Alosa alosa is an anadroumus fish, which has almost disapeared from all river basins of northern Europe and Morocco due to environmental deterioration added to fishing activities. To avoid its disapearing from others watersheds, it is necessary to establish rapidly a management plan for the existing populations. The population of the Gironde-Garonne-Dordogne system has an important size ; there is a commercial fishery in the estuary and in the lower part of the Garonne and Dordogne river. The acquisition of knowledge on this watershed will allow us to realize a population dynamic model. Our aim is to obtain simulations results that enable us to define management rules well adapted for this species. The model would be a management tool. With this in vue, we have established a first population dynamic model ; it is a translation of the Alosa alosa life history in the Gironde-Garonne-Dordogne basin. The model consider separately males and females. Individuals are structured in age classes. The life history is modelized by a group of stochastic and determinist processes. The test values for the parameters are chosen among those found in the litterature when they exist, otherwise realistic values are used. This first model have made incorrect and incomplete data appear. The model's establishement is added to a return to field's work. Improvements will brought with the new field's data.