The piscicultural state of the natural lakes of low altitude. Characteristic species and stand evaluation criteria

Abstract

The assessment of the fish community, as for the other biological indicators, is a prerequisite for the implementation of the European Water Framework Directive (EWFD). The eco-biological traits of life of the lacustrine fish species in combination with historical records and the literature validate results obtained from statistical analyses on a sample of French natural lakes (species abundance and water quality). In relation with the limnological characteristics, four fish assemblages have been identified, with their succession and relative position along an eutrophication gradient. Two assemblages with Salmonids are typical of stratified (deep) and well oxygenated lakes. An assemblage formed by the Pike, the Perch with the Rudd and the Tench is characteristic of both a more eutrophicated condition of the same lakes and shallow lakes with a belt of hydrophytes. The assemblage around the Pikeperch, with the Ruffe, the common Carp and the common Bream is formed by only two native species. Criteria are proposed to evaluate the quality of such fish assemblages. They need to be validated for their interest and ease of use. Thresholds have still to be defined (by expertise and inter-calibration) for the various grades of ecological status, as required for the implementation of the EWFD.