• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.5
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• pp.625-637
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• 2022

The southern coast of the East Sea is an important area affected by large warm currents as it connects the coastal waters of Jeju Island, the South Sea, and Dokdo. From 2017 to 2021, the average catch per unit effort (CPUE; kg/day/ship) of set net fishery at six ports in the Gyeongbuk region off the southern coast of the East Sea was the highest in Gampo, Gyeongju, and the lowest in Hupo, Uljin. Although the seasonal variation in the CPUE differed by region and year, it was generally high in autumn. In the set net fishery in Pohang from 2019 to 2021, we identified 72 species, which decreased to 56 species in 2019, 46 in 2020, and 41 in 2021. The species diversity index slightly increased over the three-year periods. We found positive correlations between the total catch (kg) of subtropical species in autumn and the water temperature at 50 m. Among the most abundant species, we found substantially positive correlations between the CPUE of Scomber japonicus, Scomberomous spp. and Carangids. We also noted positive correlations between the CPUE of Todarodes pacificus, Seriola spp. and Carangids.

• Journal of Environmental Science International
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• v.30 no.7
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• pp.585-595
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• 2021

We used seawater temperature data, measured in the Garolim Bay, to analyze temperature variation on an hourly and daily basis. Lagrange's interpolation using before and after data was applied to restore nonconsecutive missing temperature data. The estimated error of the data restoration was 0.11℃. Spectral analyses of seawater temperature showed significant periodicities of approximately 12.4 h (semidiurnal tide) and 15.0 d (long-period tide), which is close to those of M₂ and M_f partial tides. Variation in seawater temperature was correlated more with tidal height than with air temperature around the Garolim Bay. In June and December, when the seawater temperature difference between the inside and outside of the Garolim Bay was very large, the periodicities of 12.4 h and 15.0 d were highly prominent. These results indicate that the exchange of seawater between the inside and outside of the Garolim Bay induced variations in seawater temperature owing to tide. Understanding temperature variation because of tide helps to prevent abnormal mortality of cultured fish and to predict seawater temperature in the Garolim Bay.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.59 no.2
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• pp.99-109
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• 2023

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.

• Smart Media Journal
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• v.11 no.9
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• pp.64-74
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• 2022

A number of studies related to underwater robots are being conducted to utilize marine resources. However, unlike ordinary drones, underwater robots have a problem that it is not easy to locate because the medium is water, not air. The monitoring and positioning program of underwater robots, an existing study for identifying underwater locations, has difficulty in locating and monitoring in small spaces because it aims to be utilized in large spaces. Therefore, in this paper, we propose a three-dimensional positioning program for continuous monitoring and command delivery in small spaces. The proposed program consists of a multi-dimensional positioning monitoring function and a ability to control the path of travel through a three-dimensional screen so that the depth of the underwater robot can be identified. Through the performance evaluation, a robot underwater could be monitored and verified from various angles with a 3D screen, and an error within the assumed range was verified as the difference between the set path and the actual position is within 6.44 m on average.

• Journal of Korea Trade
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• v.27 no.2
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• pp.47-60
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• 2023

Purpose - This paper assesses the trade potential and efficiency of Korea and China in the aquatic products trade. Trade efficiency and potential are the main factors that affect the growth of a country's trade. In this study, a time-varying stochastic frontier trade gravity model was constructed to analyze the trade potential and efficiency between Korea and China. By integrating the results of trade theory and empirical analysis, measures and suggestions were proposed to encourage the release of trade potential of fish exports between Korea and China. Design/methodology - In this paper, GDP per capita instead of economic size was chosen as an explanatory variable, and population size and relative distance were selected as explanatory variables to measure trade potential. For trade non-efficiency terms, regional organizations, political factors, and economic factors were mainly considered, and variables such as free trade agreements, political stability, regulatory quality, government efficiency, currency freedom, investment freedom, financial freedom, and trade freedom were selected. Panel data for South Korea and 14 aquatic products trading partners (including China) from 2002 to 2020 were used in the empirical analysis. Findings - In the past 19 years, South Korea's export trade potential of aquatic products to China has never been lower than 70%. It was above 90% from 2006 to 2018, and has been at a high level for a long time. This shows that China's aquatic product market has large potential for development. Originality/value - This study examines the effectiveness and potential of South Korea's exports of aquatic items to China in a methodical and comprehensive empirical manner. The evaluation of the export trade potential of South Korea's aquatic goods to China is more precise when the effects of regional organization, political, and economic variables are taken into account in the trade non-efficiency term of the stochastic frontier gravity model. At the same time, we propose to increase the scale of South Korea's aquatic products trade from the perspective of China's demand. This issue of trade studies is underexplored both empirically and in theory, although the issue has long been important to Korean and world trade.

• Korean Journal of Ichthyology
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• v.35 no.3
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• pp.151-159
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• 2023

This study investigated the early life history of the Micropercops swinhonis in Botongcheon stream Hangang River and compared the relationship between the related species and flexibility. The fertilized egg of the ovoid type, and the average egg diameter was 1.23 mm in long diameter and 0.85 mm in short diameter. At a water temperature of 20.6℃, the hatching time took 179 hours. The newly hatched larvae measured 3.82~4.08 mm in total length (TL), and their mouth and anus were not yet open. At 18 days after hatching, the postflexion larvae reached 7.97~8.43 mm in TL, with the tip of the caudal fin bent at 45°. At 29 days after hatching, the juveniles reached 9.83~10.8 mm in TL and were differentiated by their constant number of fins (7~10 first dorsal, 10~11 second dorsal, 7~10 anal fins). As a result of the study, there was a difference from the related species in the egg diameter, the newly hatched larva size. The postflexion larvae period and the development period of the first dorsal fin were the slowest among the comparable simila species, and the size was characterized by a large number, indicating a difference from similar species in the early life history process.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.57 no.4
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• pp.389-396
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• 2024

