The South Asian River dolphin (Platanista gangetica) also locally called susu, is a freshwater or river dolphin found in the Indian subcontinent. One subspecies is found in the Ganges and Brahmaputra rivers while the other is found in the Indus river. The lovely creature diverged from toothed whales, particularly ancestors of sperm whales during the the Oligocene (30 -35 million years ago). This dolphin is the only existing species of this highly successful group.
What’s so special about the South Asian River Dolphin?
This is animal is well adapted to its environment. It has a long thin snout chock full of tiny needle-like teeth that become blunt and almost square as the animal grows older. The animal usually measure around 2 meters in length and weighs in at 80-90 Kgs. The males are larger than the females but the female’s nose keeps growing for longer ( terrible anthropomorphic thought : perhaps so that they can turn their nose up during mating rituals).
It has lost its eye lens because the rivers carry so much silt, it is really hard to see anything inside the water. It can still sense light and its intensity through which it locates prey. This adaptation is not unique to this particular river dolphin, the Amazon and Yangtze dolphins have very similar adaptations.
It has a rounded body and large flippers too. This species has a blowhole at the top of its head which acts as a nostril like other cetaceans. They have to come up every minute or so to breathe and the sound that makes gives the animal its popular name of “susu“. The dolphin has the peculiarity of swimming on one side so that its flipper trails the muddy bottom. This behaviour is understood to help it to scare up its food.
The colour of the dolphin is greyish brown. The calves and young ones are dark in colour but as the animal grows in size, the colour lightens.
Breeding and Social Habits
This species has only one baby at a time after 9 months of gestation. The young are weaned at about one year of age and become sexually mature at 10. They used to live in large schools near urban centers like Allahabad and Varanasi where they were able to get more fish and prawns. Nowadays, due to the destruction and pollution of habitat the numbers have decreased drastically to just pairs seen together. On my last trip to Allahabad in 2014, I was not able to see even one specimen, although Gangetic Gharial is still quite common.
‘Susu’ shares its habitat with crocodiles, freshwater turtles and wetland birds, many of which are fish eaters and are potential competitors. Their range is also across really polluted rivers where overfishing has killed off the prey species.
As the dolphin is at the top of the food chain, its presence in a river system is a leading indicator of the health. Extensive dams have been built across all the river systems in the subcontinent creating islands of populations. At the time of writing there are said to be about 2,000 individuals of this species. This is still a viable population but with fragmentation happening all the while, serious work is being done by the WWF to help keep this species from going the way of the Yangtze Dolphin.