Marine mammals include whales and dolphins, pinnipeds, i.e. seals, sea-lions and walruses, as well as polar bears. Some marine mammals spend their entire lives in water, while others spend varying periods of time on land or on ice.

Three marine mammal species occur in Finland’s marine waters: the grey seal, the Baltic ringed seal, and the harbour porpoise. Of these, only the grey- and ringed seals breed in Finnish waters. Only a few observations are made of porpoises each year. All other marine mammal species found in Finnish coastal areas, such as dolphins and humpback whales, are extremely rare visitors and have only ended up in Finnish waters by accident.

The common threats to marine mammals include by-catch mortality from fisheries,
environmental toxins, and underwater noise. The Baltic ringed seal is particularly dependent on ice and snow cover for its survival and its numbers are predicted to decrease due to climate
change.