Influence of sampling effort on fish-based assessment of estuarine ecological quality
Influence de l'effort d'échantillonnage sur l'évaluation basée sur les poissons de l'état écologique des estuaires
Résumé
Multimetric fish-based indices have increasingly been gaining importance in Europe, as the Water Framework Directive requires fish fauna, and particularly its composition and abundance, to be taken into account in the assessment of the ecological quality of continental surface waters, including transitional waters. These indices are composed of several metrics, mostly related with structural and functional characteristics of fish communities, such as species richness, the role of nursery areas, trophic web structure and the occurrence of sensitive species. Therefore, ecological quality assessments should ensure that these structural and functional characteristics of fish communities were covered by the sampling methods used. In the present work, the influence of sampling effort on the several metrics of the Estuarine Fish Assessment Index (EFAI) was studied. Using the bootstrapping' computer-based method, different numbers and combinations of samples were tested to evaluate the variation of the values obtained for each metric as well as the variation of the ecological quality ratio and status obtained. The study of the effect of sampling effort on multimetric fish-based indices is of great importance, to ensure that these indices actually reflect the ecological quality of estuaries.