Changes in abundance and composition of anthropogenic marine debris on the continental slope off the Pacific coast of northern Japan, after the March 2011 Tohoku earthquake

Abundance and composition of anthropogenic marine debris were assessed on the basis of six bottom trawl surveys conducted on the continental slope off Iwate Prefecture, Pacific coast of northern Japan, in 2003, 2004 and 2011, and the temporal changes due to the Tohoku earthquake and tsunami in March 2011 evaluated. In 2003 and 2004, 54-94 items km−2 of marine debris, dominated by sea-base sourced items mainly comprising fishing gear and related items from adjacent fishing grounds on the continental shelf, were quantified. In the post-earthquake period, the density increased drastically to 233-332 items km−2, due to an increase in land-base sourced items generated by the tsunami. However, a major increase in abundance after the disaster, compared to the total amount of tsunami debris swept into the sea, was not found. Additional sources of land-based debris from the adjacent continental shelf are suggested in the present waters.