Adult Baikal seals measure 1.2-1.4m in length and weigh 63-70kg, the males slightly larger than the females. Pups normally measure about 65cm in length and weigh about 4kg at birth. Females reach sexual maturity at 3-6 years of age, males at 4-7 years. Baikal seals have been known to dive for as long as 43 minutes. It has been estimated that adult males can live up to 52 years of age, females to 56 years.
The Baikal seal, one of the world's smallest pinnipeds, is in fact the only pinniped species that lives solely in freshwater. Individuals are also sometimes found wandering up the rivers surrounding the Lake, one seal having been found 400km upstream.
Pupping takes place on the Lake Baikal ice from February to March, the pups being born in lairs that have been hollowed out on the fast ice. Baikal seals maintain breathing and haulout holes in the ice, adults usually maintaining one main hole and several auxiliary holes, juveniles usually only a solitary hole.