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The Baikal seal

Baikal Seal
Baikal Seal
Extremes fascinate! Just as Ernst Bromeis is currently swimming in Lake Baikal, there are other creatures that have adapted over hundred thousands of years to the special conditions of this deepest and oldest lake on earth: the Baikal seal.
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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.

Meet and eat with Ernst ?

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.

Concern at the recent population decline and possible causes

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

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

Sources:
http://www.baikalex.com/info/nerpa.html
http://www.bww.irk.ru/baikalseals/baikalseals_01.html
https://www.pin­nipeds.org/seal-in­for­ma­tion/species-information-pages/the-phocid-seals/baikal-seal

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