Estimation of the Resident European Eel Stock in the Lesse River, Sub-Basin of the Belgian River Meuse, and Evaluation of the Physiological and Immunological State of Fish Using Non Invasive Methods

Since the beginning of the 1980s, scientists have observed a huge decline of the European eel population. The species is now considered outside safe biological limits for population survival. In response to its precarious state, the European Commission has taken protection measures in order to restore the eel stock. In order to provide effective management plans, knowledge of the status of stocks present in watersheds is necessary. As the information is missing in Wallonia, the main objective of this European project is to estimate the resident stock of eels in the Lesse river. The stock is estimated by the method of capture-recapture sampling and densities are calculated according to the Petersen method. The eels captured are individually tagged with passive integrated transponders. Morphometric measurements (total length, weight, length of pectoral fins and eye diameters) allowed us to determine the stages of eels (according to Durif et al., 2003). Blood samplings are also made on each fish in order to evaluate the physiological and immunological state of the stock. For that, thyroid, growth and gonadotropic hormones are measured as well as immunological parameters (lysozyme, immunoglobulins and complement). Results will give us some indications on the health state of eels.