According to Rathin Banerjee, a divisional forest officer, some 400 crocodiles, bred in captivity over several years and released in the Sunderbans reserve, frequently leave their aquatic habitats when the water gets cold in the winter and lie in the paths used by poachers, representing a formidable hurdle for even the most adventurous hunter.
The crocodiles can measure up to 20 feet (6 meters) in length, officials said.
"With tigers on land and the crocodile in water, the fear factor does work," Banerjee said.
A 2004 census said more than 270 tigers were roaming the mangrove forest in West Bengal state, bordering Bangladesh. The reserve is home to the largest wild population of Royal Bengal tigers.
But preliminary results of a recent exhaustive study of tiger habitats found that the tiger population in some Indian states may be nearly 65 percent less than experts had thought.
Conservationists said the early results indicated the most recent tiger census - which found about 3,500 tigers across India - was far too optimistic. The study was conducted over the past two years by the government-run Wildlife Institute of India.
Also helping to protect the tigers are India's border guards who have set up camps in the reserve.
"The use of crocodiles is one of the measures to save the wildlife there from poachers," said V.K. Yadav, a forest conservator.
Crocodiles were first brought to the reserve in the late 1990s for breeding purposes.
The state Forest Department was assessing the effectiveness of the crocodiles in controlling tiger poaching.
"It is not like you count how many hens you had and how many have been taken away by the jackals at night," Yadav said. "Here the idea is to ensure that there is no unusual changes in the demography," Yadav said referring to major species of animals in the Sunderbans.
"We are trying our best," said Yadav.