The leatherback sea turtle (Dermochelys coriacea) is a unique and striking animal with an extraordinary lifestyle. It’s the only surviving sea turtle species that does not have a hard shell. It is also the largest of all sea turtles, with adult individuals typically measuring over six feet in length and weighing around 700 kg. With their large flippers and streamlined body, they can migrate over 10,000 km between nesting and foraging areas. With adaptations to keep their body warm in colder waters, leatherbacks are also recorded diving to depths of over 1,000 m, deeper than most other marine vertebrates, in search of the jellyfish they feed on almost exclusively. Being completely oceanic creatures, they also have the widest distribution of all sea turtles and are found in all the oceans except the Arctic and Antarctic oceans.
At the ripe age of 10, I was introduced to the world of sea turtles in Chennai through the Students Sea Turtle Conservation Network (SSTCN), an NGO working with olive ridleys. I joined the team on the weekends (as I was a minor and required a guardian to accompany me), walking on the beach a little after midnight to look for nests and nesting adults. It took me nearly four years of walking, weekend after weekend, during the nesting season that runs from December to April, before I finally saw my first nesting turtle. And since 2010, I have been working on leatherback turtles in the Andaman and Nicobar Islands, which also serve as nesting grounds for olive ridley, green, and hawksbill turtles.
Leatherbacks were reported as early as the 1900s in Indian waters, with the last confirmed nest recorded was from mainland India in Calicut, Kerala, in 1956. Although they are occasionally sighted along the coastal waters of mainland India, their nesting is now completely restricted to the Andaman and Nicobar Islands.
In the Andaman and Nicobar Islands, the first leatherback nest was reported in 1978 by Satish Bhaskar, a pioneer in sea turtle biology and conservation in India. Over twenty years, Satish visited most islands of the archipelago and collected substantial information on all species of sea turtles that nest in the region. His work continues to be relevant, and leatherback populations are being monitored to this day.
Although the Andaman and Nicobar Islands consist of over 572 islands, significant nesting of leatherback turtles occurs only on three: Little Andaman Island from the Andaman group, Little Nicobar and Great Nicobar islands from the Nicobar group. When we surveyed the entire Nicobar group of Islands (21 islands) in 2016, we noted that 94 per cent of nests were found in Little and Great Nicobar alone. Unlike other sea turtles, leatherbacks only nest on wide sandy beaches with no gravel or rocks.
Setting up monitoring camps in the Little and Great Nicobar islands has always been logistically daunting, so we have monitored them through one-time surveys. Most nesting sites are only accessible by small dinghies and are used as make-shift homes for the survey period. During my first visit to Great Nicobar Island in 2012, while surveying the Galathea nesting beach, we were greeted by an earthquake and a small tsunami bringing an end to our survey on the first day. We similarly experienced earthquakes and tsunami warnings during our surveys in 2016 and 2019 as well.
On Little Andaman Island, we have been monitoring the beaches of South and West Bay since 2008. The nesting season for leatherback turtles typically runs from November to March, and we set up temporary camps with tents and tarpaulin sheets. The beach at West Bay is only accessible by dinghy and is four-hour (often rough) ride from the nearest port. We split into two teams of three and spend two to three months at a stretch with no electricity or mobile network. We patrol the beach every night to tag nesting turtles with identification tags and monitor the beach for nesting activity. In the last 14 years, we have recorded 1,754 nests and tagged 152 turtles. Sometimes, these tagged individuals return to the same beach across nesting seasons. Our findings also indicate that all the beaches, which were destroyed in the 2004 tsunami, have reformed and leatherback nesting is stable and may even be increasing.
Fortunately, all the important nesting sites in these islands are remote and fall under protected areas with very little or no human disturbance so far. This sufficiently protects nests and nesting adults from poaching and other anthropogenic (human) impacts that have caused a decline in some leatherback populations. In Galathea, one of the most important nesting sites for leatherbacks, the Andaman and Nicobar Forest Department maintains a hatchery providing additional protection for nests that are usually predated by Andaman water monitor lizards, and wild and feral pigs. Although the nests and adults are relatively undisturbed and protected here, leatherbacks are particularly susceptible to fishing pressure in the high seas as they are accidentally caught in trawl nets and longlines.
We used satellite telemetry studies to track nine leatherbacks from West Bay in Little Andaman Island. The results were awe-inspiring — some traveled east to the western coast of Australia (about 7,000 km), and others went west to the eastern coast of Africa (over 10,000 km). Imagine our excitement when we encountered a turtle in 2020, which was originally tagged in 2014 and tracked for 395 days over 12,238 km to the coast of Madagascar. Three other turtles which were attached with satellite transmitters also nested on West Bay, after a 2-3 year hiatus.
The nesting population of the Andaman and Nicobar Islands is still considered data deficient in the IUCN database, but the recent work carried out over the last four decades indicates that the Islands host over 1,000 nests annually and are critical habitats to protect. Globally, many leatherback populations have declined as a result of poaching (eggs and adults) and fishing-related mortality and have required active intervention at nesting sites through hatchery programmes for complete protection. One of the first rookeries to disappear in modern times was Terengganu, Malaysia, where over 10,000 nests were recorded in the 1950s, and over-exploitation of leatherback eggs led to local extinction.
In the Andaman and Nicobar Islands, the leatherback population continues to thrive with little or no intervention. This population, which was once considered declining, has exhibited resilience to temporary changes and natural calamities. However permanent alterations to their breeding grounds could lead to a decline in this population and these nesting sites must continue to remain undisturbed and protected.
This article has been curated in collaboration with the Dakshin Foundation.