Can trawling effort be identified from satellite-based VMS data?

Abstract

Data from satellite-based vessel monitoring systems (VMS) can, in principle, be used to measure fishing effort with a high spatiotemporal resolution. However, it can be difficult to separate between fishing activity and other activities (like steaming). The vessels’ speed (at a given time) may give an indication of whether fishing activity occurs or not. In this work VMS data from two factory trawlers in the Norwegian Reference fleet are merged with detailed logbook information. The average speed between consecutive VMS observation was estimated (using time difference and distance) and grouped according to type of activity (from the logbook records). About 70-80 % of the VMS observations below 5 knots represented trawling, but speed alone could not be used to determine with high degree of accuracy whether the vessels were trawling or not.