Distribution and composition of litter on seabed of Tokyo Bay and its age analysis

Abstract

Litter amounts and composition on the seabed of Tokyo Bay were investigated during 1995-2000. More than 30 different types of litter items were collected and the most abundant were plastics and metals, accounting for about 90% of the total. The amounts of litter decreased from 338 items/km² (20.1 kg/km² in weight) in 1995 to 185 items/km² (10.4 kg/km² in weight) in 2000. The decreasing rate during 1995 to 2000 was 45.3% in number and 48.3% in weight. This reduced trend of litter amounts during the recent six years may reflect the reduction of discarded litter in our daily life and into the sea and the removal of litter by bottom trawl fishing boats. The production year of beverage cans collected by trawl surveys during 1996-2000 were examined and age analysis of cans by the Virtual Population Analysis (VPA) method was carried out. The value of the survival rate of the beverage can in the sea estimated by the VPA method was 0.47 for alurminum cans and 0.38 for steel cans.