Tuesday, April 23, 2013

Near New Caledonia, up until the practice was banned

Near New Caledonia, up until the practice was banned, fishermen and commercial vessels used to dredge the sea floor for megalodon teeth. In Oceania and America, shark teeth were commonly used for tools, especially on weapons such as clubs and daggers, but also as blades to carve wood and as tools for food preparation. Sony Vaio VGN-FZ31ZR Battery For example, various weapons edged with shark teeth were used by the Native Hawaiians (see example here[6]), who called them leiomano.[7] Some types were reserved for royalty.[8] TheGuaitaca (Weittaka) of coastal Brazil tipped their arrows with shark teeth.[9] The remains of shark tooth-edged weapons, as well as chert replicas of shark teeth, have been found in the Cahokia mounds of the upper Mississippi River valley, more than 1,000 km (620 mi) from the ocean.[10] Sony Vaio VGN-FZ31SR Battery It is reported that the rongorongo tablets of Easter Island were first shaped and then inscribed using a hafted shark tooth. The lateral line is a system of sense organs found in aquatic vertebrates, chiefly fish, used to detect movement and vibration in the surrounding water. Sony Vaio VGN-FZ31ER Battery The sensory ability is achieved via modified epithelial cells, known ashair cells, which respond to displacement caused by motion, movement and transduce these signals into electrical impulses via excitatory synapses. Sony Vaio VGN-NR31E/S Battery Lateral lines serve an important role in schooling behavior, predation, and orientation. For example, fish can use their lateral line system to follow the vortices produced by fleeing prey. They are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill coversto the base of the tail. Sony Vaio VGN-NR31ER/S Battery In some species, the receptive organs of the lateral line have been modified to function as electroreceptors, which are organs used to detect electrical impulses, and as such these systems remain closely linked. Most amphibian larvae and some fully aquatic adult amphibians possess mechanosensitive systems comparable to the lateral line. Sony Vaio VGN-NR31J/S Battery The lateral line system allows the detection of movement and vibrations in the water surrounding an animal, providing spatial awareness and the ability to navigate in space. This plays an essential role in orientation, predatory behavior, and social schooling. Sony Vaio VGN-NR31MR/S Battery In a 2001 study, researchers demonstrated that the lateral line system was necessary to detect vibrations made by prey and to orient towards the source to begin predatory action.[2] Fish were able to detect movement, produced either by prey or a vibrating metal sphere, and orient themselves toward the source before proceeding to make a predatory strike at it. Sony Vaio VGN-NR31S/S Battery This behavior persisted even in blinded fish, but was greatly diminished when lateral line function was inhibited by CoCl2application. This cobalt chloride treatment results in the release of cobalt ions, disrupting ionic transport and preventing signal transduction in the lateral lines.[3] Further trials utilizing either a gentamicin dip or external scraping of the lateral lines,Sony Vaio VGN-NR31SR/S Battery to disrupt canal and superficial receptors respectively, demonstrated that these behaviors were dependent specifically on mechanoreceptors located within the canals of the lateral line.[2] The role mechanoreception plays in schooling behavior was demonstrated in a 1976 study by Pitcher, et al. Sony Vaio VGN-NR31Z/S Battery A school ofPollachius virens was established in a tank and individual fish were removed and subjected to different procedures before their ability to rejoin the school was observed. Fish that were experimentally blinded were able to reintegrate into the school, while fish with severed lateral lines were unable to reintegrate themselves. Sony Vaio VGN-NR31Z/T Battery Therefore, reliance on functional mechanoreception, not vision, is essential for schooling behavior. The major unit of functionality of the lateral line is the neuromast. The neuromast is a mechanoreceptive organ which allows the sensing of mechanical changes in water. There are two main varieties of neuromasts located in animals, canal neuromasts and superficial or freestanding neuromasts. Sony Vaio VGN-NR31ZR/S Battery Superficial neuromasts are located externally on the surface of the body, while canal neuromasts are located along the lateral lines in subdermal, fluid filled canals. Each neuromast consists of receptive hair cells whose tips are covered by a flexible and jellylike cupula. Hair cells typically possess both glutamatergic afferent connections andefferent connections using acetylcholine.[5] Sony Vaio VGN-NR38E/S Battery The receptive hair cells are modified epithelial cells and typically possess bundles of 40-50 microvilli "hairs" which function as the mechanoreceptors.[6] These bundles are organized in rough "staircases" of hairs of increasing length order.[7] This use of mechanosensitive hairs is homologous to the functioning of hair cells in the auditory and vestibular systems, indicating a close link between these systems.