Please meet Polly – our local celebrity. Polly is a green turtle and a frequent visitor at Teluk Pauh bay, where we conduct our daily surveys. We saw Polly feeding around the same area every year since 2013 (the start of our observations), but this year she returned with new and shiny tag on her upper right flipper! It shows that our Polly travelled all the way to Vietnam and was tagged by Vietnamese Fisheries Department. What do you think she was doing there? We can be confident, that it was her time to mate and lay eggs!
Green turtles spend most of their lives miles away from their place of birth. Some research suggests that during juvenile years turtles can feed at different bays and explore various areas. However, once they reach the maturity, they would normally stay in the same area feeding on the same sea grass beds day and day again. Polly definitely likes Perhentian Islands and we could see her in the same bay feeding almost every day from the beginning of every season, until the end. Every season except 2015. That year she was present as usually from March, but after 31 May suddenly vanished, only to appear in 2016 with a new Vietnamese tag! We do not know if green turtles always mate around their nesting beaches, or can have some fun far away in the open sea. So far, conservationists confirmed that female turtle would normally mate with several males and can store the sperm for several months. So the eggs are fertilized by a variety of males and it helps to keep generic diversity in the population.
Once a turtle is ready to lay, she would crawl on the very same beach she was born herself (sometimes even within few yards of the place of birth) to find a perfect location for her own nest. Nesting is usually done during the night. It is long and very tiring activity that can take up to several hours. It is also the only time in the life of female green turtle when she is out of water. Male green turtles never come out of the water after their natal period. For conservationists nesting is a perfect opportunity to come up close to a green turtle, measure it or put a tag on the flipper.
Why would we put a tag on the flipper of a turtle?! Well, as you already know turtles travel remarkable distances in the water and usually spend most of their lives feeding in faraway seas. More must be known about their migratory patterns and their behaviour in the water to help us protect those beautiful animals. There are different methods conservationists employ in their research. Small metal tag is usually put during nesting and will contain an alphanumeric code on the upper side and the name of the tagging organisation (for example Fisheries department or Marine park authorities) on the lower side. Polly’s tag is VN1866. Other methods of research can be satellite tracking or photo ID. Here, on the Perhentian Islands of Malaysia we apply the most uninvasive method, photographing cheeks of green turtles and creating a database of all the turtles seen feeding in this marine park. Satellite tracking is the most harmful for turtles, but at the same time delivers the most accurate and sometimes surprising results. Transmitter is usually attached to the turtle carapace (shell) right behind her neck, so that antenna can send signal to the satellite every time turtle comes to the surface for breathing. Tourists or research organisations can sponsor transmitters and tracking information is usually publicly available online.
Variety of migration patterns and places for feeding are really surprising. After mating/nesting green turtles can go in completely different directions to spend their lives feeding in remote and peaceful places. Few years later each of them will come back to the nesting beach again to lay eggs. How do they find a way to exact same location that they were born
themselves and why can’t they get to any other similar beach instead? These questions are yet to be answered, but the latest theory suggests that amount and distribution of iron in their carapaces allows them to detect the angle and intensity of the earth’s magnetic field. Using these two characteristics, a sea turtle may be able to determine its latitude and longitude, enabling it to navigate virtually anywhere. Early experiments seem to prove that turtles have the ability to detect magnetic fields, but do they actually use it and how? If only Polly could tell us!
Perhentian Islands are beautiful turtle paradise. There are several sea grass beds popular among green turtles and a few nesting beaches. When I arrived to the project I thought that turtles we survey during the day and those we see nesting during the night – are the same ones. However, now I know: turtles that nest on our beaches were born here and came just to lay eggs. They do not feed here and later on will travel somewhere else to their favourite sea grass to spend a few years getting fat and healthy. At the same time, turtles peacefully feeding around Perhentian Islands during the day most probably were born in faraway lands and will go back there once it is time to nest. Like Polly. Now we know that she herself was born in Vietnam. I wonder how many more countries are represented in our turtle database… Let us know if you are tracking a turtle with particular tag number – may be it is in our database of sightings as well?