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H L Rees - One of the best experts on this subject based on the ideXlab platform.
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the effects of marine gravel extraction on the macrobenthos results 2 years post dredging
Marine Pollution Bulletin, 1996Co-Authors: Andrew Kenny, H L ReesAbstract:Abstract An offshore experimental dredging study was initiated off North Norfolk (UK) in 1992 to investigate the impacts of marine gravel extraction on the macrofauna. A dredged ‘treatment’ and a non-dredged ‘reference’ site were selected to evaluate the initial impacts and subsequent processes of recolonization. A survey of the benthos was conducted prior to the removal of 50 000 t of marine aggregate from the treatment site. Thereafter annual monitoring surveys were conducted commencing immediately after the dredging episode. Results indicated that whilst the dominant species recolonized quickly following dredging many rarer species did not. Evidence from sidescan sonar records and underwater cameras indicated a considerable amount of sediment transport during the first two winters following dredging and the once well-defined dredge tracks have now become infilled with sand and gravel. The substantially reduced biomass at the treatment site some 24 months after dredging is thought to be due to a local increase in sediment disturbance caused by tide and wave action over the winter period. Finally, the biological findings of this study are discussed in relation to their wider environmental significance.
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the effects of marine gravel extraction on the macrobenthos early post dredging recolonization
Marine Pollution Bulletin, 1994Co-Authors: Andrew Kenny, H L ReesAbstract:Abstract A small area of sea bed off the English east coast was experimentally dredged by a commercial suction-trailer dredger. Some 50 000 t of mixed aggregate were removed, representing about 70% of the sea bed area down to an average depth of 0.3 m. Results from benthic surveys undertaken at the experimental site and at a nearby reference site, indicate that significant reductions had occurred in the variety, abundance and biomass of benthic organisms as a consequence of dredging. Subsequent recolonization of dunuded substrates by the dominant taxa proceeded relatively rapidly, although the dredged site had clearly not fully recovered some 7 months later. Differences in the recruitment success of the dominant taxa, notably Dendrodoa grossularia and Balanus crenatus, between the reference and treatment sites pre- and post-dredging were observed. Possible explanations for these differences in relation to the observed physical alterations to the sea bed are discussed.
Andrew Kenny - One of the best experts on this subject based on the ideXlab platform.
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the effects of marine gravel extraction on the macrobenthos results 2 years post dredging
Marine Pollution Bulletin, 1996Co-Authors: Andrew Kenny, H L ReesAbstract:Abstract An offshore experimental dredging study was initiated off North Norfolk (UK) in 1992 to investigate the impacts of marine gravel extraction on the macrofauna. A dredged ‘treatment’ and a non-dredged ‘reference’ site were selected to evaluate the initial impacts and subsequent processes of recolonization. A survey of the benthos was conducted prior to the removal of 50 000 t of marine aggregate from the treatment site. Thereafter annual monitoring surveys were conducted commencing immediately after the dredging episode. Results indicated that whilst the dominant species recolonized quickly following dredging many rarer species did not. Evidence from sidescan sonar records and underwater cameras indicated a considerable amount of sediment transport during the first two winters following dredging and the once well-defined dredge tracks have now become infilled with sand and gravel. The substantially reduced biomass at the treatment site some 24 months after dredging is thought to be due to a local increase in sediment disturbance caused by tide and wave action over the winter period. Finally, the biological findings of this study are discussed in relation to their wider environmental significance.
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the effects of marine gravel extraction on the macrobenthos early post dredging recolonization
Marine Pollution Bulletin, 1994Co-Authors: Andrew Kenny, H L ReesAbstract:Abstract A small area of sea bed off the English east coast was experimentally dredged by a commercial suction-trailer dredger. Some 50 000 t of mixed aggregate were removed, representing about 70% of the sea bed area down to an average depth of 0.3 m. Results from benthic surveys undertaken at the experimental site and at a nearby reference site, indicate that significant reductions had occurred in the variety, abundance and biomass of benthic organisms as a consequence of dredging. Subsequent recolonization of dunuded substrates by the dominant taxa proceeded relatively rapidly, although the dredged site had clearly not fully recovered some 7 months later. Differences in the recruitment success of the dominant taxa, notably Dendrodoa grossularia and Balanus crenatus, between the reference and treatment sites pre- and post-dredging were observed. Possible explanations for these differences in relation to the observed physical alterations to the sea bed are discussed.
L J Seiderer - One of the best experts on this subject based on the ideXlab platform.
