The Baikal seal (Pusa sibirica), locally known as nerpa. It is the only pinniped that lives solely in a freshwater habitat, the Lake of Baikal. It is one of the smallest true seals (165 cm length, 60-70 kg body weight) and their life expectancy of almost 60 years is exceptionally high for seals.
The origin of this species is still a mystery: Did they evolve in this oldest lake on earth when it was connected to an ocean in a previous ice age? Or did they migrate from the north via the rivers Yenisey and Angara? Currently, the most accepted theory is that it descended from a relative, the ring seal (Phoca hispida). It is estimated that they have been isolated geographically for about 500,000 years.
Now, you certainly ask: Will Ernst and the seal meet? The most recent estimate of the population size is 85,000 animals. Most of the seals are living in the northern part of the lake, however, in the summer season they are dispersed all over the lake. The biggest colony is found on Uchkani Islands, in the vicinity of Ernst’s route. So, from this point of view, it could well be that Ernst encounter one of the living seals. But baikal seals are nocturnal, which means that they sleep or rest when Ernst is swimming.
Do you they compete with Ernst for food? The favourite food of the Baikal seal is the golomyanka which are two fish species restricted (endemic) to the Lake Baikal. They are small (16 – 21 cm long), and one of the two species is a very fat-rich fish (almost 40% of the body weight). A grown-up seal forages 3-4 kg of fish per day, but golomyanka are the most abundant fish in terms of biomass (70% of the fish) in the lake and population is estimated at 150,000 tons. What’s more, golomyankas are not commercially harvested and are not of value as a food source for humans. So, most likely, there will be no competition between the Baikal seal and Ernst for the fish in the Lake.
You might also be interested to know whether the seal is endangered? In fact, it is ‘least concerned’, according to the IUCN lists. However, the total population dropped from 104,000 between 1994 and 2000. The mortality rate among seal pups had risen two to threefold in the same time frame. Most likely, a variety of causes contributes to the decline:
The seal is hunted for its fur, meat and oil. In 2012-2013 it was estimated that 2,300–2,800 seals were hunted per year (combined legal hunting and poaching) and especially the hunt of young animals affects the population structure. As for other aquatic mammals, many seals die due to entanglement in fishing gear and as bycatch, with a recent estimate of about 1,000 individuals each year. Another threat is the exposure to toxic heavy metals and continuous poisoning by industrial waste and persistent organic pollutants, such as dioxin, DDT and other pesticides. These compounds affect the reproduction and weaken the immune system, which makes them susceptible to diseases. In this context, mass mortalities of at least 5,000 animals due to canine distemper in 1987-88 has to be mentioned. In later years, more mortalities were reported, the last in 2017, when 140 dead animals were washed ashore, but the causes are still unclear.
Climate change will become a new threat for these animals. Due to their thick blubber, providing an extreme efficient insulation, they cannot dissipate their body heat well. Adult males, for example, become very weak after the mating season in April and in the consecutively moult season. They may then lie on the ice for a few days without entering the water or feeding. Under conditions of high atmospheric temperatures and sunny weather they were reported to die from overheating. About 1% of the males are dying this way, which could considerably harm the population under certain circumstances, such as further increases of temperatures and other causes impairing their health and fitness, as mentioned before.
Author: Patricia Holm, University of Basel, MGU, Dept. Environmental Sciences