The only mammal that live in Lake Baikal waters is the nerpa, the world’s only freshwater seal. The seal population is estimated at 100,000 animals. These are distributed all over the lake especially in the remote northern and middle portions of the lake. The adult animal is normally 1.6 m (5 ft) long and weights up to 130 kg (287 lbs). Seals reach adult age at 4-6 years and are able to give birth to the young over 30 years of age.
No one knows where nerpa had come to Baikal from. It is believed that it appeared here 2 million years ago. There is an opinion that the seal had come into Baikal from the Arctic Ocean through the Lena River. The Lena River and the lake constituted an integral system in pre-historic times. Since then it has undergone evolution and changed. Now it is the longest living seal in the world. Female animals may live up to 56 years. It cannot be compared to the average life expectancy of sea seals which is from 18 to 31 years only.
Nerpa can stay deep under water for a long time. It is due to the fact that their blood contains special substance close to human hemoglobin that can bind up more oxygen. It is believed that they sleep under water especially in winter when it is colder outside than in the water.
In March, one can see the nerpa lying in the sun on ice. It is not just pleasure but also a necessity. They need vitamin D formed in the organism with the help of sun light and ice to scratch and change old fur. In winter time when the lake is covered by the thick layer of ice the seal makes breath-throughs which are holes in ice using their sharp claws.
Near those holes in the snowy dens the nerpa cows give birth to one or rarely two seal-calves. At first the mother feeds the young with milk which is very fatty and bitter in taste. Two weeks later their white fur acquires silver tint of color. It is the protective coloration as the young are usually born in winters.
The nerpa feeds on fish that are not significant in fishery, but important for the lake’s ecosystem. Bullheads and golomyanka fish make a major part of its food ration. Seal consumes no less than 3 kg (6.6 lbs) of fish daily.