The purpose of this study is to identify the flow resistance characteristics of the trawl net according to the towing speed of the vessel using two trawl nets designed and manufactured based on 2,000 HP. The trawl net consists of wings, bag and cod-end part, two types with wall area  of 747 m 2 (Sae Dong Baek) and 1,262 m 2 (Dong Baek) with differences in the size of the trawl net. The result of sea experiments are as follows: the flow resistance of trawl net  at the flow velocity  = 1 m/s or higher is affected by the difference in the composition of the cod-end rather than the wing or bag part of the Sae Dong Baek´s trawl net, Dong Baek´s the cod-end part has a  ratio value of 1.19, compared to Sae Dong Baek´s trawl net with a size of 120 m, and Dong Baek´s trawl net is small at 60 mm. Therefore, the water entering into the net cannot easily pass, which is considered to be a factor that increases resistance at the cod-end part. In the result of the experiment, it was found that  decreases exponentially when  increases which makes  . The constant  values when  = 1 m/s were 6.72 and 3.75, and  values were 1.14 and 0.94, showing a difference between the two nets as the flow velocity  increased. The height at the mouth of bottom trawl net decreases exponentially as the current velocity  increases; such height given by   where the constant  and  values are 0.85 for the increase in the flow velocity  and the  value when =1 m/s is 4.35. Therefore, this study investigated the flow resistance characteristics of trawl net at sea. It was possible to obtain more reliable information than previous studies by using a real fishing vessel with advanced underwater measurement devices. As a result, it was possible to analyze the underwater shape change of trawl net and the resulting flow resistance characteristics more quantitatively.

This study evaluated catch selectivity differences between sea pike (Sphyraena japonica) and Spanish mackerel (Scomberomorus niphonius) using a modified codend with square mesh side panels in bottom trawl. Sea trials were conducted with the covered codend technique widely used to estimate codend selectivity curves at the coastal sea of Yokji-do, Gyeongsangnam-do, from December 2024 to January 2025. Selectivity curves were fitted using a B-spline model for sea pike and a probit model for spanish mackerel. The estimated 50% retention lengths ( ) were 26.88 cm for sea pike and 42.92 cm for Spanish mackerel, with selection ranges () of 2.42 cm and 10.76 cm, respectively. Spanish mackerel was shown the broader and more gradual selectivity curve, while sea pike showed steeper selectivity. This study found that selectivity changes depending on the change in the net structure of the trawl tip. In addition, a difference in selectivity was observed for two species with different morphological characteristics.

This study aims to estimate the trawl net width based on the design drawing and towing condition of sampling trawl used in past surveys to improve the accuracy of estimation for fishery resources. To this end, the trawl gear was modeled as a flexible structure and numerically analyzed, and the analysis results were subjected to multiple regression analysis. As a result, a model was derived to calculate the net width by the towing conditions. When the towing conditions from past surveys were input into this model, it was confirmed that the net width increased in a natural logarithmic manner with the increase in the warp length and that decreased linearly as the water depth increased at the same warp length. For verification of the model, the theoretical formula of other study and this model were compared. As a result, despite the values of the two were slightly different, the tendency of changing net width by increasing warp length was consistent each other. Therefore, it is thought that the derived model can obtain the net width according to various towing conditions and can contribute to improving the accuracy of fishery resources estimation.

This study aimed to investigate the catch selectivity characteristics related to the mesh arrangement of the codend in bottom trawl. Sea trials were conducted using the covered codend method from January 16 to 17, 2024, off the southern coast of Gyeongsangnam-do, focusing on the side panels of diamond and square mesh codend. A probit model was used in the selectivity analysis to estimate retention probability curves for sea pike comparing the  , , and  selectivity lengths, the selection range ( ), and the corresponding  and  values. The estimated 50% selection lengths were 23.82 cm for the diamond mesh and 25.20 cm for the square mesh whereas the corresponding selection ranges were 5.23 cm for the diamond mesh and 3.71 cm for the square mesh. The  and  values for the square mesh were lower, at 35.91 and 36.71, respectively, compared to 37.65 and 38.45 for the diamond mesh. Additionally, the retention probability at a fork length of 15 cm was lower for the square mesh than for the diamond mesh. These findings provide practical insights for gear design while contributing to the reduction of bycatch and small size fish catches in bottom trawl.

This study investigated the species composition and community structure of aquatic organisms captured using coastal beam trawling in Gomso Bay, Jeollabuk-do, from January to December 2022. Throughout the experimental period, a total of 20,246 individuals belonging to 94 marine species were captured, with a combined biomass of 602,828 g. Fish exhibited the highest abundance, comprising 56 species, followed by crustacea (21 species), bivalvia (8 species), cephalopoda (5 species), gastropoda (3 species), and holothuroidea (1 species). The dominant species was Leiognathus nuchalis, constituting 14.0% of the total individuals, followed by Portunus trituberculatus at 12.1%, Oratosquilla oratoria at 10.4%, Crangon hakodatei at 9.9%, and Metapenaeus joyneri at 7.9%. The diversity index ranged from 1.72 to 2.55, with the lowest diversity observed in March and the highest in July. Cluster analysis based on species composition of the 27 most common species showed that aquatic organisms were divided into three groups: spring and summer organisms (Group A) and summer organisms (Group B) and autumn and winter organisms (Group C).

