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Identifying Trawl Marks in North Sea Sediments

Senckenberg am Meer, Department for Marine Research, Südstrand 40, 26382 Wilhelmshaven, Germany
Department of Geosciences, University of Bremen, Klagenfurter Straße 4, 28359 Bremen, Germany
Leibniz Institute for Baltic Sea Research Warnemünde, Seestraße 15, 18119 Rostock, Germany
Author to whom correspondence should be addressed.
Geosciences 2020, 10(11), 422;
Received: 25 September 2020 / Revised: 17 October 2020 / Accepted: 21 October 2020 / Published: 25 October 2020
The anthropogenic impact in the German Exclusive Economic Zone (EEZ) is high due to the presence of manifold industries (e.g., wind farms, shipping, and fishery). Therefore, it is of great importance to evaluate the different impacts of such industries, in order to enable reasonable and sustainable decisions on environmental issues (e.g., nature conservation). Bottom trawling has a significant impact on benthic habitats worldwide. Fishing gear penetrates the seabed and the resulting furrows temporarily remain in the sediment known as trawl marks (TM), which can be recognized in the acoustic signal of side-scan sonars (SSS) and multibeam echo sounders (MBES). However, extensive mapping and precise descriptions of TM from commercial fisheries at far offshore fishing grounds in the German EEZ are not available. To get an insight into the spatial patterns and characteristics of TM, approximately 4800 km2 of high-resolution (1 m) SSS data from three different study sites in the German EEZ were analyzed for changes in TM density as well as for the geometry of individual TM. TM were manually digitalized and their density per square kilometer was calculated. In general, TM density was highest in August and October. Moreover, different gear types could be identified from investigating individual TM in SSS data. Beam trawl marks were observed to have widths of up to 22 m whereas otter board marks showed widths up to 6 m. The persistence of TM was estimated to 2–7 days minimum for all three sites based on the SSS data from 2015–2019. A maximum persistence could be defined at one site (Dogger Bank) and it was five months for the investigation period 2016–2017. Besides the main factors driving TM degradation (wave-base impact, sediment-type), different methods for TM detection (SSS, MBES, under-water video) are discussed. The study provides valuable information on the physical impact of bottom trawling on the seabed and can support existing monitoring strategies. View Full-Text
Keywords: seabed sediments; seabed mapping; marine habitat mapping; anthropogenic impact; side-scan sonar; German Bight seabed sediments; seabed mapping; marine habitat mapping; anthropogenic impact; side-scan sonar; German Bight
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MDPI and ACS Style

Bruns, I.; Holler, P.; Capperucci, R.M.; Papenmeier, S.; Bartholomä, A. Identifying Trawl Marks in North Sea Sediments. Geosciences 2020, 10, 422.

AMA Style

Bruns I, Holler P, Capperucci RM, Papenmeier S, Bartholomä A. Identifying Trawl Marks in North Sea Sediments. Geosciences. 2020; 10(11):422.

Chicago/Turabian Style

Bruns, Ines, Peter Holler, Ruggero M. Capperucci, Svenja Papenmeier, and Alexander Bartholomä. 2020. "Identifying Trawl Marks in North Sea Sediments" Geosciences 10, no. 11: 422.

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