Animal stories: sharks
Sharks are ancient aquamarine mammals that have been around for about 400 million years. It means they existed even before dinosaurs did. There are about 368 different species of sharks, which are divided into 30 families. These different families of sharks have different features, habitat, diet and other attributes. The most common are the dogfish shark and bull shark.
Sharks do not have bones, only cartilage. Like our nose and ears, their skeleton is made up of cartilage, which is a tough fibrous substance, softer than bone. They have the most powerful jaws on the planet. Sharks may grow and use over 20,000 teeth in their lifetime. The teeth are arranged in rows. Most sharks have about five rows of teeth. They never run out of teeth because when one is lost or damaged, another spins forward from the backup teeth.
Some of them have eyes similar to a cat. A mirror-like layer in their eyes allows them to see better in the water. Sharks are able to feel vibrations in the water with the help of a line of canals that go from its head to its tail. These canals called lateral line are filled with water and contain sensory cells with hairs. These hairs move when the water vibrates and alerts about their prey.
Sharks normally eat alone, but sometimes one feeding shark attracts other sharks. They swim up to their prey as quickly as possible and all the sharks attack a food source wildly. To get a piece of their prey, they bite anything that gets in their way and even sometimes wounding or eating fellow sharks. Sharks turn aggressive prior to an attack. They arch their back and throw back their head. This places their mouth in a better position for taking a big bite. They also move their tail more acutely to chase their prey.
Sharks live in every ocean and even in some rivers and lakes all over the world. Some sharks live in warmer waters and some like dogfish sharks lives in cool waters. Some of the sharks stay in the same region their entire lives, while others travel across oceans. They live near the surface or live deep in the water and also live on or near the ocean floor.
Sharks are all carnivores and vary greatly in their diets. Some feed on fish, squid, other sharks and sea mammals like dolphins. Slow-swimming sharks crush and eat shellfish and crabs from the ocean floor. And sharks that are filter feeders sieve tiny bits of plankton and small animals from the water as they swim with open mouths. They eat huge amounts of these tiny animals and plants. Seals, turtles and sea lions are amongst their favourite foods.
Baby sharks are called pups. The method of reproduction varies in different families of sharks. There are three ways that sharks are born — either eggs are laid, or eggs hatch inside the mother and then are born, or pup sharks grow inside the mother like humans. They can have from one to 100 babies at a time, depending on the type of shark. Sharks that lay eggs outside the body have more babies than ones with pups that grow inside the mother.
Sharks do not care for their babies after they are born. They only search for a safe place where they can lay their eggs or give birth. They just leave their young ones to survive on their own. — Compiled by Merina Pradhan