By Skip Clement
Shark Attack Deaths In The U. S. Versus Other Unprovoked Causes
Boating in Florida (2002 to 2013) 8,979. Sharks two.
Rip currents (2004 to 2013) 341,294. Sharks eight.
Lightning (1959 to 2010 1,970. Sharks 26.
Alligators (six states) 391. Sharks in those states, nine.
Dog attacks (2001 to 2013) 364. Sharks 11.
Hunting (2000 to 2007) 4,494. Sharks seven.
• Currently, there are approximately 400 described species of sharks.
• Fossil records indicate that ancestors of modern sharks swam the seas over 400 million years ago, making them older than dinosaurs. Throughout time sharks have changed very little.
• Some sharks like the smooth dogfish may only live 16 years, while others such as the porbeagle shark (Lamna nasus) may live as long as 46 years. Whale sharks, the largest fish in the world, may live over 100 years!
• It was once believed that all sharks had to swim continuously to breathe and could not sleep for more than a few minutes at a time. While some species of sharks do need to swim continuously, this is not true for all sharks. Some sharks such as the nurse shark have spiracles that force water across their gills allowing for stationary rest. Sharks do not sleep like humans do but instead have active and restful periods.
• Sharks can open and close the pupil in response to different light situations similar to humans while most fish do not possess this ability. A shark’s eye also includes a cornea, iris, lens, and retina. Rods and cones are located in the shark’s retina, allowing the shark to see in differing light situations as well as to see color and detail.
Also, sharks, similar to cats, have a mirror-like layer in the back of the eye referred to as the tapetum lucidum. This layer further increases the intensity of incoming light, enhancing the eye’s sensitivity to light.
Although it was once thought that sharks had inferior vision, we now know that sharks have sharp vision. Research has shown that sharks may be more than 10x as sensitive to light as humans. Scientists also believe that sharks may be far-sighted, able to see better at a distance rather than close-up, due to the structure of the eye. Vision varies among species of sharks due to differences in the size, focusing ability, and strength of the eyes.
• Sharks have an excellent sense of hearing with ears located inside their heads on both sides rather than external ears like humans. Sharks can hear best at frequencies below 1,000 Hertz which is the range of most natural aquatic sounds. This sense of hearing helps shark locate potential prey swimming and splashing in the water. Sharks also use their lateral line system to pick up vibrations and sounds.
• Sharks have lots of teeth arranged in layers so if any break-off, new sharp teeth can immediately take their place. Sharks can shed thousands of teeth during their life; this is why sharks teeth can be found washed onto beaches. Shark teeth also fossilize easily while the rest of the shark decomposes.
• It has been recorded to reach swimming speeds of up to 20 mph (32 km/h). It can chase down some of the fastest fishes such as tuna and swordfish.
• The largest shark, and also the largest fish in the ocean is the whale shark (Rhincodon typus). This massive plankton-feeder reaches lengths of over 20m (60-feet).
Coming soon: Part II – It’s Shark Week, Let’s Start With Some Tarnished Facts