July 3, 2018
Are sharks endangered? How many species are there? How do sharks hear? Are sharks mammals?
If you’ve always wanted to know more about these fascinating marine animals, here’s a little helping hand. Impress your friends and family with your knowledge of these (often misunderstood) underwater creatures – these are the 10 most commonly asked questions about sharks.
Sharks aren’t mammals or reptiles, they’re actually a species of fish. However, there are some similarities between sharks and other mammals, because some shark species, such as Bull Sharks, Blacktip Reef Sharks and Lemon Sharks, give birth to live offspring.
Did you know the term ‘mammal’ refers to animals that feed their young using their mammary glands? Sharks don’t do this, which is another way we know sharks aren’t mammals.
Sharks are also cold-blooded, meaning they can regulate their own body temperature and can raise it in cool water. On the other hand, many mammals are warm blooded, and use insulation to keep warm when their surroundings are cold.
There are currently 440 known species in our oceans.
It’s estimated that over 100 million sharks are killed by humans each year. This is partly due to overfishing, whilst some cultures, Japan for instance, see sharks as a culinary delicacy. The International Union for Conservation of Nature (IUCN) lists endangered sharks – and the list is a long one. The IUCN uses three different classifications — vulnerable, endangered, and critically endangered — to distinguish between the different threat levels.
The whale shark – a friendly filter-feeding species that lives to around 100 years old – is the biggest shark in the world and can grow to around 12 metres long. The smallest species of shark is the Dwarf Lanternshark. It grows to around 20 cm in length, small enough to fit into the human hand.
There are around 80 registered shark attacks on humans every year, around 10 of which result in fatalities. While this number might seem frightening, only a dozen shark species are dangerous to humans, such as the iconic Great White Shark, the Tiger Shark, the Shortfin Mako Shark, the oceanic Whitetip Shark and and the Bull Shark.
Generally speaking, sharks will only attack accidentally, but will investigate if they see splashing in the water. Many sharks prey on small marine mammals such as sea lions and seals, rather than seeking out swimmers or surfers in coastal waters.
While shark attacks kill approximately 10 people each year, human activity kills more than 10,000 sharks every hour. In reality, humans are far more dangerous to sharks that sharks are to humans.
Sharks don’t have ears on the outside of their bodies like most animals do. Instead, they have special electrical receptors called Ampullae of Lorenzini – special sensing organs that form a network of jelly-filled pores, which lead beneath the shark’s skin helping it pick up electromagnetic fields.
Fun fact: Sharks can actually pick up the earth’s electromagnetic field with this and use it for migration – now that’s impressive!
Not exactly! Some sharks have a circadian rhythm – or a body clock – which dictates when they should rest, while others are known to be more active hunters at night, which leads people to believe that they’re nocturnal. However, this is not true of all shark species because many of them reserve sleep for when they are well-fed and unthreatened.
Many shark species are known for swimming as they sleep. They do this because they need to keep water flowing through their gills to breathe, which also means they don’t enter deep sleep like we do.
Sharks have no eyelids so can’t close their eyes. But some sharks have nictitating membranes which cover the eyes, protecting them from damage when under attack. Did you know the Great White actually rolls its eyes back which makes them appear white? This makes them look incredibly scary and protects their eyes from attack too (if anything is brave enough to take them on!).
There are a few different reproductive models amongst our ocean’s 400+ species of shark. Some species lay eggs, whilst others give birth to live offspring. Mothers usually look for safe places to lay eggs or give birth to give their babies. But after birth all baby sharks must fight for their lives in the oceans, because mothers do not care for their offspring once they’re born.
Our waters are teeming with marine life. It’s possible to see around 40 species of shark off the coast of the UK. Basking Sharks swim in our waters between May and October, when the temperature suits them. The Blue Shark, which travels thousands of miles from deep tropical oceans to get here, and the shortfin mako, which is the fastest shark species, visit our waters periodically. It’s also been known for Hammerhead Sharks and Frilled Sharks to visit our waters.