Abstract 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. A comparison of their mechanical ramification shows that the fishing gear incises the seafloor and modifies seafloor structures and properties. Our investigation documents that beam trawling has the greatest physical impact and exhibits the highest furrow density in the three study areas. The created furrows can persist for at least 4 months in a substrate of very fine sand. Depending on the hydrodynamic regime, the furrows can be later refilled by finer sediments, or levelled out by storm wave-induced turbulence reaching the seafloor. The hydrofoils used in otter trawl to spread the net likewise incise the seafloor, but the furrows are much narrower. However, the ground rope of the net towed between the boards scratches the seafloor and levels the microscale topography along track widths of ca. 100 m.

中文翻译：

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德国北海地区地面捕鱼活动的声学后向散射分析

摘要 使用多波束测深仪在德国北海地区的三个不同区域研究了底层捕鱼的物理影响。这些区域代表典型的浅海硅质碎屑栖息地，距海岸线的距离各不相同。它们的海床底质主要是靠近海岸的粗粉砂和多格滩最远侧区域的细沙。该研究记录了多波束作为绘制大型海底区域以及量化和限定渔具足迹的合适工具的实用性。除了深度和幅度信息外，多波束数据还可以分析反向散射信号的入射角相关变化，从而提供有关海底阻抗、粗糙度、体积散射和基底类型的附加信息。在这三个区域观察到两种主要类型的破坏性海底格局。主要类型是成对的平行犁沟，宽度为 6-9 m，深度为 2-6 cm，与束拖网有关。一对犁沟的间隔距离为 16-23 m。第二种类型是成对的窄沟（3-4 m），间距大得多，为 110-120 m。它们归因于水獭板拖网。对它们的机械影响的比较表明，渔具切割了海底并改变了海底结构和特性。我们的调查记录表明，束拖网在三个研究区域中具有最大的物理影响，并表现出最高的犁沟密度。产生的犁沟可以在非常细的沙子基质中持续至少 4 个月。根据水动力状况，以后可以用更细的沉积物重新填满沟壑，或者通过到达海底的风暴波浪引起的湍流使沟壑平整。水獭拖网中用来撒网的水翼船同样会切开海底，但犁沟要窄得多。然而，在板之间拖曳的网的地绳划伤了海底，并沿着大约 100 米的轨道宽度平整了微尺度地形。100 米。