A 16-year-long study of the Olive Ridley turtles has revealed that the population in the Indian ocean is among the oldest in the world and that nesting in Odisha is genetically distinct from other global populations including those found in the South American coast.
The study titled “Monitoring Sea Turtles in India 2008- 2024” and done by Wildlife Institute of India, Dehradun and the Centre for Cellular and Molecular Biology was published by the Indian Institute of Science and DakShin Foundation of Bengaluru.
Olive Ridley turtles are the smallest of the marine turtles that normally lay eggs in Rushikulya and Gahirmatha beaches of Odisha. The Rushikulya beach in Ganjam district, is one of the world’s largest nesting sites, apart from the coasts of Mexico and Costa Rica. Last month, over 1.3 million Olive Ridley turtles laid eggs at the Rushikulya and Gahirmatha rookery surpassing the previous record of 1.15 million in 2023.
Scientists of WII and CCMB, who examined the molecular genetics of sea turtles along the mainland coast and islands of India, concluded that the turtles found in the Indian Ocean, particularly on the eastern coast of India, were the most “evolutionarily ancient” populations of Olive Ridley whereas the ones in the Atlantic and Pacific probably only colonized those oceans about a few hundred thousand years ago.
“In the early 2000, people believed that when the Isthmus of Panama was formed 3 million years ago separating Atlantic and Pacific oceans, it led to separation of Olive Ridley turtles — one on the Atlantic, one on the Pacific. So, if that is true, then the most ancient Olive Ridley populations should be those populations on the east coast of Central America, in Mexico and Costa Rica …,” the study said.
The study, however, found that it is the Indian Ocean population of the species, particularly on the eastern coast of India, that was the most evolutionarily ancient populations of Olive Ridleys.
It also said that the Pacific and Atlantic populations probably separated from the Indian Ocean population about 300,000-400,000 years ago.
“So, it looks like the Olive Ridleys survived in this region during a period of global climate change about 3 to 4 million years ago and then recolonized the Atlantic and Pacific much later,” said Kartik Shanker of Indian Institute of Sciences and Dakshin Foundation, which has been researching and monitoring the Olive Ridley sea turtles in Odisha and leatherback turtles in the Andaman and Nicobar Islands for two decades.
He added that some Olive Ridleys from this part of the Indian Ocean possibly migrated to the east coast of Central America, Mexico and Costa Rica for nesting.
“Our study suggests that Indian ocean Olive Ridley turtles are among the oldest in the world and provides a new perspective on their evolution,” Shanker said.
The study also found that as global temperatures rise, sea turtle populations might become increasingly feminised.
“Over the last 15 years, we have been monitoring nest temperatures and hatchling sex ratios at the Rushikulya rookery, the largest in India. Sex ratios at Rushikulya are skewed towards females but not to the extent seen in certain global sea turtle populations. The hatchling sex ratio from arribadas at Rushikulya was found to be about 71% female on average,” the study said.
Shankar said that researchers are still studying arribada (mass nesting) does not happen in some years. “We need data set for 15-20 years to see if there is a trend. The arribada itself also is a bit of a puzzling phenomenon because it is triggered by both environmental factors and maybe by some biological factors as well, which we don’t fully understand. We don’t really actually understand the underlying mechanisms by which an arribada is initiated.”