Lake Baikal seal, Nerpa
Baikal seals (Pusa sibirica) are tiny seals that are members of the family Phocidae. They are native to Siberia and live only within Lake Baikal, from where their common name comes. They are the only type of freshwater seal type and it is still unknown how they arrived in the lake, thousands of kilometers from a seal’s traditional habitat of the sea. The theory is that seals went along the Yenisey and Angara rivers to the Baikal and settled there. The existence of an underground channel between the lake and the Lena River and the lake was also proposed, but no scientific basis has been found for this.
The Baikal seal is one of the smallest true seals. The animals show very little sexual dimorphism; males are only slightly larger than females. They have a uniform, steely-grey coat on their backs and fur with a yellowish tinge on their abdomens. As the coat weathers, it becomes brownish. Pups have coats of white, silky, natal fur. This fur is quickly shed and exchanged for a darker coat, much like that of adults. Rarely, Baikal seals can be also found with spotted coats.
These seals live only in the waters of Lake Baikal. In general, a higher concentration of Baikal seals is found in the northern parts of the lake, because the longer winter keeps the ice frozen longer, which is preferable for pupping. However, in recent years, migrations to the southern half of the lake have occurred, possibly to evade hunters. In winter, when the lake is frozen over, seals maintain a few breathing holes over a given area and tend to remain nearby, not interfering with the food supplies of nearby seals. When the ice begins to melt, Baikal seals usually stay not far from the shoreline.
Baikal seals live solitary lives, but they may gather and share access holes, also sometimes gathering where there is the most favorable habitat. In spring, the time they feed the most, from 200 to 500 individuals will gather, first the juveniles, then adult males, followed by new pups with their mothers. Large groups will also form on the shores of the lake in summer. During winter when the lake is frozen, the seals maintain breathing holes. When the ice starts to thaw, seals gather around larger holes to feed and hunt. Baikal seals feed mainly during twilight and at night, when golomyankas (the main food source) occur in depths as shallow as 10-25 m (33-82 ft). During the day, golomyankas are typically found deeper than 100 m (330 ft). Baikal seals can dive up to depths of 400 m (1,300 ft) and stay underwater for more than 40 minutes. Most dives last less than 10 minutes and generally only 2-4 minutes. Baikal seals have 2 liters more blood than any other seal of their size and can stay underwater for up to 70 minutes if they are frightened or need to escape danger. According to a 2020 paper, Baikal seals also seek food through the use of filter-feeding on amphipods within Lake Baikal. Baikal seals have specialized teeth that allow the seals to expel water while feeding, allowing them to gather large amounts of amphipods while swimming. Baikal seals have one unusual foraging habit. In early autumn, before the entire lake freezes over, they migrate to bays and coves and hunt Kessler's sculpin, a fish that lives in silty areas and, as a result, usually contains grit and silt in its digestive system. This grit scours the seals' gastrointestinal tracts and expels parasites.
Baikal seals have a polygynous mating system, which means that one male mates with multiple females. Breeding occurs in the spring, usually in mid-April to early June. There is a brief period of delayed implantation, and gestation is for about nine months. Pups are born from mid-February to March on the lake ice. Usually one pup is born, though twins are not unusual. In the case of twins, both usually survive until weaning and then remain together for some time. The mothers nurse their pups from 2 to 2.5 months, though not in the southern area of the lake, where ice breaks up earlier. The pups in the south, being weaned prematurely, are smaller. Females typically reach reproductive maturity between 3 to 6 years old and males between 4 to 7 years old. Females can breed until about 30 years old.
Baikal seals have been hunted for a very long time for pelts, oil and meat. Such harvesting continues today, although at such a level that it is believed not to threaten the species’ survival. But pollution of the lake is a threat, with this ‘pearl of Siberia’ affected by towns and factories on its shores, which pollute the water with industrial waste and sewage, and the use of pesticides and fertilizers on the agricultural land nearby. Disease is also a threat; an outbreak in 1978 and 1988 of the Phocine distemper virus caused the deaths of an estimated 6,500 seals, and the virus is still alive within the population. Furthermore, global warming threatens the deterioration of the quality of the habitat of the Baikal seal, and may cause a population decline.
According to the IUCN Red List, the total Baikal seal population size was estimated to be around 108,200 individuals in 2013. Currently, this species is classified as Least Concern (LC) and its numbers today remain stable.
Being piscivores, Baikal seals affect fish populations in their range. This species is the crown of Lake Baikal’s great ecosystem and its only mammal.