The negative impacts that scientific monitoring may have on marine ecosystems has been a neglected topic, mainly on the basis that its magnitude is minor compared to commercial fisheries, even though this raises ethical and, in certain cases, conservation issues. We argue that ethical principles should lead us to reconsider marine wildlife resource monitoring such as the fish and shellfish trawl surveys providing the science-based evidence needed for fisheries management and assessment of how environmental change impacts marine shelf communities worldwide. Recent scientific and technological progress has provided methods and tools which might now be harnessed to reduce the impact of marine monitoring. We review these alternative methods, consider modifications to current practices and identify areas requiring further research
Besides understanding the effects of fishing on harvested fish stocks, effects on non-target species, habitats and seafloor integrity also need to be considered. Static fishing gears have often been mentioned as a lower impact fishing alternative to towed gears, although studies examining their actual impact on the seafloor are scarce. In this study, we aimed to describe fish trap movements on the seafloor related to soaking time and trap retrieval. Impacts on the seafloor of lightweight rectangular traps and heavier circular traps were compared. We used 3D video cameras to estimate sweeping motion on the seabed and penetration into the sediment during soaking time. The area and distance swept by each type of trap during retrieval was determined by a camera set up facing the sea bottom. The potential rotation of the traps around the mainline was assessed using an Acoustic Doppler Current Profiler. Results showed that no penetration and almost no movements could be detected during soaking time for either lightweight or heavy commercial traps, even for high tidal coefficient (maximum 6 cm). No rotation could be observed when the tide turned. The swept area covered by a trap during retrieval was low (maximum 2.04 m 2) compared to towed fishing gear and other static gear.
The pipelines and associated structures are major components of the subsea deep water oil and gas production. Deep water production requires the transportation of multiphase hot products under high pressure and temperature. In deep water the soil is usually very soft clay of high plasticity with high water content. Both of these elements are major aggravating factors for pipeline instabilities: lateral buckling and pipeline walking. The paper presents and illustrates practical measures which are developed by the contractors for mitigating the risks of failures associated to these instability phenomenons. The analyses which are carried out for the lateral buckling and pipeline walking are generally very conservative. Such attitude is fully understandable with regards to the risks of failure in deep water. However the mitigation measures should not be inducing unwanted effects.
Spatial planning, including zoning and site-selection steps, is necessary to determine locations that minimize environmental impacts of aquaculture and respect ecosystem carrying capacities. This study aimed to analyse potential benthic waste deposition in a broad range of fish farming situations to facilitate zoning. To this end, we simulated waste dispersion for 54 aquaculture scenarios combining three red drum (Sciaenops ocellatus) farm types (Small, Medium, and Large) based on real farm characteristics and 36 sites with contrasting hydrodynamics in Mayotte’s North-East Lagoon. Key forcing variables and parameters of the particle-dispersion model for farms (layout and solid waste fluxes), species (feed- and faeces-settling velocities) and sites (depth and barotropic currents) were obtained. From the outputs of the 54 simulations, relationships between hydrodynamic regimes and deposition rates, area of influence and distance of influence of the farm were analysed. Critical limits of current intensity that reduced deposition rate below selected deposition thresholds were identified. For instance, to prevent deposition rates greater than 12 kg solids m−2 year−1, the mean current intensity should exceed 10.2 and 6.8 cm s−1 for Medium and Large farms, respectively. The study confirmed that production level is not the main factor that influences deposition rates; instead, management of the entire farm (cage position, distance between cages) must be considered to predict impacts more accurately and guide site selection.
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