Common seal © Ian Cook
Common seals mostly forage in shallow coastal waters, usually on the seabed, but occasionally in mid-water. They dive for just a few minutes, swallowing their prey whole underwater or bringing larger catches up to the surface, where they shake them into more manageable pieces.
Most of their prey consists of sand eels, whiting, cod, herring and bottom-dwelling species such as flounder, octopus and crustaceans. They need to eat about 4kg of food per day (5 per cent of their bodyweight) and prefer small prey items of around 10-30cm long.
We have only recently begun to understand how common seals catch their prey, particularly in dark or turbid water. Experiments on blindfolded individuals suggest that they use their long, sensitive whiskers to follow the wake left by schools of fish, attempting to then single out and grab an individual.
Video cameras mounted on the backs of male seals show that sand eels and flounders are caught by cruising just above the sea bed. The seal thrusts its muzzle into the sand to catch fleeing fish or descends to the sea bed, digging in the sandy bottom with its flippers and seizing any sand eels disturbed.
Interestingly, seals often regurgitate prey underwater and immediately swallow it again, possibly to get rid of any excess sand and water consumed.
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