In the actual sea, the additional resistance due to external force such as wind, current and wave is accompanied, and the required power is added in response to these resistance. Especially when the ship is sailing at low speed, the effects of wind and current have a great impact on the safe control of the ship. Likewise, it is thought that the effects of wind and current have a great impact on the trawl ship control since the towing speed of a bottom trawl ship is a low speed of 3 to 4 knots. If the reduce of ship speed and the increase of engine power due to the influence of wind and current can be identified, the safe towing power can be calculated based on a given engine output. Thus, the appropriate size of a fishing gear can be determined. In this study, a total of 20 trawl operations were conducted for seasonal maritime research in the same research area according to the operation mode of propeller. Based on navigation data, trawl fishing data, and engine performance data acquired during the towing fishing gear, and data of ship speed, hull resistance, fishing gear resistance, wind force and current force according to an incidence angle were estimated. The overall power for these loads was calculated and compared with the measured engine power, and the effects of wind force and current force on the engine power were investigated.

The United States enforces the seafood import regulations so-called the Marine Mammal Protection Act (MMPA), and by 2023, all exports of aquatic products and processed fish products by fisheries which have not obtained an “Comparability Finding” from the National Oceanic and Atmospheric Administration will be completely banned. Therefore, to respond to the US MMPA, it is critical to identify technologies and methods used in worldwide for reducing bycatch of marine mammals. In particular, marine mammals are frequently caught in five fisheries (trawl, gill net, trap, stow net and set net) in Korea, which is facing a great challenge. This study presented bycatch reduction methods by five fisheries, classified the methods by country, and suggested appropriate reduction methods which can be applied in Korea.

This study was investigated in order to find composition and density of fisheries resource using bottom trawl in April, July, August, and November 2022 in the East China Sea. The average density of fisheries resource was estimated using the swept area method. As a result, 35 species were collected from the East China Sea. These included 21 fishes, six crustaceans, six cephalopods and two echinoderms. Seasonally, the average density of crustacean individuals per unit area were highest in November (692.1 inds./km 2 ), while cephalopod individuals per unit area were highest in August (39.4 inds./km 2 ). The average density of fish individuals per unit area were highest in August at 355.0 (inds./km 2 ).

This study quantitatively evaluated size selectivity for three netting shapes (T0; regular, T45, T90) and hanging ratio (35%, 70%) of T0 netting used for trawl codend. The size selectivity experiment was performed in a tank using a cube experimental model with a length of 50 cm on one side and 389 experimental individuals, jack mackerel (Trachurus japonicus). In the selectivity analysis, a selectivity curve was created based on the selection ratio using a logistic function, and the 25%, 50%, and 70% selection length and selection range  were obtained. The T0 netting was 19.54 cm when the 50% selective length, which is a selectivity evaluation index, had a hanging ratio of 35%, a selection range of 0.51 cm, and 22.70 cm and 3.08 cm for the hanging ratio of 70%. The T45 netting was 24.34 cm and 2.13 cm, and the T90 netting was 23.51 cm and 2.84 cm. The results of the T45 netting and the T90 netting are similar, and the 50% selection length and selection range were relatively larger than the T0 netting. There was a significant difference in the correlation between the circumference of the inner circle of the mesh by the shape of the netting and the body girth of the experimental individual (Pearson test,      ). There was no significant difference in the correlation between the selection ratio by the T0 netting, T45 netting, and T90 netting with a 70% hanging ratio (one-way ANOVA,   ). The results of this study showed that selectivity such as T45 netting and T90 netting appeared when the hanging ratio, which maximizes the area of T0 netting, was maintained at 70%.

In this study, a comparative test operation was conducted through the alternate haul method to examine the selectivity of the four mesh sizes (60 mm, 90 mm, 110 mm, and 130 mm) of the trawl codend. The selectivity was analyzed using the SELECT model considering the fishing efficiency (split parameter) of each fishing gear in the comparative test fishing operation in the trawl and the maximum likelihood method for parameter estimation. A selectivity master curve was estimated for several mesh sizes using the extended-SELECT model. As a result of analyzing the selectivity for silver croaker based on the results of three times hauls for each experimental gear, it was found that the size of the fish caught increased as the size of the mesh size increased. When the selectivity for each mesh size analyzed by the SELECT model considering the split ratio was evaluated based on the size of the AIC value, the estimated split model was superior to the equal split model. Based on the master curve, the 50% selection length value was 2.893, which was estimated to be 136 mm based on the mesh size of 60 mm. In some selectivity models, there was a large deviance between observed and theoretical values due to the non-uniformity of the distribution of fished length classes. As a result, it is considered that appropriate sea trials and selectivity evaluation methods with high reliability should be applied to present trawl fishery resource management methods.