There are seven species of sea turtles: Green Turtles, Hawksbills, Olive Ridleys, Kemp’s Ridleys, Loggerheads, Flatbacks, and Leatherbacks. Leatherback turtles are the heaviest reptiles in the world, and the most widely distributed. They are found all over the Pacific, Atlantic and Indian Oceans from the tropics to the polar seas north of Scandinavia. They are not very closely related to other sea turtles. They lack hard shells, but have a stiff rubbery skin with seven knobby ridges running fore and aft. They are somewhere between warm blooded and cold blooded: they have body temperatures that are typically higher than their surroundings, but their body temperatures are not constant. They eat jellyfish, which are very low in nutrients. So they eat a lot: up to 200 pounds of jellyfish per turtle, per day. Jellyfish, in turn, eat commercially important fish so leatherbacks are important ecologically and even economically. Tourists also pay to see them when they come ashore.
Three of the seven species lay their eggs here on Playa Grande, our beach, but this project is really all about the Leatherbacks. In the late 20th century over a thousand leatherbacks nested here every year. It was the biggest leatherback nesting beach in the world, but almost all the eggs were being taken by organized egg harvesters. So far this season only twenty leatherbacks have shown up. They’ve had two decades of protection but it probably takes longer than two decades for a female leatherback turtle to reach sexual maturity, so all those baby turtles that were saved aren’t laying yet. (Former egg poachers are now on board as scientific collaborators, which is actually a common story in conservation biology.)
Part of the research going on here has to do with the optimal conditions for their nests. Nests can get too hot or too dry for the eggs to survive. Oxygen, humidity and bacteria in the sand all play a role in determining whether eggs will hatch or not. Because of bacteria, the scientists here clean all of the sand out of the hatchery annually to a depth of one meter and replace it with fresh sand. This is a ridiculous amount of work because the hatchery is as big as a small house lot. Hotter temperatures result in a higher ratio of females to males; lower temperatures have the opposite effect. Part of the research is just basic counting: number of nests, number of turtles, sizes of turtles, number of eggs, number of seasons per turtle, etc.
Once a turtle has hatched it is supposed to crawl down to the water’s edge, but bright lights from houses or towns will attract it and trick it into going in the wrong direction. Once it is in the water, it faces other threats: getting caught in a fishing net, or eating plastic. Ninety percent of leatherback turtles have pieces of plastic in their stomachs. A plastic bag floating in the water looks just like a jellyfish. Maybe we should ban disposable plastic. We have plenty of other good reasons to do that.
I can’t photograph the adult leatherbacks on the beach because it is dark and I can’t use a flash. But they are BIG!! Like boats. The web site of the Leatherback Trust has some good pictures. http://www.leatherback.org/