Baikal Seal - Reproduction

Reproduction

Female Baikal seals reach sexual maturity at 3–6 years of age, whereas males reach it around 4–7 years. The males and females are not strongly sexually dimorphic. Baikal seals mate in the water towards the end of the pupping season. With a combination of delayed implantation and a nine-month gestation period, the Baikal seal’s overall pregnancy is around 11 months. Pregnant females are the only Baikal seals to haul out during the winter. The males tend to stay in the water, under the ice, all winter. Baikal seals usually give birth to one pup, but they are one of only two species of true seals with the ability to give birth to twins. The twins will often stick together for some time after being weaned. The females, after giving birth to their pups on the ice in late winter, will become immediately impregnated again, and will often be lactating while pregnant.

Baikal seals are slightly polygamous and slightly territorial, although not particularly defensive of this territory. Males will mate with around three females if given the chance. They then mark the female’s den with a strong, musky odor, which can be smelled by another male if he approaches. The female raises the pups on her own; she will dig them a fairly large den under the ice, up to 5 m (16 ft) in length, and more than 2 m (6 ft) wide. Pups as young as two days old will then further expand this den by digging a maze of tunnels around the den. Since the pup will avoid breaking the surface with these tunnels, this activity is thought to be mainly for exercise, to keep warm until they have built up an insulating layer of blubber.

The mother Baikal seal will feed her young for around 2.5 months, nearly twice as long as any other seal. During this time, the pups can increase their birth weight (around 4 kg {9 lb}) fivefold. After the pups are weaned, the mother will introduce them to solid food, bringing shrimp, fish, and other edibles into the den.

In spring, when the ice melts and the dens usually collapse, the pup is left to fend for itself. Growth continues until they are 20 to 25 years old.

Every year in the late winter and spring, both sexes will haul themselves out and begin to moult their coat of fur from the previous year, which will be replaced with a new one. While moulting, they do not eat and enter a lethargic state, during which time they often die of overheating, males especially, from lying on the ice too long in the sun. During the spring and summer, groups as large as 500 can form on the ice floes and shores of Lake Baikal. Baikal seals can live to over 50 years old, exceptionally old for a seal, although they are presumed to be fertile only until they are around 40.