Calcutta: The tiger count in the Sunderbans has gone up, suggest preliminary findings of the hidden cameras installed across the mangrove forests for the latest national census that started in February.

The cameras have clicked more than 100 pictures of tigers in just two pockets of the Sunderbans Tiger Reserve in the first phase of the census, which will end before the monsoon.

"These are raw findings and will be subjected to detailed scrutiny. There could be multiple pictures of one tiger. It is still too early to estimate the exact number but we are optimistic about the count going up this time," said Nilanjan Mallick, the field director of the Sunderbans Tiger Reserve and the nodal officer for the tiger count in the Sunderbans.

"Tigers have been clicked in more than 100 grids," Mallick said. The tiger reserve is divided into grids of 2sq km.

In the 2014 national census, the big cat count in the Indian Sunderbans had been pegged at 76. Forest department sources estimate the count has gone up to 80 since.

An independent expert in conservation science methodology said suggestions of an increase in tiger numbers based exclusively on images captured via cameras do not have a scientific basis.

"For reliable estimates, you need to combine the information from the camera pictures along with rigorous statistical analysis," said Arjun Gopalaswamy, a scientific advisor to the Wildlife Conservation Society and a visiting scientist at the Indian Statistical Institute, Bangalore centre.

"The cameras may not capture every single tiger in a given area, and the number of images captured or the number of individual tigers identified during two census exercises will also depend on, for example, the number of cameras deployed and the locations of those cameras. A statistical analysis is required to correct for differences that arise from many such factors to get reliable estimates."

The Sunderbans is spread across 10,000sq km, a little above 4,000sq km of which is in India and the rest in Bangladesh.

The Sunderbans Tiger Reserve, one of the first nine that came into being following the launch of Project Tiger in 1973, is spread over 2,585sq km. It comprises the Sunderbans National Park, marked as the core area, and the Sajnekhali Wildlife Sanctuary and the Basirhat Range, which form the buffer zones.

Altogether 300 pairs of all-weather night-vision cameras had been installed in two pockets of the tiger reserve for the pre-monsoon census - 180 pairs in the eastern part of the national park and 120 in the Basirhat Range. They had been installed one-and-a-half months ago and are now being retrieved.

Animal movements activate the sensors in the cameras, which then take photographs.

The cameras will be installed in the western part of the national park, the Sajnekhali Wildlife Sanctuary and the adjoining South 24-Parganas division in the post-monsoon phase of the census.

The images and the reports will be sent to the Wildlife Institute of India and the National Tiger Conservation Authority.

The national tiger count stands at 2,226, up from 1,706 in 2010.

The 2018 census, for the first time, includes the tigers in Bangladesh, Bhutan and Nepal. Four officials from Bangladesh attended a training session in January.

Additional reporting by G.S. Mudur