Selecting fish-based metrics responding to human pressures in French natural lakes and reservoirs: towards the development of a fish-based index (FBI) for French lakes

Fish-based indices of biotic integrity have been developed for many lotic systems but remain scarce for lakes. The goal of this study was to assess the responses of lentic fish assemblages to anthropogenic pressures when environmental variability was controlled for and to compare them between French natural lakes and reservoirs. Environmental features, catchment-scale anthropogenic descriptors and fish data were collected from 30 natural lakes and 59 reservoirs throughout France. Functional fish metrics were regressed against both anthropogenic variables and the natural environmental conditions. Our results show that fish assemblages are appropriate ecological indicators for both natural and artificial lakes. They underline the necessity to control for the environment when developing indices at broad geographical scales. The relevant metrics differ between natural lakes and reservoirs, which challenges the attempts to use natural systems as references to assess the ecological potential of artificial ones.