Modelling functional fish habitat connectivity in rivers: A case study for prioritizing restoration actions targeting brown trout

Throughout the world, decreased connectivity of fluvial habitats caused by artificial river channel alterations such as culverts, weirs and dykes is seen as an important threat to the long-term survival of many aquatic species. In addition to assessing habitat quality and abundance, wildlife managers are becoming increasingly aware of the importance of taking into account habitat connectivity when setting priorities for restoration. In this paper, a new approach of spatial analysis adapted to rivers and streams is proposed for modelling 2D functional habitat connectivity, integrating distance, costs and risk of travelling between habitat patches (e.g. daily use, spawning, refuge) for particular fish species, size classes and life stages. This approach was applied to a case study in which brown trout (Salmo trutta) habitat accessibility was examined and compared under various scenarios of stream restoration in a highly fragmented stream in Ile-de-France. Probabilities of reaching spawning habitats were estimated from a trout-populated area located downstream of the barriers and from potential daily-use habitat patches across the stream segment. The approach successfully helped prioritize restoration actions by identifying options that yield the greatest increase in accessible spawning habitat areas and connectivity between spawning habitat and daily-use habitat patches. This case study illustrates the practical use of the approach and the software in the context of river habitat management.