There is still a lot we don’t know about sea turtles.  For instance, there is no way to determine the exact age of a turtle; we think they may reach 80 years old in the wild.  Also, it is not possible to distinguish between males and females until they approach sexual maturity, when the males develop long tails.  In most species, males also have long curved claws, which may help in grasping the females' shells during mating.

Depending on their diet, sea turtles can be found in habitats as varied as coral reefs, seagrass beds, coastal shallows and the open ocean.  They leave these feeding areas every 2-3 years to travel thousands of kilometers to the beaches where they were born in order to reproduce.  Also, females often return to the same nest site as previous seasons with remarkable precision!

The nest incubates for approximately two months, buried in the sand.  Incubation conditions like temperature, gas exchange and moisture play essential roles in hatching success.  In addition, the temperature of incubation determines the sex of the baby turtles. Above 32 degrees the nest produces only females, below 28 only males. At around 29.5 the clutch is half male and half female.

At the end of incubation, hatchlings emerge from their shell by breaking out with a special temporary egg tooth. And they begin trampling in the egg chamber, shuffling the sand underfoot, slowly building the trapped air upward, and scrambling one on top of the other like a ladder.  At the surface they wait for the sand temperature to drop, usually emerging at night or in the cool dawn hours.

In the Pacific Ocean, leatherbacks have declined by 95% in the last twenty years, so have been classified as critically endangered worldwide.  We are lucky that Gabon has the biggest nesting population in the world.  Leatherbacks are the largest of the sea turtle species and also the most unique-looking.  They have a soft leathery carapace with seven longitudinal ridges and numerous white spots.  A large adult can have a carapace of 180 cm in length, a flipper-span of 270 cm and a weight of 500 kg.  The biggest recorded leatherback measured 2.91 m and weighed 916 kg!

They feed on jellyfish and other oceanic invertebrates, which they trap in their oesophagus with special spiny structures.  Floating plastic bags in the sea can be mistaken for jellyfish and kill leatherbacks who eat them.  Leatherbacks can dive for as long as one hour to depths as much as 1000 m!  In addition, they are known to feed even in cold Arctic waters, since they are unique among reptiles in their ability to thermoregulate.  Several leatherbacks which nested in Gabon and were marked with metal flipper tags were later recaptured in feeding grounds as far away as South America and South Africa.

Gabon’s Species: Green Turtles

Green turtles are the only herbivorous sea turtles, feeding on seagrasses and algae in warm shallow coastal waters.  Green turtle feeding grounds exist in only a few places around the world.  Corisco Bay, on the border of Gabon and Equatorial Guinea, is the most important green turtle feeding ground in the Gulf of Guinea and studies have shown that green turtles come to feed here from many different nesting populations, even 10000 km away!  Vice versa, individuals born on the same beach will not all feed at the same foraging ground.  Another strange thing about the migratory nature of green turtles is that they do not necessarily feed at the foraging ground closest to their nesting beach, nor do they nest at the closest available beach to the foraging ground.

Foraging grounds with large numbers of turtles are, unfortunately, particularly vulnerable to exploitation.  In Gabon, green turtles are the main target of turtle hunting and sometimes sold in Libreville markets and restaurants.  Because they are extremely slow growing and have delayed maturity (they can take as much as 30-50 years to become adults), they cannot replace themselves fast enough and their population is declining rapidly.  The depletion or disappearance of this population is likely to have serious consequences for the healthy functioning of their ecosystem.

Adults weigh between 100 and 200 kg and their carapace is around 100-115 cm long.  Their color is variable; the name actually derives from the color of their body fat, a result of their vegetarian diet. Green turtles nest on isolated predator-free oceanic islands, as well as remote mainland beaches.  During their long migrations from feeding to nesting grounds, they can survive for many months without eating.

Hawksbills live in clear shallow waters among reefs or rocks, and are usually more sedentary than the other species.  They feed primarily on sponges and corals, and have the extraordinary ability to remain unaffected by the potent toxins and spicules found in sponges.  The most tropical of all species, it is also a solitary nester, preferring remote isolated beaches, often separated in space or time from other species.  There are very few large nesting sites in the world.

Hawksbills can also be recognized for their parrot-like beak.  The carapace tends to be oval and with thick overlapping scutes, positioned a bit like the tiles of a roof.  Unfortunately this beautiful shell is in high demand for the production of jewellery, glasses frames and other trinkets.  Although, trade in these products is forbidden by international law, the hawksbill remains critically endangered worldwide.

In Gabon, hawksbills are found in Corisco Bay as foraging adults or developing juveniles; they also occasionally nest along the coast.  Two hawksbills which had been marked with small metal flipper tags by a research project in Brazil, were recaptured in Corisco Bay after having travelled almost 5000 km.

Gabon’s Species: Olive Ridleys

Olive ridleys have a carapace that is almost round, of an olive color, and a relatively small size of approximately 60 cm in length and width; the adult weight is only about 35-50 kg.  Olive ridleys live and feed in the open ocean and are rarely seen except when they approach the coast for nesting. In Gabon they are the second most common nesting species after leatherbacks.  Unfortunately, they are also very vulnerable to capture by coastal commercial fisheries during this period and we count a high number of dead strandings on Gabon’s beaches every year.

Interestingly, olive ridleys can nest in huge aggregations called arribadas, when as many as 150,000 females come ashore at the same time over the course of several days.  This however only occurs at a few sites in the world, such as Orissa (India) and Ostianal (Costa Rica).

Unfortunately, olive ridleys often drown in the nets of shrimp trawlers, fishing in the same places where they find their prey of fish and small molluscs and crustaceans.  In recent years, the nesting populations in South America have declined dramatically, almost to extinction.  For this reason, protection of the olive ridleys in Africa has become even more urgent.