- An initiative in Sri Lanka stalled by the COVID-19 pandemic is looking to get back on track to identifying individual marine turtles in the island’s waters.
- The Turtle ID project uses photos taken by recreational divers to build up a database of turtles based on their unique facial patterns.
- The initiative was launched in August 2019, but soon came to a halt as dive centers, among other tourism businesses, closed during the lockdown imposed in early 2020.
- There’s now a greater sense of urgency around sea turtle conservation in Sri Lanka, following a high number of turtle deaths linked to the sinking in June of the X-Press Pearl cargo ship that was laden with tons of plastic beads and toxic chemicals.
MATARA, Sri Lanka — The Polhena reef and the surrounding shallow seas in southern Sri Lanka are home to a number of marine turtles that stay there year round. Randunu Dimeshan, a managing partner at the Polhena Diving Center who frequently swims in the area with his diving clients, has frequently encountered these turtles and been able to identify a few individuals from notable physical features such as a scar on a flipper or a damaged carapace.
Meanwhile, Chathurika Munasinghe, a marine biologist at the Ocean Conservation and Education Alliance (OCEA), had recently returned from a research project in the Maldives armed with a special set of knowledge and skills: identifying sea turtles based on photo identification.
Dimeshan met Munasinghe during a discussion of underwater cleanups, and this gave rise to the idea of setting up a similar citizen-science initiative in Sri Lanka. After preparations, the pair launched the Sri Lanka Turtle ID project in August 2019, several months before the COVID-19 pandemic struck.
“Turtles have specific facial scale patterns that are unique to each individual,” Munasinghe told Mongabay. “Just like fingerprints [on humans], the facial scale patterns can be used to identify turtles.”
To build up this database of turtle mug shots, the researchers needed, well, mug shots: clear photographs of both sides of the face and, optionally, an image of the shell. They worked with dive centers to get the latters’ clients to take photos during dives. These photos can be uploaded to the Turtle ID project website, where special software is able to pick up facial patterns and compare them with patterns from already identified individuals stored in the database. If the facial pattern is new, the photo contributor is given the chance to name the new individual.
Facial identification
The Turtle ID project has so far identified 18 hawksbill turtles (Eretmochelys imbricata) and three green turtles (Chelonia mydas), all of them female. Of the seven marine turtle species found around the world, five can be observed in Sri Lankan waters. The olive ridley sea turtle (Lepidochelys olivacea) is the most common, but these are mostly found farther out in the open ocean.
“The hawksbill turtles stay closer to the coral reefs as they prefer to feed on sponges that are mostly found in association with coral reefs,” Munasinghe said. “These are the areas where most of the researchers and recreational tourists dive, so the chances of encountering hawksbill is higher.”
Dimeshan said they’ve put a name on all of the identified turtle faces. Tammy was the first to be identified and was named after the nickname of a mutual friend of the project founders. Some of the others are Alice, Avondster, Shelah, Polly, Keyara, Olya, and Chuta.
Creating a database of sea turtles to assess the population size of each species is the main aim of the initiative. Some of the turtles use Sri Lankan waters as feeding ground, especially where reefs abound, so learning how they use certain reefs for feeding and breeding is another project aim. The team also expects the database to shed some light on turtle migratory patterns in the long run.
Munasinghe said the idea was inspired by her firsthand experience in the Maldives initiative. There, a similar project begun in 2011 has to date compiled individual records for more than 1,270 turtles, according to Marine Savers, the group running the initiative. The results indicate that the Maldivian hawksbills remain in their home reefs throughout the year, traveling only between reefs less than 2 kilometers (1.2 miles) apart, while green turtles tend to use multiple reefs for feeding.
“The Sri Lankan data show that we mainly observe female and juvenile turtles on the reefs, with few males of either species being spotted by our researchers,” Munasinghe said.
The technique of using facial pattern-based identification was introduced by French scientist Claire Jean of the Kélonia aquarium in the Indian Ocean island of Réunion, an observatory specializing in marine turtles.
Before then, most studies on marine turtle populations relied on capturing animals and tagging them with a marker such as a flipper tag or transmitter, which can be costly. Tags are also difficult to apply to turtles, as they remain in the water unless they reach beaches for nesting. So almost all physical tags are generally applied to nesting females. The photo identification method is both more cost effective and avoids putting the animals under any stress, Jean wrote in a 2010 paper.
Turtles get unique IDS
The Sri Lanka Turtle ID project uses open-source software called I3S pattern at its back end, employing machine identification of the turtles. The process is simple: reference points are first taken at the tip of the nose, the inner edge of the eye, and the furthest scale. The software then outlines the other identification zones and automatically selects 35 points within the zones as identification marks. Once this is completed, the program shows which turtles have the closest match based on the identification marks, and a user can either mark it as a previously identified turtle or a new individual.
The same technique can be used to identify individuals from other species, including whale sharks based on spot patterns.The technology is also thought to have the potential to identify large rays.
Munasinghe and Dimeshan have led several introductory sessions for researchers and recreational divers, their main focus being to get dive centers to support the photo ID project.
But the Turtle ID project got off to a rocky start, with COVID-19 hitting just months after its launch. In Sri Lanka, the government imposed a nationwide lockdown in early 2020, forcing the closure of dive centers and scuppering the Turtle ID project. Marine research in general has come to a halt in the year and a half since then.
In recent months, however, there’s been a greater sense of urgency around turtle conservation in Sri Lanka, following the sinking of the MV X-Press Pearl cargo ship off the western coast of the island in early June. The ship was carrying a cargo of nitric acid and plastic pellets, among other items, and was also loaded with 378 metric tons of bunker fuel. In the months since its sinking, more than 200 marine turtles have washed up dead on the beaches and in the waters in the vicinity.
Munasinghe said she’s hopeful of being able to dive soon and to update the database, with a view to contributing to turtle conservation efforts.
Citation:
Jean, C., Ciccione, S., Talma, E., Ballorain, K., & Bourjea, J. (2010). Photo-identification method for green and hawksbill turtles — First results from Réunion. Indian Ocean Turtle Newsletter, 10, 8-13. Retrieved from http://www.iotn.org/wp-content/uploads/2015/09/IOTN11.pdf#page=10
Banner image of mapped facial scale patterns that are unique to individual turtles, recorded using special software, courtesy of the Sri Lanka Turtle ID project.
