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Ploughing the deep sea floor

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Abstract

Bottom trawling is a non-selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor. The direct impact of this technique on fish populations1,2 and benthic communities3,4 has received much attention, but trawling can also modify the physical properties of seafloor sediments, water–sediment chemical exchanges and sediment fluxes5,6. Most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7,8, however, where the capacity of trawling to modify the seafloor morphology coexists with high-energy natural processes driving sediment erosion, transport and deposition9. Here we show that on upper continental slopes, the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales. We found that trawling-induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time, reducing its original complexity as shown by high-resolution seafloor relief maps. Our results suggest that in recent decades, following the industrialization of fishing fleets, bottom trawling has become an important driver of deep seascape evolution. Given the global dimension of this type of fishery, we anticipate that the morphology of the upper continental slope in many parts of the world’s oceans could be altered by intensive bottom trawling, producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land.

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Figure 1: Map of known trawling grounds on the world continental slopes.
Figure 2: Bathymetric map of the study area.
Figure 3: Time series observations of trawling-induced sediment gravity flows.
Figure 4: Seafloor morphology and bottom trawling in La Fonera Canyon.

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Acknowledgements

This work was supported by various research projects: HERMIONE (226354 and CTM2010-11084-E), DOS MARES (CTM2010-21810-C03), OASIS DEL MAR—Obra Social “la Caixa”, GRACCIE-CONSOLIDER (CSD2007-00067) and REDECO (CTM2008-04973-E). We also received support from Catalan Government Grups de Recerca Consolidats grants (2009 SGR 899 and 1305). VMS data and support were provided by the Spanish General Secretariat of Maritime Fishing (SEGEMAR). Assistance at sea by the crews of RV Hespérides, RV Sarmiento de Gamboa and RV García del Cid is also acknowledged. J.M. was funded through a JAE-DOC contract granted by Consejo Superior de Investigaciones Científicas and co-financed by the European Social Fund. F. Sardà and T. Milligan provided comments on the manuscript. The final document benefited from a review by P. Talling.

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Contributions

All authors contributed to the design and implementation of the experimental strategy. P.P., M.C. and J.B.C. steered the integration and joint analysis of the data. P.P. and J.M. drafted the manuscript, which was critically revised and implemented by M.C. and J.B.C. M.C. designed and coordinated the acquisition of seafloor data, including multibeam bathymetry and ROV observations, and obtained VMS data. P.P., J.M. and A.P. acquired and processed the mooring time series and the sediment cores. J.M. and J.B.C. conducted the bibliographical survey of global slope fishing grounds. D.A., M.C. and P.P. produced the various maps in the paper, to which J.M and J.B.C. contributed. G.L. coordinated the multibeam bathymetry processing and, jointly with M.C., created the slope failures table. J.B.C. provided knowledge about local fishing activities. M.C., D.A., G.L. and A.M.C. described and interpreted the whole set of seafloor data. All authors discussed the results and commented on the final version of the manuscript.

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Correspondence to Pere Puig.

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The authors declare no competing financial interests.

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This file contains Supplementary Text, Supplementary Figures 1-5, Supplementary Table 1 and Supplementary References. (PDF 2831 kb)

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Puig, P., Canals, M., Company, J. et al. Ploughing the deep sea floor. Nature 489, 286–289 (2012). https://doi.org/10.1038/nature11410

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