Estimating local-scale patch size of seafloor litter from bottom trawling experiments

Area of Science:

• Marine pollution
• Environmental science
• Oceanography

Background:

• Seafloor litter poses a significant threat to marine ecosystems and coastal economies.
• Understanding the spatial distribution of seafloor litter is crucial for effective environmental management.
• Quantifying local-scale patchiness of seafloor litter has been a significant challenge due to limited spatial resolution in surveys.

Purpose of the Study:

• To develop and validate a novel method for quantifying the local-scale patch size of seafloor litter.
• To estimate the patch size of seafloor litter in Tokyo Bay using experimental bottom-towing data.
• To assess the temporal stability of seafloor litter patch size.

Main Methods:

• A patch size spectrum method was developed, utilizing geostatistical simulations.
• The method relates observed area-normalized catches to simulated catches across various potential patch sizes.
• Cross-validation was performed to assess the predictive accuracy of the method.

Main Results:

• The developed method demonstrated good predictive accuracy, with a typical relative error of approximately 20%.
• Application to Tokyo Bay data revealed a local-scale patch size of 134 meters for seafloor litter.
• This patch size is considerably smaller than the typical trawling transect length and showed temporal stability.

Conclusions:

• The patch size spectrum method offers a novel framework for quantifying seafloor litter heterogeneity at local scales.
• The findings highlight that seafloor litter distribution is characterized by smaller patch sizes than often assumed.
• The method is broadly applicable to other line transect sampling surveys in marine science and environmental monitoring.