By Blake Nourie
OSTIONAL, Costa Rica – Arribada, which translates to “the arrival,” refers to the multiple times a year thousands of female sea turtles return to their hatching grounds on the beach to lay eggs.
The largest arribadas of olive ridley sea turtles occur multiple times a year in Ostional. The Ostional arribadas are unique because they are one of eight arribadas around the world. Also, conservationists say that the egg harvesting project here is essential for Ostional’s local economy.
Ostional’s community harvested sea turtle eggs for human consumption starting in the 1950s when turtles began to come in the thousands to nest. Scientists don’t know why these turtles come to this location, but biologists from the Ministry of Environment and Energy, locally known as MINAE, speculate this land was opportunistic and uninhabited by many other species.
To declare an arribada 100 turtles must be seen in a given night. Law permits egg harvesting by the community when 1,000 turtles are seen.
Although controversial, biologists say the extraction of olive ridley eggs is a controlled process that aids in species growth. Paradoxically, removing some eggs from the land frees up area for future nests and promotes overall hatchling success.
Current laws in place limiting egg harvesting have not changed for 20 years. In this time, no evidence has been found of decreased nest density or total population count within the coastline of Ostional. In fact, Ostional’s egg hatching rate is 20 percent, whereas the average for the species can be 7 percent.
MINAE limits its legal harvesting area to a 200- to 300-meter coastline, depending on the size of the arribada. The community is allowed to harvest for the first three days of an arribada. The arribada can last for seven to nine days in the rainy season or five to seven days in the dry season.
From this highly monitored process, less than 1 percent of all eggs laid are harvested and sold as food across Costa Rica. Extraction practices are sustainable because 20 years of data show populations are stable. In fact, in this area the eggs extracted increase the hatch rate of future eggs. Biologists consistently observe turtles in the latter days of an arribada unintentionally digging up nests to lay their own, thereby destroying just laid eggs.
Biologists who study the olive ridley sea turtles advise MINAE to sustain the community’s harvesting percentage. Biologists fear changing the numbers of sea turtles in any way could be detrimental for the entire ecosystem.
Although a 1 percent extraction rate seems like a random number for the community harvest, 20 years of data suggest this might be the correct extraction percentage for a sustainable turtle population.
Instead of changing the harvesting percentage, biologists recommend reducing overall pollution and continuing to keep the beaches clean.
Edited by Isabella Alves
Jairo Quirós Rosales describes his biological field research. Rosales has a master’s degree in biological science from the Universidad de Costa Rica and is employed at the MINAE. Photo by Nadav Soroker.