By Adhith Swaminathan and Kartik Shanker
Leatherbacks can be dangerous. Not in the way that elephants are, where they might charge and trample you, or bears for that matter, that might attack and maul you, or vipers or cobras, that could deliver a lethal dose of venom. No, they take up residence in your imagination and lure you to remote locations that require travel by tiny boats in choppy seas, to lands mired in malaria, and hit by the occasional tsunami. We were bitten by the ‘leatherback bug’ a couple of decades apart. One of us (KS) first visited Galathea in 2001 as part of his postdoctoral project on sea turtle genetics. Years later, when we started a monitoring programme at Little Andaman Island, the other (AS) joined as a research assistant and has led the monitoring work there for over a decade. After all these years, each leatherback we see is still a revelation from the sea, an archive with over 110 million years of history, a statement of survival by an ancient reptile.
The Andaman and Nicobar Islands, located southeast of mainland India in the Bay of Bengal, is home to four of the five species of sea turtles found in Indian waters. These picturesque tropical islands are the only region in India where green, hawksbill, leatherback and olive ridley turtles nest. The archipelago is a haven for sea turtle biologists to observe these animals both on land and in water.
The surrounding coral reefs and seagrass meadows are critical survival habitats for hawksbill and green turtles. Of the four species, leatherbacks have been the focus of research for the last four decades as their nesting is restricted to these Islands. Here, nesting populations have been studied through periodic surveys of remote beaches and recently, through annual monitoring programmes.
A Forest Department hatchery in Lamia Bay of Saddle Peak National Park in North Andaman Island. Photo: Adhith Swaminathan.
Of the 500 odd islands in the Andaman and Nicobar archipelago, leatherbacks nest in particularly high numbers on three islands: Little Andaman, Little Nicobar and Great Nicobar. In our 2016 survey of the Nicobar group, Little and Great Nicobar Islands hosted 94 per cent of all the leatherback nests recorded. However, this was not a new discovery. The late Satish Bhaskar, a pioneer of sea turtle biology and conservation in India, first visited Great Nicobar Island in 1979 and recorded large numbers of leatherback turtles nesting there. He would return in the 1980s, and in the early 1990s with Manjula Tiwari, then a rookie field biologist, to confirm that these beaches were significant for these ancient and vulnerable turtles.
Since these surveys, many research and conservation projects have been initiated across the islands. The Andaman and Nicobar Forest Department patrols all the important olive ridley nesting beaches in the North and Middle Andaman Islands, and have set up hatchery programmes that have been ongoing for decades. In 2014, a new mass nesting site was discovered in Cuthbert Bay on Middle Andaman Island, where the Department has set up a permanent monitoring camp.
A leatherback turtle that emerged at Galathea beach, Great Nicobar Island, during the day in February 2001. Photo: Kartik Shanker and Meera Anna Oommen.
Although not common, leatherback turtles are sometimes found lingering on the beach even after sunrise, as the nesting process takes over three hours. Photo: Adhith Swaminathan.
In the Nicobars, a long-term leatherback monitoring camp was set up between 2000 and 2004 in Galathea Bay on Great Nicobar Island by Harry Andrews of the Andaman Nicobar Environment Team (ANET), then a division of the Madras Crocodile Bank Trust (MCBT). During this period, over 300 individuals were marked with identification tags and around 400 nests were recorded each year on this narrow beach spanning just two kilometres. However, the 2004 earthquake and tsunami severely altered coastal areas, and the nesting beaches were completely destroyed. Ambika Tripathy, a researcher with MCBT, died in the tsunami while Saw Agu’s remarkable tale of survival after 10 days on a log at sea without food and water is now the stuff of legend.
Between 2004 and 2007, surveys by Andrews and Manish Chandi of ANET/MCBT suggested that the beaches in the archipelago were slowly forming again. Preliminary surveys of Little Andaman Island in 2007 also indicated that leatherback turtles had resumed nesting. We therefore initiated monitoring protocols similar to the Galathea programme in South Bay in 2008, and further expanded its scope to West Bay in 2010. Dakshin Foundation, in collaboration with the Andaman and Nicobar Forest Department, Indian Institute of Science, Bengaluru and ANET, has been monitoring these beaches for 15 years now. Between 2010 and 2014, we also tagged leatherbacks with satellite transmitters to track their migratory paths to their foraging sites. Some individuals travelled east to the coastal waters of Indonesia and western Australia, while a few travelled over 10,000 km., reaching the coasts of Madagascar and Mozambique. Some of the individuals that were tracked also remigrated and were encountered nesting on the same beach where they were originally tagged.
Globally, leatherbacks are the most widely distributed of all sea turtles. Anecdotal evidence suggests that leatherbacks nested in small numbers on the mainland coast of India, with the last confirmed record of a nest from Kerala in 1956. They are sighted from time to time in the coastal waters of Tamil Nadu. Photo: Adhith Swaminathan.
Nesting in the Little Andaman Island has been stable or increasing in recent years and beaches that were severely affected in the Nicobar Islands have also seen nesting numbers comparable to those recorded in the pre-tsunami period. In the North East Indian Ocean region, leatherbacks also nest in small numbers on the beaches of Sri Lanka. During the COVID years when anthropogenic activity came to a standstill, leatherbacks were even reported nesting around Phuket in Thailand, a region that has had limited nesting in the last 20 years. In 2021, a leatherback tagged on Little Andaman Island was encountered nesting in Galathea, indicating that these turtles may nest on multiple beaches in the region, both within and across nesting seasons. More interestingly, an individual tagged in Galathea was found nesting 560 km. away in Simeulue Island of Aceh province of Indonesia. Further south of Aceh, they are also known to nest in the Mentawai Islands. While this population was once considered to be data deficient or declining, nesting has been relatively stable since 2004. Forty years of monitoring leatherbacks in the Andaman and Nicobar Islands has shown that these beaches host the most significant nesting population in the North East Indian Ocean.
The Andaman and Nicobar Islands consist of two island groups, which are separated by a 150 km. wide 10-degree channel. The Andaman group comprises over 300 islands, while the Nicobar group consists of only 22 main islands. Photo: Adhith Swaminathan.
While this is good news, and their recovery from the tsunami demonstrates their resilience to natural calamities, it is crucial to incorporate the lessons learnt from other populations across the world that have plunged as a result of egg depredation, fisheries bycatch and habitat destruction. Leatherbacks seem to return to their favourite beaches year after year even as the islands recuperated from the impacts of 2004. Any permanent alteration to these breeding sites could certainly impact their long-term survival.
Kartik Shanker is faculty at the Indian Institute of Science, Bengaluru; Founder Trustee, Dakshin Foundation; and Editor, Current Conservation. Adhith Swaminathan works with Dakshin Foundation, Bengaluru, on leatherback sea turtles in the Andaman and Nicobar Islands.
