The Blue Whale (Balaenoptera musculus) is the largest animal documented so far to ever have existed on earth. It has a wide distribution occurring in all the oceans of the world in three distinctive subspecies; B. m. musculus (Northern Hemisphere Blue Whale), B. m.intermedia (Antarctic Blue Whale) and B. m. brevicauda (Pygmy Blue Whale). The Blue Whales recorded around Sri Lanka reportedly belong to the Pygmy Blue Whale subspecies. However, Brown and Donahue (1994) say that the northern Indian Ocean populations of Blue Whale should be recognised as a separate subspecies, B. m. indica
During the fall and winter months these cetaceans make long migrations to the tropics from the temperate zones to calve and breed. However it is an idea that Sri Lanka has its own resident pods of Blue Whale, which are found around the waters off the island right throughout the year, but further scientific studies have to be carried out to justify this idea.