Sunderbans big cats shrink as mangroves swell?

Prithvijit Mitra The Times of India 21 Feb 11;

KOLKATA: Is the Sunderbans turning denser than ever before, making it difficult for tigers to hunt? A yearlong study by researchers indicates that the mangroves have indeed turned thicker due to the proliferation of species which are dense, making it difficult for animals to penetrate them easily. It might be a reason why tigers in the forest are losing weight and could even have contributed to their leaner look, according to the study done by a team from Jadavpur University's School of Oceanography.

While studying the salinity of water in the rivers of the mangrove forest, researchers found that the mangroves in the core area appeared denser. A scrutiny revealed that two species which are particularly dense avicennia marina and avicennia alba have multiplied in areas like Satjelia in the south and the entire western side of the forest from Namkhana to Kalas. These are within the core area where tiger population is believed to be among the highest in the forest and have recorded frequent straying over the last two years. About 15-cm long and 5-cm wide, the dark green leaves of these shrubs grow very close and make movement through very them difficult. "These are about 20% thicker than the other major mangrove variety. It's difficult to spot prey animals and hunt them down through these shrubs. This could be one of the major reasons why tigers have been finding it difficult to procure food easily in the forest. But this is an assumption since we haven't yet done enough study on tigers to conclude that their physical appearance has changed due to geographical factors," said Pranabesh Sanyal, member of the research team and former director of Sunderbans Tiger Reserve (STR).

Studies are, however, on to co-relate the weight and size of Sunderbans tigers to alteration in the nature of mangroves. While the average weight of an adult male should be around 180 kg, straying Sunderbans tigers have been found to weigh only around 100 kg. A minimum of six tigers need to be observed and studied to draw a definite conclusion. So far, five have been studied.

"We are on the verge of what could be a significant finding. Whatever be the other reasons, geographical factors are indeed responsible for tigers straying so frequently. And perhaps, even for their shrinking size," said a member.

There are others who feel that thicker mangroves could have just a marginal impact on tigers in terms of either hunting or their physical appearance. "It's physical stress due to food shortage that could be a bigger cause. And an inadequate prey base seems to be a more logical reason. A lower body weight is more likely to be the fallout of hunger than anything else. Size can't shrink in 20-30 years. This is the period when the forest has got reduced in size and prey animals have been dwindling," said Gautam Sen, oceanographer.

While dense mangroves could be a cause of worry, there was also good news for the fragile ecological system. Fiddler crabs have been found to be acting as a fertiliser, enriching the soil composition.