What is an "arribada"?

The olive ridley is one of the smallest sea turtles in the world. An adult weighs up to about 45 kilograms and is about 60 to 75 centimetres long. It takes its name from the olive-green colour of its heart-shaped shell. Olive ridleys live in the warm tropical waters of the Atlantic, Pacific and Indian Oceans, and are thought to live for between 30 and 50 years.

They are best known for the way they nest. On a few beaches, thousands or even tens of thousands of females come ashore together to lay their eggs. This mass nesting is called an arribada, and only ridley turtles do it. A female nests one to three times a season, laying about 100 eggs each time. The temperature of the sand decides whether the young turtles will be male or female. When they hatch, the young head for the brightest horizon, which on a natural beach leads them to the sea.

Olive ridleys eat both plants and animals, including algae, crabs and shellfish, and can dive to about 150 metres to feed on the seabed.

There may once have been about ten million of them; today there are far fewer. The biggest threat is being caught by accident in fishing gear, where they can drown. Turtles and their eggs are also taken by people, and nesting beaches are harmed by building, artificial lights and rising seas.