In this Daily: Arribadas de Ostional and the Life Cycle of Baby Sea Turtles
Over the course of this weekend, countless sea turtles will make landfall at the beaches of the Ostional Wildlife Refuge to lay their eggs, a process called arribadas, which is the Catalan word for arrival. Throughout the course of the next few days, these Olive Ridley Sea Turtles will continue to make landfall to spawn, returning guided by instinct to the exact same beaches in which they were born.
Between 40 and 70 days later, depending on conditions, these baby sea turtles hatch and return to the sea to start the cycle again.
The Nesting Cycle from Arribadas to Baby Sea Turtles
There are four species of sea turtles in Costa Rica: Leatherback Sea Turtles, Green Sea Turtles, Hawksbill Sea Turtles, and Olive Ridley Sea Turtles. However, among these species only Olive Ridley Sea Turtles perform these mass arribadas. In fact, along with the closely related Kemps Ridley Sea Turtles, they are the world’s only sea turtles known for this behavior.
Females tend to congregate in large numbers offshore of beaches for a few days prior to the arribadas, a grouping called a flotilla, before conditions are ideal and the arrival begins.
From an evolutionary perspective, it’s theorized that this behavior originally manifested to help provide better survivability of the species as a whole. By isolating all egg laying to a single period on a single beach, potential predators of eggs and hatchlings are simply outnumbered.
Once eggs are laid, baby sea turtles gestate for a period between 40 and 50 days, occasionally taking up to 70 days if conditions are poor. During this time, the effects of conditions are tangible with temperature capable of determining turtle gender. Temperatures at 31C or above yield only females, temperatures 28C or below yield only males, with temperatures between yielding a mixed-sex clutch.
Turtles break free of their shells using a temporary egg tooth, which follows by a period between 5 and 7 days as the hatchlings burrow until they’re close to the surface.
Once conditions are right, baby sea turtles instinctively burrow free of their nests in unison, a mass departure of the hatchlings guided by the downward slope of the beach and the reflection of the moon and the stars on the water. Once in the surf, these hatchlings swim quickly away from the shore, searching for deeper water and places where they can find safety as they grow to maturity.
Watching the Arribadas in Ostional National Wildlife Refuge
Ostional National Wildlife Refuge is located about 2 hours south of town, and is one of a few places in the world where you can watch these arribadas safely and consciously. The Ostional park rangers offer guided tours that cap off at certain numbers, which serve multiple purposes.
First, it offers guests a chance to understand more about the regional differences and histories of each specific arribada, which can vary based on weather, tides, and water conditions even at a single beach. Second, by following these limited-access guides, park rangers are able to keep the number of visitors on the beach down so as not to overwhelm the females coming to nest.
The first three days of the arribadas, which includes today and tomorrow, are an ideal time to attend. Due to the sheer quantity of turtles arriving, research showed that the vast majority of eggs laid in the first few days of an arribada end up being accidentally destroyed. This lead local governments to legalize the collection of eggs and slightly more active exploration of the beach during the first three days.
As the later days go on and turtle arrivals slow, the beach is more protected, as park rangers and the local community pitch in to guard these eggs from predators and potential mishaps.
Recommended hours for a visit this weekend are 5:30, 6:30, 7:30, 8:30, 9:30, and 10:30PM, as the turtles are arriving in the evening. Concierge can organize a trip for you with a guide and transportation, or provide information on how to get to Ostional, how to find ranger stations and pay entrance fee, and how to find a guide once in the park.
In this way, you can ensure that you’re watching this unique natural phenomenon in a conscious, sustainable way that will preserve it for the years to come.