This visualization product shows the density of seafloor litter per trawl per year.

EMODnet Chemistry included the gathering of marine litter in its 3rd phase. Since the beginning of 2018, data of seafloor litter collected by international fish-trawl surveys have been gathered and processed in the EMODnet Chemistry Marine Litter Database (MLDB). The harmonization of all the data has been the most challenging task considering the heterogeneity of the data sources, sampling protocols (OSPAR and MEDITS protocols) and reference lists used on a European scale. Moreover, within the same protocol, different gear types are deployed during fishing bottom trawl surveys.

To calculate the density, the swept area of the trawl is required. The swept area is calculated from the wingspread (which depends on the fishing gear type) and the distance trawled. In the cases were the wingspread and/or the trawled distance are unknown, effective values were calculated from available information, when possible, specifically, the distance:
Distance =Haul duration Ground speed While the calculation of the effective wingspread is based in a general formula (van Hal, 2017) which considers other parameters known of the net, thus introducing some inaccuracies: Wingspread=doordpread0.18870+5.87280 Doorspread = 14.2 * log(Depth) = 16.72 * log(Warp_length) + 18.49 This method may be improved in the future. The used formula for the swept area and density is: Density (number of items per km²)= (∑number of items)/(Swept area)

Percentiles 50, 75 & 95 have been calculated taking into account data from all years.

More information is available in the document attached.