The UK is home to two seal species, the harbour seal (Phoca vitulina), also known as common seal, and the grey seal (Halichoerus grypus). Both species are resident and breed along the Scottish coast. Male and female adult harbour seals reach similar lengths and weights, with males measuring 145 cm in length and weighting around 85 kg, and females measuring about 135 cm long and weighting around 75 kg.
Harbour seals’ coat is mottled and each individual seal has a unique pattern of spots in their pelage, which can be used to identify them individually. Newborn pups are already born in their first adult coat, which is much darker than the adult one (see below). The pelage color also changes throughout the year as seals undertake an annual moult.
Harbour seals give birth on shore to a single pup (twin births are very rare in seals) sometime in June or early July (in Scotland), although the timing of the pupping season may vary between locations. Pups are able to swim from birth and can follow their mothers into the water. Females produce very fat-rich milk and pups are weaned after three to five weeks.
Mating starts during the breeding season in June, with males defending underwater territories and attracting females with underwater calls. Males can often be seen with wounds from fights during the mating season. After the pupping season adults begin their annual moult, during which they spend longer periods ashore. During the winter, harbour seals spend less time on shore and more time out at sea.