Dolphins are the most uncontroversial of popular motifs of contemporary times, promoted on television and Hollywood movies alike as symbols of wholesome fun, innocence and gentle intelligence. The exposure, however, is biased towards marine dolphins. Freshwater dolphins, in dire need of public sympathy and protection, have gone largely neglected. Most people are not even aware of the fact that that some species of dolphins (or cetaceans) are found in habitat other than seas and oceans. In fact, four of a total of about 40 species of cetaceans inhabit rivers; three of these are found in Asia, and, of them, two belong to South Asia.
The South Asian freshwater dolphins are the Platanista gangetica minor (bhulan, sometimes also referred to as susu) in the Indus river of Pakistan and the Platanista gangetica (susu) of the Ganga-Brahmaputra system in India, Nepal and Bangladesh. The lipotes vexillifer (baiji) is confined to the Yangtze of China, and the fourth specie, inia geoffrensis (boto), belongs to the Amazon.
While there is no conclusive fossil record, estimates are that the Gangetic dolphin has been around for about 20 million years. It was not until 1801 though, that the susu was first scientifically documented and christened Platanista gangetica by William Roxburgh, a Scottish botanist who was at the time the superintendent of the Calcutta Botanical Garden. The dolphin that was thus identified lives in the highly turbid waters of the Ganga, Brahmaputra, Meghna and Karnaphuli rivers and their tributaries. It inhabits these rivers from the estuarine area to as far upstream as is navigable by them, depth and the evenness of the riverbed being crucial determinants. The Gangetic dolphin is found in Nepal too where the rivers are comparatively clear.
The Ganga dolphin has a sturdy and flexible body, large flippers and a low triangular dorsal fin. In the Ganga, on average, the maximum length that an adult female dolphin may attain is 2.5 metres while the male attains a maximum length of 2.1 metres. After a gestation period of 10 to 11 months, a fully developed calf is born that is usually about 70 cm long. Adult dolphins are light grey in colour whereas the calves are dark chocolate brown. The jaws of an adult are lined with over 130 prehensile teeth meant for capturing small fish usually not more than 10 cm long; the lower jaw is longer than the upper one.