On the turtle’s trail 

The satellite-tagging of five Olive Ridley turtles marks the beginning of a milestone project in sea turtle conservation on the western coast of India.

Published : May 30, 2022 06:00 IST

Tagged turtles heading back to the Arabian sea.

Tagged turtles heading back to the Arabian sea. | Photo Credit: Harshal Karve

In January and February this year, five Olive Ridley turtles were satellite-tagged and released into the Arabian Sea from Velas, Anjarle, and Guhagar in Maharashtra’s Ratnagiri district. The female turtles, named Prathama, Savani, Vanashree, Laxmi, and Rewa, had all come ashore to nest. Researchers from the Mangrove Foundation of the Maharashtra Forest Department and the Wildlife Institute of India (WII) had permission from the Ministry of Environment, Forest and Climate Change to tag five nesting females. Once the females had laid their clutch of eggs, they were gently confined, tagged, and then allowed to head back to sea.

The whole process, which took about 10 hours, marked the beginning of a milestone project in sea turtle conservation on the western coast. Olive Ridleys have been tagged on the eastern coast of India, but long-time scientific curiosity about the commonalities between the eastern and western units, as the turtle populations are referred to, finally led to this collaborative venture to gain a better understanding of the west coast unit. Manas Manjrekar, deputy director, research and capacity building of the Mangrove Foundation, said: “Where do these west coast turtles comes from? We know this population unit is a separate unit. Some may go to Africa or the Maldives or Oman. The thing is, we don’t know. This programme is the first step in understanding their migratory patterns.” There are also future plans to carry out a genetic population sample using blood or skin samples to compare the east and west coast units.

The team from the Mangrove Foundation led by Harshal Karve and Manas Manjrekar with a tagged turtle a few moments before its release.

The team from the Mangrove Foundation led by Harshal Karve and Manas Manjrekar with a tagged turtle a few moments before its release. | Photo Credit: Harshal Karve

The research project, titled “Tracking the migratory movements of Olive Ridley sea turtles off the coast of Maharashtra”, is being carried out by the Maharashtra Forest Department’s Mangrove Foundation in collaboration with the Wildlife Institute of India, Dehradun. The purpose is to understand the migration pattern, foraging grounds and the general behaviour of the turtles. Essentially it involves sticking a transmitter on a turtle and then tracking its movement.

Tagging procedure

After the 30 minutes or so that the turtle takes to lay her full clutch of 100 to 120 eggs, she is confined by four plywood planks that slot into each other and form a box. The base is a plastic sheet so that the turtle cannot get traction on the sand. It is a means to lessen her anxiety—if she finds she can scrabble in sand, she will continue to do so and exhaust herself. When she finds the plastic sheet prevents her getting a grip, she stays still and conserves her energy. Wet towels are then placed on and around her face and flippers so that she does not get dehydrated.

Industrial grade adhesive is being applied to the transmitter before it is fixed to the turtle’s carapace.

Industrial grade adhesive is being applied to the transmitter before it is fixed to the turtle’s carapace. | Photo Credit: Harshal Karve

The platform transmitter terminal (PTT), a satellite-linked device, is then glued on to the turtle’s carapace with a strong industrial-grade adhesive and painted with anti-fouling paint. It takes about seven hours for the glue to dry. The turtle is also flipper-tagged with a unique ID that aids in mapping her wanderings. The whole operation happens in darkness with blue or red artificial light used so as not to disturb the turtles. As dawn breaks, the restraining planks are removed, and the turtle moves into the sea, carrying her new lifelong companion, its antenna bobbing on her shell.

The device weighs about 600 grams, conforming to international standards of tagging that dictate that any device should be 1 to 2 per cent of the animal’s body weight. A female Olive Ridley can weigh up to 50 kilograms. The device is powered by a battery that lasts for 700 days and is designed to work only when the turtle surfaces. In any case, the device cannot transmit underwater and has a saltwater switch that turns it on when it is out of contact with saltwater. Thus, when the turtle surfaces, the transmitter is activated, and when the turtle dives, it switches off. This saves battery life.

Olive Ridley turtles spend most of their lives at sea and most of it underwater, often at depths of 250 metres. Though they can hold their breath for around an hour, like most reptiles, they are unable to breathe underwater and have to surface from time to time. This is the crucial moment when the transmission takes place.

The map which tracks the route of the tagged turtles.

The map which tracks the route of the tagged turtles.

Much of their lives are a mystery, and the satellite tag will go a long way in revealing what a day in the life of an Olive Ridley turtle is like. When the animal surfaces, the saltwater switch clicks on and the battery comes to life, allowing the device to send a location marker to a satellite using Argos, a satellite-based system that has a location and data collection system for the study and protection of the environment. Argos, the most widely used system for wildlife tracking, is a four-step process involving the transmitter, the satellite, a receiving station and a processing centre.

The transmitter on the turtle’s shell is certified by Argos. As soon as the turtle surfaces, it sends a signal to the satellite 850 km above earth. The transmission of each message takes less than a second, so even the briefest of surfacings will be registered. The interval between two consecutive messages varies between 90 and 200 seconds, providing an accurate picture of the location. The satellite ID is registered on the WII’s web portal. The satellite relays information twice a day, which the WII processes and shares on a weekly basis with the researchers in Maharashtra.

