River pollution due to extensive use of pesticides is dangerous for the critically endangered dolphin of river Ganga, India's national aquatic animal, says an expert. There are only about 2,000 left, down from tens of thousands just a few decades ago.
About half of these are in Bihar and Uttar Pradesh.
R.K. Sinha, an expert on Ganga river dolphins said that heavy use of pesticides in agricultural fields is dangerous for the existence of dolphins because of low metabolism capacity in their bodies.
According to Sinha, who has been researching freshwater dolphins for over two decades, rivers are major repositories of pesticides. "The toxins of pesticides enter the river system through agricultural run-off, domestic sewage and industrial effluents," he said.
He said, since dolphins are at the apex of the food chain in rivers, their condition would help assess whether the steps taken to clean the river Ganga were working.
"If the number of dolphins increases in the river, it will be a positive sign of a clean Ganga but if the number decreases, it is a negative sign of increasing pollution," he said.
Sinha, a professor of zoology at Patna University, asserted that immersion of idols in rivers also poses a grave threat to aquatic life. He suggested that "manmade water bodies" be used for immersing idols.
"The Ganga is already highly polluted and its ecosystem is under pressure. Untreated sewage, rotting carcasses and industrial effluents that find their way into the Ganga during its 2,500-km-long journey from the Himalayas to the Bay of Bengal have also affected the dolphins," he said.
Experts estimate the current population of Ganga river dolphins at around 2,000. The World Wide Fund for Nature (WWF) says that in the 1980s, there were around 3,500 in the delta region alone.
According to the WWF, Ganga river dolphins are found in seven states- Assam, Uttar Pradesh, Madhya Pradesh, Rajasthan, Bihar, Jharkhand and West Bengal.
The Ganga river dolphin (Platanista gangetica) is found in India, Bangladesh and Nepal. In appearance, it is identical to the Indus river dolphin. It is one of four freshwater dolphin species in the world. The other three are found in the Yangtze river in China, the Indus in Pakistan and the Amazon in South America.
According to WWF, Ganga river dolphins prefer deep waters, in and around the confluence of two or more rivers. They share their habitat with crocodiles, fresh water turtles and wetland birds.
It has a sturdy, yet flexible, body with large flippers and a low triangular dorsal fin. It weighs up to 150 kg. The Ganga river dolphin is blind. It finds its way and its prey in the turgid rivers water through echo-location.