The olive ridley turtles that nest in Odisha forage for food in the Bay of Bengal, migrate as far as the eastern coast of Sri Lanka, and return to the same Indian beaches, year after year, in the tens of thousands. Data on their movements has helped the Odisha government enforce protective measures and fishing bans during the mating and nesting season.
There’s another thing scientists have learnt about these turtles: They never swim around to the other coast, and never venture into the Arabian Sea. “That means the olive ridleys that visit the west coast of India could be a separate and distinct population,” says Harshal Karve, a marine biologist with the Mumbai-based Mangrove Foundation, an autonomous unit operating under the Maharashtra forest department.
Turtle nesting on the western coast of India doesn’t occur on anything like the same scale as it does in Odisha, but the numbers are still significant. About 690 olive ridley turtle nests were recorded in Maharashtra in the 2021-22 season. Where were they coming from? Where did they go? Did they too return to the same Indian beaches each year?
To try and answer some of these questions, a first-of-its-kind initiative was undertaken on the western coast. The Maharashtra forest department’s Mangrove Cell, the Mangrove Foundation, and the Wildlife Institute of India joined hands to tag five female olive ridleys with satellite trackers, in January and February 2022, before they returned to the ocean.
Two of these turtles, named Prathma and Saavani, were tagged at the Velas and Anjarle beaches; Vanashree, Lakshmi and Rewa were tagged in Guhagar near Ratnagiri.
Tagging a turtle isn’t as easy as tagging a bird or a mammal. Flippers can’t be fitted with a collar or anklet; these would fall right off. So a transmitter is fastened to the top of the turtle’s shell with industrial-strength glue, and the whole cap is then coated with anti-fouling paint (also used on the outsides of ships), to keep barnacles and other marine creatures at bay.
Transmitters must be able to link up with a satellite in order for data to be recorded. That link isn’t possible underwater. “But since turtles are reptiles, they have to keep surfacing for air, and that’s when we get a hit on their movement,” Karve says.
In the weeks just after the turtles returned to the sea, a crucial finding emerged. “Saavani visited a beach just 8 or 9 km from her previous nesting site and nested again there. Olive ridleys are known to return to the same nesting grounds, so this was very interesting,” says Karve. Researchers were also interested to find that the tagged females moved in different directions, and some didn’t venture far from the coast of Maharashtra at all.
Sadly, the researchers lost contact with the turtles sooner than they’d expected. In March, Lakshmi’s signal went silent, near Ganapatipule in Maharashtra. In June, they lost contact with Prathma, Saavani and Rewa, in the waters off Maharashtra and Karnataka. In August, Vanashree’s signal went cold off the coast of Gujarat.
Manas Manjrekar, a deputy director for research and capacity-building programmes with the Mangrove Foundation, says they’re looking into why the transmitters didn’t last longer. But already, with their findings, “we are laying the ground for conservation measures that may be needed say 10 years down the line”.
The turtle-watchers are also hoping that when the turtles return next year, some can be tagged anew, and tracked further and longer this time.