Research Projects

Common soles in the Gulf of Lyon

The Gulf of Lyon is one of the most productive regions of the Mediterranean Sea, and the origin of more than 90% of French Mediterranean fishery landings. Numerous species of cetaceans such as fin whales and pilot whales are found in the rich feeding grounds of the gulf. Overfishing, pollutants, and climate change are increasingly putting this important ecosystem at risk.

The goal of the project SOLEAMED is to elucidate the role of the Rhône river – since the damming of the Nile River the biggest river flowing into the Mediterranean – for the Gulf of Lyon's ecosystem. I am particularly interested in the role of particulate organic material (POM) carried by the Rhône in the coastal marine foodwebs, but also, to what extent pollutants (e.g., PCBs, mercury, cadmium) coming from the Rhône accumulate in marine species. The model organism that I am using for this study is the common sole (Solea solea), which is one of the most important commercial species in the Gulf.

Specific questions that I am trying to answer include: how important are effects of Rhône carried material for the growth of the common sole with increasing distance from the river mouth, and, how strongly does this influence vary over time (in particular after drought periods in which the Rhône discharge is small). Also: does the pollutant load of the sole decrease with increasing distance from the Rhône mouth, as would be expected if the Rhône was the main source of pollution?

To answer these questions, I have collected common sole specimens along a transect from Nice to Port Vendres (close to the French-Spanish border) using the scientific vessel “Europe” of the French institute IFREMER, as well as through purchase from traditional, locally operating fishermen. On these samples, I am conducting stable isotope analysis, which will allow me to determine the origin of carbon and nitrogen (terrestrial versus marine) in each specimen. Furthermore, I will determine concentrations of PCBs and heavy metals in muscle tissue of the sole using gas chromatography and atomic fluorescence spectroscopy.

SOLEAMED will thus lead to increased understanding of the coupling of terrestrial and coastal ecosystems, for good (source of nutrition) and for bad (source of pollutants). This is particularly important in the light of climate change (with decreasing precipitation and consequently river discharge in Southern Europe) and alteration of rivers, e.g., through the construction of dams or channels. In fishery management, better understanding of population fluctuations arising from this project has the potential to improve the determination of sustainable catch levels. Finally, even though the project does not directly focus on cetacean biology, it has the potential to indirectly contribute to cetacean conservation in two ways: first of all, PCBs, mercury, and other pollutants represent a serious danger to the health of cetaceans, in particular due to their position at the top of marine foodchains. The project will lead to better understanding of the distribution and sources of pollutants in the marine setting, which may assist in strategies to counter threats from increasing pollution to marine life. Secondly, with coastal regions worldwide being degraded at an increasing pace, important habitat for many cetacean species is at risk. SOLEAMED has the potential to provide information that will assist resource managers and conservation agencies in protecting natural resources in the future.