A lot of the general public’s “information” on sharks comes from films like “Jaws” or the sensational coverage they receive each year during Shark Week. But often, the apocryphal tales you hear about these apex predators of the ocean are simply not true. Here, we’ll help you set your non-diving friends straight on five common misconceptions about sharks.
Sharks attack people all the time
Sharks do not set out to attack humans, nor do they “hunt” them. In fact, sharks do not enjoy human flesh. Usually shark-on-human attacks occur because the shark thinks that the person is a seal or a turtle — its natural prey. Sharks use their teeth and gums to explore unfamiliar objects and rarely consume human flesh when they do bite. Unfortunately, especially with larger species, one bite could nonetheless be fatal to a human.
If a shark stops swimming it will die
Sharks absorb oxygen directly into their bloodstream from water flowing over small capillaries in their gills. Thus, it would make sense that they need to keep swimming in order to survive. However, some shark species have evolved a few other ways to keep from swimming continuously to ‘breathe.’
Some sharks, such as wobbegongs, angel sharks and nurse sharks, use buccal breathing, which means they hold water in their cheeks and pump it over their gills in order to absorb oxygen. These species spend most of their time stationary on the ocean floor.
Other sharks, such as Caribbean reef sharks and great whites in South Africa, station 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 think that shark cartilage contains a compound that can stop a tumor 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 killing of sharks for their fins.
All they see is the sea
There are over 400 shark species in the world. While nearly all of them live in the ocean, two can also survive in freshwater rivers and brackish estuaries — the bull shark and the extremely rare Bizant river, or speartooth shark, which lives in coastal marine waters and tidal reaches of large tropical rivers in northern Australia and New Guinea. Both freshwater and saltwater fish osmoregulate, which describes how they maintain a constant concentration of water in their bodies even when the outside environment would normally cause it to lose or gain water. The bull shark adapts to fresh water by adapting its osmoregulation to survive in a broad range of salinities.
What came first — the shark, the egg…or both?
It’s a common misconception that sharks are mammals, as they give birth to live pups. The facts, however, are a bit more complicated.
It is true that some sharks, about 70 percent of species, give birth to live, fully developed young. But this is not as simple as it may seem. Sharks generally fall into three separate categories when it comes to giving birth.
Viviparous sharks give birth to live young. The eggs of viviparous sharks are fertilized inside the female’s body and are nourished by a placenta, similar to mammal fetuses. Examples include bull sharks, whitetip reef sharks and hammerheads, among others.
Oviparous sharks deposit their eggs in the water. Male oviparous sharks fertilize the eggs inside the female’s body first then, after varying amounts of time inside her body, she lays them in an egg case. These start off soft and flexible but harden in the water, often falling victim to predators. The young develop in the eggs and hatch, leaving the empty egg case behind. Examples include bamboo sharks, catsharks and zebra sharks.
Finally, ovoviviparous sharks represent a combination of the two methods. After fertilizations, the eggs hatch inside the female shark’s body, where the young live off of the egg yolks until they are born live and fully developed. Ovoviviparous sharks include white sharks, nurse sharks and tiger sharks.
Far from the scary, predatory creatures that the media tends to portray, sharks are fascinating, complicated creatures. Educate your non-diving friends and help allay these five common misconceptions about sharks.