Procedures for evaluating and prioritising the removal of fish passage barriers: a synthesis

Techniques for assessing the impact of structural barriers on fish passage and for prioritising restoration actions are reviewed. Current survey methodologies are biased towards specific structures, primarily culverts and economically significant fish. Assessment criteria are often based on swimming capabilities of upstream migrating adult salmonids, while ignoring other life‐stages, non‐salmonid species, downstream migration and behaviour. The development of comprehensive and centrally owned geospatial inventories of barriers is essential. The collection, maintenance and dissemination of pertinent structural and environmental data can be technically, logistically and financially challenging. Standardised procedures are needed to rapidly and cost‐effectively survey large numbers of barriers over wide geographic areas. The prioritisation of barrier repair and removal projects is most often based on simple cost‐benefit analysis, whereby individual barriers are scored based on a set of assessment criteria and then ranked in order of priority. The benefits of using scoring‐and‐ranking systems, however, are unacceptably low because they consider barriers independently, thereby ignoring the cumulative, non‐additive impacts produced by multiple, spatially interconnected structures. Optimisation modelling offers a more robust approach for efficiently prioritising decision making in river restoration planning, allowing decision makers to account for key uncertainties and effectively balance multiple, possibly competing, environmental and socioeconomic goals and constraints.