(Roxburgh, 1801) - Ganges River dolphin
The Ganges River dolphin, or susu, is a very strange-looking dolphin. The body is robust and soft, with a flexible neck, often characterized by a constriction or crease. The long beak is distinct from the steep forehead, but there is no crease between them. The beak is like a pair of forceps, is laterally compressed, and widens at the tip; it is proportionately longer in females than in males. The blowhole, unlike that of most cetaceans, is a slit that runs along the long axis of the animal's body. There is a shallow ridge on the melon, in front of the blowhole. The eyes are extremely small and are located above the distinctly upturned corners of the mouth. The dorsal fin is a very low and wide-based triangle about two-thirds of the way to the flukes, which are concave along the rear margin. The broad flippers usually have a flat trailing edge, but it is sometimes scalloped.
These animals are grey, often with a slightly darker dorsal surface. Some Ganges River dolphins may have a pinkish cast to the belly.
The 26 to 39 upper teeth and 26 to 35 lower teeth are curved. The anterior teeth are longer and extend outside of the closed mouth, especially in younger animals, whose teeth have not yet become worn.
Can be confused with
Ganges River dolphins can be confused with several other small cetaceans that are found in overlapping areas, mostly near the river mouth. Finless porpoises have no dorsal fin and no beak, Irrawaddy dolphins have no beak, and bottlenose and hump-backed dolphins are much larger and both have prominent dorsal fins that are very different from the low dorsal fin of the Ganges River dolphin.
Female adults are up to 2.6 m and males 2.2 m in length. They can reach weights of at least 108 kg. Newborns are apparently between 65 and 90 cm.
The extensive range of these dolphins includes the Ganges, Brahmaputra, and Karnaphuli river systems and many of their tributaries in India, Bangladesh, Nepal, and Bhutan. Ganges River dolphins live not only in the main channels, but also during the flood season, in seasonal tributaries, and the flooded lowlands.
Biology and Behaviour
As is true for most of the river dolphins, Ganges River dolphins generally live in small groups of less than 10 individuals, and are most often seen alone or in pairs. They are active animals, but they do not often engage in leaps. In captivity, these dolphins appear to spend much of their time swimming on their sides, and they constantly emit echolocation clicks. This is understandable in light of the fact that they normally live in relatively shallow, turbid waters. In fact, Ganges River dolphins are nearly blind, and can probably only detect light levels, and perhaps direction.
Calving apparently can occur at any time of the year, but there may be peaks in December to January and March to May.
These dolphins feed on several species of fishes, invertebrates, and possibly turtles and birds.
All river dolphins face the serious threat of loss of habitat, and the Ganges River dolphin is no exception. Damming and diversion of rivers, pollution of waters, increasing vessel traffic, overfishing of prey species, accidental catches in fishing gear, and direct hunting for meat and oil all threaten the existence of these animals. There are believed to be several thousand Ganges River dolphins left in the world.