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impacts of aggregate dredging on sediment composition and associated benthic fauna at an offshore dredge site in the southern north sea
Marine Environmental Research, 2005Co-Authors: J E Robinson, R C Newell, L J Seiderer, N M SimpsonAbstract:Dredging and associated screening at a dredge site in the southern North Sea (Area 408) is associated with areas of well-sorted fine sand that extend for up to 3 km to the south-east of the dredged area and overlay sediments with a more variable particle size composition. This well-sorted fine sand may reflect deposition and transport of material mobilised by the dredging and screening processes at the dredge site. Multivariate analysis of the benthic community structure suggests that marine aggregate dredging, at the level of intensity employed in the study area prior to sample collection, has had a limited impact on benthic community composition compared with that reported from studies elsewhere. This is ascribed to the likely rapid rates of recolonisation by the mobile opportunistic polychaetes and crustaceans that dominate the macrofauna of the sandy gravel deposits at this particular dredge site. Analysis of variance showed, however, that significant differences existed between the sample treatments in terms of species evenness (Pielou's J). Dredged samples were found to have the lowest mean species evenness (0.71) when compared to controls (0.77). The present study highlights the inherent difficulties in the application of general impact/recovery predictions to dredged sites with varying environmental characteristics.
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impacts of marine aggregate dredging on benthic macrofauna off the south coast of the united kingdom
Journal of Coastal Research, 2004Co-Authors: R C Newell, L J Seiderer, N M Simpson, J E RobinsonAbstract:Abstract A survey of benthic macrofauna in the vicinity of a coastal marine aggregate dredging site off the south coast of UK was carried out in 1999. The object of the survey was to determine impact of marine aggregate dredging on community composition, the extent of impact outside the boundaries of the dredge site, and the rate of recolonization and recovery of the fauna following cessation of dredging. Part of the site was intensively dredged by vessels at anchor whilst other parts were less intensively exploited by trailer dredger. The impact of dredging within the intensively exploited anchor dredge site was limited to the dredged area. Impacts included a suppression of species variety, population density and biomass, as well as differences in species composition compared with the surrounding deposits. In contrast, trailer dredging had no impact on community composition of macrofauna within the dredge site. No suppression of benthic community structure was recorded beyond 100 m from the dredge site. ...
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organic enrichment associated with outwash from marine aggregates dredging a probable explanation for surface sheens and enhanced benthic production in the vicinity of dredging operations
Marine Pollution Bulletin, 1999Co-Authors: R C Newell, D R Hitchcock, L J SeidererAbstract:Abstract Most recent studies of dispersion of sediment plumes generated by marine aggregates dredging, including those reported here, suggest that the zone of settlement of fine material temporarily suspended by the dredging and screening process is smaller than estimates based on Gaussian diffusion models. There is, however, often a relatively larger zone of visible impact which can extend for several kilometres downstream from a dredger during normal loading operations. This paper presents evidence which suggests that the “far field” visibility of the dispersing plume is associated with organic enrichment derived from fragmented marine benthos discharged with the outwash water. The values which we have recorded for unexploited deposits off Southwold, Suffolk are as high as 1.454 g/l AFDW(ash-free dry weight) of which 0.007 g/l (0.48%) comprises lipids. Such material appears to be of sufficient concentration to match the likely removal of benthos from the sediments by the dredgehead. Even allowing for the dispersion which must occur downstream from the dredger, it seems likely that the organic enrichment derived from fragmented invertebrates in the dredger outwash may account for the enhanced species diversity and population density of benthic invertebrates recorded by others beyond the boundaries of dredged areas.
R C Newell - One of the best experts on this subject based on the ideXlab platform.
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impacts of aggregate dredging on sediment composition and associated benthic fauna at an offshore dredge site in the southern north sea
Marine Environmental Research, 2005Co-Authors: J E Robinson, R C Newell, L J Seiderer, N M SimpsonAbstract:Dredging and associated screening at a dredge site in the southern North Sea (Area 408) is associated with areas of well-sorted fine sand that extend for up to 3 km to the south-east of the dredged area and overlay sediments with a more variable particle size composition. This well-sorted fine sand may reflect deposition and transport of material mobilised by the dredging and screening processes at the dredge site. Multivariate analysis of the benthic community structure suggests that marine aggregate dredging, at the level of intensity employed in the study area prior to sample collection, has had a limited impact on benthic community composition compared with that reported from studies elsewhere. This is ascribed to the likely rapid rates of recolonisation by the mobile opportunistic polychaetes and crustaceans that dominate the macrofauna of the sandy gravel deposits at this particular dredge site. Analysis of variance showed, however, that significant differences existed between the sample treatments in terms of species evenness (Pielou's J). Dredged samples were found to have the lowest mean species evenness (0.71) when compared to controls (0.77). The present study highlights the inherent difficulties in the application of general impact/recovery predictions to dredged sites with varying environmental characteristics.
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impacts of marine aggregate dredging on benthic macrofauna off the south coast of the united kingdom
Journal of Coastal Research, 2004Co-Authors: R C Newell, L J Seiderer, N M Simpson, J E RobinsonAbstract:Abstract A survey of benthic macrofauna in the vicinity of a coastal marine aggregate dredging site off the south coast of UK was carried out in 1999. The object of the survey was to determine impact of marine aggregate dredging on community composition, the extent of impact outside the boundaries of the dredge site, and the rate of recolonization and recovery of the fauna following cessation of dredging. Part of the site was intensively dredged by vessels at anchor whilst other parts were less intensively exploited by trailer dredger. The impact of dredging within the intensively exploited anchor dredge site was limited to the dredged area. Impacts included a suppression of species variety, population density and biomass, as well as differences in species composition compared with the surrounding deposits. In contrast, trailer dredging had no impact on community composition of macrofauna within the dredge site. No suppression of benthic community structure was recorded beyond 100 m from the dredge site. ...
