Journal Article

Ploughing the deep sea floor

Palanques, Albert, Calafat, Antoni M., Amblas, David, Canals, Miquel, Puig, Pere, Lastras, Galderic, Company, Joan B., Martín, Jacobo

2012

Overview

Bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed, and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales. Sea-floor disturbance due to bottom trawling The direct impact of bottom trawling on local fish populations has received much attention, but trawling also affects other aspects of the ocean environment. This paper shows that bottom trawling — a commercial practice in which heavy nets and gear are dragged along the ocean floor — induces sediment reworking and erosion, causing the gradient of the sea floor to become smoother over time. This reduces the morphological complexity of deep-sea environments. The authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land, with the important difference that, on land, ploughing takes place once or twice a year, whereas, at sea, bottom trawling can be a frequent occurrence. 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 populations 1 , 2 and benthic communities 3 , 4 has received much attention, but trawling can also modify the physical properties of seafloor sediments, water–sediment chemical exchanges and sediment fluxes 5 , 6 . Most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments 7 , 8 , however, where the capacity of trawling to modify the seafloor morphology coexists with high-energy natural processes driving sediment erosion, transport and deposition 9 . 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.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/158/2446/1491 / 704/2151/213 / Agriculture - methods / Animals / Aquatic Organisms - physiology / Bathymetry / Benthic communities / Commercial fishing / Continental slope / Deep sea / Deep sea environments / Deep-sea ecology / Earth sciences / Earth, ocean, space / Ecologia submarina / Ecosystem / Engineering and environment geology. Geothermics / Environmental aspects / Exact sciences and technology / Fish populations / Fisheries - economics / Fisheries - methods / Fishes - physiology / Fishing / Fishing zones / Geography / Geologia submarina / Geologic Sediments - analysis / Geologic Sediments - chemistry / Human Activities / Humanities and Social Sciences / letter / Marine / Marine Biology / Marine geology / Monitoring systems / Morphology / multidisciplinary / Ocean bottom / Ocean floor / Oceans / Oceans and Seas / Pesca / Physical properties / Pollution, environment geology / Science / Science (multidisciplinary) / Sea beds / Seawater - chemistry / Sediment transport / Sediments / Slopes / Studies / Submarine geology / Time Factors / Trawling