Estimating high resolution trawl fishing effort from satellite-based vessel monitoring system data

High resolution estimates of trawling effort are needed to underpin studies of trawling impacts on species, habitats, and ecosystem processes, and to monitor responses to area closure and other management actions. Satellite-based vessel monitoring systems (VMS) were designed for fishery control and enforcement, but they provide potentially valuable source information on spatial and temporal patterns of trawling activity at multiple scales. Based on an analysis of VMS data for UK beam trawlers in the North Sea, a method is described for identifying trawling activity and estimating fishing intensity based on the minimum and maximum potential spatial extent of trawling effort from VMS data. The optimal method for identifying trawling and steaming behaviour combined speed and directionality rules and correctly identified trawling and steaming in 99% and 95% of cases, respectively. Using speed- and directionality-filtered VMS data, trawling effort can be reported as area impacted per unit time per unit area at a range of grid scales from 1 km to 100 km (10 000 km2). Trawling effort is accurately represented at a grid cell resolution of 3 km or less.