The ridley riddle

Sea turtles are studied for their migratory behaviour and faithful pursuit of nesting on specific beaches. India has at least five such species with pronounced nesting and migratory patterns. These include olive ridley sea turtles, green sea turtles, and leatherbacks. Olive ridley sea turtles nest on the beaches of Gahirmatha and Rushikulya in Odisha. These two nesting areas house some of the largest rookeries in the world. 

Recently, members of the conservation group Dakshin Foundation, Rushikulya, witnessed one of the largest arribadas or mass nesting events in recent years, with 400,000-500,000 turtles nesting in just a few days. According to the foundation, sections of the beach were packed so thick with turtles that there was barely any place to walk.

The foundation recently published a report (bit.ly/turtle-dakshin) on their observation of Indian sea turtle populations over the past 16 years (2008-2024). Since sea turtles live long and mature late, changes in their population can only be observed over long intervals. The monitoring was carried out with the Indian Institute of Science (IISc) and several State forest departments. It provides information about population trends, threats, and conservation along India's mainland and island coasts.

"The overall trend from nearly two decades of monitoring is that the ridley population is stable or increasing," says Kartik Shanker, who is with the IISc and founder-trustee of Dakshin Foundation. At the Rushikulya rookery, monitoring indicates a steady population growth: from 25,000-50,000 nests a season in the early 2000s to over 1.5 lakh in the last decade and over 4 lakh in recent years. 

However, the hatchling sex ratio favours females, raising questions about the population's long-term viability. Warmer temperatures tend to produce more females, and sand temperatures are rising because of climate change.

Also, according to Shanker, it is puzzling that arribadas (the Spanish for arrival) don't occur every year. He adds that while this may not cause immediate alarm, "we must remain wary of threats to both coastal and oceanic habitats". 

In addition to the work in Odisha, the report presents research on leatherback turtles, pointing out that since the 2004 tsunami, nesting has steadily increased in the Little Andaman Island. In Lakshadweep, an expanding green turtle population has brought about unexpected ecological changes, especially in the currently overgrazed seagrass meadows.

In India, sea turtles face threats from coastal development, pollution and climate change. The study underlines that local communities are primary stakeholders in monitoring and protecting sea turtles, and collaborations among fishers, researchers, and policymakers can lead to more sustainable conservation.