Establishing demographic reference condition procedures for Italian river fish bioindicator

The Water Framework Directive 2000/60/EC (WFD) requires Member States of the European Union (EU) to use a pool of bioindicators, that is, Biological Quality Elements (BQEs), including fish species and each Member State shall, in fact, certify the compliance with the ecological quality goals of the WFD. The New Italian Index of the Ecological State of Fish Communities (NISECI) is the WFD-compliant index for the analysis of the fish species BQE in Italian river water bodies, both wadable and non-wadable, that are not (using WFD definitions) heavily modified or artificial. The WFD requires each index to relate the conditions found in the field to reference conditions corresponding to the absence of anthropogenic alterations or to minor anthropogenic alterations. The present study defines the logical basis on the model of refinement for the reference conditions of the metrics and submetrics of NISECI relating to the biological condition of indigenous and non-indigenous species. The model was tested on an empirical basis using data from 284 ichthyological samplings taken from river basins throughout Italy. In order to clean random errors and stochastic noise due to possible different sampling methods, the data was only collected using protocols that guarantee adequately homogeneous and reliable data of abundance (overall and by size). The developed approach provided comparable and homogeneous results throughout Italian watersheds; this allowed a standardized and robust refinement of the threshold values of the demographic parameters of NISECI. The procedure used, consistent with the spatially based reference condition and expert judgement reference condition approaches envisaged by the WFD, improves the analytical performance of the NISECI by increasing its power of resolution and is applicable in every Italian zoogeographic and ecological context.