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Comparative towing experiment to evaluate efficiency between beam trawl and dredge for capturing seafloor litter
Zijiang Yang1, Ren Soejima2, Daisuke Shiode3
1Department of Marine Biosciences, Tokyo University of Marine Science and Technology, Konan 4-5-7, Minato-Ku, Tokyo, 108-8477, Japan; Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Konan 4-5-7, Minato-Ku, Tokyo, 108-8477, Japan.
Toothed dredges capture significantly more seafloor litter than beam trawls, especially when including gear-entangled samples. Relying only on cod-end data underestimates litter abundance, highlighting the need for careful gear selection in marine litter surveys.
Area of Science:
- Marine pollution
- Oceanography
- Environmental science
Background:
- Seafloor litter is a growing environmental concern.
- Accurate quantification of marine debris is crucial for effective management.
- Existing survey methods may not capture the full extent of seafloor litter.
Purpose of the Study:
- To compare the litter capture efficiency of beam trawls and toothed dredges.
- To assess the contribution of gear-entangled samples to total litter collection.
- To inform the selection of appropriate gear for future seafloor litter surveys.
Main Methods:
- Simultaneous bottom-towing experiments using beam trawl and toothed dredge in the same region.
- Characterization and comparison of litter from cod-end and gear-entangled samples.
- Analysis of litter composition, focusing on material type and polymer identification.
Main Results:
- Dredges captured substantially more litter than beam trawls (9.42 ± 2.40 times greater overall).
- Gear entanglement significantly increased sample counts, particularly for beam trawls (28.2 ± 19.3 times more).
- Dredges were more effective at collecting denser materials like glass and metals; plastics, primarily polyethylene, dominated litter composition.
Conclusions:
- Beam trawl surveys significantly underestimate seafloor litter abundance compared to dredge surveys.
- Including gear-entangled samples is essential for accurate litter abundance estimates.
- Repeated sampling is necessary due to high variability, and gear choice critically impacts survey outcomes.
