Fur seals are known and named for their thick fur, which has 300,000 hairs per square inch. Pups are born with a black pelt, which becomes dark brown with lighter coloration on the chest and belly. Adult males also have gray hair on the back of the neck.
Males are much larger than females, even at birth.
The full range of the northern fur seal extends throughout the Pacific rim from Japan to the Channel Islands of California, although the main breeding colonies are in the Pribilof and Commander Islands in the Bering Sea. Smaller rookeries exist on the Kuril Islands North of Japan, Robben Island in the Sea of Okhotsk, and on San Miguel Island off Southern California. They rarely come ashore except during these times, and are almost never seen on mainland beaches unless they are sick. Mature males establish territories in late May to early June, and aggressively guard and herd 40 or more females. Pregnant females arrive at the rookeries in June and give birth two days later.