Calcutta: Five hundred pairs of all-weather night-vision cameras will be installed across the Sunderbans Tiger Reserve and South 24-Parganas division for the second round of tiger census in the mangroves post monsoon.

The cameras will be installed in the western part of the national park and Sajnekhali range in the Sunderban Tiger Reserve and Matla, Raidighi and Ramganga ranges in the South 24- Parganas division after Puja.

"We are in the process of procuring 200 more pairs of cameras. Altogether, 500 pairs would be put to use. The second phase will cover a larger area than the first one," said Nilanjan Mallick, the field director of the Sunderbans Tiger Reserve and the nodal officer for the tiger count in the Sunderbans.

Three hundred pairs of cameras - 180 in the eastern part of the national park and 120 in the Basirhat range - had been installed in February in two pockets of the tiger reserve for the pre-monsoon census. The cameras were retrieved by April.

The exercise is part of the national tiger census 2018.

Tigers had been captured on camera in more than 100 grids in the two pockets in the first phase, triggering hopes that the big cat count would go up in the census. Several of the pictures show cubs alongside adults, a forest official said.

"But these are raw findings. It is possible that a single tiger has been clicked multiple times. The findings from these images will have to be combined with statistical analysis to reach any conclusion about the numbers," Mallick said.

A tiger needs to be clicked from both flanks at the same time for a picture to be fit for analysis, the reason why cameras are placed in pairs. The Cuddeback all-weather night-vision digital cameras have motion detectors. Animal movements activate the sensors in the cameras, which then take photographs.

More than 100 field workers are scouting the forests to find strategic locations in grids where the cameras would be installed. The forests are being divided into grids of 2sqkm each.

In the 2014 national census, the big cat count in the Indian Sunderbans was pegged at 76. Forest department sources estimate the count to have crossed 80 since.

The national tiger census in 2014 put the figure at 2,226, up from 1,706 in 2010.

The cameras will be in place for over three months. By March, the images and the reports will be sent to the Wildlife Institute of India and the National Tiger Conservation Authority.

The Sunderbans is spread across 10,000sq km - 4,000sq km in India and the rest in Bangladesh. The 2018 census will for the first time include tigers in Bangladesh, Bhutan and Nepal.