[8] Sony Vaio VGN-NR38M/S Battery Hair cells utilize a system of transduction that uses rate coding in order to transmit the directionality of a stimulus. Hair cells of the lateral line system produce a constant, tonic rate of firing. As mechanical motion is transmitted through water to the neuromast, the cupula bends and is displaced. Sony Vaio VGN-NR38S/S Battery Varying in magnitude with the strength of the stimulus, shearing movement and deflection of the hairs is produced, either toward the longest hair or away from it. This results in a shift in the cell’s ionic permeability, resulting from changes to open ion channels caused by the deflection of the hairs. Sony Vaio VGN-NR38Z/S Battery Deflection towards the longest hair results in depolarization of the hair cell, increased neurotransmitter release at the excitatory afferent synapse, and a higher rate of signal transduction. Deflection towards the shorter hair has the opposite effect,hyperpolarizing the hair cell and producing a decreased rate of neurotransmitter release.[8] Sony Vaio VGN-NR38Z/T Battery These electrical impulses are then transmitted along afferent lateral neurons to the brain. While both varieties of neuromasts utilize this method of transduction, the specialized organization of superficial and canal neuromasts allow them differentmechanoreceptive capacities. Located at the surface of an animal’s skin, superficial organs are exposed more directly to the external environment. Sony Vaio VGN-NR31E/S Battery Though they these organs possess the standard "staircase" shaped hair bundles, overall the organization of the bundles within the organs is seemingly haphazard, incorporating various shapes and sizes of microvilli within bundles. This suggests a wide range of detection, potentially indicating a function of broad detection to determine the presence and magnitude of deflection caused by motion in the surrounding water.[7] Sony VPCW11S1E/P Battery In contrast, the structure of canal organs allow canal neuromasts to be organized into a network system that allows more sophisticated mechanoreception, such as the detection of pressure differentials. As current moves across the pores of a canal, a pressure differential is created over the pores. Sony VPCW11S1E/P Battery As pressure on one pore exceeds that of another pore, the differential pushes down on the canal and causes flow in the canal fluid. This moves the cupula of the hair cells in the canal, resulting in a directional deflection of the hairs corresponding to the direction of the flow.[9] This method allows the translation of pressure information into directional deflections which can be received and transduced by hair cells. Sony VPCW11S1E/T Battery The mechanoreceptive hair cells of the lateral line structure are integrated into more complex circuits through their afferent and efferent connections. The synapses that directly participate in the transduction of mechanical information are excitatory afferent connections that utilize glutamate.[10] Sony VPCW11S1E/W Battery However, a variety of different neuromast and afferent connections are possible, resulting in variation in mechanoreceptive properties. For instance, a series of experiments on the superficial neuromasts of Porichthys notatus revealed that neuromasts can exhibit a receptive specificity for particular frequencies of stimulation.[11] Sony VPCW12S1E/P Battery Using an immobilized fish to prevent extraneous stimulation, a metal ball was vibrated at different frequencies. Utilizing single cell measurements with a microelectrode, responses were recorded and used to construct tuning curves, which revealed frequency preferences and two main afferent nerve types. Sony VPCW12S1E/T Battery One variety is attuned to collect mechanoreceptive information about acceleration, responding to stimulation frequencies between 30–200 Hz. The other type is sensitive to velocity information and is most receptive to stimulation below <30 Hz. This suggests a more intricate model of reception than was previously considered.[11] Sony VAIO VGN-NR21E/S Battery The efferent synapses to hair cells are inhibitory and utilize acetylcholine. They are crucial participants in a corollary discharge system designed to limit self-generated interference.[12] When a fish moves, it creates disturbances in the water that could be detected by the lateral line system, potentially interfering with the detection of other biologically relevant signals. Sony VAIO VGN-NR21J/S Battery To prevent this, an afferent signal is sent to the hair cell upon motor action, resulting in inhibition which counteracts the excitation resulting from reception of the self-generated stimulation. This allows the fish to retain perception of motion stimuli without interference created by its own movements. After signals transduced from the hair cells are transmitted along lateral neurons, they eventually reach the brain. Sony VAIO VGN-NR21S/S Battery Visualization methods have revealed that the area where these signals most often terminate is the medial octavolateralis nucleus (MON).[13] It is likely that the MON plays an important role in the processing and integrating mechanoreceptive information.