Learn about sea turtles in Okinawa – Okinawa Natural Monument Talk Series
On October 22, 2016, as part of a series of talks related to the natural monuments of Okinawa (沖縄の天然記念物シーリズ講演), Dr. Kawazu from the Churaumi Research Center gave a presentation about sea turtles in Okinawa. Specifically, he talked about sea turtle nesting in Japan, the six species of sea turtles that are found in Okinawa and their distribution, ecology and major threats they are facing.
There are six specie that has been seen in Okinawa (Loggerhead, Green, Hawksbill, Olive Ridley, Black and Leatherback), three of which actually nest here (Loggerhead, Green, Hawksbill). This past April (2016), a leatherback sea turtle was found at the Yomitan port, but it was already in a weakened state and died shortly after. In Japan, Yakushima ranks number one in terms of number of nests, followed by Miyazaki, Okinawa and Omaezaki.
It takes about two months before sea turtle eggs hatch. When the developing embryo is about one week old, it is only about 3mm and is still within the yolk, thus it is the most vulnerable to movement as it may drown in the yolk. When turtle researchers want to relocate the eggs for any reason, they should be aware of the timing.
There are five major threats to sea turtles that were outlined in the talk:
1. Coastal armoring causes decline in nesting spots: Coastal armoring structures such as sea walls on or adjacent to nesting beaches can cause turtles to nest in less-than-optimal nesting areas lower on the beach where their nests are more likely to by covered with water. Those turtles that do emerge in front of seawalls often return to the water without nesting, known as a false crawl.
2. Light pollution on beaches: can cause hatchlings to become disoriented and wander inland.
3. If hatchlings are released into the water after their swimming frenzy period: hatchlings can travel as fast as 60 meters per minute once they hit the ocean’s currents that helped transport them. Their speedy departure is known as a frenzy swimming and helps them escape numerous coastal predators. It lasts for about 24 hours.
4. Marine debris: Given the ubiquity of trash in the ocean, sea turtles often ingest them. Though often sea turtles are able to naturally get rid of trash in their system, when there is too much or when plastic bags gets entangled with their intestines or when trash pierces through their intestines it can result in death.
5. Fishery by-catch: Turtles often get caught in fishing gear and will often die from drowning by not being able to move or surface for air.
Out of the above listed threats, in Okinawa as well as Japan the most impactful are coastal armoring and fishery by-catch. In Okinawa, 50-60 dead turtles are found each year, most of which are due to entanglement with fishing gear.