Sharks, fun facts

Sharks have inhabited our oceans for more than 400 million years. They have survived the five great extinctions on Earth, including the one that wiped out the dinosaurs. Since then and until today, these fish have evolved in surprising ways.

They are extraordinary animals with an anatomy that does nothing but improve over time. Sharks are master hunters with incredible precision. They are found at the top of the food chain and are essential for maintaining the balance of marine ecosystems.

Marine life in Bali, diving with sharks
Video by Ludovic Amevor


Sharks live in all oceans worldwide, and their distribution depends on factors such as depth, temperature, and food availability.

Some species of sharks live in freshwater lakes and rivers. There are even some, like the bull shark, that can swim between salt and fresh water.

Sharks can adapt to a wide range of habitats, including shallow waters, the bottom of the ocean, and the open sea. However, they tend to prefer tropical and temperate zones.

Sharks come in all shapes and sizes

Some measure only a few centimeters, like the lantern or the pygmy shark, while others, like the whale shark, the largest fish that exists today, can be up to 12 meters long.

The megalodon shark lived 20 million years ago and was the largest shark ever. It was an average of between 13 and 15 meters long.

How do sharks sleep

White tip reef shark resting on the sandy bottom at Blue Lagoon, Padangbai

There are different species of sharks, and depending on how they rest, we can distinguish two types. 

The first type of animals are those that need to continuously move in order to breathe through their gills.

These sharks rest while swimming. This can be done because they do not really sleep but instead leave part of their brain inactive, resting.

Sharks control their movements with the spinal cord and not with the brain. Because of this, they can deactivate different parts of the brain and continue swimming, alternating periods of full consciousness with semi-unconsciousness. An example of this type of shark that rests while still swimming is the white shark.

The second type of sharks is those that can stop swimming to sleep. They can do this because they have structures called spiracles, through which they can obtain oxygen without the need to swim constantly.

Thanks to this mechanism, these sharks rest immobile on the seabed, so their daily energy use can be significantly reduced compared to the first group’s.

However, none of the different types of sharks has a swim bladder, so they cannot float if they are still. For this reason, sharks that have spiracles when they want to rest have to go down to the seabed or look for caves to stop swimming.

Sharks do not have eyelids and for this reason, they cannot close their eyes. They sleep with their eyes open.

Their skeleton is made of cartilage instead of bones, which makes them very light and allows for fast movement

The fastest shark is the mako. It can swim up to 74 km per hour.

Shark’s skin is rough, tough, and thick

Black tip reef shark, Drop Off, Tulamben

It is composed of dermal denticles, which are made from the same material as teeth.

Sharks have jaws with multiple rows of teeth that continually renew

Teeth are rootless and break easily. When this happens, the new tooth can appear as fast as in one day.

Although their mouths are full of teeth, sharks do not chew their food but use them to tear food apart.

A shark can lose up to 1,000 total teeth per year.


Sharks are mostly predators, so their diet is generally carnivorous. They eat fish, marine mammals, mollusks, or even other sharks, depending on their size and habitat. Some are even scavengers.

However, other shark species, such as whales and basking sharks, are filter feeders. They ingest phytoplankton, algae, and krill, as well as larvae, small crustaceans, squid, and even small fish.

Some sharks can go without food for long periods and apply energy-saving measures such as moving very slowly. This happens with the Arctic boreal shark that can live more than 400 years, this technique has made it the longest living vertebrate in the world.

They have a great sense of smell. They can smell a single drop of blood from at least 100 meters away

White tip reef shark, Gili Mimpang, Candidasa

They can sense electrical impulses

All sharks have an organ in their snouts, the ampullae of Lorenzini, that allows them to sense electrical fields in the water emitted by other fish and marine life. In addition, most sharks have a similar lateral line that detects movement in the water.

They have excellent night vision but cannot distinguish colors.

Hammerhead sharks have 360-degree vision

Sharks cannot vocalize due to a lack of vocal cords. Hence, they communicate through body language

Wobbegong shark, Gili Tepekong, Candidasa

Mating and reproduction

Sharks grow slowly and take a long time to reach sexual maturity, and when they reproduce, they produce only a few young.

Mating is a bit wild. The male holds the female with its teeth, biting her fin, often causing large wounds that will mark the female for a lifetime.

Sharks exhibit great diversity in their reproductive modes. There are oviparous (egg-laying) species and viviparous (live-bearing) species.

Gestation time is as varied as the types of sharks in the oceans. It can last between 3 to 4 months or up to 2 years.

From the moment of birth, the young do not receive the protection of their mother as other creatures of the animal kingdom, but they learn to survive independently.


There are more than 500 known shark species, and many are in danger of extinction or decline due to various factors such as overfishing.

Sharks are not dangerous to humans

Of the nearly 400 species, only 12 are considered dangerous to humans, and only three are responsible for most attacks on humans: the white shark, the tiger, and the bull. Instead, humans kill at least 100 million sharks a year and have put many shark species on highly threatened species lists.

Humans are not part of sharks’ diets. Most of the attacks happen by mistake, as the shark mistakenly mistaken a surfer for a seal or some other type of marine mammal or as a way of “proving” what this curious creature that has been found is about.

Be a responsible diver

Whenever you dive with sharks, remember:

Stay calm, and don’t make any sudden movements.

Never stand in the way of the shark.

As you move, don’t turn your back on the shark.

Where we can dive in Bali with sharks

The best place to see sharks in Bali is undoubtedly the islands of Candidasa. White-tip reef sharks live on these volcanic-formed islets. During the season we can also see wobbegong or carpet shark. And if you are lucky enough during the plankton season, you can occasionally see the largest fish that lives in the oceans, the whale shark.

Would you like to dive with us?