[13] This has been supported through other experiments, such as the use of Golgi staining and microscopy by New & Coombs to demonstrate the presence of distinct cell layers within the MON. Sony VAIO VGN-NR21S/T Battery Distinct layers of basilar and non-basilar crest cells were identified within the deep MON. Drawing a comparison to similar cells in the closely related etectrosensory lateral line lobe of electric fish, it seems to suggest possible computational pathways of the MON. The MON is likely involved in the integration of sophisticated excitatory and inhibitory parallel circuits in order to interpret mechanoreceptive information. Sony VAIO VGN-NR11Z/T Batteryshark attack is an attack on a human by a shark. Every year around 100 shark attacks are reported worldwide. Seventeen fatalities are recorded as having being caused by shark attacks in 2011, out of 118 recorded attacks.[1]Despite their relative rarity, many people fear shark attacks after occasional serial attacks, such as the Jersey Shore shark attacks of 1916, Sony VAIO VGN-NR11Z/S Battery and horror fiction and films such as the Jaws series. Almost all shark experts consider that the danger presented by sharks has been exaggerated. The creator of the Jaws phenomenon, Peter Benchley, attempted to dispel the myth of sharks being man-eating monsters in the years before his death. According to the International Shark Attack File (ISAF), between 1580 and 2011 there were 2,463 confirmed unprovoked shark attacks around the world, of which 471 were fatal.[2] Sony VAIO VGN-NR11S/S Battery Although Australia is ranked the second highest in terms of global shark attacks with 877 attacks, it is ranked the highest in terms of shark fatalities, with 217 fatalities.[3][4][5]Australia had the most shark attacks in 2008, with 48 attacks Australia wide; 11 of these were fatal. The highest death rate occurred in Queensland with the total of 6 fatal attacks.[6] Sony VAIO VGN-NR11M/S Battery In 2000, there were 79 shark attacks reported worldwide, 11 of them fatal.[7] In 2005 and 2006 this number decreased to 61 and 62 respectively, while the number of fatalities dropped to only four per year.[7] Of these attacks, the majority occurred in theUnited States (53 in 2000, 40 in 2005, and 39 in 2006).[8] Sony VAIO VGN-SR11M Battery The New York Times reported in July 2008 that there had been only one fatal attack in the previous year.[9] On average, there are 16 shark attacks per year in the United States with one fatality every two years.[10] Despite these reports, however, the actual number of fatal shark attacks worldwide remains uncertain. Sony VAIO VGN-SR11MR Battery For the majority of Third World coastal nations, there exists no method of reporting suspected shark attacks; therefore, losses and fatalities at near-shore or sea there often remain unsolved or unpublicized.Australia has the highest amount of fatal shark attacks in the world with Western Australiarecently becoming the deadliest place in the world for shark attacks.[5] Sony VAIO VGN-SR19VN Battery Less than one in every three million scuba dives in Western Australia result in a fatal shark attack.[12]Australia and South Africa's fatality rate for shark attacks is approximately 30 percent. The United States has the highest reported amount of shark attacks but has the lowest fatality rate with around 4 percent of those attacked dying. Sony VPCCW1S1R Battery The United States has had a total of 1,085 attacks (44 fatal) during the past 342 years (1670–2012).[13] According to the ISAF, the states in the U.S. where the most attacks have occurred in are Florida,Hawaii, California, Texas, and the Carolinas, though attacks have occurred in almost every coastal state.[13] South Africa has a high number of shark attacks along with a high fatality rate of 27 percent.[14] Sony VPCCW1S1T Battery The location with the most recorded shark attacks is New Smyrna Beach, Florida.[15] First world nations such as the United States, Australia, both high income countries, and to some extent South Africa, an upper middle income country, facilitate more thorough documentation of shark attacks on humans than poorer coastal countries. Sony VPCCW1S1T/R Battery The Florida Museum of Natural History compares these statistics with the much higher rate of deaths from other, less feared causes. For example, an average of more than 38 people die annually from lightning strikes in coastal states, while less than 1 person per year is killed by a shark.[16][17] In comparison, 100 million sharks are killed every year by humans. Sony VPCCW1S1T/W Battery Even considering only people who go to beaches, a person's chance of getting attacked by a shark in the United States is 1 in 11.5 million, and a person's chance of getting killed by a shark is less than 1 in 264.1 million.[21][22] In the United States, the annual number of people who drown is 3,306, whereas the annual number of shark fatalities is 1. Sony VPCCW1Z4E Battery Contrary to popular belief, only a few sharks are dangerous to humans. Out of more than 360 shark species, only three are responsible for two-digit number of fatal unprovoked attacks on humans: the great white, tiger andbull;[24] however, the oceanic whitetip has probably killed many more castaways, not recorded in the statistics.[25] Sony VPCCW12EN/BU Battery These sharks, being large, powerful predators, may sometimes attack and kill people; however, they have all been filmed in open water by unprotected divers.