Dataset containing Residual Bathymetric Maps for Assessing Bottom Trawling Intensity in the Fehmarn Belt (MPA)

What AIS misses and Acoustics reveal: Monitoring Seafloor Disturbance and Recovery from Bottom Trawling in the southern Baltic Sea over five years

Schönke, Mischa; Schulze, Inken; Gogina, Mayya; von Dorrien, Christian; Oesterwind, Daniel; Feldens, Peter

Contributor(s): Schulze, Inken [DataCollector]; Feldens, Peter [DataCurator]

Scientific purpose: Monitor potential effects of closure for bottom fishing in the marine protected areas (MPAs) of the western Baltic Sea – MGF Baltic Sea Projects (funded by BMBF)

Keywords: bottom trawling, acoustic remote sensing, seafloor disturbance, monitoring, MBES, MGF-Ostsee, Baltic Sea, MPA

Abstract. This study evaluates bottom trawling intensity and its ecological effects in the Fehmarn Belt (southern Baltic Sea) between 2020 and 2024. The region is dominated by small-scale fishing vessels (< 12 m length) and therefore, conventional Vessel Monitoring System (VMS) data are unavailable. We compare changes in seafloor integrity caused by bottom trawling with fishing activity inferred from Automatic Identification System (AIS) tracking. Trawling intensity was quantified using a previously developed trawling index (TI) based on furrow volume derived from multibeam echosounder (MBES) data. A pronounced alteration in seafloor integrity was observed between 2021 and 2022, with furrow volumes decreasing from 5,067 m3 to 1,108 m3 over an area of 3.4 km2. This trend was not recorded by AIS-derived fishing activity, which showed only slight changes in vessel track counts. Spatial and temporal fluctuations in abundance, biomass, and community structure were revealed through repeated macrofauna sampling. The fluctuations are likely linked to shifting trawling pressure, most likely based on the ban of a fishery targeting cod in the Western Baltic. These biological responses did not follow a linear trend but suggest a dynamic equilibrium may be reached over time. Although MBES data cannot replace AIS for tracking fishing effort, it can supplement and improve the AIS information, providing insights into physical impacts and benthic responses in regions of interest. Integrating MBES-derived indicators identifies the spatial extent of the seabed affected by bottom trawling, thereby strengthening ecological monitoring frameworks and supporting sustainable seabed management, including in marine spatial planning.

Citation

Schönke, M., Schulze, I., Gogina, M., von Dorrien, C., Oesterwind, D., Feldens, P. (2025). Dataset containing Residual Bathymetric Maps for Assessing Bottom Trawling Intensity in the Fehmarn Belt (MPA). Leibniz Institute for Baltic Sea Research Warnemünde. doi:10.12754/data-2025-0020

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