Have you ever seen a shark? Sharks have a fearsome reputation. However, there are more interesting facts about sharks than you may know. Nowadays, there are more than 500 species of shark in the world and come in all different shapes and sizes. Sharks are a special kind of fish that live in every ocean in the world, mostly in warm waters. Some even live in lakes and rivers. They can be found in the Atlantic, Pacific, Indian, Arctic and Southern oceans. Some live near the surface, some live in the deep water, some live on the ocean floor, and others stay near shore or on coral reefs, while some live in open oceans. They’re often known as “living fossils” as they have roamed the oceans for more than 400 million years, meaning they were even around before the dinosaurs. They are the strongest predators in the world that can adapt well to the areas that they live in.

Here are some facts about Sharks:

1. Sharks have no bones:

Most living organisms have a skeleton that is made from bone that gives their body shape and gives them strength. Sharks are one of the most powerful creatures in the ocean and have an incredible bite force. Certainly, we thought that sharks have tough bones but in fact, they have a skeleton that is made from cartilage rather than bone. They are from the class Chondrichthyes which means cartilage fish and from the subclass “Elasmobranchii” which includes all sharks, rays, and sawfish.  

Do you know what are cartilages? They are tissues that are more flexible and softer than bone, they also are much lighter than real bone. Cartilages are the clear gristly stuff that our ears and nose tip are made of. Although sharks have a cartilaginous skeleton, it does the same job that a skeleton made from bone does. The cartilaginous skeleton also protects its organs and gives their bodies shape and structure. 

How are sharks classed as vertebrates and they don’t have bones? Sharks are considered vertebrates, which means that they have a backbone. Sharks have backbones but it is not made from bones, it is made from cartilage. Their spinal column is made from cartilages, which protect the spinal cord the same way that the bones do. The cartilage that makes up the spinal column of the shark is calcified enough to protect the spinal.

Their bodies are made from different strengths of cartilage and some areas are stronger than others. Some areas are needed more protection, so they are made from calcified cartilages “calcium salts” such as sharks’ heads to protect their brains. Some parts are made from softer cartilage such as their snout, which can act like a bumper that can absorb heavy blows without suffering and help them to absorb oxygen easily. Their flexible skeleton allows sharks to open their mouth further for a strong bite and become powerful predators.

Do you know that sharks can fossilize??!! Yes even though sharks don’t have bones, they still can fossilize. Do you know what fossilize means? It is the process of an animal becoming preserved in a hard form. When the animal dies in a watery environment and is buried in mud and silt, the animal skeleton becomes fossilised. When the sharks become older, they strengthen their skeletal cartilage by depositing calcium salts in it. These minerals allow most skeletal systems of sharks to fossilize well. 

One of the greatest advantages of cartilage is that is much lighter than bone which is essential because sharks don’t have a swim bladder, which helps them swim fast and make quick turns. Sharks’ teeth are the strongest part, which is made of dentin that is tougher than bone.

2. Shark skin colour, scales, and texture: 

Sharks’ skin is unique, do you know why??? Sharks have grey colour skin that contrasts between a slippery appearance and rough texture. Their skin has been physiologically designed to suit their habits, habitats, and their hunting lifestyle. Sharks’ skin is made up of tiny teeth-like structures called placoid scales, their skin exactly like sandpaper. These placoid scales are also known as dermal denticles. When the sharks swim, these placoid scales help reduce friction from the surrounding water. Not all kinds of sharks have rough skin, some kinds of sharks, such as the nurse sharks have fairly smooth skin. Do you know that sharks’ skin is often dried and used as a leather product or sandpaper?

Their skin is characterised by a central pulp cavity, an outer layer of enamel, and a dentine layer, which make their bodies stronger and protect their skin against injury. Their skin helps them swim faster, they have grooves in their skin that water is able to flow through. Their ability to move in water generates the necessary body heat that keeps sharks alive. Also, their thick skin keeps their body temperature, such as the whale shark, which is considered the largest shark in the world. Their skin thickness is about 10 centimetres.

