The blue whale - Balaenoptera musculus is a marine mammal belonging to the suborder of baleen whales called Mysticeti. It is also arguably the most impressive creature to live or have ever lived on this planet! At 30 metres (98 ft) in length and 180 metric tons or more in weight, it is in fact both the largest and the heaviest animal ever known to have existed!

You would think then, that being the largest animal on Earth they would be quite easy to find.  However, blue whale populations have declined dramatically over the past century or so due to commercial whaling so finding them anywhere can prove to be particularly difficult.

Be that as it may, just where do you find blue whales?

Since the introduction of the whaling ban, scientific studies have failed to show whether global blue whale populations are increasing or remaining stable.

The largest known concentration, consisting of about 2,800 individuals, is the northeast Pacific population of the northern blue whale that ranges from Alaska to Costa Rica, but is most commonly seen from California in summer. Sometimes, this population is known to visit the northwest Pacific between Kamchatka and the northern tip of Japan.

In the North Atlantic, there are two further large populations of northern blue whale. The first is found off Greenland, Newfoundland, Nova Scotia and the Gulf of Saint Lawrence. This group is estimated to total about 500. The second, more easterly group is spotted from the Azores in spring to Iceland in July and August; it is presumed the whales follow the Mid-Atlantic Ridge between the two volcanic islands.

Beyond Iceland, blue whales have been spotted as far north as Spitsbergen and Jan Mayen, though such sightings are rare. However, scientists do not know where these whales spend their winters. The total North Atlantic population is estimated to be between 600 and 1,500.

In the Southern Hemisphere, there appear to be two distinct subspecies, the Antarctic blue whale, and the little-studied pygmy blue whale which is found in Indian Ocean waters. The most recent surveys provided an estimate of 2,280 blue whales in the Antarctic (of which fewer than 1% are likely to be pygmy blue whales).

Estimates from a 1996 survey show that 424 pygmy blue whales were in a small area south of Madagascar alone, thus it is likely that numbers in the entire Indian Ocean could be in the thousands.

A fourth subspecies of blue whale -  B. m. indica, was identified in the northern Indian Ocean, but difficulties in identifying distinguishing features for this subspecies led to it being used a synonym for B. m. brevicauda, the pygmy blue whale.

Migratory patterns of these subspecies are not well known. For example, pygmy blue whales have been recorded in the northern Indian Ocean (Oman, Maldives and Sri Lanka), where they may form a distinct resident population. In addition, the population of blue whales occurring off Chile and Peru may also be a distinct population.

Some Antarctic blue whales approach the eastern South Atlantic coast in winter, and occasionally, their vocalisations are heard off Peru, Western Australia, and in the northern Indian Ocean. In Chile, the Cetacean Conservation Center, with support from the Chilean Navy, is undertaking extensive research and conservation work on a recently discovered feeding aggregation of the species off the coast of Chiloe Island in the Gulf of Corcovado, where 326 blue whales were spotted in the summer of 2007.

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