Loggerhead turtles
of the cape verde Islands
Origin of the project
This project started when Oceanographers, Conservationists and Evolutionary Biologists decided to combine forces in order to set scientifically robust multidisciplinary research programs around the unifying theme of Loggerhead Sea Turtle.
The team is originally formed by Björn Fiedler (Chemical Oceanographer, PhD candidate IFM-GEOMAR), Prof. Torsten Kanzow (Physical Oceanographer, IFM-GEOMAR), Sonia Merino with her group ((Biologist, INDP, Cape Verde), and Victor Stiebens (Msc Biology, IFM-GEOMAR). Quickly the team has benefited from the addition of numerous amazing volunteers from Turtle Foundation. The work is supervised by Dr. Christophe Eizaguirre (Evolutionary Biologist- IFM-GEOMAR).
Scientific Background
Conservation of marine organisms is a true challenge as most remains to be discovered from the oceans which cover about 70 % of the world’s surface. Our project aimed at combining conservation needs of the Cape Verde Loggerhead Turtles (Caretta caretta) with oceanographic needs for a better understanding of the functioning of an important oceanic region.
Among the most striking features of Cape Verde are the powerful coastal upwellings. Upwellings are formed by water masses that result of the year-round trade winds that push surface waters away from the coast and draw cold, nutrient-rich waters from the ocean’s interior up to the surface. These rich waters meet the tropical sun to provide a perfect environment for phytoplankton - the basis of a productive food web that supports a rich biodiversity. Such highly productive oceanic systems, constraint as well by current ocean patterns are, however, poorly understood and climatic shifts could have evolutionary underestimated impacts.
Among the rich biodiversity, the Loggerhead turtle (Caretta caretta) represents the most symbolic species for Cape Verde. Only recently scientists discovered that this archipelago supports the third largest nesting population in the world. Like all Sea Turtles, the loggerhead turtles are highly endangered of extinction and listed on the Red List of the IUCN (International Union for Conservation of Nature). More than ever, this species is threatened by various direct menaces such as poaching and by-catch by large industrial fishery boats. Additionally more indirect menaces through habitat destruction due to coastal development, global warming, pollution and associated increased risks of disease are to be feared. Robust scientific monitoring and preservation of genetic diversity of the Loggerhead turtle has therefore become a crucial necessity to identify future directions of conservation efforts.
In this project, we give a particular attention to the genes of the Major Histocompatibility Complex (MHC). Those genes represent the most polymorphic genes in all jawed vertebrates. This means that within a population, at those loci, several genetic variants are presents and allow efficient immune response against constant parasite threats.
It is worth noting that there is growing evidence that MHC genotypes are a target of sexual selection in vertebrates. Sexual selection is defined as the competition between individuals of a given species for mating. Usually females (the limiting resource) exert mate choice and males compete for the females. MHC-based mate choice has been documented in numerous taxa, including rodents, birds, fish, primate and human and also reptiles (in Sand lizards). Whether MHC genes are important for turtle survival and reproduction is one of our quests.
Loggerhead turtles …
The loggerhead sea turtle is one of seven sea turtle species worldwide. Four families of sea turtles were present during the Cretaceous Period (<-75Myears), but nowadays only two families remain: the Dermochelyidae, represented solely by the leatherback turtle (Dermochelys coriacea) and the Cheloniidae, represented by six species including the loggerhead sea turtle. Although Cheloniid turtles are primarily distributed in tropical regions, the loggerhead displays a more temperate distribution.
The complex life cycle of the loggerhead sea turtle for long remained a mystery. New born turtles were seen hatching on beaches and entering the ocean, but only seen again as subadults or adults years later; in between were the “lost years”. Only the emergence of genetic tools and the improvement of biotelemetry allowed the successful characterization of the life cycle of some populations.
… in Cape Verde
The second largest rookery of the loggerhead sea turtle in the Atlantic is found in the Cape Verde Archipelago. Only the nesting aggregation in South Eastern Florida is larger. Despite the size of the Cape Verde population and alerts emitted by conservation organizations, it has only recently received attention from population geneticists and evolutionary biologists. The first genetic study, based on mitochondrial DNA, revealed significant differences between the Cape Verde and other Atlantic and Mediterranean rookeries, identifying it as an independent rookery (Monzón-Argüello et al. 2010, Conservation Genetics). The consequences of such findings are crucial since it signifies that no input of genetic material (gene flow) can be expected from other rookeries. Reduction of genetic diversity in the Cape Verde population would therefore tremendously increase risk of extinction.
The majority of the nesting happens on the islands of Boavista and Sal (around 90%). In S. Nicolau, S. Vicente, Santa Luzia and Maio Islands the number of females are already much lower and sporadic nests can be found on S. Antao and Fogo.
A special feature of Cape Verde turtles is that they are smaller than those from other populations in the Atlantic and fall into the size distribution of the Mediterranean population. Since female reproductive success is size dependent, it is not surprising that female loggerheads from Cape Verde lay smaller clutch sizes than their Atlantic counterparts.
What we do with the turtles
Our partners:
