Beyond turbine mortality. Holistic assessment of hydropower hazards for European fishes

With the increasing pressure humans exert on freshwater ecosystems arises the necessity for means of objective and systematic risk and impact assessments. In this thesis I developed two classification systems to evaluate risks of anthropogenic activities for European freshwater fish populations. The first is a sensitivity score that classifies a species' resistance to and the recovery from an anthropogenic stressor that would elevate the mortality of individuals in a population. It is based on the species-specific, unique suite of life history traits that mediate a species' resilience e.g., maximum adult size, maturation metrics and fecundity, but also the migration type of species i.e., diadromous, potamodromous and resident. Traits on a continuous scale were grouped using percentiles, binary variables like migration type were treated nominally, and aggregated into a single score ranging from 1.58 (lowest sensitivity, calculated for Sabanejewia balcanica) to 4.42 (highest sensitivity, for Petromyzon marinus), and for 168 species in total. Species with a high score are expected to resist a stressor for a longer time or resist a stressor of higher magnitude, respectively, whereas a lower score reflects a low individual resistance to a stressor but a rapid recovery after it is released. This score can be used for risk and impact evaluations of anthropogenic activities on individual species or for the response of a whole fish assemblage in various management activities like risk evaluations and impact assessments, but also restoration or conservation efforts. The second assessment system on which a particular focus is laid in this thesis is the European Fish Hazard Index EFHI, an assessment tool for hydropower risks for fishes. It uses conceptual, empirical, and modeled knowledge of the relative hazards of single hydropower components and offsets it with the susceptibility of the affected fish species. In the EFHI, the sensitivity score described above is one of the main factors determining specific susceptibility, along with body shape, swim bladder anatomy and conservation concern. The tool evaluates hazards related to the four hydropower components i) overall flow alterations, ii) entrainment and turbine mortality, iii) upstream fish passage and iv) downstream fish passage and calculates species- and components specific hazard scores that are ultimately aggregated into the final EFHI score ranging from 0 (no risk) to 1 (highest risk). It can be used to compare the relative risk of multiple existing or planned hydropower plants in the same or in different rivers, or to track improvements or deteriorations of a single hydropower plant over time, and it is applicable across the bio-geographic range of all 168 species for which a sensitivity score could be calculated.