Session C1: Assessing Longitudinal Connectivity Affected by Cross-Sectional Barriers in a Riverine Bidirectional Network

Abstract: Disruption of longitudinal connectivity is a main problem in most of the world rivers. Spain, as a country with one of highest rates of cross-sectional obstacles per river, needs a strategy to restore longitudinal connectivity in riverscapes. Graph theory based approaches have proven as a suitable tool to measure the connectivity in the landscape. Unlike terrestrial habitats, where it has been profusely used, riverine systems still remain scarcely studied under this focus. There is a need to adapt the currently available knowledge on terrestrial habitat connectivity assessment to the management of river networks. In our study the broadly used Probability of Connectivity Index has been used to assess the global connectivity loss due to artificial obstacles (dams and weirs) in two medium sized river basins networks in Central Spain (Cega and Pirón). However, unlike previous studies, this time both differential downstream and upstream passability (directional connectivity) has been accounted through a purposefully adapted version of the Conefor software package. Passability has been quantified for every obstacle by means of an index that takes into account the requirements of every fish species in the community. This procedure ranks all the obstacles in the river network according to their individual contribution to the global loss of connectivity (upstream and downstream). It is therefore a tool that provides river basin management plans (RBMP) knowledge on the expected global benefits of the removal of each obstacle