The reclaimed marshes of the French Atlantic coast have benefited from high eel abundance due to their location relative to incoming fluxes of glass-eels. This fact was at the bases of the various strategies of gathering similar to those observed in the Italian valli and Spanish esteros. The decrease in species abundance in those littoral wetlands since several decades leads to a wish of monitoring with adapted indicators and to implement estimation strategy for the population in varied marshes zones (reasoned exploitation). With this view, the sampling strategy optimisation in those places had to be researched. The result obtained notably on one site of the Breton marsh (marsh of Bourgneuf) show, in spite of the proximity of the sea, a high heterogeneity in the size class distribution in available habitat. This observation suggests the need to take into account behavioural aspects when following survey procedures and/or estimations (station choice, period and fishing tackle). Keeping track of eels with individual marks in a test zone has begun in order to precise those aspects less analysed for the moment in various continental places colonised by eels.