VARIATION OF THE OCEANIC LARVAL MIGRATION OF Anguilla anguilla (L.) GLASS EELS FROM A TWO YEAR STUDY IN THE VILAINE ESTUARY (FRANCE)

Abstract

Glass eels were sampled nearly monthly in 1990 and from September 1991 to December 1992 in the Vilaine estuary (Northern Bay of Biscay). Biometry and otolith examinations were carried out. In both years the immigration showed a continuous flow, with the same seasonal pattern. Length and weight showed similar trends, with some differences between seasonal mean values. The average total age of all the samples varied from 7 to 10 months. Although the leptocephalus phase appeared to be rather steady (160 to 210 days), the duration of transport of metamorphosing glass eels across the continental shelf varied from 50 to 70 days in 1990 and from 80 to 100 days in 1991-1992. In addition, the otolith structure was of various types as regards the end of the larval migration. This seasonal variation is supposed to affect the estuarine recruitment through the length of the starvation period.