Seafloor litter - Density per trawl normalized per km² 2011/2024 v2025

This visualization product displays the density of seafloor litter per trawl.

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).
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 bottom trawl surveys.

In cases where the wingspread and/or the number of items were/was unknown, it was not possible to use the data because these fields are needed to calculate the density. Data collected before 2011 are concerned by this filter.

When the distance reported in the data was null, it was calculated from:
- the ground speed and the haul duration using the following formula: Distance (km) = Haul duration (h) * Ground speed (km/h);
- the trawl coordinates if the ground speed and the haul duration were not filled in.

The swept area was calculated from the wingspread (which depends on the fishing gear type) and the distance trawled:
Swept area (km²) = Distance (km) * Wingspread (km)

Densities were calculated on each trawl and year using the following computation:
Density (number of items per km²) = ∑Number of items / Swept area (km²)

Percentiles 50, 75, 95 & 99 were calculated taking into account data for all years.

More information on data processing and calculation are detailed in the attached document.

Warning: the absence of data on the map does not necessarily mean that they do not exist, but that no information has been entered in the Marine Litter Database for this area.