Sharks

Sharks

  Sharks, ray, and skates, are fish that have a skeleton made of cartilage instead of bone. Cartilage is made of dense elastic connective tissues. It is the main component is collagen proteins forming the fibrous tissues. It is less rigid or as hard as bone but much lighter. All sharks have from 5 to 7 gill slits on the sides of the head depending on the species. Unlike bony fish they do not have gas filled swim bladder. Most sharks use a very large liver filled with oil instead.

 

  Earliest known primitive sharks found in the fossil record go back more than 400 million years. Sharks can be found in all but the most extreme parts of the world’s ocean. Bull sharks, sawfish, and the river sharks can survive in both seawater and freshwater. They can be found in fresh water rivers. Sharks bodies are completely covered the tooth like dermal denticles that reduces drag as the shark swims. They have several rows of teeth ready to replace those already in use. Teeth are regularly replaced throughout lifetime of the shark. Their jaws are not attached to their heads like the bony fish. Sharks have keen sense of smell and can detect as little as one part per million of blood in seawater. By swimming at different angles the can get the direction of where the blood is coming from. Sharks have organs called ampullae of Lorenzini that can detect electromagnetic fields produce by living animals and possibly used for navigation. Hammerhead sharks can find stingrays hidden in the sand by sensing the electromagnetic fields produce by the fish itself.  

  The great white shark is the largest predatory shark in the ocean. Whale Sharks are the world’s largest fish much bigger than the great white. Basking sharks and the Manta Rays can grow larger and heavier. They are filter feeders eating tiny plankton, zoo-plankton, and small fish floating in the ocean. None of these larger fishes are predators. Some individual great white’s caught by fishermen are over 20 feet long and weigh over 2 and half tons but most great whites average 15 feet and one ton.

  Great white live in sea and travel deep under water for thousands of miles to feeding or breeding grounds. But the greatest numbers of large adult great whites are found in the coastal waters of the United States, South Africa, Japan, Mediterranean, South America, and around many islands in the Pacific Ocean. Any where there are large concentrations of marine mammals they feed on.

 

  The great white shark is not an apex predator in the ocean. They are killed by bigger, smarter, faster killer whales. White sharks prey on large fish, whales and dolphins, seals, fur seals, and sea lions, along with other smaller prey. After reaching adulthood the food source becomes marine mammals because they have a large amount of fat and blubber in their bodies. The hunting method depends on the prey. For the most part it is a high speed ambush attack from below. With larger prey like the elephant seals they will wait for it to bleed to death before it starts feeding.