Rising seas could flood olive ridley nesting sites by 2050: study

The finding is predicated on the moderate climate-change scenario and is based on studies of digital elevation models.

April 30, 2023 10:30 am | Updated 11:48 am IST - New Delhi

The Rushikulya beach in Odisha hosted 6.37 lakh turtles from February 23 to March 3, 2023.

The Rushikulya beach in Odisha hosted 6.37 lakh turtles from February 23 to March 3, 2023. | Photo Credit: Biswaranjan Rout/The Hindu

Should warming continue under moderate climate-change scenarios, leave alone drastic ones, some sea-turtle nesting habitats, including those of the olive ridleys that visit India every year, will be completely flooded by 2050. In more extreme emissions scenarios, they could completely vanish, a new study has found.

An international team of researchers, from Australia, Brazil, Costa Rica, Cuba, Dominican Republic, the U.K. and the U.S., combined freely available digital elevation models for continental and remote island beaches across different ocean basins, with projections of field data and sea-level rise, to examine the possible impact on five of the world’s seven living sea-turtle species. These are the leatherback turtles (Dermochelys coriacea), loggerhead turtles (Caretta caretta), hawksbill turtles (Eretmochelys imbricata), olive ridley turtles (Lepidochelys olivacea), and green turtles (Chelonia mydas).

Of these, on the IUCN Red List, the leatherback, loggerhead, and olive ridley turtles are classified as ‘vulnerable’, the green turtles as ‘endangered’, and the hawksbill turtles as ‘critically endangered‘.

What did the researchers find?

In a paper published in Scientific Reports on April 20, they reported that in a scenario in which the world’s carbon emissions are neither high nor low, “it is predicted that at some sea turtle nesting habitats 100% will be flooded, and under an extreme scenario many sea turtle rookeries could vanish” – either by 2050.

Overall, nesting beaches that had less steep slopes and those species nesting at open beaches – the leatherbacks and the loggerheads – could be the most vulnerable to future sea-level rise, they said.

According to the team, their method showcases the use of a low-cost approach to assess the impact of various sea-level rise scenarios on different sea turtle nesting rookeries worldwide. One of their objectives was to address the uncertainties in the magnitude and on the relevance of expected increases in sea levels for marine and terrestrial species that depend on coastal habitat for foraging, resting or breeding.

Previous studies attempted to address these problems but focused mainly on local regions and considered only one or two species at a time. Their techniques varied as well: regional field surveys often suffered from low accuracy, while the combination of ‘light detection and ranging’ (LiDAR) and biological data was more accurate but also more expensive, and thus not very repeatable.

What is notable about the study?

The current team’s method, using digital elevation models, should solve these problems, according to its members. “Considering that most sea turtle rookeries across the globe are located in remote areas in low and middle income countries, less costly approaches for field surveys are often preferred and can provide baseline data to identify areas most at risk,” their paper reads.

Their own study “predicts massive flooding at important rookeries in Australia, Dominican Republic, Costa Rica and the USA”.

The findings also apply to flat beaches in all countries whose coasts host nesting sites for turtles, since sea-level rise is global, Marga Rivas, of the department of biology at the Marine Research Institute INMAR, University of Cádiz, Spain, and one of the study’s authors, told The Hindu.

How can the findings apply in India?

The scientists used a small number of case studies to show that flooding can be very severe at some beaches in the future, Kartik Shanker, a professor at the Centre for Ecological Sciences, at the Indian Institute of Science, Bengaluru, and founder-trustee of the city-based Dakshin Foundation. “The same analytical approach can be used to study the effect of sea level rise on sea turtle nesting beaches in India and across the world,” he said.

Such assessments will help identify conservation refugia and nesting beaches that are more resilient to climate change. “Although sea turtles have been around for millions of years and would be present in several climate change events, we do not know how their populations might be affected by these projected rapid changes of high loss of nesting sites in the study areas by 2050,” the Scientific Reports paper said.

Its authors also stressed the urgency of developing a multi-species assessment at a global scale, in order to develop conservation plans for the most vulnerable populations while there is still time.

Dr. Shanker also said that for too long, conservation measures in India have focussed on ‘charismatic’ species – as well as that sea turtles can’t be ‘saved’ by focusing on their protection alone. “As other evidence suggests, protection of coastal habitats from large-scale development is far more important than species-centric protection measures.”

T.V. Padma is a freelance science journalist.

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