The much-awaited tiger census in the Sunderbans, where DNA sampling would be made for the first time to establish the number of big cats, has begun.

Tiger scat will be collected for DNA sampling which is a foolproof method to establish their number, Field Director of Sunderbans Tiger Reserve Subrat Mukherjee said.

The exercise started on March 4 will continue till March 9.

Scat collection, however, would be a long-drawn process because Sundarbans has a vast and difficult terrain, Director of Sunderban Biosphere Reserve Pradeep Vyas told PTI.

"It will take an entire year to complete collection of scats in over 100 compartments in the Sunderbans which includes a part of North 24 Parganas district besides the tiger reserve," Vyas said.

Altogether 35 teams comprising 250 forest personnel and representatives of NGOs were taking part in total ecological monitoring which include tigers, co-predators, prey, habitat and human interference, Vyas said.

Asked whether it would be possible to have an approximate count of tigers in Sunderbans immediately after collection of data, he said the data would take two months to process after which it would be sent to the Dehradun-based Wildlife Institute of India.

"After this we have to add the figures from DNA sampling of the tigers," Vyas said.

On the other hand, Mukherjee said 90 per cent of locations for monitoring of tigers, co-predators, prey, habitat and human interference was expected to be over within March 8 and the remaining 10 per cent by March 9.

Tiger estimation in the Sundarbans has traditionally been done by the pug mark method in which the fresh left hind imprint was collected from the field and analysed.

The pug mark method was field friendly, but due to some drawbacks, Project Tiger developed new methodology for monitoring of tigers, co-predators, prey and habitat.

Field director of the tiger reserve R P Saini said the tiger census in the Buxa Tiger Reserve in north Bengal began last month and would continue till April.