ROV observations in heavily impacted fishing grounds of the Catalan margin (NW Mediterranean)

Abstract

In the framework of the ABIDES (Assessment of Bottom-trawling Impacts in DEep-sea Sediments) Project, a focused ROV cruise targeting heavily impacted fishing grounds of the Catalan margin (NW Mediterranean) was conducted in September 2017. Trawling fleets on this region have been specialized on a monospecific fishery targeting the blue and red deep-sea shrimp species (Aristeus antennatus), which is currently practiced at depths around 600-900 m. Vessel monitoring system (VMS) and automated information system (AIS) geographical information indicate that this bathymetric range is currently subjected to the greater fishing effort of the margin and that a sharp boundary between un-trawled and heavily trawled seafloor exists. We used replicate and stratified ROV video transect surveys aiming to cross this boundary repeatedly, characterizing the morphological and biological changes caused by intensive trawling activities. Notorious morphological changes caused by the contact of the trawling gear over the seafloor could be directly visualized. The seabed generally appeared as a ploughed field caused by the passage of the otter boards during successive fishing hauls of the trawling fleet that operates on each fishing ground. Push-cores were collected on un-trawled and trawled sites in order to characterize the changes on the surface sediment properties, and the further analysis of the video footage will be used to assess the impact on the benthic community structure