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 examined the offshore eel trap fishing process using one year of fishing logs and fishermen’s insights to identify
key operational challenges and propose equipment improvement for greater efficiency and safety. Conger eel catches varied
significantly by season, depth, and temperature, peaking in winter at 85–90 m and 23°C. The western waters of Jeju Island
were identified as a major fishing ground, with the highest catch recorded in November and the lowest in July, reflecting
seasonal trends. Each fishing operation deployed about 10,000 traps, with an average loss of 38 traps, posing economic
concerns. The process involved intensive manual labor in bait preparation, trap retrieval, catch separation, line loading, and
unloading, leading to high physical demands and safety risks. To address these issues, the study proposed automation through
the development of a line loading device, trap cleaning device, bait processing machine, and automatic catch separator.
These innovations could reduce the labor force required by one to two workers per process, alleviate workloads, and enhance
resource management. By integrating quantitative logbook analysis with field-based knowledge, this study offers practical
value. Further research is recommended on automation development, cost-effectiveness, and field validation to support safer
and more sustainable eel trap fisheries.
This study aimed to enhance the operational efficiency and safety of offshore eel trap fisheries by developing six types of automated fishing equipment: a bait crusher, bait cutter, main line arranging device, trap cleaning device, eel sorting device, and fish pump system. Sea trials demonstrated that the bait crusher and bait cutter significantly reduced manual labor and processing time while maintaining bait quality. The main line arranging device improved productivity and safety by automating the sorting of looped cords. The trap cleaning device effectively removed fouling organisms using high-pressure water and rotating brushes. The eel sorting device enabled automatic size-based selection, improving resource management and operational efficiency. The fish pump system transferred eels rapidly with minimal physical damage, reducing unloading time by over 80% and decreasing labor requirements. A satisfaction survey of fishery participants confirmed that all developed devices were highly effective in reducing workload, enhancing safety, and improving operational performance. The automated equipment developed in this study is expected to contribute to the sustainable management of offshore eel trap fisheries and to offer potential applicability to other coastal and offshore fisheries.
This study aimed to measure the in-situ target strength (TS) of the moon jellyfish (Aurelia aurita) using a 200 kHz scientific echo sounder in a natural coastal environment. The acoustic survey was conducted in the coastal waters of Soho Port, Yeosu, Korea, from June 4 to 5, 2024. TS measurements were performed by installing the transducer in both horizontal and vertical orientations, and the TS distribution characteristics were analyzed. The measured TS values ranged from -89.8 to -64.8 dB in the horizontal direction and from -90.0 to -59.1 dB in the vertical direction, showing no significant difference between detection orientations (p<0.05). Additionally, a bell diameter-wet weight relationship for Aurelia coerulea was derived based on the specimens collected at the survey site. The empirical TS model proposed by Mutlu (1996) was applied to estimate TS values using the measured morphological data, and the results exhibited a similar trend to the field-measured TS distribution. These findings provide fundamental data for acoustic monitoring and stock assessment of jellyfish populations in natural environments.
The Indian Ocean is the second-largest tuna fishing ground in the world, accounting for approximately 1.2 million tonnes (23%) of the estimated 5.2 million tonnes of global commercial tuna catch in 2023. This study examined the relationship between tuna catches, specifically skipjack, bigeye, and yellowfin tunas, and prey biomass (Nautical Area Scattering Coefficient, NASC) estimated from acoustic surveys conducted in the southwestern Indian Ocean from 20 April to 15 May 2019. Environmental variables were derived from the Copernicus Ocean Model, and tuna length data from the IOTC. The estimated total tuna catch in the study area was approximately 166,400 tonnes, with the northwestern region showing the highest catches and NASC values. Tuna catches increased with NASC; however, the relationship was non-linear. While skipjack showed no significant correlation with NASC, bigeye and yellowfin tunas exhibited weak but significant positive correlations. Environmental analysis revealed that the northern waters had high surface temperatures, low salinity, and low oxygen levels, with mid and deep layers characterized by low temperature, salinity, oxygen, and chlorophyll. These findings offer a foundation for understanding tuna distribution in relation to prey and environmental conditions, highlighting the need for future species- and fishery-specific studies to support sustainable tuna resource management.
