Fisheries Management and Ecology 1997, 4, 425–438 Presentation and first applications of a dynamic population model for brown trout, Salmo trutta L.: aid to river management C. SABATON Electricite ´ de France, Direction des Etudes et Recherches, De ´partement Environnement, Chatou, France L. SIEGLER Ecole Nationale Agronomique de Rennes, Zoologie, Rennes Cedex, France V. GOURAUD Electricite ´ de France, Direction des Etudes et Recherches, De ´partement Environnement, Chatou, France J.L. BAGLINIE ` RE Institut National de la Recherche Agronomique, Laboratoire d’Ecologie Aquatique, Rennes Cedex, France S. MANNE ´ Ecole Nationale Agronomique de Rennes, Zoologie, Rennes Cedex, France Abstract A mathematical model representing the long-term change in a trout population under different river management scenarios is presented. It describes the structure of a population broken down into age classes based on the Leslie matrix; if the population structure for any given month is known, the model should be able to estimate that of the following month. The passage from one month to the next takes into account various relevant factors: survival rate of individuals in the different age classes; fertility rate of females; linear and weighted growth rates; displacement linked to habitat fluctuations using weighted usable area (WUA) values. The model was applied to two French rivers. Regular monitoring of trout populations on the River Kernec enabled comparison of the response of the model with no displacement, with actual variations in fish stocks on the first river. In addition, the knowledge of WUA chronologies on the River Echez made it possible to carry out initial simulations of the response of a fish population to different river management scenarios at the second site. KEYWORDS: Leslie matrix, modelling, PHABSIM, population dynamics, Salmo trutta. Introduction Present development of multiple-use water management strategies requires, more than ever, tools to predict the long-term impact of modifications in the characteristics of a river on the Correspondence: Dr Catherine Sabaton, Electricite ´ de France, Direction des Etudes et Recherches, De ´partement Environnement, 6, quai Watier, 78400 Chatou, France (e-mail: catherine.sabaton@der.edfgdf.fr). © 1998 Blackwell Science Ltd 425