Sharks’ skin is so rough that it may cause a bad injury for softer animals which touch their scales. For example, bull sharks have occurred injuries to many cases of humans who accidental contact with that kind of shark. Sharks are usually grey, the top of their bodies is darker than the bottom, they are normally snowy white beneath. Most sharks are olive, brown, or greyish. Sharks which are lived on the bottom of the ocean and feed off small crustaceans are typically browner. They have a special method of camouflage that allows them to approach prey without being detected. This factor makes them the most feared aquatic predators and keeps them always safe.

3. Sharks have good eyesight:

No one can doubt that sharks have pretty impressive eyesight. Do you know that their sight is about 10 times better than yours, especially in clear water? Sharks’ eyes include the cornea, lens, iris, pupil, and retina. Their structure is very similar to that of human eyes. The same as humans, sharks have rods and cones in their retinas that are activated by light “determine light and dark”. Rods are important for vision in low light and cones are important for vision in bright light and allow them to see colours. Most studies nowadays have shown that they can see colours clearly, but it is not known to what extent.  The number of rods and cones are vary from one specie of sharks to others, so some sharks can see better than others.

One of the unique characteristics that the shark have is the “Tapetum lucidum”, which allows them to see well in dark water.  Do you know what is the Tapetum lucidum? It is a layer of mirrored crystals that is located directly behind the retina. Sharks can use stereoscopic vision, which is three-dimensional vision and allows for almost 360-degree vision, which is like how we see. In stereoscopic vision, the images from the two eyes are combined, which gives our vision depth, distance, and shape. Sharks also can see in monocular vision by seeing the image from only one eye.  Although monocular vision gives poor perception it increases the visual quality.

Although sharks have good vision, they can only see to a distance of around 50 feet. They have a blind spot behind the top of their head and in front of their snout, so they can not see far objects. So they need to be close enough to their prey before they attack, and any objects in front of their nose they can’t see at all.

One of the great facts about sharks is that they have eyelids, but they can not feel them because they don’t blink. The water cleans their eyes, so they do not need eyelids. The missing job of eyelids may lead to the risk of injury to their eyes when they attack their prey. But sharks use several ways to protect their eyes by using a nictitating membrane that is transparent and slides down from underneath their eyelid to cover their eyeball and create a protective barrier. It also can be used when sharks are hunting or fighting with other sharks. Do you know that sharks have excellent vision, their night vision is better than a wolf’s.

Sharks are well known for their ability to smell the blood of any animal, when sharks smell any blood you can see the whites of their eyes “ nictitating membrane” when they attack, they just protecting their eyes. They can also see well in dark-lighted areas because of having a reflective layer of tissue called a tapetum, which is located at the back of sharks’ eyeballs that helps them to see well with little light. 

4. Sharks can go into a trance:

Sharks can go into a trance!! What do you think about how sharks go into a trance? When the sharks’ flip upside down they go into a trance, which is like a state called tonic immobility. When they go into trances, their muscles are loosened, their respiratory processes may stop, and their dorsal fins become straighter and more streamlined. For example, “tiger sharks” that are 34 metres in length, can go into tonic immobility by placing hands lightly on the tiny sensory pores located on their snout. Researchers often use tonic immobility when handling sharks to subdue them.

5. Sharks have special electroreceptor organs:

Do you know that sharks have small black spots near the nose, eyes, and mouth? But what do you think, what are these spots? These spots are electroreceptor organs that allow the shark to sense electromagnetic fields and changes in temperature in the ocean, which are called the ampullae of Lorenzini.

Sharks are armed with this sixth sense “ampullae of Lorenzini”, especially since they have small and beady eyes. Without this sixth sense, sharks may crash. They also do not depend on their eyes only when they follow their prey, but they also depend on their sixth sense. The ampullae of Lorenzini help sharks to fierce and fast underwater. 

