The mobilisation of sediment and benthic infauna by scallop dredges.

We present the results of experiments to assess the immediate impact of scallop dredging on the seabed sediment and on the inhabiting infauna. The passage of the scallop dredge is shown to homogenise the seabed, flattening sand ripples. The turbulent wake entrains up to the equivalent of a 1 mm layer of sediment per unit of swept width, although an analysis of the finer particles material implies that the suspended silt material must originate from depths of at least 10 mm. The species most abundant in the sediment plume either swim actively in the water column or are found in, or on, the upper layers of the substrate, whereas those most abundant in core samples taken from the sediment, but not present in the net samples, are almost all tube-building or deep burrowing. The vertical stratification of sediment concentration and of animal numbers in the water column suggests that even if some of these species respond actively to the presence of the dredge, once entrained, they are transported more or less passively in the same way as the larger sediment particles. There was no difference between the core samples taken before or after towing suggesting that animals mobilised by the dredge resettle in the tow path. Our analysis does not provide any information regarding the fate of these animals.

[1]  Richard David Neilson,et al.  Modelling the physical impact of trawl components on the seabed and comparison with sea trials , 2011 .

[2]  P. Boulcott,et al.  Sedimentation patterns caused by scallop dredging in a physically dynamic environment. , 2011, Marine pollution bulletin.

[3]  P. Boulcott,et al.  The impact of scallop dredging on rocky-reef substrata , 2011 .

[4]  D. Raffaelli,et al.  In situ swimming behaviour of the amphipod Corophium volutator (Pallas) , 1998 .

[5]  Paul J. Somerfield,et al.  Global analysis of response and recovery of benthic biota to fishing , 2006 .

[6]  Saša Raicevich,et al.  A multidisciplinary study of the immediate effects of mechanical clam-harvesting in the Venice Lagoon , 2004 .

[7]  S. Løkkeborg Impacts of trawling and scallop dredging on benthic habitats and communities , 2005 .

[8]  Lael Parrott,et al.  A comparison of two techniques for the rapid assessment of marine habitat complexity , 2013 .

[9]  Dp O'Brien Direct observations of clustering (schooling and swarming) behaviour in mysids (Crustacea: Mysidacea) , 1988 .

[10]  D. E. Keith Substrate Selection in Caprellid Amphipods of Southern California, with Emphasis on Caprella californica Stimpson and Caprella equilibra Say (Amphipoda) , 1971 .

[11]  Michel J. Kaiser,et al.  The effects of fishing on marine ecosystems , 1998 .

[12]  Gary A. Gill,et al.  The impact of shrimp trawling and associated sediment resuspension in mud dominated, shallow estuaries , 2006 .

[13]  M. Breen,et al.  An underwater laser stripe seabed profiler to measure the physical impact of towed gear components on the seabed , 2009 .

[14]  Stephen J. Hall,et al.  The Effects Of Fishing On Mariane Ecosystems And Communities , 1998 .

[15]  Benedicte Ferre,et al.  Trawling-induced resuspension and dispersal of muddy sediments and dissolved elements in the Gulf of Lion (NW Mediterranean) , 2005 .

[16]  F. O’Neill,et al.  The mobilisation of sediment by demersal otter trawls. , 2011, Marine pollution bulletin.

[17]  M. Kaiser,et al.  The environmental impacts of three different queen scallop (Aequipecten opercularis) fishing gears. , 2012, Marine environmental research.

[18]  A. Eleftheriou,et al.  The effects of experimental scallop dredging on the fauna and physical environment of a shallow sandy community , 1992 .

[19]  Jeremy S. Collie,et al.  Modification of marine habitats by trawling activities: prognosis and solutions , 2002 .

[20]  E. Bresnan,et al.  The influence of demersal trawl fishing gears on the resuspension of dinoflagellate cysts. , 2013, Marine pollution bulletin.

[21]  LucchettiAlessandro,et al.  Impact and performance of Mediterranean fishing gear by side-scan sonar technology , 2012 .

[22]  I. Davies,et al.  Large-scale impacts of bottom trawling on shelf primary productivity , 2007 .

[23]  C. Dounas A new apparatus for the direct measurement of the effects of otter trawling on benthic nutrient releases , 2006 .

[24]  K. Black,et al.  Entrainment, dispersal, and settlement of scallop dredge sediment plumes : field measurements and numerical modelling , 1999 .

[25]  J. Collie,et al.  Photographic evaluation of the impacts of bottom fishing on benthic epifauna , 2000 .