WHO ARE THE SHARKS?
- Friendly Fins
- Nov 23, 2024
- 6 min read
Updated: Mar 7
Why learn about sharks?
“We are the TOP PREDATORS of all the seas, the predators for excellence! But not of men as you might think! We like fish! We will prove it to you! Follow us!”
How do they differ from other animals:
Sharks have an unmistakable physiognomy but are distinguished from fish and cetaceans by having:
A cartilaginous skeleton and therefore the absence of bones.
“We don't have “bones like fish”
They have a spiracle through which the water enters and is filtered by the gills. Therefore they breathe underwater and do not have to come to the surface to breathe like cetaceans!
“let's say a kind of second mouth that is only used for drinking”
They have a very strong tail that allows them to swim at good speeds..
One or two unmistakable triangular dorsal fins.
“We know that when you see them coming to the surface you get nervous!”
The gill slits are visible, unlike fish that have them covered by an operculum. The number of gills varies from 5 to 7 according to the different families of sharks.
The mouth is ventral to the snout in the vast majority of sharks, while it is apical in fish.
“The maxilla and mandible are very articulated and we can open our mouths very wide and excellently!”
Sharks swim by moving their tails from left to right, creating an S-shaped motion, unlike dolphins which move their tails up and down.
“So when you see us on the surface you will be able to recognize us better!”
Where do sharks live?
Sharks appeared on Earth 400 million years ago, they witnessed the extinction of the dinosaurs and only after 396 million years we humans emerged! In the meantime they have had an extraordinary evolution and a superlative adaptation to various environments, colonizing the entire globe.
Depending on the place we are going to visit there will be very specific species of shark, let's find out before going snorkeling or diving, so we will be psychologically prepared!
Many sharks live in tropical seas such as the whitetip shark, blacktip shark, nurse shark, grey shark, hammerhead shark, whale shark and many many others. We can't complain even in temperate seas: in the Mediterranean for example there are sharks such as the blue shark (it's a shark!), the dogfish, the spiny catshark, the basking shark, the thresher shark, the white shark etc.
In the Atlantic Ocean some sharks love to live in giant kelp forests like our friend the spotted seventid shark (pictured below).
“You can find us anywhere doing our business, but don’t worry, we’re too busy to take care of you too!
What do sharks eat?
Most sharks are carnivorous, feeding on fish, mollusks, crustaceans, marine mammals, turtles, and other sharks. A shark's diet is determined by its age and size.
There are also phenomena of cannibalism and food hierarchy. In front of a large prey such as a dead or dying whale, the first to feed will be the largest sharks and then the smaller ones to follow.
Some sharks, however, are planktophagous, that is, they eat only plankton and reach large sizes such as the whale shark (the largest fish in the world) and the basking shark.
Tell me what teeth you have and I'll tell you who you are
Closely related to their diet is the shape of their teeth: depending on their prey, they will have a specific shape.
The white shark has very strong, triangular, serrated teeth, used to grab and kill large prey.
“I am very fond of sea lions!”
The nurse shark has rounded teeth that are all close together to create a sort of plate, because as it feeds on molluscs and crustaceans, it will need a lot of pressure to break shells and exoskeletons.
“I love the little molluscs that pass near me unawares”
The tiger shark has very strong, serrated teeth, with a singular shape that allows it to split the shells of turtles.
“Turtles are my favorite food.”
In addition to the specific shape, evolution wanted to further advantage these TOP predators, positioning the teeth on multiple parallel rows that, like a roller, slide outwards as they grow and are ready for their task, while the older ones will fall out.
“This allows us to change our teeth many times in life and above all to always have an enviable smile!”
The Life of a Shark
Sharks have a very delicate life cycle that significantly affects their survival:
They take a long time to become adults and therefore sexually mature, some over 30 years.
They are very long-lived, especially some species of shark are thought to be able to live over 100 years.
Gestation is much longer than that of fish and varies from species to species
Reproduction has many facets: oviparity, ovoviviparity, viviparity.
Sharks have two penises, called claspers, located between the two anal fins. This feature makes them easily distinguishable from females.
The female gives birth to few young compared to fish, many of which will never reach adulthood.
“Even though we are many at the beginning, not all of us will be able to grow up!”
Newborn sharks measure a maximum of 50-60 cm (whale shark) and are completely autonomous.
Birth takes place in highly protected places (called nurseries), characterised by calm waters free of predators, so as to maximally favour the survival of the young.
There is no parental care of the mother after giving birth.
“You are not born as a TOP Predators, you become one!”
The senses of sharks
Sharks aren't at the top of the food chain for nothing, thanks to their highly developed nervous systems and sense organs they are formidable hunters!
Smell:
Sharks have nostrils located on the ventral part of their snout, which allow them to smell even from a great distance. Sensing the presence of blood or food in the water, some sharks become aggressive.
“To be clear… It’s not that if you get a scratch in the water, we’ll sense it and come and eat you! We smell at great distances but very strong odors like, for example, the scent trail produced by a dead whale!”
Sight:
Sight is a highly developed sense and of excellent capacity, so much so that sharks are able to see both in very bright light and in dim light. Some species even have color vision. The eyes are therefore an extremely delicate part and many of them protect them thanks to a membrane, called nictitating membrane, which covers the eye while the shark feeds.
Some sharks, like the white shark, do not have it, but to protect itself, it rolls its eyes backwards during the attack. So at that moment it is completely blind and will rely on its other senses.
“For this reason when I bite the prey, you see my eye white and not black, I cannot risk damaging it!”
The lateral line:
The lateral line is a line of sensory receptors that runs along the sides of the shark from its head to its tail. These cells are sensitive to pressure and mechanical movement, so the shark can sense both the direction and amount of movement of an object or animal around it.
“If you come near me, I’ll know right away from the awkward movements you make!”
Hearing:
Closely related to the lateral line, hearing is very sensitive to low-frequency vibrations.
“For example we feel very well the presence of an animal in difficulty.”
Electroreception:
Sharks are able to detect electrical currents generated by the nervous systems of other animals, but at very short distances. In addition, some sharks, such as the hammerhead shark, can also perceive the Earth's magnetic field.
The protagonists of electroreception are special sensors called “Ampullae of Lorenzini”, that is, very small cells filled with electroconductive gelatin that communicate with the outside through a small cilia.
They can be seen well on the snout of sharks, as they are very concentrated small black dots.
“Feeling the electrical impulses released by other animals is very useful in the final phase of an attack, because they give us the exact location of the prey even if we can't see it!”
Sharks' Enemies
Natural Enemies
The natural enemies of sharks are other sharks and some marine mammals such as killer whales and sea lions.
However, they often depend on the size of the shark itself: it is easier for sharks to be hunted at a young age than when they are adults and able to both hunt and defend themselves.
The enemy for excellence
Always demonized, the shark has been hunted far and wide by humans, for a variety of reasons: for fear that it would attack humans, for its jaws and teeth (used as “souvenirs”), for its liver, cartilage, meat but above all for its fins.
It is precisely the relationship between humans and sharks that is very close to our hearts, so we would like to dedicate more time to it, showing you that they are not really what they are shown on TV! Come and learn more by clicking here!
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