The Truth About Sharks – By Gloria Hoffner, BA, ADC, AC-BC, CDP

Sharks. They have lived on Earth over 400 million years and became the staring nightmares of popular movie, television shows and summer reading lists for over 50 years.  While the opening scenes of the movie “Jaws” may be the first thing most people think of when hearing the word ‘Shark!’, here are some facts and a fun experiment.

1. What is a shark? Answer – A shark is NOT a fish. Sharks are in a group called Class Chondrichthyes. Unlike fish, sharks have no bones, only cartilage and no gills, but rather slits on the side of their bodies to extract oxygen from water.
2. How long have sharks been on Earth? Answer – Sharks appeared on Earth about 450 million years ago. Fish appeared about 510 million years ago and the first multi-cell life on the planet appeared in the ocean about 580 million years ago.
3. How many kinds of sharks live on our planet? Answer – About 470. They range in size from a seven-inch Spined Pygmy to a 50-foot Whale Shark.
4. What do sharks eat? Answer – Most eat fish, squid and crustaceans.
5. Where do sharks live? Answer – Most sharks swim in warm waters between 68.9- and 86-degree Fahrenheit. The Greenland Shark is an exception living in arctic and sub-arctic waters at a depth of 600 to 2,400 feet.
6. How long do sharks live? Answer – On average 20 to 30 years. However, Whale Sharks can live 100 years and Greenland Sharks can live over 400 years.
7. What is the life span of a Great White Shark (star of the movie “Jaws”)? Answer – A Great White can live to be 70 years old.  A male is about 20 feet long and a female about 15 feet long.
8. How do sharks mate? Answer – There are many different kinds of sharks and mating rituals vary however in general, the females release chemicals into the water indicating their interest in mating.  A male picks up the smell and bit the fin of the female to get her attention.
9. How long is a female shark pregnant? Answer – It is hard to observe, but scientists believe some sharks, such as Basking Sharks, are pregnant for three years.
10. How do sharks give birth? Answer – There are two methods. Some, such as Blue Sharks, have fertilized eggs that hatch inside their bodies. Others, such as Hornsharks, deposit eggs in a coral reef where the eggs later hatch.
11. Why do we need sharks? Answer – There are several reasons.

•  Sharks feed on the weak and diseased ocean population and keep species volume in check. 
• Scientists have found shark tissue has qualities that might be used to cure cystic fibrosis in humans. 
•  Deep sea sharks feeding on dead creatures in the ocean help remove carbon from the oceans.
• Energy researchers are building models of shark tails seeking a way to generate pollution free energy. Shark tourism, people who want to see, swim and learn about sharks, generates over $300 million a year worldwide.

12. How do sharks help fight cancer in humans? Answer – Shark oil is used in the treatment of leukemia and cervical cancers by reducing the radiation illness caused by cancer x-ray therapy.

13.  How many humans a year are harmed by a shark? Answer – According to National Geographic, 2010 was the most dangerous year for shark attacks with 79 humans being harmed worldwide. Surfers are the usual victims of shark attacks. Your chances of being killed by a shark are one in 3.7 million. Compare this to your chance of being killed by the flu which is 1 in 63.

14. How many sharks are killed by humans? Answer – Scientists estimate is it 273 million every year.

15.  Why do humans kill sharks? Answer – Sharks are killed for their fins, used in Asia to make soup. They are also killed for food, sold in U.S. fish markets and sometimes killed and used as bate by fishermen.

16. What would happen if sharks went extinct? Answer – It would upset the balance of life in the oceans and create overpopulation and limited food supplies for some species.

Experiment: How do sharks swim?

Materials: Empty paper towel tube, scissors, balloon, large clear bowl, water and cooking oil.

Process: Cut the paper towel tube into two equal parts. Fill the bowl with water. Place one paper tube on the top of the bowl of water and observe.

Remove the paper tube. Fill the balloon with cooking oil and tie shut. Place the filled balloon into the second paper tube. Place the paper tube on the top of the bowl of water and observe.

Result: The tube of paper fills with water and sinks, but the tube with the balloon filled with oil floats. The oil in the balloon filed tube represents the oil in a shark.

A sharks’ liver has two parts filled with oil and fat. Oil and fat are lighter than water and thus float. The shark’s liver is 30 percent of the sharks’ weight thus the buoyancy helps them to float.

Gloria Hoffner is the author of the book Science for Seniors and can be reached at: Scienceforseniors.net