Fishing effects on diversity, size and community structure of the benthic invertebrate and fish megafauna on the Bay of Biscay coast of France

Abstract

Within the framework of the 'dynamic equilibrium model', we tested the hypothesis that fishing causes major disturbance to benthic communities on deeper bottoms of the continental shelf. Benthic megafauna on the Bay of Biscay coast of France was sampled on fishing grounds subject to various conditions of exploitation. Samples were taken at around 100 m depth to avoid strong natural disturbances. Species diversity and the largest body mass class of invertebrates were smaller in strongly exploited areas than in moderately exploited ones. Biomass size spectra in strongly exploited areas were characterised by a comparatively large biomass of small invertebrates, hence the K-dom- inance curve of abundance was either above the biomass curve, or the curves intersected. In moder- ately exploited areas, the K-dominance biomass curves were above the abundance curves; the dom- inant species were a commercial species and a benthic species sensitive to the physical effects of the fishing gears. In the heavily exploited areas, the dominant species were opportunistic carnivorous species of minor or no commercial interest. There were no dominant fish species in the most strongly exploited areas, while 2 fish species were found in the moderately exploited areas. No fragile species were found in the most exploited areas, whereas 6 fragile species were found in the moderately exploited ones. It is concluded that the differences between the most strongly exploited and the moderately exploited areas were consistent with the hypothesis.