Bhagalpur: The Wildlife Institute of India (WII) will conduct a census of dolphin, tortoise, otter, gharial and other endangered aquatic species at the 60km Vikramshila Gangetic Dolphin Sanctuary on the Ganga.

Bhagalpur divisional forest officer S. Sudhakar confirmed the survey by the institute, an autonomous body under the Union forest and environment department.

"The officials had intimated us about the proposed census," Sudhakar said. "They had earlier urged me to send a report on the sanctuary, like its topography, and suggest a suitable time period in which to conduct the census."

The WII team is now conducting the census in neighbouring Sahebganj district of Jharkhand, he added.

A source at the WII said the census is to be conducted under the Centre's Namami Gange project and will also do a comparative study on the quality of water. "The survey will help in identifying steps to purify the river water," the source said.

This is possibly the first time that a government agency would conduct such a census on the sanctuary, which stretches from Sultanganj to Kahalgaon and which was notified in 1991 to protect aquatic species like dolphins.

"In 1998, we had conducted a dolphin census from Sultanganj to Farakka (in Bengal) on the river," said Arvind Mishra, ornithologist and coordinator of Mandar Nature Club, a Bhagalpur NGO. "Dolphin experts like R.K. Sinha and Gopal Sharma were with us during the census."

A census by the Vikramshila Biodiversity Research and Education Centre, a wing in the postgraduate zoology department at Tilka Manjhi Bhagalpur University, in 2015 had recorded 207 dolphins in the sanctuary.

Experts here say the Ganga's ecology changed during last year's floods.

It is not yet known what toll the floods took on the fauna of the sanctuary.