Moulting grey seal. Blood supplies nutrients to the epidermis and dermis, and is essential for the growth of new skin and hair. When the seal is in the water (swimming, resting, diving), circulation to the skin is restricted in order to conserve heat and oxygen. So, leaving the water is necessary for rapid and safe replacement of skin and hair. Most seals bask in the sun to warm the body surface and promote blood flow to the skin.