Ship-based visual observation underestimates plastic debris in marine surface water

Area of Science:

• Marine Biology
• Environmental Science
• Oceanography

Background:

• Ship-based visual observation is a common method for monitoring floating marine debris.
• The accuracy and limitations of visual observation methods for marine debris detection remain insufficiently verified.

Purpose of the Study:

• To assess the detection performance of visual observation surveys for floating marine debris.
• To identify the characteristics of marine debris overlooked by visual observations.
• To compare the effectiveness of visual surveys with surface trawling in diverse South Korean coastal areas.

Main Methods:

• Conducted simultaneous visual observation surveys and surface trawling in three distinct coastal regions of South Korea.
• Quantified floating marine debris using both methods.
• Analyzed the characteristics of debris missed by visual surveys, focusing on factors like buoyancy and color.

Main Results:

• Visual observation recorded a mean floating debris density five times lower than surface trawling.
• Debris with reduced buoyancy and transparent characteristics were significantly underestimated by visual surveys.
• Coastal areas with high densities of plastic bags and sheets showed the greatest discrepancies between methods.

Conclusions:

• Visual observation surveys alone can significantly underestimate the true density of floating marine debris.
• Loss of buoyancy and transparency are key factors leading to underestimation.
• Integrating supplementary methods, such as surface trawling with macro-mesh nets, is crucial for accurate marine debris assessment.