Spawning behavior of Leatherback turtle at World Heritage of South Africa -an attempt of contribution for conservation of the endangered species-

Under the request from the authority of Ishmangaliso Wetland Park, world heritage of the South Africa, we cooperate to investigate the spawning behavior and to promote conservation of the leatherback turtle, Dermochelys coriacea, an endangered species of IA. To clarify their demand for spawning, environmental factors such as nest temperature and humidity will be monitored and process of hatching will be observed.

What have been clarified.

The leatherback turtle can be easily identified from other sea turtles by its unique feature, lacking of hard-shell, but with five ridges together with its extraordinary large size. Their ancestor parted from ancestor of the living other hard-shelled seven species, at late Cretaceous period, around 80 million years ago. And thus the leather back turtle may be regarded as a living fossil.
Size exceeding more than 2.5m, weighing about 1 ton, is the largest not only among the sea turtles but all the living reptiles. Together with its diving ability more than 1200 meter deep recorded off the coast of Cape Verde, and the ability migrating up to sub-boreal waters, are unique and miraculous feature of the animal.
Although their extraordinarily high ability of migration, they are grouped into seven sub-populations, viz East Pacific, West Pacific oceans of Pacific; North Indian Ocean of Indian Ocean, Northeast Atlantic, Northwest Atlantic, Southwest Atlantic, Southeast Atlantic oceans of Atlantic. Unfortunately, the species is listed as an endangered species. According to Carl Safina (2014) sub-populations of Pacific and Indian Oceans, are regarded as extinct in actual state. While the Atlantic sub-populations are regarded relatively healthy.
Especially, in South Africa, protection of the group started in early as 1963 and the number of nest were maintained around 300 per year. On the contrary, judging from the nesting activity, most sub-populations of the Pacific leatherback turtle are declining significantly.
In several thousands of nest were observed in early 70’s in Malaysian coast decreased less than few hundreds, and in Mexico, nests were counted as high as 10 thousands in early 80’s but was decreased few hundreds in recent years.

Why are they threatened for the extinction?

The main causes of the decline of the populations in the Pacific were regarded as the harvesting adult and egg collection for local subsistence, followed bycatch by gill-net, and by the destruction of spawning site such as deposition of artificial debris and logs on the beach become obstacles for nesting. Also lighting around nesting beach will result disorientation of hatchlings.
Plastic bags floating in the surface water will be mistaken as food organisms by adults.
Sex of hatchlings of leatherback turtles is regulated by temperature-dependent sex determination (TSD) like other sea turtles.
Higher incubation temperature (>30) produce female hatchlings and primary sex rations are often highly female-biased, and lower incubation temperature (<28) produce male hatchlings. Also higher temperature reduce emergence of hatchlings from their nest. Thus global warming also threatens the leatherback turtle. Thus, in the treatment of artificial incubation of leatherback turtle, temperature dependence in sex determination should be taken into consideration.

Sustain the living fossil in healthy level to the following generations.

We have to promote more active conservation of the leatherback turtle.
Our action plan is as follows: Observation on the spawning female at the coast of northern South Africa ie.
emergence from sea and search for nesting site, and return to sea.
Protection of spawning female
1.Collection of detailed information of survival of hatchlings such as incubation period, emergence time, air temperature, weather conditions, water temperature, lunar cycle, solar activity. These criteria will be compared in relation with activity of each hatchling and the survival rate. Conservation of hatchlings
2.Observation of hatchlings emergence from nest, orientation to the shore, and their offshore migration
Most observation above mentioned will be filmed and presented for the promotion of social awareness on the protection of the species.