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organic enrichment associated with outwash from marine aggregates dredging a probable explanation for surface sheens and enhanced benthic production in the vicinity of dredging operations
Marine Pollution Bulletin, 1999Co-Authors: R C Newell, D R Hitchcock, L J SeidererAbstract:Abstract Most recent studies of dispersion of sediment plumes generated by marine aggregates dredging, including those reported here, suggest that the zone of settlement of fine material temporarily suspended by the dredging and screening process is smaller than estimates based on Gaussian diffusion models. There is, however, often a relatively larger zone of visible impact which can extend for several kilometres downstream from a dredger during normal loading operations. This paper presents evidence which suggests that the “far field” visibility of the dispersing plume is associated with organic enrichment derived from fragmented marine benthos discharged with the outwash water. The values which we have recorded for unexploited deposits off Southwold, Suffolk are as high as 1.454 g/l AFDW(ash-free dry weight) of which 0.007 g/l (0.48%) comprises lipids. Such material appears to be of sufficient concentration to match the likely removal of benthos from the sediments by the dredgehead. Even allowing for the dispersion which must occur downstream from the dredger, it seems likely that the organic enrichment derived from fragmented invertebrates in the dredger outwash may account for the enhanced species diversity and population density of benthic invertebrates recorded by others beyond the boundaries of dredged areas.
Eric Matzen - One of the best experts on this subject based on the ideXlab platform.
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Using Sea Turtle Carcasses to Assess the Conservation Potential of a Turtle Excluder Dredge
2020Co-Authors: Ronald Smolowitz, Heather Haas, Matthew Weeks, Henry O Milliken, Eric MatzenAbstract:Abstract.-Fisheries observers have documented interactions between sea turtles in the family Cheloniidae and the Atlantic sea scallop Placopecten magellanicus fishery. Sea turtle injuries resulting from interactions with scallop Dredges are being mitigated through shifts in fishing effort and modifications to fishing gear. The standard New Bedford dredge can trap objects and crush them as they pass between the dredge frame and sea floor, so a modified turtle excluder dredge has been designed to reduce the likelihood of a turtle's passing under the frame when the dredge fishes on the seafloor. The key elements of the modified design are a forward cutting bar (which results in a sloping rather than a vertical face), a reduced number of bale support bars (just the center and outer bales), extension of the outer bale bars before tapering to the gooseneck (hauling point), and a reduction in the sources of entrapment between the depressor plate and the cutting bar via reduced spacing of struts. We evaluated the ability of the modified dredge to cause live sea turtles to pass over it by using loggerhead sea turtle Caretta caretta carcasses as a proxy. The carcasses were placed on the seafloor in the path of a towed dredge equipped with video cameras. Nine interactions between carcasses and the modified dredge were documented on video recordings. In each of the interactions, the carcass hit the dredge and passed over the dredge frame with little or no physical damage to the recovered carcasses. These carcass studies suggest that the turtle excluder dredge reduces sea turtle injuries associated with interactions between sea turtles and scallop Dredges fishing on the seafloor
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Using Sea Turtle Carcasses to Assess the Conservation Potential of a Turtle Excluder Dredge
2013Co-Authors: Ronald Smolowitz, Heather Haas, O. Milliken, Matthew Weeks, Eric MatzenAbstract:Abstract.—Fisheries observers have documented interactions between sea turtles in the family Cheloniidae and the Atlantic sea scallop Placopecten magellanicus fishery. Sea turtle injuries resulting from interactions with scallop Dredges are being mitigated through shifts in fishing effort and modifications to fishing gear. The standard New Bedford dredge can trap objects and crush them as they pass between the dredge frame and sea floor, so a modified turtle excluder dredge has been designed to reduce the likelihood of a turtle’s passing under the frame when the dredge fishes on the seafloor. The key elements of the modified design are a forward cutting bar (which results in a sloping rather than a vertical face), a reduced number of bale support bars (just the center and outer bales), extension of the outer bale bars before tapering to the gooseneck (hauling point), and a reduction in the sources of entrapment between the depressor plate and the cutting bar via reduced spacing of struts. We evaluated the ability of the modified dredge to cause live sea turtles to pass over it by using loggerhead sea turtle Caretta caretta carcasses as a proxy. The carcasses were placed on the seafloor in the path of a towed dredge equipped with video cameras. Nine interactions between carcasses and the modified dredge were documented on video recordings. In each of the interactions, the carcass hit the dredge and passed over the dredge frame with little or no physical damage to the recovered carcasses. These carcass studies suggest that the turtle excluder dredge reduces sea turtle injuries associated with interaction
