This video from India says about itself:
7 Wonders of India: Vikramshila Gangetic Dolphin Sanctuary
11 February 2009
Located in the Bhagalpur district of Bihar, Vikramshila Gangetic Dolphin Sanctuary is a 50 km stretch of Ganges River from Sultanganj to Kahalgaon. The dolphin population across India is estimated to be a little over 1,500. Half of these are found in the Ganga in Bihar. It is the only protected area for these endangered dolphins in Asia.
From Wildlife Extra:
Improved monitoring gives Ganges river dolphin better survival odds
Using a combined visual-acoustic survey method could be a more effective way of monitoring the endangered Ganges river dolphin, scientists have found.
Previously it was believed that visual survey methods – reliant on conservationists spotting and recording surfacing dolphins – were the most cost-effective way of surveying the species. The study revealed that detecting the sound that dolphins emit using a method called a combined visual-acoustic survey, can improve the ability to detect population trends and reduce survey costs.
Scientist Nadia Richman from the zoological Society of London (ZSL) said: “Freshwater cetaceans occupy some of the most densely populated and polluted river systems in the world. We need to make decisions about the best way to manage these species before another becomes extinct. However, these decisions need to be based on evidence which means we need methods that can detect changes in population size in the quickest time possible and for the least cost.”
The ability to detect changes in population size of a species helps to inform conservationists how fast a population is declining, and whether a conservation action has been effective in stopping a decline.
The study was undertaken by scientists from ZSL, Bangor University, the University of Chittagong in Bangladesh, the Wildlife Conservation Society (WCS), the Bangladesh Cetacean Diversity Project, and the Fisheries Research Agency of Japan.
These findings have been published 8th of May 2014 in the journal PLOS ONE. Read the paper here.