2013 Volume 26 Issue 2 Pages 150-157
Ropes are recognized as an insidious ocean pollutant. Using a two-stage monitoring method, we estimated the proportion of ropes in marine debris: the weight of whole debris items including short ropes ( ≧6mm diameter, ＜5m length) that accumulated on a 5-m length of beach was measured 198 times; and the weight of polyolefin long ropes ( ≧0.3m length) that washed up on a 500-m length of beach was investigated monthly for 3 years. The weight of polyolefin ropes was estimated based on diameter and length due to the difficulty in disentangling ropes. On the beaches of Tottori Prefecture, the weights of accumulated short ropes, resin pellets and non-foamed plastic fragments were 9.92, 0.13, and 6.75 kg/hm, respectively; the weights of washed-up long ( ≧0.3m) and medium sized (0.3-5m) ropes were 35.1 and 15.1kg/(hm･Y), respectively. The half-lives of these items on beaches are not thought to be significantly different, suggesting that ropes are the heaviest debris in the Sea of Japan. Polyolefin ropes degrade to form fine fiber, which has a far larger surface area than polyolefin resin pellets. Therefore, ropes are considered to be the worst type of marine litter.
