In light of Discovery Channel’s annual Shark Week, it felt timely to discuss the prehistoric cartilaginous creatures.
Since the feature film Jaws was released, sharks have been stereotyped by media as man-eating killers and have intrinsically been feared. While Shark Week 2014 was full of exaggerated images of Megalodon and far-fetched thrillers like Sharkageddon; sharks are remarkable and their true beauty is known to few.
Sharks are part of the class chondrichthyes, meaning their skeleton is made of cartilage, rather than bone. There are hundreds of species of sharks that range in size from only 17 centimeters to 12 metres in length. Sharks are found in every ocean region around the world, including off the coast of British Columbia, and are known to exist to depths of 2,000 metres.
I distinctly remember loosing my first tooth – and boy was I excited when the tooth fairy left a shiny dollar under my pillow. If ocean tooth fairies existed, they would have a full time job with sharks, which have up to 30,000 teeth over their lifetime.
Sharks have rows of teeth, which lay in a groove on the inside of their jaw. When a tooth (or teeth) is lost, another tooth from the row below simply pops up, almost like a conveyor belt.
Depending on the species, sharks can loose teeth anywhere from every eight days to every couple of months. Just like other animals, the shape of the shark’s teeth reflect their food choices; for example, sharks with flatter teeth use them for crushing shelled animals, whereas sharks with sharp-serrated teeth use theirs to tear through the tough skin of larger fish and mammals.
When sharks are filmed in the wild they are almost always moving. In fact, most sharks move at approximately eight km/h, but can increase their speed upwards of 19 km/h when hunting. If sharks don’t constantly move they can sink.
Most fish in the ocean have something called a swim-bladder, which is a gas-filled organ that allows fish to change their buoyancy and remain at a specific depth without swimming. Sharks do not have swim-bladders and instead they have a very large liver filled with a special oil called squalene. However, the liver is still often too heavy and thus most sharks must continually swim to stay buoyant.
Senses are an important part of survival and sharks are no exception. Like many other ocean animals, sharks have a keen sense of smell, sight and sound.
Sharks have such a keen sense of smell that they can even determine the direction from which it came.
A shark’s sense of sight is often debated. While sharks have relatively good eyesight and some unique adaptations, it is unconfirmed how much they actually use their eyesight in hunting compared to their other senses.
While testing a shark’s sense of hearing is difficult, it is thought they can hear prey from miles away. Furthermore, like many other fish, sharks can detect vibrations in the water.
Sharks however, have a “sixth sense” that is, sharks can detect electromagnetic fields that are produced by living creatures, using specialized electroreceptor organs called, ampullae of Lorenzini. Sharks have the greatest electrical sensitivity of any animal and use this special sense to find prey, orient themselves and possibly even navigate throughout the ocean based on the Earth’s magnetic field.
Sharks brood their young in three different ways. Some species bare live young, others nourish the embryo internally, while other species lay eggs. “Egg laying” sharks (and skates) produce a special pouch, called a Mermaid’s Purse that protects the eggs until they hatch. Mermaid’s purses have a leathery texture and resemble dried up seaweed; they can be found washed up on the beach, so keep an eye out for them.
Although sharks often don’t get a lot of empathy, they are remarkable animals and have outlived many species over the last 400 million years. As scientists continue to study and understand these creatures, I hope the public’s perception of them will continue to change for the positive – from feared to loved.
There is still much to learn about sharks and protecting the remaining populations is crucial for their survival. To learn more about these sea giants and to share your voice for their protection, check out the following links: sharkwater.com and fin-free.com.
Combining her passions for education and the marine ecosystem Natasha Ewing inspires K-12 teachers and students to incorporate hands-on experiential ocean science into the classroom for Ocean Networks Canada.