Human Influence on Connectivity and Population Structure for River Fishes

Stream connectivity allows fishes access to the suite of habitats necessary for different life history stages and is, therefore, of conservation concern. Human activities alter natural connections over broader spatial extents and for longer periods than do the natural disturbances under which many species have evolved. Fishes that survive in dendritic river systems are especially threatened by anthropogenic factors that fragment habitats and create dispersal barriers because fish must move within the pathways of a river network. Impacts from hydropower dams, water withdrawals, and climate change prevent movement either physically (dams, low water conditions) or by altering habitat quality (high temperature barriers) or ecological interactions. Conversely, humans have also increased connections among waterways with inter-basin transfers, canalization, and the spread of nonindigenous species. In this symposium, we will (1) describe theoretical implications of alterations to connectivity for riverine species, (2) evaluate case studies for empirical effects of altered connectivity on population structure, and (3) consider the utility of alternative conservation approaches, focusing on trade-offs between benefits provided by re-establishing lost connectivity and risks associated with increased connectivity (e.g., nonindigenous species, pollutants, pathogens). This symposium will provide an excellent opportunity to bridge knowledge from a variety of subdisciplines to think critically about how humans influence the connections experienced by lotic fishes.