Ecological continuity

Fish species belonging to the Clupeidae family (such as sardine and herring). The allis shad are among the anadromous species (i.e. which swim up rivers to spawn in the middle part of the rivers). As such, their populations have paid a heavy price to river development (dams without fish pass facilities, extraction of gravel changing the spawning, etc). Their presence is therefore a good indicator of the status of a river development. Two species of allis shad are present (and exploited) in French waters: the allis shad (Alosa Alosa) and twaite shad (Alosa fallax).

All living organisms (animals and plants including microorganisms) that occupy a given ecosystem. This group of living organisms is characterized by a specific composition and by interdependence phenomena. It occupies an area known as biotope and with the latter makes an ecosystem. A biocenosis changes over time (pioneer phase, intermediate phase and equilibrium phase).