Do you know how electroreception works? It’s a sophisticated process because these electroreception organs are more or less invisible to the naked eye. Sharks have developed openings around their faces which act as honing devices. Sharks have developed openings around their faces which act as honing devices. They find out the electrical currents of other creatures, which travel through the water and are processed by the shark’s brain in the form of neurotransmitters.

Simply, you can compare electroreception to batteries, which completely emit positive and negative charges In the same way as batteries. The same as salt water does to the presence of sodium and chlorine ions. During swimming, Fish and sea creatures‘ muscles contract, and their bodies create a faint electrical charge. When energised cells that come from fish into contact with free-floating sodium and chlorine ions in water, an electron exchange takes place in an attempt to stabilise the collision. Sharks can feel their electrons through electroreception. Not only sharks can detect electrical impulses, but also another animal’s beating heart.

6. Some species of sharks have a spiracle:

Do you know what are spiracles? Did you hear about it? Do you know who has these spiracles? They are considered breathing openings found on the surface of some cartilaginous fish such as some species of sharks except chimaeras sharks, hammerhead sharks, requiem sharks, mackerel sharks, and chimaeras sharks.

There are some kinds of sharks that have spiracles. These spiracles are located just behind the eyes, which are used to suck water into the buccal space before it is pushed back out through the gills. They also allow sharks to breathe without needing to swim. Bottom-dwelling sharks are a great example that has spiracles, which supply oxygen directly to the shark’s brain. 

These spiracles are so important for bottom-dwelling sharks because often lie in wait for their prey before lunging at them, so they do not need to swim. That mean, they can use this extra respiratory organ to breathe, while they are at rest on the seafloor and also when they use their mouth for eating.

Spiracles are found on most sharks except hammerheads, mackerel sharks, and requiem sharks, these kinds of sharks need to swim constantly. But others that have spiracles can stop swimming as they want such as sand tiger sharks and nurse sharks. 

7. Different ways of reproduction in Sharks

Do you read about sharks’ reproductive mode? Sharks have great diversity in their reproductive modes. Their sexual organs vary from other animals. That is so creepy to know that most sharks take years or decades to reach the age of reproductive maturity. Most of them will not mate in captivity, it is known that many shark species migrate to open waters for mating season, but no one knows where or when this happens with most species.  Sharks search for a suitable environment for their youngest. The only thing that scientists have observed is that many pregnant sharks have bite marks on their fins and bodies. When the eggs are fertilized, there are many ways the shark pups will develop, including viviparity, oviparity, and ovoviviparity.

Viviparity

This way is similar to how humans give birth. Viviparous sharks have placental viviparity. The eggs are developed inside of the womb, which leads to giving live birth. Sharks’ eggs hatch inside the womb and live off a placenta until they are ready to be born. How do we know that this shark is a viviparous species?? When they are born, they will have an umbilical cord located between the pectoral fins. This umbilical cord transfers to sharks’ babies nutrients and oxygen from the mother’s bloodstream the same as human beings. Viviparous sharks give birth to about 2-20 babies, which depends on the species. Also gestation period varies greatly from one species to another. Viviparous sharks, including Blue Sharks, Hammerhead Sharks, Lemon Sharks, Mako Sharks, Requiem Sharks, Salmon Sharks, Sandbar Sharks, Sharpnose Sharks, Silvertip Sharks, Sliteye Sharks, Whale Sharks, and White cheek Sharks.

Oviparity

Have you ever heard about the oviparous species? They are kind of sharks that lay eggs shark in a deposit in the water. The egg of oviparous species is fertilized in the womb and can spend weeks in it then laid. The eggs contain a yolk sac and zygote. The eggs are considered typical encased in a leathery pouch, which is called a “mermaid’s purse.”  The eggs develop and hatch outside the mother’s body. Do you know that these kinds of eggs develop with no parental care after the eggs are laid!!! The eggs may be eaten by predators before they can hatch. They may take months to hatch. These oviparous species lay anywhere in water about 10 to 200 eggs, which depends on the species of sharks. Oviparous shark species include Catsharks, Bamboo Sharks, Epaulette Sharks, Swell Sharks, Zebra Sharks, Horn Sharks, Necklace Carpet Sharks, and Port Jackson Sharks.

