Phenology and environmental drivers of glass eel entrance in a Mediterranean lagoon

Abstract

The European eel, Anguilla anguilla, is an emblematic facultative catadromous species that spawns in the Sargasso Sea and grow in continental waters of Europe and North Africa. In most of its growing habitats its population has dropped since 1980. Although Mediterranean lagoons represent particularly important habitats for eel, knowledge of eel ecology in lagoons is not as developed as it is in rivers. Particularly, data on the phenology, drivers and biometrics characteristics of glass eel entering lagoons are scarce. To address this lack of data, the abundance, pigmentation stage, size, and weight of glass eel entering the Bages-Sigean lagoon (western French Mediterranean) were monitored during 647 d from December 2018 to April 2021 using passive floating traps. Simultaneously, different environmental drivers were measured (flow velocity, temperature, rainfalls…). The highest abundances of glass eels were observed between mid-November and mid-March especially when the discharge of the main tributary of the lagoon was higher than its base flow. The glass eels captured during the peak of entrance were less pigmented, longer, and bigger than during other months. This work enabled us to identify periods when anthropogenic activities should be limited to decrease human-based impact on glass eel in similar habitats.