Larval history of glass eels, Anguilla anguilla, (Linne, 1758) in migration in coastal and estuarine areas (Adour, Bay of Biscay) as revealed by otolith structure.

The embryonic past of glass eels vas studied from the interpretation of mic rostructures registered on otoliths. The aim of this work is to put in evid ence possible seasonal modifications of the growth of otoliths so that diff erences between otoliths of glass eels caught off marine and estuarine envi ronment. So during the season 1999-2000, from November till March, otolith sampling was realised in the Southwestern part of France, in an estuarine a nd coastal zone. We observed a spatial and temporal evolution of proportion s of the three various types of otoliths taken into account. Glass eels sam pled at sea sometimes have a mark on their otoliths indicating the transiti on in the estuary, especially at the end of the fishing season. Measures of growth marks of otoliths showed that there were no seasonal differences du ring phases of the transoceanic migration and the crossing of the continent al shelf. The radius of otoliths of glass eels sampled at sea was significa ntly smaller than those sampled in estuary. These results translated homoge neous environmental modifications met by the various larvae groups during t he oceanic crossing and during the principal migration season as well as a turn over of these groups during the transition between marine and continen tal environment. (C) 2001 Academie des sciences/Editions scientifiques et m edicales Elsevier SAS.