A green sea turtle's shell - called a carapace - can be up to a metre long, and an adult weighs about as much as a large motorbike. The shell is smooth and streamlined, perfect for slipping through the water. The turtle's front flippers are shaped like long, flat paddles and are so powerful that a swimming turtle looks like it is flying in slow motion through the sea.
Female turtles return to the same beach where they were born to lay their eggs. They crawl up the sand at night, dig a deep hole with their back flippers, and lay around 100 eggs before covering the nest and returning to the sea. The eggs are roughly the size and shape of ping-pong balls. They hatch after about two months, and the tiny hatchlings scramble together down the beach towards the water.
Green sea turtles are called 'green' because of the colour of the fat inside their bodies - which comes from eating so much seagrass. Seagrass meadows are found in the shallow lagoons around the Bijagós, making the islands a perfect feeding ground as well as a nesting place. Turtles can hold their breath for several hours when resting at the bottom of the sea.
The beaches of the Bijagós are protected so that turtles can nest safely. Local communities and conservation volunteers monitor the nests and make sure hatchlings reach the sea. It takes around 25 years before a green sea turtle is old enough to return to its birth beach and lay eggs of its own.