| Summary: | European eel (Anguilla anguilla L. 1758) is becoming scarce in most of the inland waters. Monitoring programmes of its abundance are planned in numerous areas especially in the reclaimed marshes (230,000 ha) of the French Atlantic coast. Well situated with regard to glass-eels arrivals, they represent about 20,000 km of narrow ditches (3-4 m) with variable characteristics (dredging, silting up). Between 1987 and 1998, 204 stations were sampled by electric fishing in the north of the Marais breton, in a freshwater marsh (3,000 ha) close to the sea. Moreover, 326 trapping operations were performed on the same area between 1994 and 1999. A first overview of data obtained by the two sampling methods confirms the significant presence of eel in this marsh, but highlights a high temporal and spatial variability of its distribution (individuals, size groups). Such observations will have to be taken into account in the future monitoring programmes (sampling by ditch category) and in the analysis of results (analysis by size groups). The analysis of the main explanatory factors is being performed. Moreover, inadequate management of the main sluice-gates resulting in insufficient colonization by young stages and the existence of a non mesh-size dependent selectivity of the traps are also revealed. L'anguille (Anguilla anguilla, L. 1758) semble se raréfier dans les eaux continentales européenne et la surveillance de son abondance est à l'ordre du jour dans de nombreuses zones censées l'abriter. Les marais atlantiques, pourtant bien situés vis-à-vis des arrivées de civelles, n'échappent pas à la règle. Leurs 230 000 ha sont sillonnés par 20 000 km de fossés dont les caractéristiques évoluent rapidement (curage, colmatage). L'analyse des données recueillies au cours de 204 opérations de pêche électrique dans le Marais breton entre 1987 et 1998, sur une zone homogène et proche de la mer, y révèle une colonisation non satisfaisante et une notable hétérogénéité de répartition des individus et des groupes de taille. Le même ...
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