Rising temperature, changing weather patterns and shift in the nesting season has a profound and direct effect on the incubation temperature of Olive Ridley turtles, a study to assess the incubation temperature of nests along the Maharashtra coast has found.
After a shift in the nesting season of Olive Ridley turtles, which nest in the three coastal districts of the state, from winter to early summers was recorded, the Mangrove Foundation under the state government commissioned a research study to assess the incubation temperature of nests. The project, which is in its third phase, is being undertaken by Sumedha Korgaonkar, a PhD scholar from the Wildlife Institute of India, Dehradun.
The preliminary results show increased mortality of embryos, decreasing the hatching success due to high temperature. At some sites, emergence success is negatively affected due to increased temperature and hardness of sand, the study found. Under the study, customised digital temperature data loggers were installed across seven sites in the three coastal districts, Raigad, Ratnagiri and Sindhudurg, March to May 2019.
Olive Ridley sea turtles are found in warm tropical currents of the Indian and Pacific oceans. Sporadic nesting is recorded across three districts in the Konkan region. In 2021, the number of nests in the state was more than two times the previous year — from 228 in 2019-20 to 472 in 2020-21.
Olive Ridley turtles travel thousands of kilometres in the ocean with only the females returning to their original nesting sites within a minimum of two years to lay eggs. Males never return to the land. Among sea turtles, temperature plays a significant role in sex determination, embryonic development and growth, hatching and emergence and locomotory movements of hatchlings.
After a 50-60 day incubation period, juvenile turtles break the eggshell and crawl to the sea.
“Global warming increasing the ambient temperature coupled with a shift in nesting season extending in summer is a major threat to this nesting population,” noted the study. The threat is in the form of an increase in the female-biased sex ratio of the population, a decrease in hatching and emergence success and the development of small hatchlings, which might have defects in locomotory moments, reducing their survival rate in open waters.
The study has suggested efforts like the use of sheds, inverted cane baskets with wet jute gunny bags over the hatchery to reduce the temperature of the nest as soon as the temperature crosses 33 degrees Celsius, as well as regular real-time temperature monitoring of the nests.
“There is a marked shift in the nesting season from winters to now even in May. Some mitigation measures at the nesting site were tried this year. The final report, which is in its final stage, will help us understand the nesting ecology and the success of the mitigation measures,” said Manas Manjrekar, deputy director, research and capacity building, Mangrove Foundation.
A similar study was undertaken by the Mangrove Foundation – comparing nesting data from 2002 to 2006 and 2014 to 2019 – had showed that the peak nesting period has also shifted from winter months (December) to early summer months (February-March). So, the incubation period is now coinciding with the high ambient temperature, which at some sites was observed to reach 40 degrees Celsius in the afternoon, affecting the success rate and sex of the hatchlings.
In 2020-21, the hatchling success rate was 46.66 per cent, a slight increase from 44.4 per cent the previous year. In 2018-19, the hatchling success rate was higher at 54.47 per cent. Hatchling success is the ratio of the number of eggs laid to the number of turtles surviving the nesting period.
On Tuesday, the Mangrove Foundation launched a mobile application – mTurtle — to collect the real-time nesting data. Sahyadri Nisarga Mitra (SNM), an NGO, developed the application where the turtle nest managers appointed by the Forest Department at various turtle nesting can directly update data, like the number of eggs laid, sea turtles and hatchlings. The data will be stored on cloud space accessible to the Forest Department.