Blue whales live in every one of the world's oceans. There are three subspecies. Those found in Canada belong to the Northern Hemisphere subspecies-of which there are both North Atlantic and North Pacific populations. The Atlantic population of Blue whales frequents waters off eastern Canada: along the north shore of the Gulf of St. Lawrence; off eastern Nova Scotia; off the south coast of the island of Newfoundland and in the Davis Strait; and between Baffin Island and Greenland. While they usually go south in winter, some do linger in the St. Lawrence during years of light ice cover. The Pacific population is found off the west coast of Canada; it migrates past Vancouver Island in spring and fall.

The Blue whale is the largest animal on Earth today-and the largest known to have ever existed. The Blue whale is a rorqual whale-one of a group that has expanding grooves in the skin of the neck; these allow it to take in huge volumes of water while feeding. One quarter of its entire length is made up by its head. It has a smallish dorsal fin and pointed pectoral flippers. Despite its name, the Blue whale is actually coloured dark and light grey; every whale has a unique pattern of mottling that makes it identifiable. Living between 70 and 80 years, Blue whales reproduce every two or three years. Calves at birth measure seven metres and weigh some two tonnes. The largest adult on record measured 29.5 metres.