In an article published in the PLOS One journal, Liège and French researchers have confirmed the existence of two important nutrition zones for leatherback turtles in the Atlantic: one in the highest latitudes of the North Atlantic Ocean and the other closer to the Equator along the African coasts. This is a factor that needs to be taken into account if we want to effectively protect this threatened species.

Leatherback turtles (Dermochelys coriacea) are fascinating sea reptiles in more ways than one. They are in effect the most imposing of all sea turtles, with a size reaching two metres and an average weight of four hundred kg. But there exist species which can touch 900kg. They are in addition the sole representatives of the Dermochelyidae family, a very ancient family because it cohabited with the dinosaurs, which disappeared around 65 million years ago. They moreover have a distinctive feature in that they possess no shell, but a pseudo carapace covered with skin, blue in colour and with white blotches. The way they reproduce is also very special: during the laying season, which can last four months, the females lay, at night, around every ten days or so, dozens of eggs on a beach to which they return at regular intervals throughout their lives. In between two laying periods they hardly leave the seashores. The eggs are placed at the bottom of nests which are dug into the sand, sometimes to depths of one metre. A very intriguing distinctive feature: the female places within the nests two kinds of egg: ‘normal’ fertile eggs that can reach weights of 80g (and are much sought after by the local population!) and smaller eggs, whose role we do not understand, which consist of just albumen and a shell. Finally, one last peculiarity: leatherback turtles feed uniquely on jellyfish. This is quite unbelievable if we remind ourselves that jellyfish are composed of 95% water! As for the rest, they are animals that we still don’t know much about. However, their species is threatened by human beings, their only predator once they have reached adult age: by accidental fishing intake, by the gathering of eggs on the beaches, the pollution of the water and the destruction of their egg laying sites. It is thus important to understand better the habits of these sea turtles if we want to protect them effectively.

The article (1) published in the PLOS One journal is the result of a collaboration between researchers at the University of Paris-Sud and the ULg. Its departure point is a doctorate thesis produced by Elodie Guirlet, then a doctoral student at Paris-Sud, but now carrying out post-doctoral studies at the University of Liège. She wanted to understand why eggs laid at the Awala Yalimapo beach in French Guyana had very low incubation rates even though it is one of the species’ major reproduction sites. She thus studied how the site functioned over three years in order to work out the factors that might affect embryo development. Amongst the factors considered were obviously the quality of the eggs, in other words notably their potential contamination by pollutants brought in by the sea. That required the study of contamination in the females, which itself depends on the food consumed. It was thus necessary to understand better the composition of the turtles’ diet and to pinpoint their feeding zones: the females do not really feed themselves during the laying period, so where do they subsequently go in order to eat? It was in order to work out the location of the feeding zones that Elodie Guilet leant on the help of the stable isotopes analysis method and that of Doctor Krishna Das, a Qualified FNRS researcher at the ULg’s Oceanology Laboratory. The Liège laboratory has in effect developed great expertise in this domain, acquired by the study of sea mammals (in this respect, read the results of a study carried out on Brazil’s tucuxi dolphins).

(1) Caut S, Guirlet E, Angulo E, Das K, Girondot M. 2008. Isotope analysis reveals foraging area dichotomy for Atlantic leatherback turtles. PLOS one 3:1-10 . Read the article