Standing on the Howrah bridge, a pedestrian can spot small disturbances in the Hooghly river. Small heads, bobbing up and down, breaking the surface of the water, and diving back in. They are not fish, they are mammals. To be specific, they are dolphins. These dolphins might not do ball tricks, or jump through hoops, but they are present, and they are endangered.
There are two major species of dolphins in our rivers. The Ganges River Dolphin (Platanista gangetica), and the Irrawaddy Dolphins (Orcaella brevirostris) in the more saline parts of the river, and the Sundarbans.
Scottish botanist William Roxburgh, then superintendent of Calcutta Botanical Garden, first officially documented the Ganges river dolphins in 1801.
On National Dolphin day, My Kolkata spoke to two researchers, who have spent years with these marine mammals, and worked for their conservation.
“Over the past 20 years, there has been leaps in the technology that records the dolphin populations. Previously we had very primitive technology, but with time we have evolved a lot. Now the readings are more accurate,” said Punyasloke Bhadury, Department of Biological Sciences, IISER Kolkata.
These dolphins inhabit freshwater rivers, particularly in the deep and slow-flowing sections. Adult dolphins typically measure between 2 and 2.5 meters in length and can weigh up to approximately 150 kilograms. Their bodies are smooth and grey in colour. One of their most distinctive features is a long, slender snout, which features visible teeth and a rounded forehead.
“As the Bengal tiger is an indicator species for the jungle, Gangetic dolphins are the tigers of the river, because they are the top predators of their food chain,” said Dipanwita Chattopadhyay, chief coordinator for Micro Solutions, and a professor at Behala College.
They rely entirely on echolocation — or echo-determination — which helps them create a complex acoustic map of their surroundings through high-frequency sound waves. “This is essential because finding food in the murky waters of the river is otherwise impossible,” said Chattopadhyay.
Mentioned by Emperor Ashoka in his fifth pillar verdict, the Puputaka (gangetic dolphins) was declared inviolable and barred from hunting or killing. From puran to mythology of the Sundarbans, shushuk (local name) is mentioned in various folklores. These are not just myths. There have been behaviours recorded where Irrawaddy dolphins have helped fishermen locate schools of fish, and regularly visited boats to interact with humans.
With various conservation methods, and awareness among people, the number of dolphins remains at 6,324, Irrawaddy dolphins at 108 on the Diamond Harbour delta and Indus River dolphins (Platanista minor) remain at three. While fish nets, large vessels, and oil spills remain a constant threat to these mammals, dolphins are present in our city.
Amitav Ghosh’s novel Hungry Tide records these dolphins as well. These creatures are on the endangered species list according to the IUCN Red List, and are placed in Schedule I in the Indian Wildlife (Protection) Act, 1972.