Every year, between January and March, thousands of female olive ridley turtles converge on the shores of Gahirmatha and Rushikulya beaches in Odisha, to lay eggs. Under moonlight, the females slowly make their way across the beach, one flipper after the next, until they find a suitable spot to make a nest. This mass nesting phenomenon is called arribada (Spanish for arrival) and occurs at only a handful of beaches across the planet, but not all olive ridleys practice mass nesting.
The arribada is surreal to witness — over two lakh turtles were recorded in Gahirmatha alone in 2019. In addition to the congregation in Odisha, there are a number of sites all along the coast of India, from the shores of West Bengal down to Tamil Nadu, and in the Gujarat as well.
What makes this turtle’s nesting behaviour special is that pregnant females return to the same beach where they were born to lay their eggs. This means that a female hatched in Rushikulya will not nest elsewhere. Two months after the eggs are laid, hatchlings emerge — each about the size of a matchbox — and make their way to the ocean, where they spend the rest of their lives swimming, eating, and travelling great distances. When the turtles attain sexual maturity, thirteen years later, they make the journey back to their natal home, often travelling for months (and hundreds of kilometres) in the process. Why they do this remains a mystery for the most part, though the how of it is pretty fascinating.
To understand this, let us first consider how a compass works (stick with me, it’ll make sense soon enough). All compasses have two basic components: A dial with the directions neatly marked, and a magnetic needle which points north-south. The Earth too has a magnetic field of its own — thanks to the planet’s core of molten metal — and has its own north and south poles. Your compass’s magnetic pin responds to the Earth’s magnetic field in the same way two magnets act when placed together.
Unlike humans, olive ridley sea turtles have the innate ability to sense the Earth’s magnetic field, a trait that is shared by many migratory species. When baby ridleys hatch from their leathery egg shells, the precise geomagnetic location of the beach is imprinted on their brain, along with other factors like light, smell, temperature, etc. This is why it’s crucial to avoid contact with the hatchlings when they make their way to the ocean for the first time.
Olive ridley turtles are named for their dark green carapaces, or shells. These newborns will first make their way to the ocean and then travel thousands of kilometres through the oceans in their life spans (cover photo). Photos: Dhritiman Mukherjee
Then there are ocean currents to consider: Ocean waters are constantly moving in a pattern that has remained largely constant for millennium. Underwater, these currents move at a fairly rapid pace, and are used by a number of migratory sea creatures as a kind of transport system (remember the turtles from Finding Nemo?). This is similar to the way birds like eagles, use wind currents to soar.
Others researchers believe the turtles rely on astrological cues, and a few more think the young females simply follow elders to the breeding site. Research is ongoing, tedious, and slow, but it is a subject of deep interest to marine biologists, especially in times of climate change and unchecked development.
As travellers we too can do our bit for them: Admire the turtles from a respectable distance at all times, choose environmentally-conscious tour operators, and do not use flash photography in the presence of turtles. Better still consider participating in a beach clean-up every time you visit the coast. It’s a great way to give back to the environment, and helpful to the survival of the gentle olive ridley turtles.
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