Named for their pale olive colouration, Olive Ridley turtles (Lepidochelys olivacea) are the most abundant turtle in the world with an estimated 800,000 nesting females. They are nicknamed the dancing turtles. While the bigger species have enough weight to compact the sand on their nests, the smaller olive ridley must perform a dance, thumping up and down on the sand. This moonlight dance is a magnificent sight to behold.
Adult olive ridley are omnivores. They eat crabs, snails, clams, barnacles, fish, algae and jellyfish. The species thrives in tropical to warm-temperate areas throughout the Pacific and Indian oceans. Populations can also be found in the Atlantic ocean along the west coast of Africa and north east coast of South America.
Adult olive ridleys spend much of their time diving deep into the cooler waters under tropical seas. They have been captured in fish nets as deep as 350 feet down. After a deep dive they spend time on the surface basking. This behaviour is presumably an effort to speed up their metabolism and digestion processes.
True nomads of the ocean, after nesting they embark on complex migrations, swimming hundreds of thousands of miles over vast oceans. Like other sea turtles, we think that the olive ridleys use the position of the sun as well as magnetic signals to locate general areas in the ocean. The large amount of magnetites in their brains may help them to detect the earth’s magnetic field.
As mentioned the olive ridley has been nicknamed the dancing turtle. Whilst nesting they prop themselves up on their flippers and bounce up and down to compound their nest. They are too light to use their hind flippers to do so, hence the need for this hammer like dance. Interestingly this behaviour can also be seen in the day time. The light coloration and small size of the olive ridley means that they can nest in the daytime (when it’s not too hot).
Perhaps the most astonishing aspect of the olive ridleys nesting behaviour, is the fact that they nest together in huge nesting colonies. The Spanish named these nesting colonies arribadas, meaning arrivals in Spanish. These arribadas are truly phenomenal, the turtles come ashore in groups of many thousands. These nesting beaches can be just a mile long but accommodate 50,000 turtles laying on average 110 eggs each, that’s around 5.5 million eggs on one beach.
When the hatchlings emerge the beach erupts with tiny turtles. This eruption of so many turtles essentially swarms predators, ensuring as many hatchlings as possible survive the dangerous journey to the ocean. It is thought that this is the reason why olive ridleys have evolved to nest in these arribadas. Their nests are very shallow and easy to dig out, and so by having so many in one place there is a much greater chance an individual nest will be successful.
Despite this swarming effect, the arribadas still provide a feast for predators, providing sustenance for animals from miles around. Vultures sit on tree branches and coatis line the edge of the forest. Coyotes and racoons prowl the beaches at night. Even jaguars hang around. All waiting for their chance to join the feast. These predators continue to feast on eggs for the entire incubation period, and when the hatchlings emerge the animals gorge themselves on the baby turtles. And despite this banquet, enough turtles reach the ocean to eventually return in the following years. These events are vital for transferring nutrients from the seas onto the land and into nearby forests, acting as an important part of the food web.
Regardless of having large populations, olive ridleys are suffering from serious population declines. Mexico had populations numbering 10 million in 1950 and India had 600,000 in 1994. Arribadas are now only found in a handful of places (Costa Rica, Mexico, India and small ones in other Central American countries). The reasons for these declines are clear, over consumption from humans.
Nowhere has the hand of man been so destructive to turtles than on the nesting beaches and surrounding waters. Industrial turtle harvesting began in Mexico in the 1960’s and the death toll was horrendous. Between 1965 and 1970 2 million olive ridleys were taken from Mexican beaches. In Ecuador 150,000 turtles were killed annually in the 1970’s.
The Mexican government realised the extent of their destruction and banned harvesting in 1990. However, this was too little too late as 3 of the 4 major arribadas had already disappeared. Tighter regulations have led to some beaches been able to bounce back but not all. For example in Honduras people were allowed to harvest 88% of eggs at Punta Raton, but had to protect 12% in hatcheries. This clearly is not enough in order to maintain a sustainable population.
There are 4 important arribada beaches left in the world. These form the nucleus for rebuilding olive ridley populations elsewhere. It is important that these beaches continue to be protected in order to safe guard the species. We also need to enforce better protection in the oceans. South American shrimp boats rarely use TEDs and have been killing large numbers of olive ridleys over the years.
The key to restoring populations is improved laws, improved law enforcement, economic development for local communities and local community involvement in conservation. People once thought the passenger pigeon was invulnerable to hunting. People were shocked when flocks that once darkened the skies over the US disappeared. It’s important that we don’t take species populations for granted, we need to monitor and protect olive ridleys to avoid complete loss of this dancing turtle.