Northern fur seals occur from southern California north to the Bering Sea and west to the Okhotsk Sea and Honshu Island, Japan. During the summer breeding season, most of the worldwide population is found on the Pribilof Islands in the southern Bering Sea, with the remaining animals on rookeries in Russia, on Bogoslof Island in the southern Bering Sea, and on San Miguel Island off southern California. At the rookeries, adult males set up territories in May, females arrive in June and give birth to one pup a few days later. Most pups are weaned at about 4 months in November. After the breeding season, adult males from the Pribilof Islands migrate to the Gulf of Alaska , while adult females and juveniles migrate through the Aleutian Islands into the North Pacific Ocean, often as far south as the Oregon and California offshore waters. Many pups may remain at sea nearly 2 years before returning to their rookery of birth. Pups weigh up to 5.4 kg at birth; adult males average 2.1 m in length and can weigh up to 275 kg. Adult females are much smaller; they weigh 30 to 50kg.