ETD

• dab
• diet
• infauna
• plaice
• prey choice
• trawl fishery

Bottom trawl fishing has widespread impacts on benthic communities and habitats. In this study we investigated the effects of changes in the infaunal community caused by an otter trawl fishery on the diet of two benthivorous flatfish species, Limanda limanda (dab) and Pleuronectes platessa (plaice). Samples of fish and infauna were collected from fifteen stations in an active fishing ground of Nephrops norvegicus in the NE Irish Sea, which is subject to a steep gradient of trawling frequency. Within the study area, otter trawling had a significant, negative effect on abundance, biomass and species richness of the infaunal community. The brittle star Amphiura filiformis and the phoronide species Phoronis sp., both vulnerable to the trawling, dominated the community at low levels of disturbance. Significant effects of the trawling frequency on fish diet were detected for plaice, but not for dab. Moving from low to high levels of disturbance, a significant increase in abundance of the infaunal prey species not affected by trawling in the stomach contents of plaice was detected. For dab, decreased abundance of the brittle star A. filiformis seemed to increase the potential to feed at intermediate levels of disturbance. Bottom trawls may therefore also indirectly affect the benthic communities, influencing the diet of demersal fish species. The results presented here are an important step toward understanding the global ecosystem effects of bottom trawling.