With migratory path and nesting instincts of endangered Olive Ridley turtles still largely shrouded in the realms of mystery, the scientists at Zoological Survey of India are of the view that the tagging of nesting turtles at nesting grounds in Odisha needs to be heightened to a large scale to further unravel the delicate marine animals’ migration and nesting behavior.

The observation of researchers at the premier ZSI assumes significance given the fact that an Olive turtle tagged at Odisha four years back covered 3,500 kilometres to nest and lay eggs at a beach in Ratnagiri district of Maharashtra recently.

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The Olive turtles turn up in millions for mass nesting along the Odisha coast every year. Gahirmatha beach off the Bay of Bengal coast in Kendrapara district is incidentally acclaimed as the World’s largest known nesting ground of these animals. Apart from Gahirmatha, these threatened aquatic animals turn up at Rushikulya river mouth and Devi river mouth for mass nesting, otherwise called arribada.

”It was for the first time that a turtle which nested at Odisha beach in the past skipped the nesting to lay eggs elsewhere. Besides, the turtles tagged at Odisha nesting grounds to study migration behavior did not travel such long distances. In the past years, the tagged turtles were rescued from the Northern Sri Lanka coast by marine fishermen. But there is no history of turtles tagged at Odisha, laying eggs at Sri Lanka,” Zoological Survey of India (ZSI)’s scientist Dr Basudev Tripathy said.

Most sea turtles migrate between foraging and nesting grounds.  Both male and female turtles migrate to nesting areas to breed, generally in the area where they were born, he said.

 “To identify and strategise to effectively protect Olive turtles’ feeding and breeding along the Bay of Bengal coast, further study and tagging of these delicate marine animals is the need of the hour. Keeping in view the fact that a tagged turtle from the Odisha coast was spotted for the first time at the Maharashtra coast in western India to lay eggs, an elaborate scientific study of these itinerant marine species has come under focus”, Zoological Survey of India (ZSI)’s scientist Dr Basudev Tripathy said.

”It’s a new finding that has opened the floodgates for intense study on turtles and their behavioral instinct for foraging and breeding. Earlier tagged Olive Ridley sea turtles travelled around 1000 kilometers in the sea to reach the north of Sri Lanka sea within a month from Gahirmatha Marine Sanctuary in Odisha‘s Kendrapara district. But they did not nest. After travelling the Sri Lanka coast, they used to return to Odisha nesting grounds for mass nesting. The solitary turtle, tagged by ZSI in 2021, has been found nesting at Ratnagiri beach in Maharashtra. The female turtle undertook an arduous journey of not less than 3,500 kilometres to nest at the Maharashtra nesting ground,” Tripathy said.

The studies that included the tagging turtles (that turned up at Odisha nesting ground to lay eggs) has so far established the fact that Odisha is the most preferred and favoured nesting destinations of turtles as arribada ( synchronised mass nesting of sea turtles ) has been reported elsewhere in India barring Gahirmatha, Rushikulya and Devi river nesting grounds in the eastern State, he said.

The tagged turtles that were sighted at the northern Sri Lanka coast incidentally did not indulge in instinctive nesting as was the case in the tagged turtle sighted at Maharashtra. Therefore, it has now become a matter of vital importance to undertake large-scale tagging of nesting turtles every year to throw further light on their nesting behavior, Tripathy opined.

The Odisha Forest Department took up the tagging exercise in 1999 by tagging around 1000 turtles. At least two turtles tagged then were sighted on the Sri Lanka coast. The tagging was later suspended and was resumed by ZSI in 2021. Between 2021-2024, around 12,000 turtles were tagged in Gahirmatha and Rushikulya river mouth nesting grounds in the last four years.

The mass nesting turnout of turtles continues to remain on an impressive scale. This year, around 10 lakh turtles invaded the nesting beaches in Odisha for arribada. ”The tagging needs to be done on a larger scale. Annually, around 3,000 turtles are being tagged. We are of the view that at least 1 lakh turtles are required to be tagged for obtaining better information on turtles’ reproductive biology, movements, and growth rates, migratory route, and areas of foraging,” he concluded.