Chronic ®shing disturbance has changed shelf sea benthic community structure

1. Bottom ®shing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively ®shed areas. Nevertheless, to date it has been dicult to attribute habitat and benthic community changes to ®shing e€ort at a spatial scale that is truly representative of commercial ®shing activities. 2. In this study we present convincing evidence that chronic bottom-®shing disturbance has caused signi®cant 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 exposed to either high or low levels of bottom-®shing disturbance over the past 10 years. We were able to validate the ®shing e€ort data in some areas using scars in the shells of a long-lived bivalve mollusc (Glycymeris glycymeris) which result from ®shing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest ®shing e€ort. 4. Multivariate analyses and the response of abundance/biomass curves indicated that chronic ®shing 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 degraded the topographic complexity of seabed habitats in areas of high ®shing e€ort. The communities within these areas currently may be in an alternative stable state.