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March 24, 2016 | Author: | Posted in literature and language

Throughout time sharks have been deemed man-eaters ‘ or dangerous animals . However , there are over 365 species of sharks and only a select few have inflicted fatal , malicious human attacks : tiger , great white bull , and white-tip oceanic sharks . Although sharks are large and powerful creatures , they are also very curious and many attacks are they result of an exploratory bite

Sharks belong to the Chondrichthyes elasmobranchii and are fish , but unlike fish have a completely cartilaginous skeleton that is light and flexible (Hamlett , 1999 . The body is covered with small outgrowths called [banner_entry_middle]

denticles . These denticles are incredibly rough and are similar in structure to their teeth . Studies have found that denticles create vortices that reduce drag as the shark swims to become more efficient (Hamlett , 1999

Caudal fins of sharks vary between species . The tail provides speed and acceleration is depended on the caudal shape . For example , the tiger shark ‘s large upper lobe gives maximum power and sudden busts of speed (Nelson , 1994 . An average shark will cruise at five miles per hour yet when attacking prey , can reach speeds of 12 mile per hour . The short fin mako shark is considered to be the fastest shark reaching speeds over 30 miles per hour (Martin , 2006 . Tail adaptations have other purposes than speed . The cookie-cutter shark has broad lobes that are luminescent , which are believed to entice prey towards the shark (Nelson , 1994

These creatures respire by extracting oxygen from the saltwater environment and pass it over the gills . Due to the shark ‘s large size many require a higher supply of oxygen than other fish and must be continually swimming in to meet the demands or the shark will suffocate (Hamlett , 1999 . This process is known as ram ventilation Fishes have gas-filled swim bladders – sharks do not . They have a large oil-filled liver , which can compose up to 25 percent of the weight , for buoyancy . Nevertheless , their buoyancy is limited , and they will sink if swimming is halted (Compagno , et al , 2005 . It is also noted that if inverted , sharks enter what is called a natural state of tonic immobility . Researchers use this as a safe handling technique (Pratt , et al , 1990

Carnivorous sharks do not have teeth at the mandible , but embedded in the flesh that are constantly replaced throughout the shark ‘s life . Sharks have multiple top and bottom rows of teeth that are replaced every 10 days to several months depending on the species . Teeth are in various shapes that serve many purposes from gripping , cutting or crushing shellfish (Hamlett , 1999

Sharks have keen olfactory senses that can detect one part per million of blood in their environment . Sharks rely on the sharp sense of smell to detect prey . Their sight is similar to vertebrates that consist of lenses , corneas , and retinas Hamlett , 1999 . Sharks eyesight is adapted to dark waters with the help of a specialized tissue called the tapetum lucidium , which reflects light back to the retina allowing them to see in… [banner_entry_footer]

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