Green Sea Turtles
Early reports about the Ogasawara Islands from passing ships told of beaches carpeted with sea turtles. Although far fewer turtles inhabit the islands now than they did two centuries ago, a number of different species of sea turtle can still be found swimming in the waters around Ogasawara. Most of the turtles that come to Ogasawara are green sea turtles, but loggerhead and hawksbill sea turtles can also sometimes be spotted near the islands.
Green sea turtles can travel more than 2,500 kilometers in a single year. Turtles tagged in Ogasawara have been spotted in the waters near the Japanese mainland, the Izu Islands, Kyushu, Okinawa, and as far away as China and the South Seas. Yet for all their long-distance traveling, they always return to the same beaches to lay their eggs.
Ogasawara is the largest breeding ground in Japan for green sea turtles. The turtles come to the islands to mate in the spring, and mature turtles can be seen offshore beginning in March. Individual female sea turtles mate in cycles, coming to the island every two to four years, but it is unknown whether males follow a similar pattern or if they come every year. Female turtles will usually lay two to four clutches, each in a different location and ranging from 60 to 150 eggs. They lay their eggs between May and September, and the babies hatch and head for the sea between July and November.
Darkness and light are important factors for both the female turtles and the hatchlings. Before females approach the shore to lay their eggs, they raise their heads above the water to survey conditions on land and will not come ashore if they see lights or people. Even after landing, a female will return to the water without laying eggs if startled. After the eggs hatch, the baby turtles head toward the ocean, instinctively drawn to the bright reflection of the moon and stars on the water. However, artificial lighting like streetlights can cause baby turtles to head away from the ocean, exposing them to danger from predators, motor vehicles, and other threats.
Researchers and volunteers at the Ogasawara Marine Center are working to protect and document the turtles. In areas like Omura Beach, where city lights are likely to disorient hatchlings, the Center moves the eggs to a protected area at the marine center, where they can develop and hatch in safety. The baby turtles are then raised at the center for a year before being released into the wild. Because the one-year-old turtles are large enough to survive most attacks from predators, they are believed to be far more likely to survive to adulthood. This type of program is called a head-start program and has been used around the world to help boost sea turtle populations since the 1980s.
Visitors to the marine center can see and feed the baby turtles swimming in outdoor tanks. The center also has detailed information on the sea turtles’ ecology and their relationship with the people of Ogasawara.