Is Restocking an Efficient Measure to Sustain Eel Populations? Three Years of Glass Eels Restocking in France

As part of the French Eel Management plan, extensive glass eel restocking was operated since 2010 in French rivers from the Belgium to the Spanish borders. From 34 km to 960 kgs of glass eels were restocked during 29 different operations, totalling 6900 kgs of glass eels. A total of 18 catchments were restocked including lakes, marshes, small and large rivers, according to a national methodology aiming to select most suitable habitats (reduced mortality, low density, good environmental quality). In sites without natural recruitment, glass eels were not marked. When natural recruitment occurred, between 7% and 70% of them were marked using alizarine red. Mortalilty of glass eels was analysed in aquaria and in the field in order to test effects of marking. Electrofishing surveys were then operated in each site, 6 months, 12 months and 3 years after restocking. Eels were sampled to search for marks and cohort analysis were undertaken to analyse the effects of restocking of the eel populations. Here we present the first analysis of the restocking surveys in order to assess the effect of restocking as a measure to enhance the European eel population. Methodological and management perspectives will be discussed.