Sampling of fish diversity in estuaries: strategy and representativeness in the context of the European Water Framework Directive

Abstract

The estuarine fish fauna is both diverse and heterogeneous. Its main ecological features make difficult the development of a monitoring program. A retrospective sampling of the trawling data collected by the Cemagref since 1994 allowed us to define the basis for a monitoring protocol of the estuarine fish species diversity consistent with the objectives of the new Water Framework Directive (WFD). A sampling effort between 20 and 30 trawl hauls twice a year, in autumn and spring, can be sufficient to correctly describe the species richness of the year. We recommend to adopt a strategy that would consist to sample 3 consecutives years every 3, 4 or 5 years.