one Olive Ridley Turtle nests here every 6 Hours AVERAGE.

Ostional Wildlife Refuge was created in the 80´s to protect the mass nesting of Olive Ridley turtles. The black sand and tropical waters hatch millions of baby turtles a year.
Predicting the arribada is not possible. We have one nesting event a month,  most of the time (not always) the arribada  starts between the last quarter moon and the new moon, lasting  a couple of nights to about a week. THE FIRST  DAYS ARE THE BEST WITH TURTLES DURING SUNRISE, The number of turtles decreases each night until it is over.  Some turtles nest alone outside the main event. To spot one you need to patrol the beach at night with a red flashlight.

Olive Ridley Turtles come to Ostional Beach to nest in big numbers in an event called Arribada . They gather out in the ocean and sometimes around the last quarter moon fill up the beach coming ashore at night and for as long as a week.
Leatherbacks season goes from November to March and Black Turtles  also nest here in fewer numbers.   
The arribada produces massive hatchings that last for about two weeks. Bigger arribadas occur during the rainy season (July  to November)  which provides the necessary temperature  to incubate from 90 to 120 baby turtles per nest.  Millions of baby turtles hatch between September and January every year. (Massive hatchings)

Official Guide Required to get in the Refuge for Turtle Watching.

The numbers of turtles coming to Ostional beach for nesting purposes increases as the rainy season peaks, the biggest arribadas occur on the coolest months from May to November, with a 40 to 50 days hatchling period.  Sand temperature determines the baby turtle´s sex. In the absence of arribadas turtles may also nest alone.

There are volunteer programs for both Olive Ridley, as well as Leatherback Turtles.
 The University of Costa Rica has a Station here, as well as a MINAET, that in cooperation with Tourist Police regulate the only legal turtle egg harvest project in the world.  
The community of Ostional works through their association (ADIO) and under the biologist supervision on a conservational plan that has progressively increased the number of turtles to nest and hatch here. 

EGG EXTRACTION PROJECT
The plan allows for the extraction of eggs during the first three days of Arribada in an eight hundred meter stretch of beach, this eggs may be damaged by turtles digging to lay their own eggs on later days. They calculate extraction to be  1% total, taking into account that all eggs layed between January and April will never hatch due to high temperatures  and that a big Arribadas (August to November)  will cover eight kilometers of beach.

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