Sharks are a group of fish characterized by a cartilaginous skeleton with five to seven gills slits on the sides of the head and pectoral fins. Their size ranges from small, only 17 centimeters in length to 12 meters in length. They are usually found in all seas in depths of 2,000 meters (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark who can survive in both salt and fresh water.
Sharks that are apex predators are the great white shark, tiger shark, blue shark, mako shark and hammerhead shark.
Sharks have been in existence since before the time of dinosaurs, but their long reign at the top of the ocean food chain may be ending. Over the past 60 years, industrial fishing has drastically depleted the…
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