More dense litter items sink when they enter the marine environment and therefore it is essential to assess the amount of litter on the seafloor, as well as that washing ashore or floating on the surface, to get a complete picture. To do this OSPAR has developed an indicator using information on litter caught during fisheries survey trawls to assess the relative distribution of litter on the sea floor. In future years, when a longer data series has been recorded, it will also be possible to assess trends in the relative abundance of seafloor litter over time.
Litter from the seafloor caught during a fisheries survey trawl ©Cefas
The most recent assessment of seabed litter was undertaken in 2017 as part of OSPAR's Intermediate Assessment of the state of the marine environment of the North-East Atlantic. This showed Litter is widespread on the seafloor across the areas assessed, with plastic the predominant material encountered. In the areas assessed, higher amounts of litter and plastic are found in the eastern Bay of Biscay, southern Celtic Sea and English Channel than in the northern Greater North Sea and Celtic Seas.
This could be due to larger anthropogenic inputs, rivers, prevailing winds and / or currents. Previous studies have shown the Bay of Biscay to receive large amounts of litter from local rivers and transport that may result from large-scale circulation in the sub-region as a whole. Floating and sinking litter also follow different pathways, and gather in different hotspots, which do not necessarily overlap. For example, the beach litter hotspot in the Skagerrak is not replicated in the seafloor litter.
IA2017 - Composition and Spatial Distribution of Litter on the Seafloor - Total Counts of Plastic Items Caught in Trawls:
Data available here: https://odims.ospar.org/maps/861/view