Sharks belong to the same group of fish as skates and rays, which are all elasmobranchs. Species in this group differ from other fish in that they have no bones. Instead their skeletons are made up of cartilage (this is the tough, bendy stuff you have in your ears and nose) which is flexible, strong and lightweight.
There are 35 species of sharks that have been encountered living in British and Irish waters. One of which is the basking shark, the second largest fish in the world. Some sharks, including the small-spotted catshark (commonly called a dogfish) lay tough leathery egg cases on the seabed which are commonly referred to as a ‘mermaid’s purse’. Empty eggcases can be found washed up on beaches after the young have hatched out. Other species of shark will give birth to live young, the gestation period for some sharks such as the Leafscale Gulper is two years and they don’t reach sexual maturity until they are 12-16 years of age.
- They can have between five and fifteen rows of teeth in each jaw, teeth can be replaced throughout their lives.
- A group of sharks is called a gam, herd or shiver.
- Fossil records suggest that sharks have been swimming in our seas for more than 450 million years.
“How do they move?”
Sharks are very flexible, bending their bodies in an undulating s-shaped motion to swim. As water flows over their pectoral fins lift is generated meaning that sharks can swim gracefully through the water column. The liver of a shark also contains an oily substance called squalene which helps them to float or sink. The fastest shark in the world is the shortfin mako, capable of speeds of 80KPH!
“What do they eat?”
Sharks consume a wide range of prey, most are predatory, with feeding behaviours and teeth adapted to suit their preferred prey. Sharks such as the white shark have long dagger-like teeth, and often prey on large fish or marine mammals such as seals. Shortfin mako and blue sharks have small, sharp backwards-pointing teeth. These are useful for catching fish and squid in open water. The Port Jackson shark has blunt teeth, used for crushing shellfish. Some sharks have very tiny teeth, but feed by swimming open-mouthed through the water, filtering tiny plankton. These include the two largest sharks in the world, the whale shark and the basking shark.
“How do they feed”
Feeding habits vary among species, for example the Basking Shark is a filter feeder that will swim along with their mouths wide open and filter plankton using a row of bristles called gill rakers. Other species that feed on fish, crustaceans and mammals will hunt for their prey and use their sharp teeth to cut, crunch and tear. Some sharks also have specially adapted mouths for feeding, for example the jaw of a tiger shark is only loosely connected to its skull so that it can push out its jaws out and eat larger prey. Other sharks have teeth that face backwards so that fish will be trapped inside their mouths.
“What is the biggest and smallest?”
The biggest shark in the world is the whale shark which can grow more than 12m. One of the smallest sharks measuring 22cm is the smalleye pygmy shark (Squaliolus aliae). In the British Isles, the largest species is the basking shark with a maximum length of around 10m and the smallest shark found in our waters is the cookiecutter shark measuring 34cm.
“Where do they live?”
Sharks can be found in all areas of the ocean, ranging from deep sea, open water, to shallower coral reefs. The bull shark can even survive in freshwater and is found in African river systems.
“How long do they live?”
Some of the larger sharks such as the Whale Shark are thought to live for anything up to one hundred and fifty years.
Some species found around the British Isles
Basking Shark (Cetorhinus maximus) – is the second largest fish on the planet. Most records of the basking shark are from off the coasts of South West of England, the North Irish Sea and North West Scotland between the months June to September.
Blue Shark (Prionace glauca) – is a scarce seasonal visitor, most commonly spotted off the South West coast of England. It is a large predatory shark feeding mainly on squid and fish.
Small-spotted catshark – (Scyliorhinus canicula) – is one of the most common sharks in British waters. It is commonly known as the dogfish and is regularly caught by anglers. It lays egg-cases on the seabed, known as mermaid’s purses.
Angel Shark – (Squatina squatina) – is a flattened, bottom dwelling shark, thought to be found in all British waters. It is sometimes called a monkfish.