Seals belong to a group of mammals known as the 'pinnipeds' (flap footed animals).
There are three distinct families within this group:
- Phocidae - true seals (earless seals) 18 species
- Otariidae - fur seals and sea lions (eared seals) 14 species
- Odobenidae - walrus 1 species
Collectively they may be found in all the worlds' oceans. However, they are most numerous in terms of both numbers and species in the cooler waters of the Artic and Antarctic. Around the UK and Ireland, there are only two species of resident seal; the common or harbour seal and the grey seal. Both belong to the family Phocidae. A number of other species of seal may occasionally be seen in our waters usually to the North, however these animals are rarely resident.
 What do they eat?
Seals feed on a wide variety of fish species including sand eel, cod, herring and flatfish however they will also eat crustaceans (crabs and shrimps etc) and molluscs (mainly squid and octopus).
Seals are superbly adapted to swimming rapidly and they swim after fish and catch them with their sharp teeth. Depending on the size of the fish, it is either swallowed whole or it is grasped in the front flippers and eaten in a series of bite-sized chunks. Seals have well developed eyes that are a specially flattened shape to allow them to see well under water. However, they appear to rely mainly on their highly sensitive whiskers to sense their surroundings and to sense the movement of prey such as fish. This allows seals to catch fish effectively in very murky waters where sight would be limited.
 How do they breathe and dive?
All seals breathe air however, unlike most land living mammals they are 'voluntary breathers'. They do not breathe unconsciously as we do.
When seals dive their nostrils close automatically. Unlike human snorkel divers, seals will breathe out before diving. This may seem odd however there are several very good reasons for doing this. Firstly a huge bag of air in their body would play havoc with their buoyancy, they would have great problems getting beneath the surface of the water. Secondly, like divers, the seals would be prone to problems of the bends with bubbles of nitrogen forming in the body. Seals get around these problems by high concentrations of oxygen-storing pigments in the blood (haemoglobin) and in the muscles (myoglobin). Seals have a comparatively large blood volume compared to humans. Their heart rate also changes when they dive. Below the surface their hearts beat at around 40 beats per minute, but this rises to about 120 beats per minute when they surface. For longer dives, their heart rate is reduced to a few beats per minute and blood flow is cut off to all but essential organs such as the heart and brain.
Dives can last for 20-30 minutes. The northern elephant can dive to over 1,000m (3,280 feet).
 How do they keep warm?
Like humans, seals are warm blooded. They do not rely on their fur to keep them warm in the water, although it can help block wind chill when seals dry out on land. Their main source of insulation from the cold is the thick layer of blubber under the skin. The blubber can be up to 10cm (4 in) thick.
Senses
Sight
Seals have large slightly flattened eyes that work effectively underwater at low light levels. In air, their eyesight is good in bright conditions; however, in dim conditions they tend to be short sighted - rather like we are in water!
Smell
The nostrils are closed under water, however, scent is very important in air for detecting predators, and for mother-pup bonding.
Hearing
Hearing is less sensitive in air than it is in water.
Touch
The seal's main sensory organs are their long, thick whiskers, which pick up vibrations from moving prey. They enable seals to locate and catch food in murky water. There are many documented cases of blind seals living in the wild in good body condition.
How do they move?
 On land, seals appear ungainly, moving around by 'humping' along on their bellies but do not be deceived! An enraged adult seal can move considerably faster than a person can over a short distance, especially over slippery rocks.
In water, seals are masters of their element. Seals propel themselves through the water by sideways movements of their powerful hind flippers.
When moving at speed the front flippers are held tight to the body but are used to great effect when the seal has to turn tightly.
Where do they sleep?
Seals can sleep on land and in the water. In water they often 'cat nap' just below the surface with their nostrils closed.
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