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The impacts of bottom trawling in Marine Protected Areas

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The fishing lobby has been violently reacting to the European Commission’s Action Plan that seeks a timid and slow phase-out of bottom trawling inside Marine “Protected” Areas (MPAs). Many false arguments are being used to oppose an obviously needed measure that is crucial for the restoration of biodiversity, protection of carbon stocks and regeneration of fish populations – and hence the future of fishing itself.

One such claim is that Special Protection Areas (SPAs) which are part of the Natura 2000 network, have been designated for birds, so have nothing to do with bottom trawling. The science is with Commissioner Sinkevičius, not with the trawling industry and their tamed agriculture ministers.

There is ample peer-reviewed research demonstrating that the level of protection afforded to MPAs—the extent to which extractive and other harmful activities are excluded—has a significant impact on the ecological benefits they deliver (e.g., increased biomass, numerical density, species richness, size of organisms etc.) compared to weakly protected areas. [1][2][3][4]

Great Shearwater, copyright Richard Stonier, from the surfbirds galleries

An ecosystem-based approach to MPA management requires looking at the whole ecosystem, recognising the complex interactions between its different components, and applying measures that maintain the integrity and functioning of the entire ecosystem.

A feature-based approach to MPA management focuses on managing the direct impacts of certain activities on the protected features rather than on ecosystem processes and interactions taking place within the site (e.g., the reasons why species such as seabirds are using certain sites for feeding). Broader protection should enable the recovery of other/new features and natural dynamics within sites thus delivering wider conservation benefits.[5]

Bottom trawling is a fishing method that involves dragging heavy nets along the seafloor to catch fish and other marine organisms. It has a range of negative impacts on biodiversity and climate that make it incompatible with MPAs.

Damage and modification of benthic fauna

  • Demersal fisheries, especially bottom trawling is the most widespread source of anthropogenic disturbance to the seabed.[6] Bottom trawling can impact benthic fauna either directly through physical damage due to interactions with the trawl net or indirectly through the resuspension of seafloor sediments leading to reductions in fauna biomass, numbers, and species richness.[7],[8]
  • Some fauna can take several years to recover following fishing disturbance[9] leading to changes in benthic communities favouring short-lived fauna in areas regularly exposed.[10] These changes to benthic communities affect ecosystem dynamics within sites with potential negative impacts for higher marine taxa such as seabirds e.g., through damage to habitats important for their prey species.
  • Emerging research increasingly links upper-ocean communities and processes to seabed ecology and biogeochemistry presenting a strong case for surface to seabed protection within MPAs.[11]

Food depletion

  • Bottom-trawling can also cause reductions in the prey abundance of commercial fish species[12]. A high proportion of several forage fish species—small to medium-sized fish species that form a key component of the diets of seabirds and other marine animals—are caught in bottom-trawl fisheries reducing the availability of this food source for marine predators.

Bycatch

  • Bottom trawling is a non-selective fishing method catching a high proportion of non-target fish species and accounting for 92 % of recorded fisheries discards in the EU.[13] It is also responsible for bycatch of sensitive species[14] including sharks, rays, sea turtles, cetaceans, and seabirds (although it is not a gear of primary concern for seabird bycatch). By removing key stone species, bottom trawling weakens the whole ecosystems, with impacts rippling right across the food chain.

Climate impacts

  • Globally marine sediments are a significant store of carbon.[15] Bottom-trawling hinders the capacity of the ocean to mitigate climate change by altering or triggering geochemical processes[16][17][18][19] and releases large amounts of carbon by disturbing seabed sediments[20] contributing to climate change which is driving the loss of marine biodiversity.
  • Limiting the spatial extent of bottom-trawling by excluding it from protected areas is key to mitigate carbon emissions.
  • Current MPA networks were not designed with blue carbon considerations in mind, therefore, it is important that this is considered during the expansion of MPA networks to prevent disturbance in areas of high carbon storage.
  • Bottom-trawling in nearshore areas can damage other high blue carbon marine habitats (e.g., kelp forests, seagrass meadows) releasing carbon and compromising their ability to continue to capture and store carbon[21]. Protecting these habitats from disturbance from bottom-trawling will safeguard them and support their recovery.
  • While not directly relevant to the discussion of bottom-trawling within MPAs it should be noted that bottom-trawling is one of the fishing methods with the highest emissions from fuel use[22] with the overall carbon footprint of bottom-trawl fisheries estimated to be 2.8 times higher than non-trawl fisheries[23].

Impacts on small-scale fishers

  • Bottom-trawling competes for resources with small-scale fishers with lower impacts. Phasing out bottom trawling is essential for transitioning towards more sustainable, low-impact, low-carbon fishing in the EU and for giving small-scale fishers preferential access to fishing areas, and thus helping to restore vibrant coastal communities.

To sum it up, bottom trawling is a highly destructive practice that has no place in MPAs, regardless of what species or habitats those MPAs have been designated for. Banning it is a precondition for ecological restoration, sound management and the continuation of low-impact fishing activities.