The Ganges and Indus river dolphins (also called susus or bhulans) are very strange-looking animals. The body is stocky, 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 tends to be 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 longitudinal 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 low and wide-based triangle about 2/3 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 gray, often with a slightly darker dorsal surface. Susus may have a pinkish cast to the belly. The 26-39 upper teeth and 26-35 lower teeth are curved. They are sharply pointed in young individuals. The anterior teeth are longer and extend outside of the closed mouth, especially in younger animals, whose teeth have not yet become worn.
Female susu adults are up to 2.6 m and males 2.2 m in length. They can reach weights of at least 85 kg. Bhulans are considered to reach slightly smaller sizes than the maximums of 2.6 m (females) and 2.2 m (males) for Ganges River dolphins. Length at birth is between 70 and 90 cm. However, it is unclear if these differences are real, or simply artifacts of limited sample sizes. No other external differences are known between animals from the two river systems.
Can be Confused With
Susus and bhulans can be confused with several other small cetaceans that are found in overlapping areas, near the mouths of the rivers in which they live. They might be confused with Irrawaddy dolphins, finless porpoises, bottlenose dolphins, or Indo-Pacific humpback dolphins. The dorsal fins of bottlenose and humpback dolphins, complete lack of a dorsal fin in finless porpoises, and absence of a beak in Irrawaddy dolphins should make them distinguishable. Also, adult bottlenose and humpback dolphins are much larger.
The extensive range of the susu includes the Ganges, Brahmaputra-Megna, and Karnaphuli-Sangu river systems and many of their tributaries in India, Bangladesh and Nepal (and possibly Bhutan). Though formerly much more widely distributed in the Indus and some of its tributaries, the bhulan's range is now restricted to the lower Indus River. It is centered between Taunsa and Sukkur barrages.
Ecology and Behavior
Susus and bhulans inhabitat main river channels, and during the flood season, in tributaries and appended lakes.
As is true for most of the river dolphins, susus and bhulans generally live in small groups of less than 10 individuals, and are most often seen alone or in pairs. Bhulans have occasionally been reported in loose aggregations of up to 30 individuals. Other than the mother/calf bond, affiliations between individuals are thought to be ephemeral. These are active animals, but they do not often engage in leaps. At least 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, susus are nearly blind, and can probably only detect light levels, and perhaps direction.
Almost nothing is known of the reproductive biology of this species. Calving apparently can occur at any time of the year, but for the susu there may be peaks in December to January and March to May. Newborn bhulans have been observed mainly in April and May. Newborns are apparently between 75 and 90 cm.
Feeding and Prey
Susus and bhulans are mostly bottom feeders, feeding on invertebrates (prawns and clams) and several species of fish. Some evidence suggests that they may possibly even consume birds on occasion.
Threats and Status
Main threats include:
• Direct killing in both the Indus and Ganges/Brahmaputra systems (for use of their meat as human and livetock feed,susus as a fish attractant and for medicinal purposes)
• Entanglement in various types of fishing nets
• Vessel strikes
• Environmental contaminants
• Placement of dams and barrages across rivers in this species’ habitat (these structures fragment populations and reduce available habitat by altering riverine ecology)
While the susu has a moderately large range and is probably not in immediate danger of extinction, the bhulan’s range is extremely restricted, making it one of the most endangered types of cetaceans in the world. Current status are “Endangered” (IUCN); “Endangered” (ESA - bhulan), “Not Listed” (ESA - susu).
Leatherwood, S., and R.R. Reeves. 1994. River dolphins a review of activities and plans of the Cetacean Specialist Group. Aquatic Mammals 20:137-154.
Perrin, W.F., R.L. Brownell, Jr., K. Zhou, and J. Liu. 1989. Biology and conservation of the river dolphins. Occasional Papers of the IUCN Species Survival Commission No. 3, 173 pp.
Reeves, R.R. and A.A. Chaudhry. 1998. Status of the Indus River dolphin Platanista minor. Oryx 3235-44.
Reeves, R.R., and R.L. Brownell, Jr. 1989. Susu Platanista gangetica (Roxburgh, 1801) and Platanista minor Owen, 1853. pp. 69-99 in S.H. Ridgway and R. Harrison, eds. Handbook of marine mammals, Volume 4 River dolphins and the larger toothed whales. Academic Press.
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Smith, B.D. 2002. Susu and bhulan Platanista gangetica gangetica and P. g. minor. pp. 1208-1213 in W.F. Perrin, B. Würsig and J.G.M. Thewissen, eds. Encyclopedia of marine mammals. Academic Press.