Inside the retina are rod cellswhich recognize the difference between lightness and darkness. To control the amount of light they're exposed to, sharks dilate and contract their pupils. To focus, muscles surrounding the lens pull it closer or farther away from the retina. The retina also contains cone cellswhich allow an organism to see color. For many decades, scientists thought that shark eyes had more rod cells, and that sharks couldn't see color, but it appears that more and more sharks have cone cells.
Scientists are still determining how sharks interpret color. Another unique thing about shark eyes is the eyelid. Sharks use their eyelids primarily as a protective measure. When it's feeding time, or when the shark has an encounter with another shark, it will close the eyelids to protect the eyes from abrasion.
In addition to a hammerheadBelon included a woodcut of a shark he named Canis carcharias. Some readers may recognize that "Canis" is the genus currently assigned to dogs. Belon was not attempting to classify sharks with dogs by asserting this name. Indeed, systematic classification based on ranked hierarchies would not come onto the scene for over two hundred years.
The common practice at this time was to choose descriptive names based on physical characteristics. Colloquial speech referred to sharks as "sea dogs," and carcharias comes from the Greek "Carcharos" raggedwhich Belon associated with the appearance of the shark's teeth. InFrench physician Guillaume Rondelet gave us another illustration of a Great Whiteunder the name De Lamia a child-eating demon in Greek mythology.
Along with his illustration, Rondelet conveyed a tale of one specimen found with a full suit of armor in its belly. He also proposed that it was this fish, and not a whale, that was the culprit behind Jonah's Biblical plight. A whale, he postulated, did not have a throat wide enough to swallow a man whole and regurgitate him later.
The study was based on a dried specimen, thus accounting for the rather desiccated appearance. Finally, inthe word "Sharke" finally finds its place in the English language, popularized by Sir John Hawkins' sailors, who brought home a shark specimen that was exhibited in London that year. Influenced by the violent, and commonly exaggerated, Sharks Teeth, stories circulated by sailors and explorers, general perception pegged sharks as ravenous beasts intent on devouring everything in sight.
By the s, a more widespread attempt to classify fish according to form and habitat, and a fresh curiosity in shark research and diversity, found a footing in scientific research. In the mids, a famous figure emerged. InSwedish botanist and physician Carl Linnaeus published his first version of Systema Naturaeat a mere 11 pages. Within this first edition, he classified sharks in the group Condropterygiialong with lampreys and sturgeon. Linnaeus continued expanding his classification system, and in he published the tenth edition of Systema Naturae —the work we consider the beginning of zoological nomenclature.
Within this edition, Linnaeus introduced binomial nomenclature, a naming scheme which identifies organisms by genus and species, with an attempt to reflect ranked hierarchies. This system provides the foundation of modern biological nomenclature, which groups organisms by inferred evolutionary relatedness. Within Systema Naturae 10th ed.
He also presents his binomial for the Great White: Squalus carcharias. And he, like Rondelet before him, suggests that it was indeed a Great White that swallowed Jonah whole in ancient times. By the late s, we see a greater attempt to distinguish between the varieties of white sharks. FromMarcus Elieser Bloch published twelve volumes on fish under the title Allgemeine Naturgeschichte der Fischewith illustrations. And inFrench naturalist Pierre Joseph Bonnaterre gave the porbeagle shark its first scientific nameSqualus nasusdistinguishing another "white shark" as a distinct species.
French zoologist Bernard Germain de La Cepede grouped sharks, rays, and chimaeras as "cartilaginous fish," identifying 32 types, in his work Histoire Naturelle des Poissons. He describes the "white shark" as the largest shark a distinction truly held by the whale shark.
In his work The Animal KingdomFrench anatomist Georges Cuvier listed sharks as "selachians," a term still in use today as the clade including sharks: Selachimorpha. In we see the first use of the modern Great White genus name. Thus, Smith was proposing a name meaning "ragged tooth.
Finally, inSmith's genus name "Carcharodon," and Linnaeus' species name "carcharias" were pulled together to form the scientific name we know the Great White by today: Carcharodon carcharias. 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.
Template:Fact 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 may be used in navigation. This system Alex Marse - Smoky Light / Visible Darkness (File) 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. Studies on the behaviour of sharks have only recently been carried out leading to little information on the subject, although this is changing.
The classic view of the shark is that of a solitary hunter, ranging the oceans in search of food; however, 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. Some sharks can be highly social, remaining in large schools, sometimes up to over individuals of scalloped hammerheads congregating around seamounts and islands e.
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. There are many stories of dolphins protecting humans from shark attacks. This phenomenon was investigated in an episode of Discovery Channel 's Mythbustersin which a feeding great white shark did not attack either a seal cutout or raw bait when a mechanical dolphin was placed in the water nearby.
There has been no conclusive scientific study to explain this behaviour. All sharks are carnivorous. Some, including the whale shark, are filter feeders. They sieve plankton and small animals. The only larger animals that filter feed are baleen whales.
Other sharks, like the great white shark, eat fish and even marine mammals. Many bottom living shark like the zebra shark eat mollusks and crustaceans. 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. Innear Smitswinkle Bay, South Africaa 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. 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 Alex Marse - Smoky Light / Visible Darkness (File) chasing an individual trailing a piece behind them.
