The incredible sea turtle arribadas in Costa Rica

Costa Rica is one of the most-important sites in the world.

The Guanacaste, Costa Rica, beach of Ostional is home to a truly incredible phenomenon. About once a month during the peak season, tens of thousands of sea turtles come ashore to lay their eggs into the dark sand in a massive, coordinated arribada.

During an arribada, hundreds of thousands of sea turtles can arrive at the beach over several days in an event unlike virtually anything else.

Per the World Wildlife Fund:

The Ostional National Wildlife Refuge, together with Nancite beach at Santa Rosa National Park, is one of the two most important areas in the world for nesting of the Olive Ridley turtle (Lepidochelys olivacea).

Once the female turtles have reached a suitable site, the turtles use their back flippers to excavate a nest, leaving behind about 100 leathery eggs, each about the size (and appearance) of a ping-pong ball.

After the eggs are in the sand, the turtles cover up the nest. For good measure, the turtles rock back and forth, making loud thumping sounds as they “dance” over the nest to compact the sand and camouflage it.

About 50 days later, the baby turtles hatch, and a lucky few survive a litany of predators to reach the ocean.

When to see an arribada

The peak season for arribadas is July through December, with September and October typically the busiest months. (The September arribada just started; that was the inspiration for this story.)

Scientists aren’t quite sure what triggers an arribada, but they almost always occur about 10 days before a new moon.

The 2015 incident

In 2015, a mass of tourists at Ostional — some using flash photography and being generally disruptive — prevented many turtles from reaching their nesting sites.

Since then, access to Ostional beach has been restricted during arribadas. Visitors can only enter with a guide who ensure proper protocols are followed. Thankfully, a repeat of the 2015 incident hasn’t occurred since.

Why Ostional is special

Ostional is the only place in the world where it’s legal to harvest turtle eggs. This is a strategy meant to support the local community and involve them in conservation.

Because the first eggs laid during an arribada are typically destroyed by subsequent turtle mothers, residents of Ostional can legally collect and sell a portion.

The income from the turtle eggs helps fund the guards that patrol the beach and drives the local economy.

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