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Development in the Baltic ringed (Phoca hispida) and grey seal (Halichoerus grypus) populations during the past century is reconstructed using uniquely detailed hunting records from the Nordic countries and published data on demographic parameters. A projection model was elaborated where annual variations in the composition of catches by sex and age were taken into account. Grey seals decreased from 88 000-100 000 in the beginning of the century to approximately 4000 in the late 1970s. The Baltic ringed seal population decreased during the same period from 190 000-220 000 to approximately 5000. In the mid-1960s, the remaining populations were afflicted by sterility, probably caused by organochlorines, which inhibited natural growth during a 25-years period. Thus, the decrease in seal numbers was a consequence of excessive hunting, but the present low numbers are due to lowered fertility rates after 1965.