Ovoviviparity

This kind is different from other species, here egg hatches inside of the womb and the shark has live birth. The living embryos “pups”inside the womb will live off a yolk sac from the egg till they are ready to hatch. The pregnant females’ bodies just provide their pups with oxygen, they do not have a placenta to provide their pups with nutrition. 

For some species of shark, the first shark that hatches from their egg will then consume the other shark fetuses and their yolk sacs. The ovoviviparous sharks give birth to very small litters with only 1-8 pups, they include Cookiecutter Sharks, Crocodile Sharks, Great White Sharks, Pacific Angel Sharks, Pelagic Thresher Sharks, Sand Tiger Sharks, Soupfin Sharks, Pygmy Sharks, Greenland Sharks, Gummy Sharks, Nurse Sharks, Sawsharks, and Tiger Sharks.

Asexual Reproduction

These three ways are not the only ways sharks can reproduce. That is amazing to know that sharks can reproduce, asexually. So what do asexual means? A female shark gives birth without any contact with a male. These asexual species are very rare and may limit the genetic diversity of the species. But they may be useful in propagating the species under environmental stress. Females can asexually reproduce when there are no available male sharks in the wild or when they are in captivity. There are some kinds of sharks, which are asexual including leopard sharks, zebra sharks, white-spotted bamboo sharks, blacktip sharks and bonnethead sharks.

Facts about Sharks:

• There are a few ways scientists know how old a shark is, the same way we can tell how old a tree is, that is by counting the rings! Rings are found on the vertebrae, which contain concentric pairs of opaque and translucent bands. So, if the vertebrae have 20 band pairs, it is supposed to be 20 years old.
• The spot pattern of each whale shark is unique as a fingerprint.
• Sharks are older than dinosaurs, which are based on fossil scales found in Australia and the United States, scientists assume that sharks first appeared in the ocean around 450 million years ago.
• Not all kinds of sharks have the same teeth, for example, White sharks have triangular and serrated teeth, while Mako sharks have pointed teeth. And each species of sharks numbers of teeth throughout its lifetime. Sharks have from 35,000 to 50,000 teeth in a lifetime.
• Sharks are considered the thickest skin of any sea creature, their skin is around 10 cm in thickness. Their skin provides them vital protection and insulation from other animals.
• Sharks’ ears are located inside their head. They do not have visible ears, but they have incredibly acute hearing. They can hear their prey at distances of more than 800 feet.
• Baby sharks are born with all of their teeth and won’t fear biting.
• Contrary to popular belief, not only do sharks live in saltwater, but also in freshwater.
• Not all sharks can tolerate Arctic temperatures, but the Greenland shark is the only species that can do. The Greenland shark has a special skin that allows it to withstand the subzero temperatures of the Arctic.
• Sharks don’t eat humans. They may bite humans out of curiosity and then swim away.
• Female sharks can be pregnant by multiple males at once.
• Some sharks have bio-fluorescent properties that give them green-glowing skin in the dark such as swell sharks.
• Sharks have different eye colours, which means sharks living close to the surface have darker-coloured eyes to protect them from the light, while sharks living deep in the water tend to have light-coloured eyes to help them to attract more light.
• Some sharks use body language to communicate with one another by using zigzag swimming, head shaking, and hunched backs.
• Female sharks lose their appetite before giving birth, which prevents them from eating their babies.
• Sharks can go as long as three months without eating.
• Sharks’ jaws are not attached to their skull. Both jaws can move freely and even possess the ability to extend them.
• Most sharks’ lifespan averages at 20-30 years.

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