Reactive oxygen species (ROS) generated by harmful algal blooms (HABs) exert detrimental effects on aquaculture systems. Fish gill cells deteriorate upon exposure to HABs, suggesting that internally generated ROS in HABs influences the external environment. Therefore, we investigated the internal and external changes in ROS concentrations during growth using fluorescence staining of four representative HABs: Alexandrium affine, Chattonella marina, Karenia mikimotoi, and Margalefidinium polykrikoides. The concentrations of H₂O₂ and O₂^- produced by A. affine were low; H₂O₂ from M. polykrikoides was primarily detected internally throughout the experiments, and O₂^- was not detected. High H₂O₂ and O₂^- concentrations were observed in K. mikimotoi during the death phase, with weak external O₂^- concentrations. Regarding C. marina, which produces large amounts of ROS, H₂O₂ was observed internally during the exponential phase, whereas weak O₂^- concentrations were measured externally in the stationary phases. Collectively, our results highlight that ROS concentrations and internal/external distributions are functions of HABs and growth stage. These differences indicate the potential allelopathic mechanisms of proliferating HABs and suggest a possible impact of ROS on aquaculture organisms.

• Journal of Food Hygiene and Safety
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• v.23 no.4
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• pp.304-308
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• 2008

We investigated temperature management for refrigerated foods in large discount markets, department stores, and convenience stores. Eleven stores in the Seoul area were used to examine temperature maintenance for frozen and refrigerated foods, including soybean curds (tofu), fish surimi, mook, wet noodles, kimbab, and salads. The surficial and central temperatures of foods in a refrigerator and a freezer were examined. While the difference between the highest ($7.5^{\circ}C$) and the lowest ($6.4^{\circ}C$) temperature spaces in a refrigerator was $1.1^{\circ}C$, the corresponding difference between the highest ($8.9^{\circ}C$) and lowest ($7.5^{\circ}C$) food surface temperatures was $1.4^{\circ}C$. The average temperatures of both chilled food surfaces and refrigerator spaces were $7^{\circ}C$ (max. $22.9^{\circ}C$) and 8.2 degrees C (in. $-0.4^{\circ}C$), respectively. The temperatures of chilled food surfaces were $6.1{\times}10.6^{\circ}C$ for soybean curds, $6{\sim}12.3^{\circ}C$ for fish paste, $2.3{\times}18.2^{\circ}C$ for kimbab, $4.6{\times}12.2^{\circ}C$ for salads, $3.4{\times}12.6^{\circ}C$ for wet noodles, and $7.1{\times}19^{\circ}C$ for mook. Our results indicate that chilled foods require careful management for storage at temperatures below $10^{\circ}C$ with careful recording of the warmest area of the refrigerator.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.44 no.4
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• pp.323-344
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• 2008

To examine species composition, abundance and biomass of demersal organisms in the East Sea, bottom trawl survey was conducted at 7 sea areas from 2005 to 2007. A total of 107 species were collected and were composed of 54 fish species, 16 crustacea, and 37 mollusks in the East Sea from 2005 to 2007. Yearly abundance per area which caught by trawl survey in the East Sea from 2005 to 2007 ranged from a high of $292,234inds./km^2$ in 2005 to a low of $192,092inds./km^2$ in 2006. The abundance by sea area showed a peak in 76 sea area, and the lowest in 63 sea area. The abundance per area by season showed a peak in summer, and the lowest in spring. The most dominant species in abundance were Clupea pallasii, Neocrangon communis, Chionoecetes opilio. Yearly biomass per area which caught by trawl survey in the East Sea from 2005 to 2007 ranged from a high of $10,322kg/km^2$ in 2006 to a low of $7,096kg/km^2$ in 2005. The most dominant species in biomass were Chionoecetes opilio, Clupea pallasii, Dasycottus setiger. The biomass by sea area also showed a peak in 76 sea area, and the lowest in 93 sea area. The abundance by season also showed a peak in summer, and the lowest in spring. As a result of cluster analysis, demersal organisms community of 76 sea area showed a large difference with other sea area, and that of summer showed a large difference with other season.

• Korean Journal of Ichthyology
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• v.1 no.1_2
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• pp.1-8
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• 1989

In August, 1988, matured adults of devil stinger were collected from Jinhae Bay and Jaran Bay, Kyongsangnam-do, Korea and kept in the aquarium (1 ton) for spawning. The egg development was observed with the eggs laid in the aquarium of adult fish. The diameters of eggs ranged from 1.2 to 1.3 mm (n=6), and no oil globules were found in the eggs. The hatching took place from 26 to 29 hours after eight cells stage at the water temperature of $24.9-26.5^{\circ}C$. The newly hatched larvae were 2.47~3.10 mm in total length with xanthophore on the body and yolk sac. Myomere number was 13+16-17=29-30. Two days after hatching, larvae were 3.61-4.16 mm in total length, and 3 to 4 large spots of melanophore appeared on the large pectoral fin. Three days after hatching, larvae were 3.97-4.29 mm in total length, and the larvae absorved the yolk material completely to become post larvae with 4-5 rays of the pectoral fin. Six days after hatching, larvae attained 4.07-5.46 mm in total length, and 11 rays and 8-9 spots of melanophore were developed on the pectoral fin.