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A Natural Phenomenon: Sea Turtles Nesting and Hatching in Playa Ostional

Updated: Oct 24, 2019

One of the most unique and awe-inspiring natural events to witness in Costa Rica is the arrival of thousands of sea turtles in Playa Ostional, locally called the Arribada (the Arrival).

Playa Ostional Arribada

How it Begins: The Flotilla

During rainy season, large groups of Olive-Ridley sea turtles return to the beach where they were born and begin gathering in the ocean a few miles from shore. As the turtles arrive, some travelling thousands of miles, they gather and await a secret signal to begin the Arribada. This pre-nesting congregation in the water is called the Flotilla. For a long time it was a mystery to scientists how the turtles navigated the massive expanse of the worlds oceans to find the exact place they were born, but a recent study has proven a long standing theory that sea turtles use magnetic fields to navigate the oceans just as sailors use latitude and longitude to do the same. Each coastline has a unique magnetic signature which the turtles remember and later use as an internal compass to find the beach where they will lay their eggs. Male turtles will typically never return to the beach where they were born.

Sea Turtles use Earth's Magnetic Fields as a Compass

Although the turtles nest in Ostional year-round, the best time to see these large gatherings is between August and December. During this time, every week before a new moon, there is an Arribada. They choose the darkest time to start their arrival, but once it begins they arrive en masse for 3-7 days. The best time to view the arrival is at sunset, but early morning is also a great time. If you decide to do a night tour, keep in mind you will not be permitted to use flash photography or flashlights. Only red lights are accepted because bright lights can scare and confuse the turtles.


The Arribada is a unique phenomen unique to the Olive-Ridley and related Kemp-Ridley seas turtles. Out of 7 species on the planet, Ridley turtles are the only ones to have these massive communal nesting events. This interesting occurrence only happens in eight beaches around the world (two in Cost Rica), and Ostional is considered to have the highest reproduction of Olive-Ridley sea turtles and is therefore a very important to area to protect.


The Ostional National Wildlife Refuge was established in 1984 and since then they have been working with local residents to protect and assist the turtles in their reproductive journey, from nesting all the way to hatching. At Guana Adventures, we work directly with the Wildlife Refuge and Association of Local Guides to make sure we are supporting the people that are responsible for protecting the turtles and not the ones just profiting off them. The money contributed to the refuge goes directly to helping them protect, research, and aid the turtles and the local community. Without this contribution, the association would not be able to organize important events like beach clean ups, aiding the hatchlings, educating tourists, and the important research of biological anomolies. For example, at the recent hatching in October 2019, it was discovered that some of the baby turtles could not seem to find the ocean and sadly kept going around in circles. Upon closer inspection, it seemed as if the mothers might have been exposed to a chemical in the water because several hatchlings were born blind, their eyes white and clouded over. The importance of this refuge cannot be overstated. They are responsible for taking some of these baby turtles back to a lab and researching what happened so they can inform the public and hopefully prevent it from happening in the future.


Educating both tourists and locals is pivitol in the continuing health of sea turtle populations, that's why we consider it an honor to share this knowledge with as many people as possible.


8 species, ridley is smallest leatherback biggest 150 eggs at a time the clutch ensures survival .1% survive. emerging large numbers ensure some will survive. sex determined by temperature. ostional black sand. temp determines sex warm temps 88 F female cooler less than 82 male. magnetic fields to navigate geo magnetic abilities serve as internal gps magnetite in brains. plays a role to orient to poles similar to compass. babies imprint on unique magnetic signature on unique signature of beach and guides them back in future to lay eggs. all 7 speicies treatened with extinction. once abundant, populations have dratically reduced in last two centuries. fishing major threat caught in nets as by catch or accidental catch illegal harvesting of eggs trafficing turtle products and ocean pollution major oncerns, policies have been enacted to help. humans can help decline of sea turtles.

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