Modelling Functional Fish Habitat Connectivity in Rivers: A Case Study of Brown Trout Spawning Habitat Restoration in Ile-De-France Streams

Throughout the world, decreased connectivity of fluvial habitats caused by anthropogenic river channel alterations such as culverts, weirs and dykes is pointed out as an important threat to the long term survival of many aquatic species. However, assessing functional habitat connectivity for a target species and life stage can pose a challenge to wildlife managers. In this study, we suggest a method to quantify hydrological distances (i.e. along the river) and biological distances (i.e. relative distances weighted by costs and risks experienced by a particular fish) between river habitat patches using the freeware Anaqualand 2.0. Through a case study in an Ile-de-France stream, we measured and modelled brown trout (Salmo trutta) habitat connectivity and probabilities of reaching spawning sites before and after a scenario of removing mill weirs and other obstacles along the channel planned in an ongoing restoration plan. Our results present quantitative estimates of rates of increase of availability of spawning sites and carrying capacity. Along with a few other applications, this case study illustrates the management functionality of the method in evaluating the connectivity improvement or deterioration following the construction of roads and other infrastructures.