These are the ‘moustached’ or baleen whales, one of the two extant branches of the cetacean group. There are about 10 species in three families in this group, rather less than the toothed whales, the other major cetacean branch. What the suborder Mysticeti lacks in variety it makes up in size, being the largest animals of all time on earth.
One family, the Eschrichtiidae, which has one species, the Grey Whale Eschrichtius robustus, is not represented in Indian waters. There are only stray records of one species of the next family, the Balaenidae or Right Whales. All species of the third and largest family, the Balaenopteridae, or rorquals, have been recorded.
All baleen whales filter relatively small living things from the water with baleen. Baleen, which used to be called whalebone, is a flexible substance made of keratin. It forms a series of vertical plates. These plates, with a fringed edge, hang in the mouth of the whale from the upper jaw. Baleen plates strain out large amounts of tiny animals from the water at a time. They are not modified teeth. The teeth themselves are vestigial in baleen whales.
Zooplankton, consisting of small animals such as shrimplike krill and other crustaceans, fish such as mackerel and herring, and bottom fish such as cod are all eaten by baleen whales. They use various feeding techniques to harvest their food. Some, such as the Right Whales, and the Sei Whale Balaenoptera borealis, swim slowly through a swarm of zooplankton with the mouth open. Water flowing into the mouth is continuously filtered. This is known as ‘skim feeding’. Other species, such as most of the rorquals, indulge in ‘gulp feeding’. They have grooves or pleats running along their throats, which expand when a mouthful of water is taken in. Humpback Whales Megaptera novaeangliae rise slowly from below a school of their prey, blowing out bubbles from their blowhole. A net of bubbles is thus created, encircling the prey animals. As they panic and converge, the Humpback rises to the surface with its mouth open, capturing the concentrated prey. This form of gulp feeding is called ‘bubble netting’. Grey Whales Eschrichtius robustus scrub the bottoms of shallow waters, seeking out mud-dwelling creatures. This is ‘bottom feeding’.
The Killer Whale Orcinus orca is the main predator of baleen whales. Next come sharks. Small, circular bites are often seen in whale blubber. These bites are made by the small Cookie-cutter Shark. It sinks its teeth into the skin and blubber of a whale, and twists its body free with the forward movement of the whale. As it moves away, it takes a small piece of flesh with it. All cetaceans commonly have internal parasites such as nematodes and flatworms. Baleen whales are also plagued by external parasites like barnacles and cyamids or ‘whale lice’.