Analysis of distribution patterns of yellow European eels in the Loire catchment using logistic models based on presence-absence of different size-classes

We used logistic models to analyse the longitudinal distribution patterns of yellow European eels in the Loire catchment (France). Our models for predicting the presence of yellow eels supported contrasting spatial patterns according to the size of individuals and catchments. The smallest eels (mainly <150 mm and secondly 150-300 mm) were confined to downstream areas, but rapidly colonised upstream reaches. By contrast, larger eels were distributed further inland but tended to become more sedentary. In addition, a higher density of barriers to migration in the Maine catchment (a large catchment within the Loire catchment) probably delayed the upstream colonisation compared with the rest of the Loire catchment. These results suggest that logistic models may be a useful and efficient tool: (1) for the assessment of eel status and trends in freshwater systems; and (2) for the assessment of the consequences of local perturbations or conversely improvement of colonisation.