Acoustic backscatter analysis of ground-fishing activity in the German North Sea sector

摘要

The physical impact of demersal fishing was studied in three different areas of the German North Sea sector by use of a multibeam echosounder. The areas represent typical shallow seas siliciclastic habitats in variable distance to the coastline. Their seabed substrate is dominated by coarse silt close to the shore and by fine sand in the most distal area on the Dogger Bank. The study documents the utility of the multibeam as a suitable tool to map large seafloor areas, as well as to quantify and qualify the footprints of the fishing groundgear. Besides the depth and amplitude information, the multibeam data allows the analysis of the incidence angle-dependent variation of the backscatter signal that provides additional information on the seabed impedance, roughness, volume scatter and substrate type. Two main types of destructive seafloor pattern were observed in the three areas. The dominant type are pairs of parallel furrows exhibiting widths of 6-9 m and depths of 2-6 cm and is related to beam trawling. Separation distance of the pair furrows is 16-23 m. The second type are pairs of narrow furrows (3-4 m) with much larger separation distance of 110-120 m. They are attributed to otter board trawling.