In the austral spring (October – December) bulls establish breeding territories, approximately 50 square meters in area. Although they try to herd females and create harems, females typically move about freely. Dominant males are more successful at mating with more females. Non-breeding males are pushed to a separate part of the rookery, closer to the ocean. There, the younger males will engage in mock territory battles.
Mating System: polygynous
For South American fur seals, sexual maturity is reached at 3 years for females and 7 years for males. Females begin estrus usually 6 to 8 days after they give birth and, though all will mate, only about 15% will give birth the next year if they are nursing a pup. After mating, implantation is delayed for 4 months. Total gestation time averages 11.75 months. Litter size is limited to one pup. Reproduction is synchronous in rookeries, with a peak birthing period at a time of peak food availability. If rearing takes longer than a year, a second pup will be born, resulting in competition for the mother’s milk. After birth, the pup is nursed for 7 months to 3 years, depending on environmental conditions. Lactation period may vary and can overlap with pregnancy, resulting in energetic costs that are paid by smaller young being born. It can also result in successful births only occuring every few years, rather than yearly. This phenomenon is unique for Arctocephalus australis among otariids. In addition, an Uruguayan study showed a significant difference in pregnancy rates in Arctocephalus australis from year to year, indicating that both environmental and demographic stochasticity play a role in population dynamics. Pups are born throughout November and December along the Uruguayan coast, a bit earlier in Peru. Pups’ average weight is 3-5 kg. Studies have shown that females that lactate during pregnancy give birth to smaller young. Growth rates of young are slow, varying between 0.05 – 0.09 kg/per day. The average pup length at birth is 60-65 cm for males, 57-60 cm for females. Females reach full size in ten years. Both male and female pups are born with a dark coat of fur but, as they mature, females develop lighter coloration ventrally. Mortality of pups can be caused by maternal aggression during times of movement to or from the water and is considered to be higher than in other species of otariids (10 – 48%). Death can also be caused by aggressive males or by males of South American sea lions, Otaria byronia. However, a study in Uruguay showed South American fur seals to have an overall high survival rate for young adults. (Trillmich 1990, Harcourt 1992, Majluf 1992, Harcourt 1993, Nowak 1999)
Breeding season: Mating and birthing occurs from October through January.
Average number of offspring: 1.
Average gestation period: 11.75 months.
Range weaning age: 7 to 36 months.
Average weaning age: 12 months.
Average age at sexual or reproductive maturity (female): 3 years.
Average age at sexual or reproductive maturity (male): 7 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous ; delayed implantation
Average birth mass: 4250 g.
Average gestation period: 236 days.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (male)
Sex: male: 2556 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 1095 days.
Pup rearing is done by the mother, with no help from the male. After birth, the mother will remain with the pup for 5 to 10 days before leaving to forage. Mothers will alternate between average foraging trips of 4.6 days and nursing their young for 1.3 days. (Majluf 1992, Reeves, et al. 1992, Jefferson, et al. 1994, Lima and Paez 1995, Couturier 1996, Nowak 1999)
Parental Investment: precocial ; female parental care