Warming slows down 'arribada'

India’s coastline is home to five of the eight species of turtles found in the world’s oceans. Over the years, the number of turtles coming out of the water to lay eggs offshore has dwindled drastically.A new study blames global warming. Atula Gupta examines.

Most turtles have a peculiar habit. They spend their lives in the deep blue seas all their lives but when it is time to bring the next generation into the world, they are land bound. Every year, during nesting season, would-be mothers of the turtle world wade through the ocean waters, sometimes thousands of miles to reach a predestined beach, where they lay eggs and leave it in the hands of Mother Nature to take care of their spawn.

What is now a critical matter is that these nesting sites are disappearing owing to the rising temperature of the planet, washing away the future of marine turtles too.
Marine turtles are found in tropical and temperate seas throughout the world. Adults of most species are found in shallow coastal waters, bays, lagoons and estuaries. Some also venture into the open sea.

Of the eight species of turtles found in the world’s oceans, Indian coastal waters are home to five of them — Olive Ridley, green turtles, leatherback, hawksbill and loggerhead turtles. But over the years, the number of turtles coming out of the water to lay eggs off shore has dwindled drastically. A new study suggests that global warming might be the number one cause.

Nesting plight

The study conducted by Mariana Fuentes from the ARC Centres of Excellence for Coral Reef Studies (CoECRS) and James Cook University has found that in order to protect the world’s turtles, it will be first very crucial to save their nesting grounds being plundered due to global warming and climate change. They have pinpointed areas that are already showing notable climate-led changes in the West Indian Ocean, Northeast Indian Ocean, North Pacific Ocean, East Atlantic Ocean and the East Pacific Ocean. Thus, the Indian coastline in its entirety is no more an ideal ground for turtle eggs and hatchlings.

The coastline of India, extending to over 7,500 km, harbours many specialised marine ecosystems like coral reef, sea grass, mangroves, nesting and lagoons, supporting a variety of resources. But the beaches that turtles find the most effective for their nests are the ones with very little or no rocks and plenty of sand.

Females of most species usually come ashore at night, most often during high tide. A female sea turtle crawls above the high tide line and, using her front flippers, digs out a ‘body pit’. Then using her hind flippers, she digs an egg cavity where she deposits 50 to 200 (depending on the species) ping pong ball shaped eggs into the egg cavity and covers it up with sand.

Burying the eggs serves three purposes: it helps protect the eggs from surface predators; it helps keep the soft, porous shells moist, thus protecting them from drying out and ensures that the eggs maintain the right temperature.

The new study finds that it is this crucial thermal environment needed for the incubation of eggs in the customised nests which is now changing due to climate change.

Because the earth is heating up, the sand temperature of many beaches is higher and turtle eggs therefore either hatch too early or die without hatching.

The study authors also note that beach side developments and threat of by-catch due to fishing makes the turtles’ existence even more imperilled.

Course of action

Fuentes, though, has gone a step further and provided a solution to these problems. She says, “At present there are three ways we can tackle climate-related threats. We can reduce global greenhouse emissions, actively manage for direct impacts from climate change by manipulating the nesting thermal environment with shade, for example, and build the turtles’ resilience, that is, their ability to recover from the negative impacts.”
But these are still theoretical ideas and it is not known whether relocating, manipulating or managing turtle populations will help reverse their decline. The scientist adds that the best course of action would be to better understand factors that influence their ability to recover from the negative effects of climate change and then help the turtles adapt to what has already changed.

In India, Andaman and Nicobar Islands, Andhra Pradesh, Kerala, Maharashtra, Goa, Karnataka, Lakshadweep, Tamil Nadu, West Bengal, Pondicherry and Orissa are regions where turtle nesting sites are present.

Apart from the four other species, it is the endangered Olive ridley turtles that are truly of Indian origin. Orissa’s beaches are known to be the largest nesting grounds in the world for this species, with millions of turtles arriving here at the same time. This unique gathering, called ‘arribada’, is as much a proclamation of their love for the topography of the country as for the need to find a safe place to bring young ones into the world.

That the visit of the turtles to give birth has been known for generations is also evident from the oldest known references to marine turtles in a poem of the Tamil Sangam literature (400 AD) in which the egg-laying of turtles has been described. Protecting the turtle today is, therefore, akin to preserving national heritage.