Visual observation surveys from ships are commonly used for monitoring floating marine debris, but their detection performance has not yet been fully verified. Here, simultaneous visual observation surveys and surface trawling were conducted in three coastal areas of South Korea, each with distinct characteristics. The extent of floating debris missed by visual observations was assessed, and the characteristics of overlooked debris were identified. The mean density of floating debris observed visually was five-fold lower than that obtained from surface trawling. Loss of buoyancy and transparent colour of debris were identified as major factors contributing to the significant difference in density between the two survey methods. Our findings suggest that visual observation can underestimate the density of floating debris, especially in areas with abundant plastic bags and sheets. Supplementary methods such as surface trawls with macro-sized mesh are recommended to accurately assess the level of contamination from floating debris.

中文翻译：

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船基目视观测低估了海洋表层水中的塑料碎片


船舶目视观测调查通常用于监测漂浮的海洋垃圾，但其探测性能尚未得到充分验证。在这里，在韩国的三个沿海地区同时进行了目视观测调查和水面拖网捕捞，每个地区都有其独特的特点。评估了目视观察遗漏的漂浮碎片的程度，并确定了被忽视的碎片的特征。目测观察到的漂浮物的平均密度比从水面拖网中获得的密度低 5 倍。浮力的损失和碎片的透明颜色被确定为导致两种调查方法之间密度显着差异的主要因素。我们的研究结果表明，肉眼观察可能会低估漂浮物的密度，尤其是在塑料袋和塑料片丰富的地区。建议使用补充方法，例如使用大尺寸网眼的表面拖网，以准确评估漂浮物的污染水平。