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  • 1
    Publication Date: 2021-04-22
    Description: Bottom trawling in shelf seas can occur more than 10 times per year for a given location. This affects the benthic metabolism, through a mortality of the macrofauna, resuspension of organic matter from the sediment, and alterations of the physical sediment structure. However, the trawling impacts on organic carbon mineralization and associated processes are not well known. Using a modelling approach, the effects of increasing trawling frequencies on early diagenesis were studied in five different sedimentary environments, simulating the effects of a deeper-penetrating gear (e.g. a tickler chain beam trawl) versus a shallower, more variable penetrating gear (e.g. an electric pulse trawl). Trawling events strongly increased oxygen and nitrate concentrations in surface sediment layers and led to significantly lower amounts of ammonium (43 %–99 % reduction) and organic carbon in the top 10 cm of the sediment (62 %–96 % reduction). As a result, total mineralization rates in the sediment were decreased by up to 28 %. The effect on different mineralization processes differed both between sediment types and between trawling frequencies. The shallow-penetrating gear had a slightly smaller effect on benthic denitrification than the deeper-penetrating gear, but there were no statistically different results between gear types for all other parameters. Denitrification was reduced by 69 % in a fine sandy sediment, whereas nitrogen removal nearly doubled in a highly eutrophic mud. This suggests that even relatively low penetration depths from bottom fishing gears generate significant biogeochemical alterations. Physical organic carbon removal through trawl-induced resuspension of sediments, exacerbated by a removal of bioturbating macrofauna, was identified as the main cause of the changes in the mineralization process.
    Print ISSN: 1726-4170
    Electronic ISSN: 1726-4189
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
    Publication Date: 2020-12-01
    Print ISSN: 0278-4343
    Electronic ISSN: 1873-6955
    Topics: Geosciences
    Published by Elsevier
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  • 3
    Publication Date: 2022-03-10
    Description: The Working Group on Fisheries Benthic Impact and Trade-offs (WGFBIT) develops methods and performs assessments to evaluate benthic impact from fisheries at regional scale, while con-sidering fisheries and seabed impact trade-offs. In this report, new fishery benthic impact assessments are carried out for several sub-regions in the Mediterranean (Greek waters, South Adriatic Sea, Sicily waters). For other regions, updates of the whole assessment or specific steps only were presented. A standard advice sheet for the regional benthic assessments, intended as input to the next generation of the ICES Ecosystem and Fisheries Overviews, was finalised and compiled for some regions as example (Greek wa-ters, Baltic Sea). A validation of the longevity relationships using new data was executed for the Kattegat area and the Southern North Sea. In relation to the methodology, some recommenda-tions were formulated concerning the update on depletion rates, the use of epifauna- or infauna-based data, guidance on which set of epibenthic species to include and the time scale for setting the average swept-area-ratio (SAR) used in model fitting and assessment. A benchmarking pro-cess comparing available benthic impact assessment approaches for MSFD descriptor 6 “Seafloor integrity” is needed, as the WGFBIT approach (relative benthic state) is not the only way to assess benthic impacts from physical disturbances. A start was made to explore how to incorporate more explicitly ecosystem functioning in to the WGFBIT seafloor assessment methodology. An improved understanding of the relationships between total community biomass and ecosystem functioning may assist in setting acceptable thresholds for ecosystem impacts from trawling. Furthermore, an improved understanding of the link between species functional effect traits and proxies and processes for specific ecosystem functions could help increase our ability to predict the impact of fishing disturbance on benthic ecosystem functioning more accurately. The ecosys-tem function we focus on is the biogeochemical cycling of organic matter. Two approaches were discussed (i) Biological traits approach focusing on the linkage between biological traits and eco-system functions and (ii) biogeochemical modelling approach using the established the OMEXDIA model.
    Description: FBIT
    Description: Published
    Description: Non Refereed
    Keywords: Fishery ; Fishing pressure ; Fisheries Benthic Impact ; Trade-offs ; AIS data ; VMS data ; Longevity ; Fishing gear technology ; Spatial modelling
    Repository Name: AquaDocs
    Type: Report
    Format: 133pp.
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