Monk seals are brownish when mature. Mature females may also bear scars from aggressive males encountered during mating. Newborn pups display a jet-black coat.
Females grow slightly larger than males and display more variation in weight.
Adult females range between seven and eight feet while adult males measure approximately seven feet at maturity. Newborn pups are 30 to 40 inches in length. During successive annual molts, the epidermis peels off with the old hair to reveal the bright new pelage underneath. This epidermal molt is like the snake's shedding of skin. The only other seal known to molt like this is the elephant seal.