Supervisors: prof Alar Karis; dotsent Tero Härkönen (PhD, Swedish Museum of Natural History)
Opponent: prof Rune Dietz (PhD, Aarhus University)
Over the millions of years marine mammals have explored the full range of climatic and geographic latitudes of the Earth, at present several seal species show circumpolar distribution ranges. Post-glacial rebounds or other geo-morphological changes during have locked several seal populations into fully or partly isolated water bodies where they are adapted to live in seasonally widely fluctuating environments which in one hand provide diverse habitat but in the other hand challenge the adaptivity of the seals. This thesis is discussing the landlocked seals in their captive habitats and ecological implications therein. In this thesis the possible impacts of climate change on the fitness and survival of the land-locked grey seal (Halichoerus grypus) and ringed seal (Pusa hispida botnica) in the Baltic Sea and the Caspian seal (Pusa caspica), inhabiting the Caspian Sea are analyzed. The four original publications form a firm basis to approach this analysis, as they are covering spatially, temporally or topically several key aspects relevant to the climate change. In the context of probably ongoing global warming they provide reference to the times when the change was not expressed yet (II, III, IV) or focus on ecological challenges which will gather force with warming Earth (I, also II-IV). All the involved species and subspecies are to greater or lesser extent ice-related as their distribution ranges freeze over partially or wholly during the winter months. Ice forms a temporary critical habitat to the study species so winter severity and its potential changes are discussed in the context of seal distribution, breeding strategy and success. The current ecological balance is determined by long term average ecological conditions while climatic models show increasing temperatures in close future. Change of the ice conditions in warming climate would bring about critical conditions for the southern populations of the Baltic Ringed seal and the Caspian seals. Deficit of ice will lead to change of seal distribution to areas where the habitat quality, measured by both physical and biological parameters is lower compared to the present situation. The seals' breeding area will become restricted and thus the conservative, ice related breeding strategy of the seals appears to become a major negative factor during current changes which take place during only some generations. The grey seal would be less affected due to plasticity in breeding strategies, but loss of the ice platform and access to several current land breeding sites would also restrict the breeding range of the species, all the three species would lose in breeding success through reduced offspring quality on unstable ice. The reduced ice cover makes the seals vulnerable to terrestrial and avian predation. Climatic changes in the environment are amplified by the anthropogenic factors like pollution, intensive fishing and disturbance which add to the environmental stress and challenge further the survival of the land-locked seal populations.