In the Sundarbans, tigers are everywhere and nowhere, says Amitava Ghosh in his book The Great Derangement, Climate Change and the Unthinkable .
Camouflaged in the mangrove forest and living in a unique water-dominated habitat with a minimal prey base, the Sundarbans tiger remains one of the most mysterious animals.
One of the questions that forest officials and scientists have been grappling with for decades is this: how can tigers be counted in the Sundarbans? Until a few years ago, it was impossible to get an estimate with existing techniques. While individual estimation of tigers was out of the question, tides twice a day in the region (high tide and low tide at an interval of 12 hours) made identification by pugmarks and fecal DNA extremely difficult.
In 2006-07, attempts to set up camera traps were unsuccessful as saline water entered the camera, destroying the equipment. The traps were placed at knee height.
It is only after 2014 that camera traps began to give positive results, and the latest results have been encouraging. With years of experience and trial and error methods forest officials and experts found strategic locations to put camera traps in the Sundarbans, in the higher areas of the forests not inundated during high tide. The camera traps are set about 40 cm to 50 cm above the ground here.
The photographs reveal 87 ‘adult individuals’ in the Sundarbans, a significant increase from the earlier camera trap exercises. Earlier, camera traps yielded photographs of about 62-63 adult tigers.
“In 2015 we got photographs of 63 adult tigers. Six of them could not be located this year. Fifty-seven of the remaining tigers were located once again using the camera traps. We also got photographs of new 30 adult tigers taking the number to 87,” Ravi Kant Sinha, Principal Chief Conservator of Forests & Chief Wildlife Warden, West Bengal told The Hindu .
Mr. Sinha said with a minimum of 87 adult tigers (cubs were not included) the ecosystem with a potential tiger area of 3,200 sq km can host more than a hundred tigers.
The Status of Tigers in India 2014, published in 2015, stated, “Sundarbans has now been camera trapped with 62 unique individual tigers photo-captured”. According to the report, “Tiger population in the Sundarbans has remained stable and is estimated to be about 76 (62 to 96) tigers.”
Officials including Mr Sinha say tiger estimation in the unique habitat is still a work in progress and only over the next few years with more results of camera traps could a more precise number be ascertained.
Software analyses photos
These camera trap images are fed into software which uses statistical extrapolation based on the number of days and the images to come up with a tiger number. Since each tiger has a unique pattern of stripes the images help count adult tigers. In every assessment some new tigers are found and some are recaptured. Some tigers which were photographed earlier may not appear again.
The results of the camera trap exercise pointed to the presence of 24 tigers in South 24 Parganas forest division which is outside the Sundarbans Tiger Reserve Area. In this region which is closest to human habitation, 10 new adult individuals were photographed in the latest estimate. Images of 16 adult tigers were captured in the National Park East Range, 19 in West Range and 15 each in Basirhat Range and Sajnekhali Wildlife Sanctuary. In each of the tiger zones there was a minimal increase of at least five adult tigers. The camera traps also revealed that two individuals captured in Basirhat range were recaptured in Sajnekhali Wildlife Sanctuary.
Yet experts admit that estimations by camera traps have limitations in the Sundarbans particularly because of tidal variation leading to inundation in large parts of the tiger ecosystem and difficulty of access to remote areas of the forest to set up camera traps.
Experts and forest officials said the number of tigers which the ecosystem can accommodate may also be estimated using the prey base.
Wild pig main prey
The Sundarban tiger’s main prey is the wild pig, said Biswajit Roychowdhury, Secretary, Nature Environment & Wildlife Society, (NEWS). A number of tiger scats were examined and found to contain pig hair. They also eat swamp deer, rhesus monkey, monitor lizards, even crabs and fish. The region is the only forest in India where no cattle or other easy prey is available to tigers which forces them to swim across water channels.
Mr. Sinha said to get an estimate of the prey base, even the fish in the region would have to be taken into account. According to Mr. Roychowdhury, if tigers here regularly feed on fish, it would place the tiger atop both the terrestrial and aquatic food chain.
In July 2009, the remains of two cobras, a king cobra and a monocled cobra were found in the stomach of a 12-year-old dead tigress, an anomalous occurrence as the big cats are not known to eat venomous snakes. There were no external injuries on the body of tigress and lungs, liver and spleen of the animal were found to be infected. But forest officials could not confirm that it was snake venom that resulted in its death.
Tiger behaviour
The elusive nature of the tiger here has led to many questions on its behaviour.
A paper titled Ranging, Activity and Habitat Use by Tigers in the Mangrove Forests of the Sundarbans published in April 2016 in PLoS One , a peer reviewed journal by researchers Dipanjan Naha, Yadvendradev V. Jhala , Qamar Qureshi, Manjari Roy, Kalyansundaram Sankar and Rajesh Gopal sheds some light.
“It appears that tigers moved most during dawn and early morning hours. Sunrise in the Sundarbans region was between 4.45 a.m. to 6 a.m. and tiger activity coincided with this period,” the paper states. Tigers are nocturnal and try to avoid confrontations with humans and the paper suggested that if human activity were reduced in the early morning hours , attacks by tigers could potentially be reduced.
An estimate provided by the Forest Department claims that tigers between 1985 and 2010 attacked 410 people, leaving only 95 survivors.
Post-2010, the number of tigers straying and attacks on human decreased. The latest figure of deaths from attacks by Sundarban tigers in 2014-15 is 10. Even in July 2017, a tiger from the forest jumped on a boat carrying a fisherman and took away 62-year-old Sushil Majhi into the deep forests. In another instance this year, a tiger which had had strayed near human habitation was released in South 24 Parganas Forest on October 26.
The problem of straying has come down by laying nylon net along the vulnerable areas of interface of forest and human habitation. Between 2007 and 2010, seven tigers were radio collared.
In some cases, radio collars slipped off the neck indicating that tigers in the islands are smaller and weigh less than those in north and central India and have higher level of adaptation. The satellite-based radio collaring, some of which have GPS attached gave locations of the tigers.
This exercise was carried out to ascertain whether the tigers in Sundarbans are territorial.
Interestingly, a male tiger captured in May 2010 which was released near Katuajuri camp near the Bangladesh border crossed the mighty Raimangal river and remained on Talpatti Island of Bangladesh for a long time, as its activities were studied by researchers.
A trans-border habitat
This phenomenon highlights the Sundarbans as a habitat requiring a Trans Border Protected Area involving India and Bangladesh.
The Sundarbans are the only mangrove forest in the world to be home to tigers. The sea level rise is posing a threat to the tigers’ survival. Pranav Chanchani , National Coordinator for Tiger Conservation, WWF- India said , “Certain studies have predicted that a 28 cm rise in the sea level (which is possible in the next 50 - 90 years), could result in more than 90% loss of mangrove habitats in this landscape, and catastrophic declines in the area’s tiger populations.”
