This study examined the relationships between acoustic activity of the finless porpoise (Neophocaena asiaeorientalis) and marine environmental variables in Hadong, in the southern coast of Korea, using long-term passive acoustic monitoring. Acoustic data were collected with a hydrophone (F-POD) from July 8 to August 16 2023, and acoustic indices (DPM, DP10M, and click-based metrics) were integrated with in situ observations and model analysis environmental data. Generalized additive models indicated that chlorophyll-a and dissolved oxygen were the main predictors of acoustic activity whereas physical oceanographic variables (temperature, salinity, and sea surface height) had no significant effects. Chlorophyll-a showed a strong non-linear positive effect with finless porpoise activity increasing rapidly up to approximately 2 mg/m³ and then reaching a plateau. Dissolved oxygen exhibited a negative linear relationship, implying indirect ecological effects mediated by prey availability. In addition, current velocity was negatively related to click intensity. These results indicate that finless porpoise habitat use is more closely associated with productivity-related factors than with physical conditions. This research offers quantitative insights into prey-driven habitat selection, supporting the development of management and bycatch mitigation strategies.

This study aimed to improve safety and reduce labor intensity in offshore crab pot fisheries through the development of six types of automated fishing gear: a bait cutter, bait crusher, mainline arranging device, automatic pot hauler, cold water tank system, and crab pot unloading device. Sea trials demonstrated that both the bait cutter and bait crusher effectively reduced overall operation time. The mainline arranging device lowered the risk of injury compared to the conventional manual handling. The automatic pot hauler enabled the automated separation of crab pots, significantly decreasing the physical workload. The cold water tank system facilitated the efficient sorting of live crabs while enhancing onboard safety. Additionally, the crab pot unloading device reduced physical strain on workers and minimized catch damage. A satisfaction survey revealed high levels of approval among fishers, particularly regarding labor reduction and improved safety. Economic analysis indicated that vessels equipped with the automated gear experienced reduced overall operating costs. These findings suggest that the developed technologies will contribute to the long-term sustainability and modernization of offshore crab pot fisheries.

This study examined the operational characteristics and fishing performance of an offshore pot fishery targeting swimming crabs (Portunus trituberculatus) to identify key issues and proposed strategies for improving efficiency and fisher safety. Analysis was based on approximately one year of fishing logbook data recorded by a pot fishing vessel. The total annual catch amounted to 30,084 kg, with the highest catch per unit effort of 0.07 kg per trap observed in autumn at depths of 20–25 m. No crabs were caught below 15℃ while the peak catch occurred at around 25℃. Catches were geographically concentrated in the mid-northern West Sea, especially near Taean and Boryeong. Economically important bycatch species, including sand crabs, octopus, and turban snails, exhibited distinct spatial distributions. An average of 1,996 traps were deployed per operation with a low loss rate of 1.6 traps. Based on field-level observations, this study proposed the development of automated or semi-automated equipment, such as bait cutters, automatic mainline arranging devices, pot-hauling and separation systems, chilled water tanks for sorting, and automated unloading systems. These technologies are expected to reduce labor demands, improve safety, and enhance the overall operational efficiency of the pot fishery.

We presented foundational findings regarding the occurrence and acoustic characteristics of the finless porpoise through passive acoustic and visual surveys conducted on the southern coast of Korea, specifically at Hadong Jungpyeong Port. Over a survey period spanning from July 8 to August 16, 2023, totaling 40 days, we observed peaks in the number of clicks produced by this species on July 15, July 24, August 4, August 11, and August 16. The highest count, totaling 18,924 clicks, was recorded on July 15th, while the lowest count, at 3,888 clicks, occurred on August 8th. Examining the acoustic characteristics throughout the diurnal cycle, we found that the peak activity in terms of DPM (detection positive minute for one hour), DP10M (DPM for ten minutes), and overall number of click sounds was observed between 05:00 and 08:00, with a secondary peak occurring from 17:00 to 18:00. The quietest period was noted between 23:00 and 02:00. Furthermore, there was a significant increase in the number of clicks from sunrise, with the maximum count of 21,581 clicks recorded at 6 AM. This count gradually decreased until noon, experienced a slight increase thereafter, peaked again at sunset, and then declined. The dominant frequency mode of this species was 126 kHz, with a concentration ranging from 112 to 136 kHz. The average duration of a click sound was 127 ㎲, with approximately 16 sinusoids (cycles) within each click sound and an average cycle length of approximately 7.9 ㎲. These findings from our study are anticipated to serve as foundational data for the development of a Korean pinger and acoustic warning system.

Recently, domestic fishing production of Japanese horse mackerel has been continuously decreasing. To achieve sustainable fishing of this species, it is essential to acquire its target strength (TS) for accurate biomass estimation and to study its ecological characteristics. To date, there has been no TS research using a broadband echosounder targeting Japanese horse mackerel. In this study, for the first time, we synchronized an underwater camera with a broadband frequency (nominal center frequency of 200 kHz, range: 160-260 kHz) to measure the TS according to the body size (16.8-35.5 cm) and swimming angle of the species. The relationship between Japanese horse mackerel length and body weight showed a general tendency for body weight to increase as length increased. The pattern of the frequency spectra (average values) by body length exhibited a similar trend regardless of body length, with no significant fluctuations in frequency observed. The lowest TS value was observed at 243 kHz while the highest TS values were recorded at 180 and 257.5 kHz. The frequency spectra for the swimming angles appeared to be flat at angles of –5, 0, 30, 60, 75, and 80° while detecting more general trends of frequency spectra for swimming angle proved challenging. The results of this study can serve as fundamental data for Japanese horse mackerel biomass estimation and ecological research.