Marine Conservation, Science and Research

Osa Conservation Supports Research in Golfo Dulce: So Many Sea Turtles!

Side by side, you can begin to see the characteristics that visibly differentiate the three sea turtle species we documented inside Golfo Dulce.

When we began our research, nobody expected us to find very many sea turtles inside Golfo Dulce — most sea turtle activity was thought to occur on the Pacific side of the Osa Peninsula. It turned out that chelonids were the most frequently seen family of animals, accounting for 38 percent of our total sightings. Discovering such significant numbers of sea turtles was one of our most important findings. Sadly, fishermen with many years of experience in Golfo Dulce say the sea turtles there have declined at least 30 percent in recent years.

Jorge and I documented three species: Pacific Black sea turtles, still commonly referred to as “Greens” (Chelonia mydas agassizii), Olive Ridley sea turtles (Lepidochelys olivacea) and Hawksbill sea turtles (Eretmochelys imbricata). Locals also reported seeing near-extinct Pacific Leatherback sea turtles (Dermochelys coriacea) inside Golfo Dulce. That’s four endangered species of sea turtles utilizing the embayment. Amazing!

Our biseasonal data show Golfo Dulce to be a year-round feeding and breeding area for endangered Green sea turtles. We logged over a hundred sightings of them between both surveys. This species, by far the most common, was usually observed in the upper regions of the gulf resting at the sea surface. But we also documented Green sea turtles mating in all four quadrants of the inlet, so their use of the fiord waters appears widespread.

Although some amount of nesting may occur throughout the year, the primary nesting period for Olive Ridley sea turtles in Costa Rica is from July to December — the rainy season. Although we did see a couple Olive Ridleys in January/February, we weren’t surprised that the numbers and frequency of sightings rose dramatically in July/August. During the rainy season survey, nineteen Olive Ridley sea turtles were documented, including a pair mating just off-shore from Puerto Jiménez. Every lora, as the Olive Ridley is called in Spanish, was observed in the lower half of the gulf, suggesting that is the primary sector for them

Between 2010 and 2011, we saw only ten Hawksbill sea turtles. They were found in various locations around the gulf, although all close to the shoreline. The small population of Hawksbills in Golfo Dulce is particularly important because this species is critically endangered. In fact, until recently Hawksbills were considered functionally extinct in the eastern Pacific! Called carey in Spanish, this species is often locally described as “the little turtle”, something that was confusing to me at first, since the Olive Ridley is published as the smallest species inhabiting Costa Rican waters. But of course the locals were right. The Hawksbills seen during our surveys were unquestionably the tiniest.

Since sea turtles nest along the shores of Golfo Dulce, people who find their tracks are often curious which species left them. While Olive Ridleys and Hawksbills crawl one front flipper over the other, leaving an asymmetrical track in the sand, Greens pull with both flippers—like dual canoe oars—creating a more balanced print. The size of the tracks can also help determine the species.

Anyone with interest in learning more about sea turtles or working with them on the Osa Peninsula should check out the Osa Conservation’s Sea Turtle Conservation Program.

Brooke Bessesen conducted Marine research at the Osa in 2010 and 2011 as a recipient of the Greg Gund Memorial Fellowship. Check out her Golfo Dulce Report on our website.

Golfo Dulce report