Electrofishing versus gillnet sampling for the assessment of fish assemblages in large rivers

摘要

During three consecutive years, two fishing techniques were used to sample fish assemblages in a large river (River Meuse, Belgium). In order to sample both pelagic and benthic species, electrofishing was used along the river banks while gillnet leadlines were placed on the bottom of the main channel. Electrofishing sampled more species (up to 22 species) but principally small individuals (young of the year or small-size species), while gillnet sampled fewer species (up to 16 species), but larger individuals. Capture variability of species richness was lower with electrofishing (CV = 16.6 %). However, gillnet sampled some species (e. g., Abramis brama) better than electrofishing. In order to evaluate the influence of fishing gear on the proportion of species belonging to the different ecological guilds, values of some biological parameters (number of native species, number of tolerant species, etc.) were calculated on the electrofishing and gillnet data. Gillnets caught principally tolerant individuals (i. e. fish belonging to species that are classified as tolerant to water, habitat and chemical degradation) (88 %), but fewer "indicator species" (i. e. species that are indicators of good ecological quality). Such differences in guilds collected by the different gears indicate that consistent methods are needed to make assessments.