The rorquals, six species in all, make up the largest family of baleen whales. All of them, in two genera, have been recorded from India.
The word rorqual is derived from an old Norse word meaning “groove-throat”. All the rorquals have a large number of throat pleats or furrows running along the throat. These pleats allow the vast mouth to expand and take in large quantities of water. The Blue Whale Balaenoptera musculus can take in 60 to 70 tons of water with one gulp. The rorquals differ from the other baleen whales in having dorsal fins, short baleen plates, and heads that are flat on top, rather than arched or curved. They are slim and fast swimming, with the exception of the Humpback Whale Megaptera novaeangliae. The Humpback differs from the other rorquals in having very long flippers. These are about one-third as long as its body. In other rorquals these measure only one-twelfth to one-seventh of the body length.
Rorquals are powerful swimmers. The Blue Whale and the Fin Whale Balaenoptera physalus are known to be capable of attaining speeds of 37 kilometres per hour when being pursued, whilst the Sei Whale Balaenoptera borealis is said to travel at 65 kilometres per hour for short bursts. Even the largest whales can leap clear of the water, and some can tow large boats. The slow Humpback Whale is particularly acrobatic. All these animals perform great migrations, travelling between the poles and the tropics. Some populations of Bryde’s Whale Balaenoptera edeni alone remain throughout the year in warm seas.
Earlier this century, rorquals formed the mainstay of the whaling industry. These whales were vulnerable because they assembled in large groups in feeding and breeding areas. The Humpback Whale, being a much slower swimmer than the other rorquals, was a particularly easy target for whalers.
One of the products whalers sought from the rorquals was the layer of fatty tissue, or blubber, that lies beneath the skin. Blubber serves to keep the whale warm and stores energy. The insulating layer of blubber may be many centimetres thick, reducing heat loss in cold waters. Blubber provides energy for the animal when it does not feed. Such periods without food may be long, during breeding and migration. Whale calves are born without blubber, and put it on quickly. A Blue Whale calf consumes 590 litres of milk in one day, an amount, it has been pointed out, more than an average human household consumes in a whole year. Indeed, the weight the calf gains in the first six months of life is at a rate greater than three kilograms per hour!
Whalers often located their quarry by the blow, or spout, and skilled observers can recognise the species from its spout. The visible part of the blow is moisture in the air exhaled by a whale. Rorquals produce a single plume, whilst the Right Whale has a V-shaped spout.Spouts may not be visible under all conditions.