The Blue Whale

(Balaenoptera musculus)

Length: 24-27 metres (78-88 feet) Lifespan 35-40+ years.

The Blue Whale is the largest of all rorquals and indeed all whales. The body is long, streamlined and ends with an extremely thick tail stock. It is blue-grey in colour but the true colour varies between individuals from a very light blue (with extensive mottling) to a uniform dark slate-grey (with little mottling). The head is very distinctive. It is long and very broad compared to other rorquals. From above it is U-shaped and has a single ridge along the top of the rostrum. A most prominent feature is the exceptionally large, fleshy splashguard at the front and to the sides of the twin blowholes.

The dorsal fin is small and triangular with a tip which may be rounded or pointed. It is set three-quarters of the way back and can be moderatly falcate. The most characteristic feature of the Blue whale is its enormous size. With a length of more than 33m (110ft) and a weight of around 190 tonnes it is the largest animal on earth.

The underside of the whale is yellow or mustard-colourd and is not a natural pigmentation but is caused by the presence of algae, called diatoms, which attach themselves to the whale's body. This is most commonly observed in animals living in cold waters near the poles. It has broad flukes with slightly concave or straight trailing edges and a small notch in the middle. The flippers are long and slender and about one seventh of body length.

The blow is spectacular, rising to 9 metres (30ft) high it is a slender, straight column. Breathing sequence usually involves 2-6 minutes at the surface, blowing once every 10-20 seconds, followed by a dive for 5-20 minutes. The fin is visible briefly before the whale arches its back in preparation for the dive. Its tail stock may arch and its flukes may be visible but often they simply sink below the surface.

Blue whales rarely ever breach clear of the water. Juveniles have been observed breaching and landing on their sides or stomaches. Some individuals are easy to approach while others can be difficult. The whale can accelerate to speeds of over 30km/h (19mph) when chased, but usully much slower, and can dive to depths of 150m (490ft) or more.