Defining reference parameters of NISECI ecological index sub-metrics for freshwater fish community monitoring in the Emilia region

NISECI, The New Italian Index of the Ecological Status of Fish Communities, is the biological quality indicator to assess Italian fish communities according to the Water Framework Directive 2000/60/EC. Although NISECI is an improvement of the previous ISECI index, it also requires refinement regarding its reference conditions. The present study, focused on the Emilia area, applied and further tested the refinement procedure previously developed for the Romagna sub-region, with the dual aim of refining NISECI reference conditions at the regional scale and evaluating the transferability of the methodological framework to a different geographical context. The dataset consisted of 109 ichthyological samplings, distributed in 91 collection sites among 39 watercourses, collected from 1996 to 2022. Ichthyological data was classified into six homogeneous ecological zones, belonging to the basins of the tributaries of the Po River, and threshold values for the species-specific abundance of the fish species were obtained. These results redefined the reference conditions for NISECI sub-metric x 1 (presence/absence of native species), and x 2, b (population size), to apply NISECI in the selected geographical context. Twenty sites were selected to apply the new reference conditions. On these test sites, the refined NISECI was calculated and compared with the NISECI in its general version. The analytical validity of the refined index was ascertained by subjecting the test stations to three blind experts who returned their judgement on the ecological status of fish communities. The refined NISECI showed greater agreement with expert-based assessments compared to the general version. • NISECI sub-metrics were regionally refined in the Emilia area. • Refinement improved ecological status classification at test sites. • Six ecological zones replaced the three-zone NISECI framework. • The method shows transferability potential, pending further testing.