What role can acoustic telemetry play in the assessment of the European eel stock? Preliminary results from ongoing research in the Mediterranean area

The European eel (Anguilla anguilla, L. 1758) is an iconic species, renowned for its unique life cycle. This catadromous species migrates between its spawning grounds in the Atlantic Ocean and its coastal or continental growth habitats across Europe and the Mediterranean. The species is of high ecological, cultural and historical importance, often being a top predator and an important resource exploited by fisheries. Over the years, attention has increasingly focused on its conservation, as several anthropogenic impacts, compounded by the effects of climate change, have led to a consistent decline in global eel stocks beginning in the early 1980s. Various frameworks and strategies have been implemented to promote recovery, attempting to reconcile the dual objectives of protecting the global eel stock and ensuring its sustainable exploitation. As a migratory and widely distributed species, the eel has been studied using tagging and telemetry techniques, which have proven invaluable for tracking migratory movements and routes. This study aims to evaluate the role of acoustic telemetry in enhancing the assessment of the European eel. Specifically, our research focuses on the Mediterranean portion of the eel stock, for which a recent assessment has been conducted. The selected pilot site is the Orbetello Lagoon in Italy, one of the largest basins in the western Mediterranean (2,700 ha), where eel fishing holds significant economic and cultural value. In this study, acoustic telemetry is used in combination with a mark-recapture survey to quantify the silver eel escapement from the lagoon. In addition, yellow eels were tagged to investigate the habitat use and spatial behavior across different seasons in the lagoon. Dynamic Brownian Bridge Movement Models (dBBMM) are used to calculate utilization distribution areas, considering spatial and temporal overlaps between different maturation stages and sexes, and to examine environmental factors and the distribution of seasonal fishing gears that may influence movement patterns in the study area. The results will help define management measures aimed at regulating fishing activities (spatially and temporally), refine population estimates and survival rates, and validate key assumptions and the accuracy of the existing eel stock assessment model used in the Mediterranean (ESAM 3.0).