This species is gregarious; on land it forms groups to breed, rest and moult that are generally small but may number up to 1,000 individuals (5). Common seals feed mainly on a variety of fish, but squids, whelks, crabs and mussels are also taken. Juveniles feed on shrimps before progressing to the adult diet (2). When feeding, common seals travel up to 50 kilometres from haul-out sites to feed and may stay out at sea for days. They can dive for up to 10 minutes, and reach depths of 50 metres or more (3).
With regards to breeding, there is apparently no social organisation, but females often give birth in small groups (7). Females give birth to a single pup at the end of June to early July (8). The pups weigh 11 to 12 kilograms at birth and are able to swim and crawl almost immediately (2). Pups are nursed for about four weeks, after which they may disperse over long distances (5). Around the time that the pup is weaned, females become receptive and copulation occurs. Males frequently engage in underwater displays and fights around this time and can lose up to 25 percent of their body weight (5).