Tagged turtles.

Tagged turtles. | Photo Credit: Harshal Karve

A map follows the route of the five turtles. Each turtle has been given a colour, and the maps are a seemingly haphazard mess of lines that zigzag all over, but of course they must be guided by currents, food sources and some instinct. The map shows that Savani, who had been tagged at Anjarle on January 25, nested at Kelshi beach in Ratnagiri on February 25. The aerial distance between her tagging and nesting sites is around 8 km. Prathama has travelled widely and, around mid May, was 65 km from Diu on the coast of Gujarat. She has moved a straight-line distance of 330 km north-west of her tagging beach at Velas. Savani stayed closer home and was about 90 km in a straight line from the Maharashtra coast. An alert beach manager identified Savani from her flipper tag and reported that she had returned to Kelshe beach a month after her tagging and laid a second clutch of eggs. Interestingly, females can nest thrice after one mating. Harshal Karve, a marine biologist at the Mangrove Foundation, said: “The first clutch will be between 100 and 120 eggs. The second less than 90 and the third less than 60.”

Vanashree, the third turtle, was plotted on the map as turning south along the coast and was 25 km straight line from Ambolgadh beach. Rewa also turned south, crossed Goa and was in Karnataka waters about 40 km offshore from Karwar. Laxmi is a source of worry because no signals have been received since March 2. It could be either a malfunctioning transmitter or a fatality.

Maharashtra does not have the turtle population that Odisha has. It has been a matter of scientific curiosity as to why this is so, considering that there is a small Olive Ridley population on the west coast that seems to belong here. Manjrekar and Karve say that Maharashtra’s beaches see sporadic nesting. Manjrekar said: “On a four-kilometre beach you might have one turtle nesting.” Others could easily go undetected because the beaches are long and turtles nest at night. To try and get more accurate information, beach managers, who are locally hired, patrol the beaches every couple of hours through the night.

Data showed that January and February are when the nesting season peaks. The beaches of Guhagar and Velas have the highest nesting rate. This year Guhagar had 90 nests. Beach managers are integral to the research. For instance, spotting Savani’s second nesting was possible because a beach manager was on patrol. Manjrekar said: “We were lucky to get that information.”

The turtle named Savani nesting at Kelshi beach in Ratnagiri district.

The turtle named Savani nesting at Kelshi beach in Ratnagiri district. | Photo Credit: Harshal Karve

Patrolling is done late in the evening, night and early morning. Beach managers look out for newly patted down nests, flipper tracks or even an ongoing nesting. When a nest is found the eggs are gently dug out and taken to a hatchery. This is to ensure a higher hatchling rate. Turtles nest above the high tide line to prevent the tide from washing away the nests, but Manjrekar says that beaches are becoming narrower and the tide usually inundates the nests.

Researchers have observed that the nesting season is gradually shifting towards summer. “The increasing exposure to heat is a concern,” says Karve. He explains why. “The sex of turtle hatchlings, like many reptiles, is temperature-dependent. At 29.5 degrees centigrade you get the ideal 50-50 sex ratio. Below 29 there are more males and above 29 there are more females. And above 32 degrees its 100 per cent female. And if it is above 33 degrees then there is high mortality.” Karve says that in March, April, and May the temperature inside the sandy nests was probably above 32 degrees. “An April hatchling has less survival success than a February one,” he says. It is not yet understood why the nesting is shifting towards summer. A graphical map of data from 2004-2007 shows that December to January was the peak nesting period. This has now shifted to February-March.

The Sahyadri Nisarga Mitra, an environmental NGO, has spearheaded turtle conservation with its hatchling nursery programme started in 2003 in Velas. Olive Ridleys come under Schedule 1, the highest level of protection under the Wildlife (Protection) Act, 1972. Worldwide, too, Olive Ridleys have fared better and are now classified as Endangered by the International Union for Conservation of Nature instead of the earlier Critically Endangered. To add to the concerns of conservationists, Olive Ridleys have a late sexual maturity. “It’s 15 or 20 years before they can reproduce,” says Karve. And while it is a point of fascination that they return to nest in the place where they were born, as studies from Florida (US) and Costa Rica have shown, it is also a point of worry. It means that it is crucial to save their nesting sites.

Local participation

Wildlife enthusiasts watch as a tagged turtle enters the waters.

Wildlife enthusiasts watch as a tagged turtle enters the waters. | Photo Credit: Harshal Karve

Manjrekar and Karve agree that there is a sense of ownership by the local people. In 2006, Velas village started turtle tourism. The Turtle Festival saw a boom in homestays, leading to an improvement in the local economy. Poaching is practically non-existent. Local awareness has contributed greatly to the conservation programme. Beach managers are paid Rs.400 a day during the nesting season, which spans December to May. At a monthly Rs.12,000, local residents are keen to support the conservation programme and highlight the mantra that ideal wildlife conservation is one in which both wildlife and humans benefit.

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