Reconstructing reliable length composition data is critical for applying length-based age-structured stock assessment models, particularly in data-limited situations. This study suggests an approach to reconstruct the length composition of small yellow croaker (Larimichthys polyactis) caught by the offshore gillnet fishery in Korean waters where existing length data often lack temporal coverage and representativeness. To address this issue, measured data by size-specific boxes were integrated with auction-based landing data. Using the number of individuals per size-specific box as a proxy, a nonparametric bootstrap resampling method was applied to generate probabilistic length composition estimates. Normality tests and ANOVA revealed non-normal and non-linear patterns in data, supporting the use of nonparametric methods and the classification of size-specific boxes. Approximately 130,000 boxes (30 million individuals), including those with partial missing data, were analyzed using an automated R-based workflow, and a hot-deck method was used for imputation. The reconstructed length compositions showed stable distributions with low standard errors, indicating improved representativeness compared to the raw data. This approach provides a practical framework for generating reliable length composition inputs to enable the application of length-based age-structured stock assessment models, particularly when age composition data are limited or poor.
The intensity of typhoons is increasing due to the effects of global warming. These typhoons pass through the coast of Korea on an average of two to three times a year, causing a lot of damages. The harbor shelters for avoiding typhoons are congested with large and small vessels, so the distance between vessels is short, the veered out anchor chain is long, and there is a risk of collision due to dragging anchor caused by powerful winds. Therefore, this study aimed to quantitatively identify the degree of influence of external force factors on the experimental vessel during anchoring, and to provide basic data for setting the critical point of tension that can cause dragging anchor. The range of outlier of tension observed in the experimental vessel was -0.90 to 4.60 tons, and the ratio of outlier was approximately 5.07%. As a result of analyzing 184,008 samples of external force corresponding to this, a weak negative linear relationship was shown in the correlation between tension and external force for the current and wind direction whereas a positive correlation was shown for wind speed and current velocity. In this study, the effects of external force during anchoring on tension were in the order of wind speed, current velocity, current direction, and wind direction, and the ratios were 85.46%, 6.28%, 4.79%, and 3.47%, respectively. In future studies, we plan to quantitatively understand the relationship between holding power and tension indicated by the tension meter to determine the tension value that becomes the critical point of the dragging anchor.
This study was attempted to solve the problem that the current training is not consistent with the actual working environment of the fishing vessel, even though the advanced fire extinguishing training for international fishing vessels is mandatory. As a result of the survey, the lack of timely use of fire extinguishing equipment and the difficulty of organizing the fire extinguishing organization were found, and the main problems were analyzed as low understanding of fixed fire extinguishing facilities, low awareness of fire-related laws and regulations, and inefficiency of fire extinguishing training. It was found that the current Seafarers Act does not clearly define the roles and responsibilities of advanced fire extinguishers, and lacks specific standards for designated educational institutions, so there is a problem that the accuracy and reliability of the training contents with the STCW-F Convention and STCW Convention are inconsistent. In addition, it has been confirmed that the fire extinguishing organization, internal communication, and fire extinguishing training in ships, as stipulated in international agreements, are not properly reflected in the domestic curriculum. In particular, the current training consists of general contents that do not take into account the characteristics of fishing vessels, so there is a lack of practical emergency response fire extinguishing training manuals. Therefore, this study proposes the development of customized training content for fishing vessels considering the special working environment and risk factors of fishing vessels based on international agreements, and emphasizes the need for policy support, such as strengthening participation of fishing vessels in education and training, and establishing a legal basis for the operation of emergency fire extinguishing organizations.
This study presents the implementation of a direct power control (DPC) system based on virtual flux for an eco-friendly ship utilizing a low voltage DC distribution within a Simulink environment. The proposed system regulates the DC bus voltage and the instantaneous power of the generator. The electrical load of the generator is classified into three levels (low, medium, and high) and subjected to ±10% variations. Under these conditions, the characteristics of the DC bus voltage and current, instantaneous active and reactive power as well as the voltage and current of the generator, are thoroughly analyzed. The simulation results indicate that the DC bus voltage and instantaneous active and reactive power remain stable and well-regulated at their set-points despite load fluctuations. Furthermore, the voltage and current of the generator, consistently maintain sinusoidal waveforms and remain in phase. These findings validate the effectiveness of the proposed virtual flux-based direct power control strategy, demonstrating its suitability for DC distribution applications in maritime vessels.