COS 82-8
The role of Mediterranean lagoons in the European eel (Anguilla anguilla) stock recovery process
The European eel (Anguilla anguilla L., 1758) is facing a dramatic decline in most of its distributional range and the species is now considered critically endangered according to the IUCN Red list. In 2007 the European Commission issued a Regulation (EU 1100/2007) for eel recovery and the sustainable use of eel stocks. Accordingly, management measures need to be implemented so as to guarantee, for each water basin, the downstream migration of at least 40% of silver eel biomass with respect to the historical baseline. A crucial step of the EU eel management plans is thus to estimate spawner escapement under current and pristine conditions. Although in central and northern Europe the estimation of eel baselines has received considerable study, very little is known about the eel productivity of Mediterranean coastal (MC) lagoons under historical and present conditions. These data are critical to effective management as coastal lagoons are characterized by very high biological productivity and can sustain eel densities substantially higher than rivers and lakes.
Results/Conclusions
We performed a preliminary stock assessment of the European eel in MC lagoons and estimated pristine and current escapement. Through an extensive review of both peer-reviewed and grey literature spanning a period between 1950 and 2012, we collected yield, climatic, geographical and other environmental and fishery data for over eighty MC lagoons corresponding to roughly 75% of the overall lagoon area in the Mediterranean. Our analysis showed that eel catch declined by 80% over the entire distributional range, while total catch across all fisheries including species other than eel also declined but less sharply. We used linear mixed-effect models to determine that variability in productivity per hectare was partially explained by latitude, longitude, lagoon area, and salinity type in addition to the temporal trend. Using an age-structured model to simulate eel population dynamics, we estimated that current escapement is <3,000 metric tons per year and only 10% of the estimated escapement under pristine conditions. Our analysis showed that the MC lagoons contribute a small but significant fraction of total spawning stock, and effective restoration of the Mediterranean sub-population will substantially contribute to the recovery of the overall Anguilla population.