Journal Article

RoxAnn bottom classification system, sidescan sonar and video-sledge: spatial resolution and their use in assessing trawling impacts

Odd-Børre Humborstad, Leif Nøttestad, Svein Løkkeborg and Hans Tore Rapp

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 61, issue 1, pages 53-63
Published in print January 2004 | ISSN: 1054-3139
Published online January 2004 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1016/j.icesjms.2003.10.001
RoxAnn bottom classification system, sidescan sonar and video-sledge: spatial resolution and their use in assessing trawling impacts

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Three complementary seabed characterization tools with different spatial resolution were used to locate a research site and to assess physical effects of experimental otter trawling in the Barents Sea: an acoustic seabed classification system (RoxAnn), sidescan sonar and a video-sledge. The marine protected area (MPA) around Bear Island was chosen as it offered unfished reference sites. The area was topographically complex which resulted in certain challenges for choice of the experimental site due to the requirements of representativity and homogeneity and suitable sampling substrate. Systematic waylines with RoxAnn gave broad-scale patterns of bottom conditions, the more informative sidescan revealed topographic reliefs, whilst detailed information on sediment composition and small-scale seabed features was provided by the video-sledge. Accurate positioning of towed gears (trawl, sidescan and video-sledge) ensured unbiased data acquisition. Trawl doors and rockhopper gear created furrows that were visible by sidescan sonar and video. Intensive trawling also caused changes in the acoustic properties by increasing roughness and decreasing hardness. Results are consistent with a possible resuspension of the sediment and a homogenizing effect from the trawl doors and ground gear ploughing the area. The suitability and advantages of using spatially overlapping tools in trawl impact studies are discussed.

Keywords: impact studies; ITI positioning system; otter trawling; RoxAnn; sidescan sonar; video-sledge

Journal Article.  5267 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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