Establishment of coastal visual survey method for floating marine plastic debris

Abstract

Visual survey is the most basic and simple method to assess the pollution status of floating plastic debris (FPDs). Most of the visual surveys were conducted using a ship of opportunity, and it is difficult to compare data produced among different studies because the survey methods and parameters such as observing transect width and minimum cut-off size and type of plastic items are not unified. The purpose of this study is to systematically evaluate the survey method in coastal areas using a small vessel to contribute to the production of unified data. We compared two boat speeds (5 and 10 knots) and recorded the floating items as follows: distance of item from the boat (0-10, 11-20, 21-30, 31-40, 41-50, 51-100, >100 m), size of item (2.5-5, 5-20, 20-40, 40-60, >60 cm) and type of item (plastic fishing gear, plastic packaging, other plastic and non-plastic products). A survey area in this study was set as 0.42 km2. The density of FPDs was 2.18 times higher at 5 knots than 10 knots, and more FPDs were identified at 5 knots in all FPD size ranges. As the distance from the ship increased, the density of items gradually decreased. Although there was a variance depending on the sampling season, the FPD density steeply decreased from 11-20 m range. As a result, it was recommended for the coastal visual survey for FPDs using a small scale boat that covering minimum of 0.42 km2 study area at 5 knots, and recording the size > 2.5 cm and type of items within 10 m distance from the boat. A pilot visual survey was done using the established method in aquafarm area (Jinhae, JH), urban and riverine area (Suyeong, SY), and rural area (Geoje, GJ). The FPD density was ranked in order of JH (243 items/km2), SY (236 items/km2) and GJ (143 items/km2). The items in 2.5-5 or 6-20 cm size range and plastic packaging were dominant in all three areas. A relatively high proportion of plastic fishing gear was observed in JH (44%).