Comparative towing experiment to evaluate efficiency between beam trawl and dredge for capturing seafloor litter

In this study, bottom-tow experiments using beam trawl and toothed dredge were conducted simultaneously in the same region to collect seafloor litter. Litter from both gear types, and from different collection parts (cod-end and gear-entangled samples), was characterized and compared. The results showed that dredges captured substantially greater amount of seafloor litter than beam trawls. For cod-end catches, dredge was 38.5 ± 12.7 times more efficient than beam trawl in terms of litter count, while for total catches (cod-end and gear-entangled samples), dredge collected 9.42 ± 2.40 times greater. Gear entanglement increased the total number of samples collected. In beam trawl, entangled litter has 28.2 ± 19.3 times larger number of samples than the cod-end, whereas in dredges, the ratio was 3.55 ± 1.45. These findings demonstrate that relying solely on cod-end samples can cause substantial underestimation of seafloor litter abundance, and that beam trawl surveys underestimate abundance compared with dredge surveys. Composition analysis revealed that dredges were more effective than beam trawls at capturing heavier and denser materials such as glass and metals. In addition, plastics dominated seafloor litter, and polyethylene (PE) was the dominant polymer type. On the other hand, large variability among sampling events indicates that estimates from a single tow are unreliable, highlighting the need for repeated sampling. This is the first study to directly compare the capture efficiency of different bottom-tow gears in the same area. The results provide a reference for future seafloor litter surveys, particularly in selecting gear type and developing sampling plans.