Effect of management measures on glass eel escapement

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The continuous and steady decline in glass eel (Anguilla anguilla, L.) recruitment and more generally in the eel stock has risen the ICES concern about the status of the eel stock. The European commission pointed out the need to develop management plans at the water district level and for all stages. We developed a Glass Eel Model to Assess Compliance (GEMAC) with eel recovery objectives. In this study we briefly describe this model already presented in working group on eel (ICES, 2005) and as part of the SLIME project. Then, we apply it on the two well documented Vilaine and Garonne basins, which have contrasted anthropogenic pressures. The model allows to assess the proportion of settled glass eels relative to unimpacted conditions (%S/R). A sensitivity analysis of the model is done showing that the assessment of %S/R is quite accurate. The %S/R is estimated to 0.19 for the Vilaine basin and to 0.78 for the Garonne basin reflecting a contrasted level of anthropogenic pressure. The %S/R is also estimated in a data poor context considering only administration data and no scientific survey and in this case the computation of the %S/R follows the precautionary approach by under-evaluating it (0.19 and 0.64 for Vilaine and Garonne basin). Finally 7 management scenarios that all halve the anthropogenic pressures are tested and we demonstrate that they are far for being equivalent and that the level of increase of %S/R depends upon the estuary. Although no model is needed to take immediate measures, we believe that our model could help in the future to build assessment and management tools along with the national management plans.