Sea turtles have long held a place in our mythology and beliefs. In Hindu mythology, our world rests on the backs of four elephants, standing on the shell of a turtle. In other cultures around the world as well, these seafaring animals are a symbol of longevity and stability, and are part of many creation myths. In Native American culture, the continent of North America is referred to as ‘Turtle Island’, resting, you guessed it, on the back of a giant sea turtle.
In fact, traditionally, cultural beliefs have helped conserve these turtles: for instance, turtle meat is outlawed by Hinduism and Islam. In Odisha, many local fishing communities avoided both turtle meat and eggs, because of religious beliefs. A few communities from Andhra Pradesh used to return the sea turtles trapped in their catch to the sea, because of their belief that turtles are an incarnation of Vishnu. Historical studies have even shown that in the past, communities who hunted turtle eggs would leave a few eggs in the nest, as a mark of respect for sea turtles and their sustaining populations.
Their importance is not just cultural; sea turtles occupy a significant niche in marine ecosystems as well. They serve as indicators for the overall health of the marine ecosystem. As omnivores (with the exception of the aptly-named, primarily vegetarian Green Turtle), they consume a large variety of prey, such as crustaceans, sponges, puffer fish and even jellyfish. No other animals eat jellyfish because of their stinging tentacles – so sea turtles help keep their populations in check. Because of their nesting habits, sea turtles are also largely responsible for the transportation of highly productive nutrients from marine habitats to sandy beaches, which helps reverse the flow of nutrients from land to sea. Although there’s plenty we still need to learn about sea turtles, here’s a short primer on what we do know about the five species – the Green Turtle, the Hawksbill, the Loggerhead, the Olive Ridley and the Leatherback – we find along India’s 7,500-km coastline.
Distribution and nesting populations
Sea turtles are generally found in the waters over continental shelves – relatively shallow areas typically upto 600 metres deep, extending from continental landmasses. Of the five species found in India, four are found on either the mainland or offshore islands – the Leatherback, the Green Turtle, the Hawksbill and the Olive Ridley. Of these, the Olive Ridley is the only one known to nest along the majority of the mainland coast, most notably in three areas of Odisha: at Gahirmatha, Rushikulya and the mouth of the River Devi. Leatherbacks nest in in Little Andaman Island and the Nicobar Islands, while the Green Turtle and the Hawksbill have their feeding and nesting grounds in the Andaman and Nicobar Islands and the Lakshadweep islands. While the Loggerhead has been spotted in Goa, Maharashtra, Tamil Nadu, Andhra Pradesh and West Bengal, it is the only species that does not nest here, but in Sri Lanka, Bangladesh and Myanmar.
In an extraordinary display of navigational ability, female sea turtles return to the same beaches every two to four years to lay their eggs after mating at sea, sometimes even to the exact beach where they themselves hatched. The number of nesting beaches across the world are limited, because of their penchant to return to the same sites.
Once turtle hatchlings make their way successfully to the sea from the nesting sites where they hatch, they have a one in three hundred chance of survival – so they have to try very hard. They spend the next three to five years in the pelagic zone, the ecological zone covering that part of the open ocean which is neither close to the seabed nor the shore. They then age in the ocean, taking decades to reach sexual maturity.
Because of the long distances they travel, estimates of turtle populations are difficult to make. Their movements across wide swathes of open sea are hard to track long-term, despite efforts to tag them, analyse more data and improve tracking technology. In fact, for this very reason, the years between hatching and the return to coast are often called the ‘lost years’. For this reason, most estimates of populations are made on the basis of nesting female populations, which are easier to map annually at nesting sites.
Sea Turtles of India
Loggerhead (Caretta caretta)
The world’s largest hard-shelled turtle, Loggerheads nest in Sri Lanka – although their major nesting site is in Oman in the Arabian Peninsula. They are usually found in the Gulf of Mannar between India and Sri Lanka. They have been seen off the coast of Maharashtra, Goa, West Bengal, but it has been difficult to establish their current occurrence in a number of sites they were historically recorded in. In fact, the most widely quoted reference of the loggerhead in India is based on second-hand information from fishermen in the Gulf of Munnar – and it could have been a misidentified Olive Ridley!
Loggerhead turtle shells are home to countless smaller animals and plants. As many as a hundred different species have been identified resting on loggerhead shells – the chances of their survival are higher there, than when they are in the open ocean. Loggerheads are also one of the best migrators – even juveniles have been known to cross the Pacific. However, they suffer from low reproductive rates, and have also been known to display female-female aggression over hunting grounds. Loggerheads are over-harvested for food and turtle products.
