Modificar] Habitat

A December 10, 2006 report by the Census of Marine Life group reveals that 70% of the world's oceans are shark-free. They have discovered that although many sharks live up to depths as low as 1,500 m, they fail to colonize deeper, putting them more easily within reach of fisheries and thus endangered status. [28]

[Modificar] Las làmias en captivitat

Doas làmias balenas dins l'Okinawa Churaumi Aquarium
Doas làmias balenas dins l'Okinawa Churaumi Aquarium

Until recently only a few benthic species de làmias, coma hornsharks, leopard sharks e catsharks podián subreviure dins las aquaria conditions for up to a year or more. Aqueste facj faguèt nàisser la cresença que las làmias, as well as being de mal capturar e transportar, were difficult to care for. A better knowledge de las làmias has led to more species (including the large pelagic sharks) being able to be kept for far longer. At the same time, las tecnicas de transportacion se son melhoradas e now provide a way for the long distance movement de las làmias.[29]

Despite controlled feeding behaviour being considered critical for the health of the shark, very few studies on this topic have been carried out. Since food is the reward for appropriate behaviour, trainers must rely on control of feeding motivation.

[Modificar] Conservacion

Imatge:Global shark catch graph 1950 to 2004.png
Lo nombre de làmias pescadas a aumentat lèu lèu over las 50 darrièras annadas.

The majority de fisheries de làmias de la planeta have little monitoring or management. With the rise de la demanda de produches a basas de làmia s'es producha una pression mai importanta sus fisheries.[30] Stocks decline and collapse because sharks are long-lived apex predators with comparatively small populations, which makes it difficult for them breed rapidly enough to maintain population levels. Major declines in shark stocks have been recorded in recent years - some species have been depleted by over 90% over the past 20-30 years with a population decline of 70% not being unusual.[31] Maites govèrns e l'ONU an reconegut lo besong for shark fisheries management, but due to the low economic value of shark fisheries, the small volumes of products produced and the poor imatge public de las làmias, little progress has been made.

Many other menaças per las làmias include habitat alteration, damage and loss from coastal desvolopaments, la pollucion e l'impacte de las fisheries on the seabed e prey species.

[Modificar] Shark fishery

Imatge:Tiger shark caught in bay.jpg
A 14-foot, 544 kg (1200 pound) Tiger shark caught in Kaneohe Bay, Oahu in 1966

Every year, an estimate states that 26 to 73 million (median value is at 38 million) sharks are killed by people in commercial and recreational fishing.[32] In the past, sharks were killed simply for the sport of landing a good fighting fish (such as the shortfin mako sharks). Shark skin is covered with dermal denticles, which are similar to tiny teeth, and was used for purposes similar to sandpaper. Other sharks are hunted for food (Atlantic thresher, shortfin mako and others), and some species for other products.[33]

Las làmias son a common seafood in many places del mond entièr, including Japon e Austràlia. In the Australian State of Victoria la làmia es lo peis mai emplegat dins lo fish and chips, in which fillets are battered e deep-fried or crumbed e grilled and served alongside chips. When served in fish and chip shops, se sona flake.

Sharks are often killed for shark fin soup: the finning process involves capture of a live shark, the removal of the fin with a hot metal blade, and the release of the live animal back into the water. Sharks are also killed for their meat. The meat of dogfishes, smoothhounds, catsharks, skates and rays is in high demand by European consumers.Modèl:Fact The situation in Canada and the United States is similar: the blue shark is sought as a sport fish while the porbeagle, mako and spiny dogfish are part of the commercial fishery.Modèl:Fact There have been cases where hundreds of de-finned sharks were swept up on local beaches without any way to convey themselves back into the sea.Modèl:Fact Conservationists have campaigned per de canvis serioses de las leis per far make finning illegal dins los Estats Units.

Shark cartilage has been advocated as effective contra lo cancèr e dins lo tractament de l'osteoartriti. Malgrat aquò, un ensag menat per la Clinica Mayo trobèt pas cap d'efièch en cò dels pacients advanced cancer.

Las làmias atenhon en general sa maturitat sexuala lentament e produce very few offspring se los comparam amb los autres peisses que son harvested. This has caused concern demest los biologistas regarding the increase in effort applied per caçar las làmias over time, e se considera que maitas espècias son en perilh d'extincion.

Qualques organizacions, coma lo Shark Trust, menan campanha per limitar la pesca de làmia.

[Modificar] Sharks in mythology

Sharks figure prominently in the Hawaiian mythology. There are stories of shark men who have shark jaws on their back. They could change form between shark and human at any time they desired. A common theme in the stories was that the shark men would warn beach-goers that sharks were in the waters. The beach-goers would laugh and ignore the warnings and go swimming, subsequently being eaten by the same shark man who warned them not to enter the water.

Hawaiian mythology also contained many shark gods. They believed that sharks were guardians of the sea, and called them Aumakua:[34]

  • Kamohoali'i - The best known and revered of the shark gods, he was the older and favored brother of Pele,[35] and helped and journeyed with her to Hawaii. He was able to take on all human and fish forms. A summit cliff on the crater of Kilauea is considered to be one of his most sacred spots. At one point he had a he'iau (temple or shrine) dedicated to him on every piece of land that jutted into the ocean on the island of Moloka'i.
  • Ka'ahupahau - This goddess was born human, with her defining characteristic being her red hair. She was later transformed into shark form and was believed to protect the people who lived on O'ahu from sharks. She was also believed to live near Pearl Harbor.
  • Kaholia Kane - This was the shark god of the ali'i Kalaniopu'u and he was believed to live in a cave at Puhi, Kaua'i.
  • Kane'ae - The shark goddess who transformed into a human in order to experience the joy of dancing.
  • Kane'apua - Most commonly, he was the brother of Pele and Kamohoali'i. He was a trickster god who performed many heroic feats, including the calming of two legendary colliding hills that destroyed canoes trying to pass between.
  • Kawelomahamahai'a - Another human, he was transformed into a shark.
  • Keali'ikau 'o Ka'u - He was the cousin of Pele and son of Kua. He was called the protector of the Ka'u people. He had an affair with a human girl, who gave birth to a helpful green shark.
  • Kua - This was the main shark god of the people of Ka'u, and believed to be their ancestor.
  • Kuhaimoana - He was the brother of Pele and lived in the Ka'ula islet. He was said to be 30 fathoms (55 m) long and was the husband of Ka'ahupahau.
  • Kauhuhu - He was a fierce king shark that lived in a cave in Kipahulu on the island of Maui. He sometimes moved to another cave on the windward side of island of Moloka'i.
  • Kane-i-kokala - A kind shark god that saved shipwrecked people by taking them to shore. The people who worshipped him feared to eat, touch or cross the smoke of the kokala, son peis sacrat.

Dins d'autras culturas de l'Ocean Pacific, Dakuwanga èra un dieu làmia que was the eater de las armas perdudas.

[Modificar] Las cresenças a prepaus de las làmias

Dins la Grècia antica, èra enebit de manjar de carn de làmia als festivals women's.

Demest los mites populars se pensa que las làmias son immunizadas a las malautiás e al cancèr. Aquò es fals, existisson a l'encòp de malautiás e de parasits que pòdon afectar las làmias. The evidence that sharks are at least resistant to cancer e malautiá es mostly anecdotal e there have been few, if any, scientific o statistical estudis that have shown sharks to have heightened immunity to disease.[36]

[Modificar] Vejatz tanben

  • Lista de làmias


[Modificar] Ligams extèrns

Wikimedia
D'articles sul subjècte son disponibles suls autres projèctes Wikimedia sus Wikimedia Commons Làmia
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