Summary1. 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.

When two commercially important marine species coexist in the same habitat, conflict may arise between different sectors of the fishing industry. A good example of this situation is when fishers using towed bottom‐fishing gear ( scallop dredges, beam trawls, and otter trawls) operate in the same areas in which fixed‐bottom gear ( crab pots) are deployed. We examined an area subject to a voluntary agreement between these two sectors of the fishing industry such that some areas are used exclusively by fixed‐gear fishers, some are shared seasonally by both sectors, and others are open to all methods of fishing all year. This agreement was enacted to resolve conflict between the two sectors of the industry. An additional possible benefit of this agreement is the protection of the seabed from towed bottom‐fishing gear, which is one of the greatest sources of anthropogenic disturbance of seabed habitats worldwide. Previous studies have demonstrated that complex emergent epifaunal communities are substantially altered by such activities. This habitat alteration in turn influences closely associated species, some of which may be of commercial importance. We undertook comparative surveys of the benthic habitat and communities within the area covered by the agreement and compared different areas subjected to a range of fishing disturbance regimes. Communities found within the areas closed to towed fishing gears were significantly different from those open to fishing either permanently or seasonally. Abundance‐biomass curves demonstrated that the communities within the closed areas were dominated by higher biomass and emergent fauna that increased habitat complexity. Areas fished by towed gear were dominated by smaller‐bodied fauna and scavenging taxa. Scallop dredges and beam trawls used on more stable habitats appear to have greater impacts on the environment than lighter otter trawls used in shallower water with less stable sediments. It would appear from our data that conflict management in the form of gear‐restriction measures has the added benefit of conserving habitats and benthic fauna sensitive to bottom‐fishing disturbance.

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