Two major aquatic species facing extinction in Ganga are the gharial – a species of crocodile – and Ganga Dolphin. There are only about 200 gharials and 2500 Ganga Dolphin left. In fact, Ganga is often depicted in art wearing a white saree and riding a crocodile.
Ganga River dolphin or Susu is an endangered river dolphin inhabiting the Ganga, and Brahmaputra (in Nepal, India & Bangladesh) and their tributaries. It is also found in Karnaphuli, a 270-km river in Bangladesh.
It is a subspecies of the South Asian river dolphin, which also has a second sub-species, the Indus river dolphin (or bhulan), found in the main channel of the Indus in Pakistan.
In India, Ganga river dolphins are found in seven states: Assam, Uttar Pradesh, Madhya Pradesh, Rajasthan, Bihar, Jharkhand and West Bengal.
Ganga Dolphin is consider the ‘Tiger of the Ganga’, in the sense that it is an indicator species: the health of this species is a representation of the health of the entire aquatic environment. The government of India declared it the National Aquatic Animal in 2009.
There are three other fresh water dolphins in the world: the baiji in Yangtze river in China, the bhulan of the Indus in Pakistan and the boto of the Amazon. Although there are several species of marine dolphins whose ranges include some freshwater habitats, these four species live only in rivers and lakes.
During the Mughal period, villagers used to burn dolphin oil to light their homes.
The dolphin is found in the Sunderbans alongwith the Irrawaddy Dolphin. The Irrawaddy Dolphin is not a river dolphin. It enters the delta from the Bay of Bengal.
Physical Description: About 2.5m in length. Females are larger than males. Weighs upto 150 kg. It has a long thin snout, rounded belly, stocky body and large flippers.
They have very poor eyesight. Their eyes cannot resolve images very well and function as basic light receptors. They locate prey through echo location. They eat shrimp, fish, birds and turtles.
Being a mammal, Ganga River dolphin cannot breathe in the water and must surface every 30-120 seconds. Because of the sound it produces when breathing, the animal is popularly referred to as the ‘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 find food.
There around 1800 individuals in India, and 2500 in total. In 1982 there were 5000-6000.
Hundreds of kilometers of tributary habitat has been lost since the 19th Century – mainly because presence of dams ensures no water flows downstream during summers.
In the 19th century, these dolphins were found in large schools, close to even urban centers along the river. Nowadays, average size of groups surveyed was two individuals. Individuals may also be found alone.
Conservation Efforts: The dolphin is considered Endangered. A strategy and Action Plan for dolphin conservation has been formulated for Uttar Pradesh. The dolphin has received protection in nine protected areas in India. Out of these nine, only one protected area ‘Vikramshila Ganga River Dolphin Sanctuary’ near Bhagalpur, is specially notified for Ganga river dolphin.
Threats: Unintentional killing through entanglement in fishing gear. Bycatch in gillnets and line hooks is also a major source of mortality
These dolphins can survive in brackish water (where river water meets sea water) to some extent. But reduced flows have caused saltwater to intrude an additional 160 km into the Sundarbans Delta of the Ganga, further decreasing the amount of suitable habitat for freshwater dolphins.
The dolphins also need at least about 1.5 m of water depth to swim. Once rivers deplete in summers, the dolphins cannot cross beyond certain points of the rivers, which reduces their habitat.
Killing for dolphin oil, which is used as a fish attractant and for medicinal purposes
Water development projects: More than 50 dams and irrigation-related projects have had an adverse impact. These projects result in major changes in the flow, sediment load, and water quality of rivers, which affects the quality of waters downstream.
Dams also disturb the migration, breeding cycles and habitat of fish and other prey species, and so reduce the food supply. They also cause genetic isolation of dolphin populations.
Ship traffic: They rely primarily on echolocation to navigate and find food. Ship traffic noise pollution can interfere with this, and sometimes collision with boat propellers
Overexploitation of prey, mainly due to the widespread use of non-selective fishing gear.