A lot of things we think we know about sharks come from films like Jaws, ‘shark week’ on television and tales passed down the diving grapevine like urban legends. These things are often misleading or only partly true. Fear not, we have compiled a list of 5 things that you thought you knew about sharks that might not be true.
- Sharks attack people all willy-nilly
Sharks do not go out to attack humans, in fact, they do not enjoy human flesh. Usually shark attacks on humans occur because the shark thinks that the person is a seal or a turtle – sharks’ natural prey. Sharks use their teeth and gums to explore objects that are unfamiliar to them and rarely consume human flesh when they do bite. Unfortunately, especially with larger species, one bite could be fatal to a human.
- If a shark stops swimming it will die
Sharks absorb oxygen directly into their blood stream from water flowing over small capillaries in their gills. Thus it would make sense that sharks need to keep moving in order to survive. However, there are two ways that some shark species have evolved so that they do not need to swim continuously to ‘breathe’.
Some sharks like wobbegongs, angel sharks and nurse sharks use Buccal breathing. They hold water in their cheeks and pump it over their gills in order to absorb oxygen.
The second method that some sharks, like Caribbean reef sharks and great whites in South Africa, use is to place themselves in an area with a strong current. This allows the current to move water over the sharks’ gills while they remain relatively stationary.
- Sharks don’t get cancer
Some researchers believe that shark cartilage contains a compound that can stop a tumour from forming the new blood vessels it needs to survive and grow. This, however, does not mean that sharks cannot get cancer.
It also does not mean that shark cartilage can cure cancer in humans, as many believe. Even though research attempting to prove that shark cartilage can cure cancer has been inconclusive, it has led to a greater demand for shark cartilage products, leading to further culling of sharks for their fins.
- All they see is the sea
There are over 400 shark species in the world. While most of them live in the ocean, two species can also be found in rivers and brackish estuaries. The bull shark and the Bizant river shark has the amazing ability to survive in fresh water and can often be found in rivers.
- What came first, the shark or the egg… or both?
The common conception is that sharks are mammals as they give birth to their pups. The facts are a bit more complicated than that though.
It is true that some shark (about 70% of species) give birth to live young, but even this is not as simple as it may seem. The eggs of viviparous sharks are fertilised inside the female’s body and are nourished by a placenta, similar to mammal babies. Sharks that are born live and fully developed are bull sharks, white tip reef sharks and hammer heads among others.
Male oviparous sharks, like Zebra and cat sharks, fertilise the eggs inside the female’s body. These eggs are then laid in an egg case which starts off being soft and flexible but hardens in the water. The young develop in the eggs and hatch, leaving the empty egg case behind.
Ovoviviparous shark have eggs that develop within the female’s body. The eggs develop inside the female shark’s body, where the young live off of the egg yolks. The young hatch from the eggs in the oviduct of the mother and are then born live and fully developed. Ovoviviparous sharks include white sharks, nurse sharks and tiger sharks.
Far from the scary, predatory creatures that they are often betrayed as, sharks are fascinating and amazing creatures. Now go on and impress your dive buddies with these new facts, you shark boffin, you!
*A version of this article was first published at www.scubadiverlife.com
