Blue Whale

Balaenoptera musculus

Key Facts

Size: The largest animal on earth, up to 29m

Range: All open oceans

Threats: Loss of food, pollution

Diet: Small krill and small schooling fish

Physical description

The blue whale is the largest animal ever to have lived on earth The record length is 33 metres with a weight of 190 tonnes though most males reach only 23 metres and females 24.5 metres. The calves measure 7.5 metres at birth and weigh about 2.5 tonnes. Their mouths can be up to 6 metres long and the tail flukes 4.5 metres from tip to tip. The body is long and slender and the head is broad and flattened with a single central ridge running from the tip to the blowhole. This is surrounded by a large raised splashguard. The ridge continues along the spine to the small dorsal fin located three-quarters of the way down the back. The tail stock is extremely thick and the tail flukes are relatively small. The pectoral fins are long, slender and curved on the leading edge. Most blue whales are blue-grey and mottled with lighter spots but some appear yellowish underneath due to algae growing on them.

Distribution

Although never common, the blue whale used to be widespread throughout all the open ocean areas. Mechanised whaling has brought it almost to the brink of extinction and it is found now only in small populations. It is estimated that there are only 6,000 to 14,000 left worldwide. There are three main populations of Blue whales: the North Atlantic, North Pacific and the Southern Hemisphere. Some scientists believe that these are actually 3 different sub-species: Balaenoptera musculus subspecies intermedia in the southern hemisphere, the slightly smaller subspecies musculus in the northern hemisphere and the even smaller subspecies brevicuda (also known as the Pygmy Blue whale) which occurs mainly in tropical areas of the southern hemisphere.

Behaviour

Blue whales are so large that it is easy to distinguish them from other whales and they produce a spectacular tall blow. At sea they usually feed alone or in pairs, often widely spaced because of the enormous area they hunt across. They are very fast moving and can accelerate to 30 kph. When relaxed they blow about every 10 to 20 seconds for a total of 2 to 6 minutes before diving. They dive up to depths of 150 metres and more and remain submerged for up to 20 minutes. Youngsters may be seen to breach but adults very rarely do so.

Breeding

Sexual maturity is reached at two to twelve years or when a length of 22.5 metres is reached in males and 24 metres in females. Gestation takes 11 months and once born the calves suckle 190 litres of milk a day and can gain 90 kilograms every day. At about eight months of age when the calves are weaned they can measure up to 15 metres and weigh 23 tonnes.

Feeding

In the southern hemisphere the blue whales feed on small krill which is supplemented in the northern hemisphere by small schooling fish and other crustaceans. They are baleen whales whose baleen is relatively short since they feed on such small prey. However their baleen is still the longest of all the rorqual whales.

Top of page