Trapped twice: Discovering the impact of marine benthic plastic debris on small organisms caught in trawl nets
A research group led by Professor Yoshiki Matsushita of the Graduate School of Integrated Science and Technology at Nagasaki University is studying the impact of seafloor plastic debris on small benthic organisms caught by bottom trawling. As part of this research, the team collaborated with local fishers from the Tachibana Fisheries Cooperative Association in Nagasaki City to investigate the quantity, weight, and types of debris collected in bottom trawl nets. Their findings revealed that the amount of seafloor debris in Tachibana Bay is lower than that reported in any other coastal area around Japan where similar surveys have been conducted.
This study quantifies the marine benthic debris caught in a coastal trawl fishery and its impact on capturing small organisms and codend selectivity. From April to September in both 2023 and 2024, marine debris caught during regular fishing operations by two beam trawlers in Tachibana Bay, Nagasaki, was collected and analysed. Any marine organisms found within the debris were identified and measured. The selectivity experiment was conducted in October 2024, adding five plastic bags inside the codend for experimental tows and without plastic bags for control tows. The codend selectivity for the experimental and control tows was estimated either from logistic or contact probability models. There were 1,249 pieces of marine debris weighing 45.04 kg collected, which is a small quantity in the coastal waters of Japan, with plastic exceeding 94% by both number and weight. Among the plastic debris, 250 organisms of 23 species were found trapped, showing a positive correlation (r = 0.71, p<0.001) between marine benthic plastic debris and bycatch. Three species, Metapenaeopsis barbata, Acropoma japonicum, and Nuchequula nuchalis, were selected for the selectivity analysis. The contact probability model fits better for experimental tows, while the logistic model fits better for control tows for all three species. The estimated contact probabilities were 0.62, 0.48, and 0.59 for the three species. The selectivity curve indicated higher retention probabilities for smaller fish in nets containing plastic bags, suggesting that marine debris adversely affects the selectivity of trawl nets by trapping small organisms.
Keywords: Marine debris impact; Trawl net selectivity; Benthic megafauna; Contact probability model; Blocking of mesh; Trapped in debris; Trawl gear-debris interaction
Study location and GPS tracks of two trawlers operated in Tachibana Bay during 2023. The lines, shown in different colours, represent tracks of some of the fishing operations conducted by the two trawlers during the study period.
Covered codend setup of the codend selectivity experiment; trawl net codend (brown) and cover net (black). (A) Before fishing operation and (B) After fishing operation with catch in the codend
Composition of marine benthic debris by main categories collected by the two trawlers during the study period: (A) Percentage of debris by number; (B) Percentage of debris by weight.
Organisms found trapped inside marine benthic plastic debris: (A) Fish and shrimp inside a convenience store bag, (B) Fish inside the food packet.
Plot showing the relationship between the number of benthic plastic debris and the number of bycatch organisms trapped inside the trawl net over two years of study (r=0.71); the grey shaded area represents the 95% confidence interval
Portion retained and the estimated selection curve of (A) M. barbata, (B) A. japonicum, and (C) N. nuchalis in both the experimental tow and control tow.
Journal: Marine Pollution Bulletin
Title: Trapped twice: Discovering the impact of marine benthic plastic debris on small organisms caught in trawl nets
Authors: Saranya Raju a, Yoshiki Matsushita a, b, *
aGraduate School of Fisheries and Environmental Sciences, Nagasaki University, Nagasaki, Japan
bOrganization for Marine Science and Technology, Nagasaki University, Nagasaki, Japan
*Corresponding Author: Yoshiki Matsushita (ORCID: 0000-0002-7109-9779)
DOI: 10.1016/j.marpolbul.2025.118127
Publication Date: 15 May 2025
For more details, please see the full article in Nagasaki University’s Academic Output SITE.
