The breeding cycle of the Australian sea lion is unusual within the pinniped family. It is an 18 month cycle and is not synchronised between colonies. The duration of the breeding season can range from five to seven months and has been recorded for up to nine months at Seal Bay on Kangaroo Island.
Bulls do not have fixed territories during the breeding season. The males fight other males from a very young age to establish their individual positions in the male hierarchy and during the breeding season, dominant males will guard females for the right to breed with her when she comes into season.
A female comes into season for about 24 hours within 7 to 10 days after she has given birth to her new pup. She will only look after the new pup and generally fights off the previous season’s pup if it attempts to continue to suckle from her.
Male Australian sea lions are also known to kill young as an act of defence of territory.
Australian sea lions also practice alloparental care, in which an adult may adopt the pup or pups of another.