10 Interesting Facts About Sharks
Sharks are thought of as murderous and bloodthirsty animals, but not all species live up to this stereotype. Here are 10 interesting facts about sharks, as these cartilaginous fish have fascinating traits that go far beyond their jaws and predatory nature.
Sharks represent the pinnacle of the food chain in the marine ecosystem and, moreover, their appearance dates back to ancient times. These living fossils have archaic traits from an evolutionary point of view, but still remain the undisputed kings of the seas. Learn more about them in the following lines.
1. Sharks have no bones
It’s often said that all sharks are fish, but it should be noted that this classification is of little taxonomic interest. In reality, sharks are located in the class Chondrichthyes, characterized by the absence of bones. Sharks, rays, and chimeras are in this group and have a cartilaginous skeleton.
Specifically, all sharks are grouped in the superorder Selachimorpha. There are thought to be about 500 species within this taxon (plus all those yet to be discovered) and they’re notable for their behavioral and ecosystemic variability. In other words, sharks are fish in the strict sense of the word, but they don’t share a class or order with those that have a bony skeleton.
2. Their skin is real armor
Unlike bony fish, sharks have special scales made of flexible collagen fibers. These structures are called placoid scales and are analogous to vertebrate teeth. They’re very strong, but create vortices in the water current and greatly reduce the energy expenditure of the shark when swimming.
These scales are hydrodynamic, so they allow the shark to swim with as little energy expenditure as possible.
3. An overwhelming body variety
One of the most striking curiosities of sharks are the adaptions they have undergone since their appearance (420 million years ago). All sharks have a fusiform body, gills, and 8 fins: 2 dorsal, 2 pelvic, 2 pectoral, one anal and one caudal. Beyond these common features, the variability is very strong.
For example, the smallest species recorded to date is Etmopterus perryi,at about 20 centimeters (8 inches) in length. On the other extreme is the whale shark (Rhincodon typus), whose size can easily exceed 18 meters (60 feet). Its mouth alone measures more than 1 meter (3,3 feet) and its skin is 10 centimeters (4 inches) thick.
Sharks have immense variability, as they have adapted to a wide range of environments and strategies in their long history.
4. A different type of jaw
As is the case with rays and other cartilaginous fish, sharks’ jaws aren’t attached to their skulls. For this reason, they’re able to open it much more than most vertebrates without hurting themselves. However (and due to the mechanical stress it suffers), the jaw apparatus requires constant support: the tesserae.
Tesserae are crystalline blocks of calcium in a mosaic pattern. Thanks to them, the jaw is strong and ready to absorb mechanical stress.
5. Experts at staying afloat
Another of the sharks’ curiosities is that they don’t have a swim bladder, a gas-filled structure that allows bony fish to modulate their buoyancy in the water column. How can sharks float in the vastness of the sea? The answer lies in their liver, which is filled with a substance known as squalene.
The liver environment accounts for 30% of the shark’s weight and enables its buoyancy. However, its usefulness is limited and the animal must rely largely on the lift force of locomotion in the aquatic environment to stay afloat.
6. Natural born trackers
As indicated by the Oceana website, sharks are excellent predators and must have an infallible tracking system to locate their victims. For this reason, they have specialized olfactory receptors capable of detecting even a drop of blood among a million units of fresh water. Their detection range can exceed 100 meters (330 feet).
7. Teeth in rows
Another of the most striking curiosities of sharks is detected by observing their jaws. While humans have an average of 32 permanent teeth, sharks have rows of teeth underneath the ones they use and these never stop growing. Sharks can lose up to 1000 teeth per year, but they renew them without any difficulty.
A tiger shark (Galeocerdo cuvier) can lose up to 24,000 teeth in just 10 years.
8. Sharks can’t stop swimming
Surely this fact is already familiar to you, as it’s one of the best-known facts about sharks. Due to their primal physiology, some sharks must remain all the time with their mouths open and their bodies moving in order to pump water through their gills. If they were to stop, they would drown due to a lack of oxygen in their tissues.
Although this may seem surprising, it should be noted that not all sharks have this limitation. Some bottom-dwelling species have spiracles behind their eyes, a feature that allows them to oxygenate their brain and ocular apparatus even when they’re standing still. They can, therefore, rest on the seabed without drowning.
9. An accessory sense
In addition to their powerful sense of smell, sharks have an accessory sense that helps them hunt. These cartilaginous fish carry ampullae of Lorenzini distributed throughout their cephalic region (from hundreds to thousands) whose function is to register the electrical signals emitted in the environment. Therefore, they’re able to detect prey underground, thanks to the electromagnetic field emitted by their bodies.
Hammerhead sharks (belonging to the genus Sphyrnidae) have the most finely tuned sense of electroreception.
10. Sharks are endangered
Unfortunately, it’s very difficult to end an article like this on a positive note. Sharks are the kings of the seas, and have survived thousands of years of evolutionary pressure, but they can’t stand up to the biggest threat on Earth: human activity.
It’s estimated that 100 million sharks are killed each year by fishing (accidental or voluntary) for monetary purposes. Shark populations have declined by 71% in just over 50 years. If the populations of these cartilaginous giants aren’t protected, soon there’ll only be bibliographic records remaining.