Spatial distribution of floating marine debris in offshore continental Portuguese waters

This study presents data on abundance and density of macro-floating marine debris (FMD), including their composition, spatial distribution and potential sources off continental Portugal. FMD were assessed by shipboard visual surveys covering ± 252,833 km2 until the 220 nm limit. The FMD average density was 2.98 items/km2 and abundance amounted to 752,740 items. Unidentified plastics constitute the major bulk of FMD (density = 0.46 items/km2; abundance = 117,390 items), followed by styrofoam, derelict or lost materials from fisheries, paper/cardboard and wood material. The North sector of the area presents higher FMD diversity and abundances, probably as a result of the high number of navigation corridors and fisheries operating in that sector. Most FMD originate from local sources, namely discharges from vessels and derelict material from fisheries. Considering the identifiable items, cables and fishing lines were the only fishing related items among the top ten FMD items in Portuguese offshore waters.