Long Term Evolution of Silver European Eel Indicator of Abundance in the Loire Watershed (France) (1987-2013), a Unique Data Set for Europe

The Loire River is one of the largest rivers in Western Europe and the less impacted by big dams. A stownet silver eel fishery exists since the thirties and this fishery started cooperation with scientists, in the eighties, in order to contribute to research and to participate to eel management programs. These fisheries provided long term series on yields and daily CPUE of silver eel captures which now constitutes one of the most robust data set on silver eels in a large river system of Europe. These data were used to produce a silver eel abundance index. Calculations were conducted with pooled data of four representative fisheries, during 26 years combining daily efforts and catches from October to February. The analysis reveals a strong quality of the data and large interannual variations. Although yields and efforts are decreasing since the beginning of the period (1987), the trend of the index is stable till 2010. The very recent drop of this index is discussed because this situation of the Loire basin is inconsistent with the situation in Europe and the decrease of the other eel stages in the river Loire.