Faculty of Fisheries, Kagoshima University, Kagoshima 890-0056
Plastic pipes are a major item of beach litter on the shores of the Seto Inland Sea. They are also frequently seen on the shore of the north Pacific. This paper investigates the scattering of plastic pipes on the coast of the Seto Inland Sea. The pipes are used in oyster farming, and are divided into “pipes” about 205 mm long used for hanging, “broken pipes” cut at harvesting time, “short pipes” about 15 mm long used for spat collection and “washers” attached to the end of collectors. Scattered pipes were collected from 251 beaches, and the locations of drifting pipes on the sea surface were verified by visual observation from a ship. On average, 7.5 short pipes, 4.5 broken pipes and 2.9 pipes were found per m2 of beach. The discovery rate of pipes, broken pipes and washers on the coast was higher in the western part of the Seto Inland Sea than in the eastern part. The average density of pipes and broken pipes floating on the sea surface tended to vary in the same way as their presence on the coast. Short pipes, however, were relatively evenly distributed along the entire Seto Inland Sea coast.