| Summary: | The Water Framework Directive (WFD) aims at achieving good ecological status (GES) for surface water bodies throughout Europe, by 2015. Consequently European countries are currently developing and intercalibrating methods based on biological, hydromorphological and physico-chemical quality elements for the assessment of their transitional waters, including fishes. The present work focuses on the response of fish indicators and indices to anthropogenic pressures and natural factors. For doing that, datasets from the Basque and Portuguese estuaries, in the North East Atlantic, have been used. Hence, biological data from fish (and in some cases, crustaceans), together with different types of pressure (population, industry, ports, dredging, global pressures, pollution, channeling, etc.) and hydromorphological data (flow, estuary volume, depth, intertidal surface, residence time, etc.) have been analyzed. Together with fish assemblages composition and individual metrics (richness, trophic composition, etc.), two fish indices (Basque AFI and Portuguese EFAI) have been investigated. Additionally, the response of five fish indices (AFI, EFAI, ELFI, TFCI, Z-EBI) were tested on a common dataset, within Portuguese estuaries, to check the time lag in the metrics’ response to different human pressures and the variability in the strength of responses to those pressures. This work also focuses on the sensitivity analysis of two European fish-based indices (French ELFI and British TFCI) to changes in their respective metric scores through their observed dynamic range. Sensitivity analyses were run simulating different scenarios of metric score changes, taking into consideration the relationship between metrics. This allowed the metrics with stronger influence in the index score and the resulting water body classification to be highlighted. Importantly, the identification of the most influential metrics could help to guide management efforts in terms of achieving GES by 2015. In general, the fish metrics and indices tested ...
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