A density dependent model describing Salmo trutta population dynamics in an arborescent river network. Effects of dams and channelling

Our aim is to model the Salmo trutta population dynamics (th ree age-classe s) in an arborescent river network (four levels, 15 patches), by considerin g both migrations (fast time scale) and demography (slow time scale). We st udy how the environmental management can influence the global population dy namics. We present a general model coupling both a linear discrete model fo r constant migrations and a non-linear density-dependent Leslie model for t he demography, with (15 x 3) difference equations (15 patches, three age-cl asses). The variable aggregation method applied to discrete time models all ows us to aggregate the previous model into a new one with only three equat ions. We assume fecundity and survival gradients with respect to the river network levels. The Salmo trutta whole population tends towards an equilibr ium state depending on the environmental structure, and we show that dams h ave a stronger influence than channelling on this equilibrium. ((C) Academi e des sciences / Elsevier, Paris.).