20 Shark Facts

The history of sharks dates back millions of years. Mankind's fascination with sharks is a mix of myth and reality, fact and superstition, and it is punctuated with fear of the unknown.

Divers appreciate sharks because sharks are intelligent yet primal predators. The excitement and drenaline rush of observing these creatures in their natural environment keeps divers coming back for more. A little knowledge goes a long way in making shark diving a wonderful experience. Here are twenty of my favorite shark facts.

• Great White Sharks grow about 10 inches per year. Great Whites can grow to mature lengths of 12 to 14 feet.
  
• New teeth are constantly being formed in rows in a shark's jaw. Shark's teeth are normally replaced every eight days.
  
• Some species of sharks can shed as many as 30,000 teeth in their lifetime.
  
• Whale Sharks have approximately 300 rows of teeth, with hundreds of tiny teeth in each row.
  
• Dried shark skin (shagreen) was used in the past as sandpaper. In Germany and Japan, shark skin was used on sword handles for a non-slip grip.
  
• In 1937, shark liver oil was discovered to be rich in vitamin A. Sharks were hunted for the vitamin until 1950, when a synthesizing method was developed for vitamin A.
  
• The average life span of a shark is 25 years, but some sharks can live to be 100.
  
• The dogfish sharks are named for their tendency to attack their prey as a pack of wild dogs would.
  
• Great White Sharks can go as long as three months without eating.
  
• Not all sharks have to be in continuous motion to breathe.
  
• Bull Sharks can tolerate a wide range of salinity and are often found in freshwater rivers and lakes in Africa and South America.
  
• More people are killed each year by dogs, pigs and deer than by sharks.
  
• The Pygmy Shark has a maximum length of 11 inches.
  
• Sharks have no bones. A shark's skeleton is made up of cartilage.
  
• There are more than 340 known species of sharks.
  
• Sharks first appeared in the fossil record over 400 million years ago.
  
• A significant physical trait that separates a modern shark from an ancient shark is the protrusile jaw, which gives the modern shark more biting force.
  
• Sharks can generate about six and a half tons per square inch of biting force.
  
• A shark's skin is embedded with dermal denticles, which resemble teeth.
  
• The Shortfin Mako shark is probably the fastest fish in the ocean, clocked at about 60 mph.