Heterogeneity of the European eel distribution (Anguilla anguilla) observed by electric fishing in a reclaimed marsh of the French Atlantic coast (Marais breton).

European eels (Anguilla anguilla, L. 1758) are becoming scarce in most of t he inland waters. Monitoring programmes of eel abundance are planned in num erous areas especially in the reclaimed marshes (230,000 ha) of the French Atlantic coast. Well situated with regard to glass-eels arrivals, they repr esent about 20,000 km of narrow ditches (3-4 m) with variable characteristi cs (dredging, silting up). Between 1987 and 1998, in May, June and July, 20 4 stations were sampled by electric fishing in the north of the Marais bret on, in a freshwater marsh (3,000 ha) close to the sea. A first overview of data confirms the significant presence of eels in this marsh, but highlight s a high temporal and spatial variability of their distribution (individual s, size groups). Such observations will have to be taken into account in th e future monitoring programmes and in the analysis of results even if expla natory factors have not yet been identified. Moreover, inadequate managemen t of the main sluice-gates resulting in insufficient colonization by young stages is also revealed in this littoral marsh.