Seafloor litter - Density per trawl normalized per km² 2011/2021 v2021

This visualization product displays the density of seafloor litter per trawl per year.<br><br>EMODnet Chemistry included the collection 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). <br>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.<br><br>In cases where the wingspread and/or number of items were unknown, data could not be used because these fields are needed to calculate the density. Data collected before 2011 are affected by this filter.<br><br>When the distance reported in the data was null, it was calculated from:<br>- the ground speed and the haul duration using this formula: Distance (km) = Haul duration (h) * Ground speed (km/h);<br>- the trawl coordinates if the ground speed and the haul duration were not filled in.<br><br>The swept area is calculated from the wingspread (which depends on the fishing gear type) and the distance trawled:<br>Swept area (km²) = Distance (km) * Wingspread (km)<br><br>Densities have been calculated on each trawl and year using the following computation:<br>Density (number of items per km²) = ∑Number of items / Swept area (km²)<br><br>Percentiles 50, 75, 95 &amp; 99 have been calculated taking into account data for all years.<br><br>More information on data processing and calculation are detailed in the document attached.