Changes in the Ice Regime of Lake Baikal in Spring and the Impact on the Baikal Seal (Pusa sibirica, Pinnipedia)

Lake Baikal freezes annually for a long period of time, and the life of the Baikal seal (Pusa sibirica Gmelin, 1788), which inhabits the lake, is closely intertwined with ice; therefore, its well-being is determined by the ice regime. The dynamics of the ice regime in 2002–2023 generally corresponds to climatic forecasts about the shortening of the ice period, but the processes of ice cover formation and decay were very dynamic. In the cold 2000s, the ice cover remained 7–14 days longer; the water area of the southern part of the lake became clear between May 20 and 28. In the relatively “warm” 2010s, ice disappeared by May 10 in 50% of the seasons, and between May 12 and 28 in the other 50% of the seasons. In the 2020s, the weather was unstable but generally colder; in 2020 and 2022, Baikal ice cleared early (May 1 and 6), and in 2021 and 2023, later (May 20 and 25). Ice clearance of the NPB in the “zero” years was predominantly completed in June (75% of seasons); in the 2010s, 70% of the seasonal ice clearance occurred in May, and in the 2020s ice disappeared in May (2020 and 2022) or in the first decade of June (2021 and 2023). A review of published data related to the ice period of the seal’s life (including paleoclimatic reconstructions) has shown that, against the background of global warming, the habitat conditions of the species are changing mainly in a negative direction; reproduction conditions are deteriorating, in particular. The reduced duration of floating ice in some years leads to the appearance of a large number of animals that did not have time to molt on ice, and molting is delayed indefinitely, probably creating physiological preconditions for pathologies. This leads to a change in the time budget of these animals in favor of coastal rookeries, where they continue molting, to the detriment of feeding time. Presumably, warming has provoked the emergence and spread of alopecia, which was absent in the 1970s–1990s. Critically significant changes for the population of the Baikal seal have not been noted, but some adjustments in behavior during the feeding period have been observed (disruption of migrations and increased role of the coast). It is stated that the Baikal seal has a high ecological plasticity, thanks to which the population will be preserved even in conditions of further warming.