Temporal aggregation of bottom trawling and its implication for the impact on the benthic ecosystem

Understanding trawling impacts on the benthic ecosystem depends to a large extent on the ability to estimate trawling activity at the appropriate scale. Several studies have assessed trawling at fine spatial scales yearly, largely ignoring temporal patterns. In this study, we analysed these temporal patterns in beam trawl effort intensity at 90 stations of the Dutch continental shelf of the North Sea for a period of 10 years, at a fine temporal (weekly) and spatial (110 × 70 m) scale using Vessel Monitoring by Satellite (VMS) data. Our results show that trawling is aggregated in time and shows clear seasonality, related to the behavior of the fleet and migration patterns of the target fish species. The temporal patterns affect the overall impact on and the recovery of the benthic community, as is illustrated with a benthic population model. Our results imply that trawling impact studies using high-resolution data like VMS should take account of the possibility of temporal aggregation and seasonality in trawling to improve the assessment of the impact of trawling on the population dynamics of benthos.