[26][27] The 2010 French film Oceans shows footage of humans swimming next to sharks deep in the ocean. It is possible that the sharks are able to sense the presence of unnatural elements on or about the divers, Sony VAIO VGN-FW139E Battery such as polyurethane diving suits and air tanks, which may lead them to accept temporary outsiders as more of a curiosity than prey. Uncostumed humans, however, such as those surfboarding, light snorkeling, or swimming, present a much greater area of open meaty flesh to carnivorous shark predators. Sony VAIO VGN-FW139N Battery In addition, the presence of even small traces of blood, recent minor abrasions, cuts, scrapes, or bruises, may convince sharks to attack a human in their environment. Some sharks such as the hammerhead sharkseek out prey through electroreception, sensing the electric fields that are generated by all animals due to the activity of their nerves and muscles. Sony VAIO VGN-FW140E Battery Most of the oceanic whitetip shark's attacks have not been recorded,[25]unlike the other three species mentioned above. Famed oceanographic researcher Jacques Cousteau described the oceanic whitetip as "the most dangerous of all sharks".[28] Modern-day statistics show the oceanic whitetip shark as being seldom involved in unprovoked attacks. Sony VAIO VGN-FW145E Battery However, there have been a number of attacks involving this species, particularly during World War I and World War II. The oceanic whitetip lives in the open sea and rarely shows up near coasts, where most recorded incidents occur. During the world wars, many ship and aircraft disasters happened in the open ocean, and due to its former abundance, the oceanic whitetip was often the first species on site when such a disaster happened. Sony VAIO VGN-FW160E Battery Infamous examples of oceanic whitetip attacks include the sinking of the Nova Scotia, a British steamship carrying 1,000 people, that was sunk on 28 November 1942 near South Africa by a German submarine in World War II. Only 192 people survived, with many deaths attributed to the oceanic whitetip shark.[29] Sony VAIO VGN-FW180E Battery The same species is probably responsible for many of the of the 60–80 or more shark casualties following the torpedoing of the USS Indianapolis on 30 July 1945.[30] Tiger sharks may also have been involved. Sony VAIO VPCS11X9E Battery In addition to the four species responsible for a significant number of fatal attacks on humans, a number of other species have attacked humans without being provoked, Sony VAIO VGN-FW190E Battery and have on extremely rare occasions been responsible for a human death. This group includes the shortfin mako, hammerhead, Galapagos, gray reef, blacktip reef, lemon, silky, and blue sharks.[24] These sharks are also large, powerful predators which can be provoked simply by being in the water at the wrong time and place, but they are normally considered less dangerous to humans than the previous group. Sony VAIO VPCS11B7E Battery A few other shark species do attack people every year, producing wounds that can potentially kill, but this occurs either specifically because they have been provoked, or through mistaken identity due to water conditions or the like. In the evening of 16 March 2009, a new addition was made to the list of sharks known to attack human beings. Sony VAIO VPCS11M1E/W Battery In a painful but not directly life-threatening incident, a long-distance swimmer crossing the Alenuihaha Channel between the islands of Hawai‘i and Maui was attacked by acookiecutter shark. The 2 bites, delivered about 15 seconds apart, were not immediately life-threatening.[31] A great white shark is believed to be responsible for an attack on a swimmer at Muriwai Beach in Auckland, New Zealand in February 2013. Sony VAIO VPCS11M9R/B Battery It was the first confirmed shark attack fatality in the country since 1976. Shark attack indices use different criteria to determine if an attack was "provoked" or "unprovoked." When considered from the shark's point of view, attacks on humans who are perceived as a threat to the shark or a competitor to its food source are all "provoked" attacks. Sony VAIO VPCS11V9E/B Battery Neither the International Shark Attack File (ISAF) nor the Global Shark Attack File (GSAF) accord casualties of air/sea disasters "provoked" or "unprovoked" status; these incidents are considered to be a separate category.ostmortem scavenging of human remains (typically drowning victims) are also not accorded "provoked" or "unprovoked" status. Sony VAIO VPCS12A7E Battery The GSAF categorizes scavenging bites on humans as "questionable incidents." Provoked attacks occur when a human touches a shark, pokes it, teases it, spears, hooks, or nets it, or otherwise aggravates/provokes it in a certain manner. Sony VAIO VPCS11V9E Battery Incidents that occur outside of a shark's natural habitat, e.g., aquariums and research holding-pens, are considered provoked, as are all incidents involving captured sharks. Sony VAIO VPCS12A7R Battery Sometimes humans inadvertently "provoke" an attack, such as when a surfer accidentally hits a shark with a surf board. Sony VAIO VPCS12B7E Battery,Sony VAIO VPCS12C5E Battery,Sony VAIO VPCS12D7E Battery

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