Green Turtle (Chelonia mydas)
Named for the colour of its body fat, this turtle is truly ‘green’ – it is the only herbivore of all the sea turtle species, though juveniles occasionally stray from their diet to snack on jellyfish and some other animal species. They have sharp, serrated beaks, which allow them to graze on seagrass beds and scrape algae off rocks. Ironically, Green Turtles are themselves harvested extensively for their meat, even though the primary threat they face is the overexploitation of their eggs.
Green Turtles play an important role in regulating ocean currents – without them grazing on seagrass beds, seagrass tends to overgrow and obstruct currents. Gujarat is an important nesting and foraging site for Green Turtles, while Tamil Nadu, Maharashtra, Kerala, Goa and Karnataka have recorded sightings too.
Leatherback (Dermochelys coriacea)
The only existing species of the family Dermochelyidae, the Leatherback is the largest marine reptile on Earth, weighing up to 500 kilograms – as much as a large horse! They are named after their shell, a leathery carapace which is not as hard as other turtle species’ shells. Leatherbacks migrate much larger distances than other turtle species. They’ve been known to cross both the Atlantic and the Pacific Oceans, and can migrate more than 10,000 kilometres across oceans from breeding to feeding grounds. Unlike other marine turtles, Leatherbacks regulate their body temperature through a blood circulation mechanism known as a countercurrent heat exchanger. This adaptation, along with their large size, helps them stay warmer than surrounding water and deep dive in colder anaerobic waters – as deep as 1,200 metres!
Current nesting populations of Leatherbacks in India are entirely restricted to the Andaman and Nicobar islands, however it is possible that the tsunami of 2004 may have affected the nesting sites and habitat here. Nesting females are often killed for their meat and oil.
Hawksbill (Eretmochelys imbricata)
The Hawksbill turtle shell is known for its intricate colours and patterns – unfortunately making it the only source of commercial tortoiseshell in the world. This is why Hawksbills are far more threatened than other species of turtles. Their populations have fallen by 80 percent in just the last century. Yet, they are vital to the ocean. Hawksbills feed almost exclusively on sponges. It is estimated that an adult can eat upto half a ton of sponges in a year. By doing so, they allow species such as corals to grow and colonise, as sponges can overpopulate and suffocate reefs. This specialised diet makes their meat poisonous for human consumption, which is why they are not consumed even by fishers who sometimes harvest them for their shells.
Not seen in large numbers, Hawksbills nest individually in far apart locations and prefer to lead independent lives. Hawksbills are found in the two states where the occurence of all five sea turtle species has been recorded – Tamil Nadu and Andhra Pradesh, and also in Odisha, West Bengal, Kerala and Karnataka, as indicated by the hawksbill carapaces found in the possession of fishers.
Olive Ridley (Lepidochelys olivacea)
The Olive Ridley gets it name from its olive-coloured carapace. The smallest and most abundant sea turtles in the world, these turtles are frequently associated with seabirds – as they surface from of the water, seabirds often perch on their shells, finding a resting place that’s safely away from other predators. They are the most numerous sea turtles in India as well, found on most of the East and West coast. While they are found in larger numbers in Odisha, Andhra Pradesh and Tamil Nadu on the East coast, there are smaller nesting sites in Maharashtra, Goa, Karnataka and Kerala as well..
‘Arribadas’ are a phenomenon specific to Olive Ridleys – events in which thousands of female ridleys arrive at their nesting sites together, over the course of five to seven days every year. Arribada or ‘arrival’ season is usually between October and April, and is considered to be a method of increasing the chances of hatchling survival. Gahirmatha in Odisha, one of the world’s largest mass nesting sites, is said to support a nesting population of more than half a million Olive Ridley turtles. Over the course of a week, each female can lay upto 120 eggs. But the rate of hatchling survival is low – it is estimated that only one in a thousand turtles survives to maturity. Sea turtle hatchlings, once they emerge from their shells, have an uncanny knack of finding their way back to the ocean from their nesting site – and if you’ve ever been on one of the Madras turtle walks at Elliot’s Beach or Marina Beach, you’ll know the rush that comes from seeing hundreds of these tiny baby animals rush across the sand, following an invisible path that invariably leads them to water.
To learn about the threats to sea turtle survival, and the ongoing conservation efforts to protect their populations, click here.