Strength and time lag of relationships between human pressures and fish-based metrics used to assess ecological quality of estuarine systems

Fish-based multi-metric indices have been widely developed in ecological quality assessments of estuaries in the past few years, but the ability of these indices and their respective metrics to respond to human pressures may be quite different. Based on a group consensus approach eliciting information from multiple experts integrating published literature, this work evaluated the strength and time-lag of the response of eight fish-based indices (AFI, EFAI, ELFI, Z-EBI, TFCI, EBI, EFCI, IBI), and their respective metrics, in relation to several human pressures (chemical pollution, eutrophication, loss of habitat, water turbidity, habitat fragmentation, fishing mortalities, invasive species, water temperature changes and flow changes). Results pointed out that most of the metrics detect several human pressures, being difficult to identify a particular pressure effect and its source. The majority of the metrics analysed presented a weak relationship with pressures and/or respond in a long time period. The metrics responding to chemical pollution and loss of habitat were generally the ones with stronger relationships, but their responses were often in a long time period. Consequently, the fish-based indices analysed did not detect all the pressures with the same sensitivity in terms of strength and time lag. This clearly collides with the needs for water ecological quality assessments, management and rehabilitation of estuarine ecosystems, and highlighted the value of metrics, especially the ones that are specific of certain pressures.