22-01-16
On January 10 we had a Zoom call from Dr. Pilar (“Bibi”) Santidrian Tomillo about sea turtles in the age of climate change. On a bright moonlit beach last night we saw them.
Dr. Santidrian is the research director of The Leatherback Trust, an organization working to monitor, understand, and conserve the three species of sea turtles found in Costa Rica: Green, Olive Ridley, and Leatherback sea turtles. On Tortuguero (a primary nesting beach in the Caribbean, but where the turtles nest from March to August) we saw full-sized models of the Green and Leatherback turtles. Green sea turtles can grow slightly over 1 meter long, a respectable size for a turtle. A nesting female Leatherback, though, can exceed 2 meters and 600 pounds! We had hoped to see some turtle activity on the night of the 16th, but not-so-secretly hoped to have one of the extremely rare gigantic Leatherbacks come to shore. That didn’t happen, but we did have more turtle activity than we expected.
Playa Cabuyal is a remote beach just south of Santa Rosa National Park, framed by the Papagayo peninsula to the south and the Santa Elena peninsula to the north. It is a “secondary” nesting beach, meaning that compared to other beaches (e.g. Playa Grande farther south) fewer turtles nest there. But last night we got lucky: we saw three adult and three newly emerged nestling Green turtles.
We were met by Keilor Cordero, the field coordinator for the Leatherback Trust, when we arrived at 9:30pm. (We meant to arrive at 9:00, but the road to the beach was hard to find!) He gave us the good news that they had a Green turtle in the midst of digging her nest just 15 minutes down the beach and he would take us there to see her. Then the bad news: we could use no lights and take no pictures. Okay, for viewing sea turtles we could live with that!
The walk down the beach was magical. The surf crashed on the sand to our right, the air was fresh and salty, and though we used no lights all was brightly illuminated by a full moon overhead. Partway to the nesting female Keilor stopped us—another Green turtle was emerging from the surf! The moonlight reflected off its wet carapace as it slowly humped its way up the sand, using both its front flippers to heave its weight up and forward, pause, then repeat. We stayed quiet about 40 meters away because Keilor said that Green turtles are very skittish, especially on moonlit nights, and if it got scared it would turn around and go back into the ocean. It struggled up the foot-high erosion terrace, and once it was well up into the dry sand we quietly filed by on the ocean side.
At the nesting female we met Vera, the other Leatherback employee on duty this night. She had their materials spread out on a blanket well away from the turtle and had already marked the turtle with a “pit tag” (an electronic transponder injected below the skin) and a numbered metal tag on its right front flipper. At this time the turtle was still preparing the nest. Once it was laying eggs they said we could approach it closely as when laying a turtle will ignore everything else.
In the meantime Keilor led us down to a nest that had hatched earlier that night. As he dug in the nest he unearthed two hatchlings that hadn’t made it with the main exodus! Green turtles like to nest under vegetation, and this one was under a spreading bush so Keilor brought the hatchlings out and laid them on the dry sand with us gathered eagerly around. At first the turtles just lay there, as if damaged by the hatching, but after a few minutes they began moving and orienting themselves. Turtle hatchlings use the brightness of the ocean to know where it is (and can easily get confused by the lights of houses or businesses near a hatching beach) and it was fascinating to see them turn toward the water and start the long journey up and down over rough sand. They started slow, but as they warmed up via muscle action they got going faster and faster until they were almost “flying” across the sand (Keilor’s description) with their big front flippers alternating. One of the little turtles got a head start, and about half the class followed it while the rest of us followed the laggard. As the laggard arrived at the wet sand in the surf zone something dark emerged from a hole and seemed to pursue the hatchling. The students were outraged at the idea of a crab attacking the poor little turtle, but held back from clobbering it, which turned out to be good as it was another turtle hatchling that had emerged from the crab hole. Probably it had made the journey to the water earlier and had bee captured by a crab which was trying to drag it under the sand. The vibrations from our feet probably scared the crab into letting go. A few meters later and all three of the hatchlings were taken by the surf into their new home.
At this time Keilor led us back to the nesting female, but by the time my half of the class got there she was done laying eggs and was filling it in with sand, “camouflaging” it. We could stand just a few meters away and see her clearly, partially buried in the hole she dug as she moved sand from in front of her to behind her, a moving excavation. Eventually the nest itself would be indistinguishable from the rest of the beach, with a depression somewhere nearby where the turtle finally finished digging.
Later that night we encountered a third turtle emerging from the surf, and sat and watched as she made her way up to the vegetation and started flinging sand. By this time it was nearly midnight, and we followed Keilor and Vera back to the vehicles when their midnight-4am replacements showed up. It was a good turtle night!