Standardized lake fish community assessment using modified multi-mesh gillnets to minimize fish mortality

Abstract

Systems for assessing the ecological status of lakes with respect to fish population are normally based on catches using conventional European Committee for Standardization (CEN) gill nets. A modified gillnet (MOD) design with less small-mesh and more large-mesh panel area , developed to reduce catch and mortality while retaining the information needed for ecological assessment, was previously demonstrated in two large, deep peri-alpine lakes. The present work investigated its utility in smaller water bodies including two natural lakes, two reservoirs, and six excavated lakes, from 2018 through 2022. Compared to CEN nets, MOD nets reduced fish catch/mortality by 42.0 ± 15.94% (range 4.0%–59.4%). Sampling with MOD nets yielded results comparable to CEN nets with respect to number of species detected, community composition, and catch per unit of net area consistently across lakes and sampled years. The net types did not differ with regard to the length-specific catchability of key species. The MOD nets showed a higher rate of species accumulation in the artificial lakes. With respect to Water Framework Directive metrics, which is likely the most important application for ecological fish surveys in Europe, the net types yielded similar data, confirming the novel MOD net as an ecologically beneficial and economical alternative in fish community monitoring.