NORTHERN FUR SEAL BIOLOGY
The Pribilof Islands (St. Paul and St. George) in the eastern Bering Sea are the main breeding islands for the northern fur seal. Large territorial males (bulls) arrive to the islands in May to establish breeding territories on rookeries. While defending territories, bulls do not return to the ocean to feed, but fast for 3 – 4 months during the breeding season.
In mid-June the older pregnant females start arriving to the Pribilofs, with the peak of pupping occurring in early July. As the season progresses younger pregnant and non-pregnant females of all ages return to the rookeries.
Fur seals (male and female) often return to their rookery of birth (natal site). As with females, males arrive onshore in descending order of age, with the younger males (ages 3 – 5 years old) arriving to the haulouts (areas adjacent to rookeries) in late June through September.
A few yearlings arrive in late September and October, however most remain at sea and do not return to their island of birth until they are two years old. One or two days after a pregnant female hauls out on land, she gives birth to a single pup.
The initial bonding of the female and pup is very crucial; the female and pup must learn to recognize each others smell and “voice” in order to find each other on the rookery after long periods of separation.
Once the female and pup have bonded and nursed for 5 – 10 days, the female comes into estrus and is ready to mate, usually with the male in whose territory she gave birth. After mating (usually one day later) the female returns to the ocean for her first feeding trip after fasting for approximately 10 days.
During the next four months, lactating (nursing) females make repeated trips to sea to feed (spend 7 – 10 days at sea) and return to land (spend up to 2 days on land) to nurse their pups. Females deliver fat-rich milk to their pups, which depend on their mother for food until they are approximately 4 months old. In October, females, juveniles of both sexes and pups begin to leave the islands and migrate south for the winter.