Chronic fishing disturbance has changed shelf sea benthic community structure

1. Bottom fishing using towed nets and dredges is one of the most widesprea d sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has bee n difficult to attribute habitat and benthic community changes to fishing e ffort at a spatial scale that is truly representative of commercial fishing activities. 2. In this study we present convincing evidence that chronic bottom-fishing disturbance has caused significant and widespread changes in the structure of two distinct soft-sediment benthic assemblages and habitats. 3. Our study compared the benthic fauna found in areas that have been expos ed to either high or low levels of bottom-fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas u sing scars in the shells of a long-lived bivalve mollusc (Glycymeris glycym eris) which result from fishing disturbance. Shell scars occurred most freq uently in bivalves collected from the area of highest fishing effort. 4. Multivariate analyses and the response of abundance/biomass curves indic ated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller-bodied fauna. Removal of emergent fauna has thus degr aded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternat ive stable state.