The green turtles (Chelonia mydas) have been the emblem of Ascension for more than 200 years. The island would not have been the same today without their presence in this region. Once, they were the main motives for which ships were anchored the island’s coast for a few days. Indeed, the turtle was an important source of fresh meat for the ships passing through Ascension. They were kept in ponds at Georgetown and later on, were transferred alive on the ships. Today still, they are often the main goal of visits in the island, but fortunately for entirely different reasons: observation and scientific research on this nearly extinct species.
Every year, the green turtles, both male and female, migrate from Brazil to Ascension and thus swimming a total distance of more than 2'000 km across South Atlantic. We are unaware of the reason for which these turtles lay their eggs on this small island, nor how they succeed in finding such a tiny plot of land in the ocean. Turtles marked previously with distinguishing signs have proved that Ascension is not a random choice; the same turtles can be seen on the island year after year.
A certain theory leads to say that this migrating itinerary dates back to million of years ago and has been developed when South America was detached from the African continent. Nevertheless, it is said to have remained deeply anchored in the memory of the turtles. Other scientists are of the opinion that they follow oceanic currents. However, their instinct must have been acutely developed to distance them from their native grounds for a 4’000 km round trip without any food.
Every year, the basic estimate is that 3’000 to 5’000 female green turtles lay their eggs on the beaches of Ascension. This is surely a representative of the biggest colonies in the Atlantic Ocean.
Biology of the green turtle
The reproduction sites of the green turtles are situated on numerous tropical and sub-tropical coastlines around the world. However, the green turtles which lay their eggs on Ascension are the biggest in their race: their size ranges from 1.5m to 1.75m in length and their weights can easily reach the 250kg. It is most probable that these characteristics allow them to cope up with their long and laborious migration and also, to brave the enormous waves breaking on the island’s beaches. In addition, they are herbivorous creatures and feed solely on seaweed and grass; however, the latter being practically inexistent around Ascension, it is possible that neither the males nor the females take in food during the migrating trip and the nesting season, that is for approximately 3 to 6 months.
The green turtles must imperatively be 20 to 40 years old to reach maturity and thus effectuate the trip for the first time. Most of the females will undertake the voyage every 3 or 4 years. The estimation of their lifespan ranges from 60 to 100 years.
Mating occurs in the sea shortly after their arrival. Then the female turtles undertake the nesting process: about 10 times at intervals of 10 to 17 days. They are obliged to lay their eggs on land; the embryo found inside will never be able to survive in water as it breathes through the pores of the shell. The process is a very laborious one; the female turtle must drag its own weight of 250 kg along the beach by the sole strength of its flippers. She then looks about for an appropriate site and can nor dig some trial holes. Using her four flippers, she first digs a hole equal to her size. Then, she digs an orifice with the help of her rear flippers in which she lays approximately 120 eggs the size of a golf ball. This particular process might as well last for 2 or 3 hours. Tears that help to cleanse her eyes from the sand usually accompany this exploit. Afterwards, she covers up the nest by throwing sand on the lain-eggs with her rear flippers before partially concealing the hole. The best time to look at the females laying the eggs is between 22h00 and 2h00 of the morning but it is common to still come across them on the beaches at dawn.
After 50 to 60 days of incubation in the sand, the eggs will hatch out and the hatchlings will then dig to come out of the sand. This task is particularly tiresome and can last for 3 or 4 days. Once they are near to the surface, they await the cooling of the sand before coming out and moving downward to the sea. They must then be wary of their predators: birds, crabs, wild cats and fishes. We estimate that one young turtle out of a thousand ones will survive to adulthood. Once they have reached maturity, the turtle will go back to its place of birth and will complete the reproduction cycle. The time of the births is normally in the period of Mars to June. The juveniles appear mostly at night and this makes the observation still more difficult. However, on a full moon night or early in the morning, it is often possible to see them rushing off to the sea while attempting to escape the awaiting predators. Just like the adult turtles, the young ones also start off towards the brightest spot (normally the sea) on the horizon at night. However, if there are lights or fires on the beach, they will set off towards those bright spots instead of the ocean. This can seemingly lead to disastrous consequences.
Necessary precautions while observing the turtles
It is absolutely essential not to disturb the turtles. The latter are very cautious when they crawl along the beach and begin to dig. At this point, they are easily frightened off by noise, people or fire. Once they begin to lay the eggs, they can be observed at ease, but they must always have a secure environment. People using the beach or simply observing the turtles should bear in mind the following instructions:
- Do not drive any type of vehicle on the beaches and refrain from lighting up powerful headlights.
- Do not make fires on the beach.
- Avoid the turtles until they have truly begun digging their nests. Before that, the turtle is easily disturbed.
- Approach them from behind.
- Do not aim lights directly at them; always use the more feeble light of a torch.
- Do not create excessive din or make any sudden move.
- Never try to touch them or climb on their backs.
- Always take flash-equipped photos from behind or sideways so as not to blind or disorientate them.
Photos: © Fabrice Bettex / Mysterra