It is unclear how sharks sleep. Some sharks can lie on the bottom while actively pumping water over their gills, but their eyes remain open and actively follow divers.
When a shark is resting, it does not use its naresbut rather its spiracles. If a shark tried to use its nares while resting on the ocean floor, it would be sucking up sand rather than water. Many scientists believe this is one of the reasons sharks have spiracles. The spiny dogfish 's spinal cordrather than its brain, coordinates swimming, so it is possible for a spiny dogfish to continue to swim while sleeping.
It is also possible that sharks sleep in a manner similar to dolphins one cerebral hemisphere at a time, thus maintaining some consciousness and cerebral activity at all times. In the International Shark Attack File ISAF undertook an investigation into 96 alleged shark attacks, confirming 62 of them as unprovoked attacks and 16 as provoked attacks.
The average number of fatalities per year between and from unprovoked shark attacks is 4. Contrary to popular belief, only a few sharks are dangerous to humans. Out of more than species, only four have been involved in a significant number of fatal, unprovoked attacks on humans: the great whiteoceanic whitetiptigerand bull sharks. The perception of sharks as dangerous animals has been popularized by publicity given to a few isolated unprovoked attacks, such as the Jersey Shore shark attacks ofand through popular fictional works about shark attacks, such as the Jaws film series.
The author of JawsPeter Benchleyhad in his later years attempted to dispel the image of sharks as man-eating monsters. A whale shark in Georgia Aquarium. Until recently only a few benthic species of shark, such as hornsharksleopard sharks and catsharks had survived in aquarium conditions for up to a year or more. This gave rise to the belief that sharks, as well as being difficult to capture and transport, were difficult to care for.
A better knowledge of sharks has led to more species including the large pelagic sharks being able to be kept for far longer. At the same time, transportation techniques have improved and long distance movement of sharks is becoming easier.
But in September the Monterey Bay Aquarium successfully kept a young female great white shark for days before releasing her back into the wild. Sharks are found all around the globe from the north to the south in all seas, they generally do not live in freshwater except for a few exceptions like the bull shark and the river sharks which can swim both in seawater and freshwater. Sharks are common down to depths of Template:Convertand some live even deeper, but they are almost entirely absent below Template:Convert.
The deepest confirmed report of a shark is a Portuguese dogfish that was found at Template:Convert. The majority of shark fisheries around the globe have little monitoring or Sharks Teeth. With the rise in demand of shark products there is a greater pressure on fisheries.
Many other threats to sharks include habitat alteration, damage and loss from coastal developments, pollution and the impact of fisheries on the seabed and prey species. The practice of shark finningcutting the fin from a shark and discarding the live animal, attracts much controversy and regulations are being enacted to prevent it from occurring.
A Canadian-made documentary, Sharkwater is raising awareness of the depletion of the world's shark population. An estimate states that, every year, 26 to 73 million median value is at 38 million sharks are killed by people in commercial and recreational fishing. 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 othersand some species for other products. Sharks are a common seafood in many places around the world, including Japan and Australia. In the Australian State of Victoria shark is the most commonly used fish in fish and chipsin which fillets are battered and deep-fried or crumbed and grilled and served alongside chips. When served in fish and chip shops, it is called flake.
In India small sharks or baby sharks called sora in Tamil language are caught by fishermen routinely and are sold in the local markets.
Since the flesh is not developed completely it just breaks into powder once boiled and this is then fried in oil and spices called sora puttu.
Even the bones are soft and these can be easily chewed and considered a delicacy in coastal Tamil Nadu. Sharks are often killed for shark fin soup : the finning process involves the removal of the fin with a hot metal blade. Fishermen will capture live sharks, fin them, and release the finless animal back into the water. The immobile shark soon dies from suffocation or predators.
Millions of sharks a year are being illegally poached for their fins and not many governments are enforcing the laws of protecting these apex predators. The dish is considered a status symbol in Asian countries, and is considered healthy and full of nutrients, with some even claiming they prevent cancer and other ailments. Sharks are also killed for their meat. Conservationists have campaigned for changes in the law to make finning illegal in the U.
The meat of dogfishes, smoothhounds, catsharks, makos, porbeagle and also skates and rays are in high demand by European consumers. FDA lists sharks as one of four fish with swordfishking mackereland tilefish Sharks Teeth, that children and women who are or may be pregnant should refrain from eating.
For details see mercury poisoning. Shark cartilage has been advocated as effective against cancer and for treatment of osteoarthritis.
This is because many people believe that sharks cannot get cancer and that taking it will prevent people from getting these diseases, which is untrue. However, Alex Marse - Smoky Light / Visible Darkness (File), a trial by Mayo Clinic found no effect in advanced cancer patients.
Sharks generally reach sexual maturity slowly and produce very few offspring in comparison to other fish that are harvested.
This has caused concern among biologists regarding the increase in effort applied to catching sharks over time, and many species are considered to be threatened. Some organizations, such as the Shark Trustcampaign to limit shark fishing.
According to Seafood Watchsharks are currently on the list of fish that American consumers, who are sustainability minded, should avoid. Sharks figure prominently in the Hawaiian mythology.
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