Reproduction Male leopard seals reach sexual maturity around their fourth year, females in their third. Mating occurs in the water from November to February, and males are probably serially polygynous. Gestation lasts around 11 months, but implantation seems to be delayed for about 2 months. Partuition occurs from September to January, with the concentration of births in October and November. The female gives birth to a single pup weighing about 30 kg and about 160 cm long.
Lactation can persist for up to four weeks.
The pup's coat is soft and thick, dark grey above with a dorsal stripe, pale on the sides and with black spots below. The leopard seal is primarily a solitary species. Animals of different age groups are often segregated in different areas. Mature animals normally occur on the outer fringes of the pack ice. Young animal disperse to subantarctic islands during the winter, and it is debated whether or not these movements are migrations or periodic dispersals due to intraspecific competition.