Physical Impact of a Roller Clump on the Seabed

The envionmental impact of towed demersal gears on benthic communities has been of concern for the last couple of decades. Knowledge of the response of benthic habitats to impacts from fishing gears is of great importance to the ecosystem and the long-term management of sustainable fisheries. An on-going EU project, DEGREE (DEvelopment of Fishing Gears with Reduced Effects on the Environment), addresses this concern by focusing on quantifying the environmental and ecological impacts of fishing, developing fishing gears with reduced environmental impact, and assessing the socio-economic consequences of these changes. This paper focuses primarily on the modelling of the interaction between a gear component, the roller clump of a twin trawl, and the seabed in terms of penetration and disturbance of the seabed. A finite element model of this interface has been developed and is able to predict the penetration depth, sediment displacement and the pressure field associated with each gear component. In order to verify these predictions, sea trials have taken place over a range of sediment types at depths accessible to scientific divers using SCUBA diving techniques. This has allowed sampling of the seabed and profiling of the disturbed region for comparison with the model results. Good agreement is found.