The grey seal is the largest mammal in the Baltic Sea. Adult males reach over 2 m in length and weigh up to 300 kg; females are smaller.
Grey seals are real offshore animals, roaming across the entire Baltic Sea. They are also relatively social animals, gathering year-round in large herds of several dozen or even several thousand animals in their haul-outs. Their main haul-outs are located in the central part of the Baltic Sea, in Estonia, Sweden and the Åland Archipelago. Three haul-outs are known in the Estonian waters of the Gulf of Finland: the area of Krass Island and the Uhtju and Malusi Islands. The latter is a permanently inhabited haul-out.
The grey seal population in the Baltic Sea declined to about 4000 specimens by the 1970ies. The application of effective conservation measures since the 80ies of the last century has increased the present population to an estimated 23 000–24 000 specimens, with approximately 1000 of them living in the Gulf of Finland.
Grey seals feed mainly on fish, whose species composition in their diet varies between seasons.
Grey seals pup in February-March. The mother seal gives birth to a single white-furred pup on offshore drifting ice. Its white baby fur is moulted and replaced with adult fur at about 3 weeks. In warm winters, grey seals pup on islets or islands. The pup weighs 10–12 kg at birth and gains a couple of kilograms per day by nursing on the mother’s fat-rich milk. Pups start to feed on their own at about a month old.
The lifespan of grey seals is 15–25 years but there are reports on even 40-year-old specimens.
The health status of grey seals has not considerably improved despite the reduced quantity of environmental toxins like PCB and DDT in marine organisms and they still suffer from many health problems (pathologies). This may be due to new toxic compounds whose effects have not been studied yet.
Adult grey seals have no enemies. Pups can fall prey to white-tailed eagles and great black-backed or herring gulls.
Fishermen have always blamed seals for damaging their nets and taking toll from them. Part of the reason behind this certainly lies in the general decline in fish stocks in the Gulf of Finland but there are also other reasons. Consistent research, incl. the use of radio tags in seal research, helps us understand the life of seals.
The grey seal is protected in all countries around the Gulf of Finland: in Estonia, Finland and Russia.