Kurma mela: The science of the mass nesting of Olive Ridley turtles

The Olive Ridley turtle (Lepidochelys olivacea), a vulnerable sea turtle species, made headlines earlier this year: arecord-breaking seven lakh turtles had nested at Odisha’s Rushikulya beach alone in March.These turtles are renowned for their synchronised mass nesting events called arribada, a Spanish word that means “arrival”.

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For many people, the Rushikulya arribada signalled hope — but for conservation biologists, it raised critical questions about the future of these vulnerable animals and whether human interventions, even well-meaning ones, could change the course of nature itself. While some localised populations of Olive Ridley turtles have expanded, the IUCN Red List has estimated that the number of Olive Ridleys worldwide has dropped by 30-50% since 1960. The Olive Ridleys’ primary nesting sites are along the Pacific coasts of Mexico and Central America, although Odisha is also a particularly critical location.

The State’s 480-km-long coastline hosts three major nesting beaches: Gahirmatha, between the Brahmani and Baitarani river mouths; Devi, 100 km south of Gahirmatha; and Rushikulya, 320 km further south.Research has found that Olive Ridley turtles that hatch at a nesting site are ‘imprinted’ with a map of the local magnetic field. Decades later they return with remarkable precision to the site by following this map. The phenomenon is called philopatry: a blend of memory, environmental factors, and the earth’s geomagnetic cues. Philopatry is reinforced by a multiplier effect: as females with strong philopatric tendencies increase in number, they reinforce site fidelity across generations.