Flow-carried and active swimming migration of the glass eel (Anguilla anguilla) in the tidal area of a small estuary on the French Atlantic coast

Abstract

The study of the migration dynamics of glass eels (Anguilla anguilla) in a small estuary of the French Atlantic coast shows a two-stage sequence: (1) From November to March, the glass eels migrate upstream by using the tidal currents. The estuarine hydrology leads to a natural trapping of migrants in a typical area where the current speed slows down. The location of this zone depends on hydraulic conditions. The greater the tide is the farther upstream this area will be. This phenomenon leads to an increasing catchability of elvers. (2) From April onwards, when the water temperature reaches 10-12 °C, the glass eels swim actively upstream in the estuary. Then, fish concentrate just below the first dam. This behaviour shift shows the beginning of the colonization process of the whole riverine system. © 1986 Biologische Anstalt Helgoland.