Sharks. The name alone instils fear. These ancient beings have combed the depths since before the dinosaurs, placing them among the most fascinating creatures beneath the waves. Why then do they attract such stigma? And should we really be scared of them?
At Blue Planet Aquarium, we think it’s high time people gave sharks a second chance. Ever since Spielberg’s Jaws hit the big screen in 1975, sharks have attracted more fear than they have fascination – with myths and half-truths gaining attention ahead of facts and conservation.
But with shark numbers now in sharp decline, it’s time to get wise to these amazing creatures before it’s too late. To help, we’ve put together a guide on everything you need to know about sharks, so you can get to grips with just how wonderful and valuable they really are.
Use the links below to explore our guide or read on for the ultimate guide to sharks.
First things first: sharks are fish. Given the size of some species of shark, it’s easy to see why some people mistake them for mammals, but they are indeed fish – albeit, very big ones!
The simplest way to determine a shark’s fish pedigree is to note the gills just in front of the pectoral fins on the side of their body. As with all fish, these gills take in water, forcing it through lots of tiny blood vessels. These vessels absorb oxygen from the water, allowing sharks to breathe underwater without rising to the surface. Clever, eh?
Sharks account for some of the largest species of fish in our oceans, with the biggest being the mighty whale shark. These enormous fish can reach a length of 10 metres and weigh in at over 19 tonnes – the equivalent of 15 Ford Fiestas! Basking sharks and megamouth sharks complete the top 3 biggest species, while the smallest known shark is the dwarf lantern shark, which averages just 6 inches in length.
There are over 1,000 species of sharks that we know of, with new species discovered every year. As our understanding of the seas and oceans widens, and technology continues to improve, it’s guaranteed that hundreds of new shark species will be discovered in the coming years.
Sadly, however, shark numbers are in decline, which is why organisations like the WWF are campaigning for greater conservation efforts to protect their numbers. Every species of shark, from the great white to the bonnethead, plays a crucial role in our marine ecosystems – helping to balance a delicate natural order that would otherwise suffer.
It’s hoped that, as our understanding of sharks deepens and more countries introduce legislation to stop shark hunting, their numbers will return – as has been the case with several species of protected whales. The next few years will prove critical in safeguarding these incredible animals, with a view to not only discover more species, but protect those we already know about.
Sharks are opportunistic feeders, eating everything from small fish and invertebrates, to seals, penguins, sea birds, and whale carcasses. They detect their prey in several ways, including by sight, sound, vibration and, of course, smell – with a shark able to pick up the smell of blood from over a quarter of a mile away.
You’d be forgiven for thinking that larger shark species eat bigger prey, but this isn’t always the case. Sure, a great white could pick off something as formidable as a leopard seal with ease, but bigger species, like basking and whale sharks, are filter feeders, preferring to munch on microscopic plankton.
And, despite what films like Jaws may have led you to believe, sharks don’t eat humans and would always prefer to stay out of our way. When attacks do happen, it’s usually the case that a shark has got confused or feels threatened.
Some sharks lay eggs and others give birth to live young. This is what’s called ‘viviparity’ or ‘ovoviviparity’; there are more sharks which bear live young than those that lay eggs, and it differs from species to species.
Take the whale shark for example, the classic example of ovoviviparity. Here, this species produces eggs but doesn’t lay them. Instead, the young hatch inside the female’s body, only to emerge when they’ve reached a particular size.
When we refer to viviparity, this is when a shark releases a capsule containing an egg and a yolk sac, with tendrils designed to anchor it to the seabed. When the baby sharks hatch inside the capsule, they get nutrition from the yolk sac, before eventually being released from the capsule.
Some sharks, like the shortfin mako, give birth in an altogether different way known as oophagy. This is when unfertilised eggs are ‘eaten’ by embryos inside the shark, before babies are released.
So yes, sharks do lay eggs, but it’s not quite as simple as that – another reason why they’re such fascinating animals.
Most species of shark live between 20-30 years in the wild, though this can vary widely depending on the size and species. Greenland sharks, which are found in the North Atlantic Ocean, are thought to be the oldest known species. These elders of the deep grow just a 1cm a year, and scientists believe that the oldest known example was estimated to be around 512 years old – so it’s been around since Henry VIII was on the throne.
The mighty whale shark is the biggest species of shark in our oceans, with an average length of around 12 metres, though specimens of up to 19 metres have been reported (that’s larger than a football penalty area). Despite their size, these huge animals pose no threat to humans, and are only ever found in subtropical waters above 21°C – so there’s little chance you’ll spot one while eating your fish and chips at the seaside.
Here’s a look at the top 10 biggest shark species, ranked by average size order.
Sharks live in all five oceans, from the Pacific and Atlantic to the Indian, Arctic and Southern, as well as in some freshwater lakes and rivers. The majority of shark species are migratory, meaning they travel vast distances to remain in temperate waters with a good stock of prey.
Such is the diversity of shark species that they’ve adapted to live in both warm, shallow coastal waters and deep, very cold waters close to the Polar regions. That’s why shark sightings are common in countries like Australia, South Africa and the USA, as well as in much colder regions like Greenland and the southern coast of South America.
Sharks don’t sleep. Instead, they have active and rest periods, wherein they either preserve or expel energy.
That’s not to say that all sharks are forever swimming. Some species, like the nurse shark, are known to rest in a stationary position. The majority of sharks, however, do swim even when they’re in a state of rest, but do so in deeper waters, where they’re less likely to be disturbed.
Yes, many species of sharks are classified as endangered by the WWF, including the great white, the hammerhead and the whale shark. Sharks face all kinds of threats, from rising sea temperatures to overfishing, habitat loss, illegal fishing and an increasing demand for shark fin – which is used to make an expensive soup in some Asian countries.
Organisations like the WWF are doing all they can to safeguard shark numbers, from pressuring governments to pass legislation making shark fishing illegal to tagging endangered species in an effort to monitor their numbers. By spreading awareness and understanding of sharks and their value to marine ecosystems, it’s hoped that their numbers will recover when illegal fishing practices cease.
The biggest and most damaging myth about sharks is that they eat humans, which isn’t true. When shark attacks happen, it’s a matter of wrong place, wrong time – not of predator and prey. So, the next time you take a swim and start thinking about the Jaws theme tune, put it out of your mind and remember: the likelihood of being attacked by a shark is 1 in 3.75 million.
So, there you have it, our no-nonsense guide to one of the ocean’s biggest and best creatures of the deep. For more information on these incredible animals, and for an opportunity to swim alongside them, visit the Blue Planet Aquarium homepage or give us a call on 0151 357 8804.