Grey seals are the largest breeding seals found in the UK. Half of the world's population of grey seals are found around British coasts, and numbers here have doubled since 1960. In the autumn, females congregate at traditional pupping sites called rookeries. Pups weigh 14 kilograms at birth, but since their mother's milk contains 60% fat, they quickly balloon and develop the blubber layer essential for maintaining body temperature out at sea. When feeding, these seals can dive to a depth of 70 metres.

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