• The Korean Journal of Malacology
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• v.29 no.3
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• pp.239-244
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• 2013

Mass mortalities of farmed shellfish, mostly in summer season, thus named mass summer mortalities, have been a global issue in shellfish aquaculture. The 2013 mass summer mortalities in the confined waters of Goseong Bay, Goseong, Korea were quite a unique and intensive for two farmed species, the Pacific oysters, Crassostrea gigas, and bay scallops, Argopecten irradians. The mortalities were progressive from the bottom of the suspended oysters and caged scallops in the waters, reaching up to 80% for the oyster and 95% for the scallop in about 20 days after the first occurrence, early August, 2013. We monitored a wide range of environmental factors, including water temperature, dissolved oxygen (DO), salinity, turbidity, acidity (pH), organic and inorganic matters, chemical oxygen demand (COD), suspected pathogenic agent, and phytoplankton composition throughout the water column where the two species were suspended or caged. Our survey concluded that the hypoxia or anoxia might be a major cause of the mortalities. Here, we detailed the mortalities and ways to arrive at the conclusion.

• Korean Journal of Environmental Biology
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• v.17 no.2
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• pp.175-182
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• 1999

An unprecedented mass mortality of commercially important macrobenthic animals, including Haliotis discus discus, H. diversicolor, Batilus cornutus, Sticopus japonious and Hemicentrotus puzoherrimus, occurred off the west coast of Cheju Island in summer of 1996. Phytoplankton blooms were absent along the coast. The appearances of the surface low-salinity water (SLSW) off the coast of Cheju Island preceded the mass mortality, leading to speculation that the low-salinity stress may have a crucial role in the mass mortality. Since there was no heavy rain for the same period, the precipitation was not a possible explanation for the decrease of salinity. Physical oceanographic data taken by NFRDI (1997) clearly indicated that the SLSW was present in the area between China and Cheju Island in August 1996. This is most likely due to a freshwater supply resulting from the existence of large river runoff. Evidence of the current and the distance between the Yangtz River and Cheju Island also supports the hypothesis that source of the SLSW was the freshwater originated from the Yangtz River runoff.[macrobenthic animals, mass mortality, surface low-salinity water].

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2006.10a
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• pp.189-190
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• 2006

• Journal of fish pathology
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• v.22 no.2
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• pp.155-162
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• 2009

The mass mortality of Korean rockfish, Sebastes schlegeli that occured at the fish farms in Tongyeong and Geoje City regions between late August and early September in 2006 was investigated. Sixty two fish showed no significant external symptoms except ulcerative lesions with reddish foci on the skin. From the internal observations and diagnosis results, some yellowish brown liver, intestine bleeding, atrophy and congestion in the abdominal cavity of the fish were found. In the gill, swelled filaments caused by foreign material accumulation and mucus secretion were observed. However, the main cause of the fish mass mortality in both sampling regions could be due to physiological weakness induced by significant change of water temperature causing by typhoon Wookong during the summer in 2006.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.1
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• pp.52-58
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• 1991

Mass mortality of Halocynthia roretzi has been occurred in culturing grounds of southern coast of Korea during the long period of summer drought and the unusal high water temperature in 1988. Especially Halocynthia roretzi was damaged severely in 2 years group. Therefore we verified these phenomena by observing the environmental factors of culturing grounds and by evaluating oxygen consumption rate in indoor experiment. In culturing grounds, the mortality rate was high in Namhae Mizo area where water temperature was the highest and the lowest in dissolved oxygen concentration as low as 3.76m/l in field observation. In indoor experiment, the higher the water temperature, the more mortality was occurred and the salinity above 30 had no effect on its mortality. In oxygen consumption rate experiment, the smaller needs more oxygen than larger one, i. e., oxygen demand per unit weight was higher in 2 years group than that of 3 years. The theoretical and the actual minimum oxygen demands(MOB) for preventing asphixation was 3.7ml/kg/h at $20^{\circ}C$ and 6.3ml/kg/h gat $25^{\circ}C$, But actual MOD was 4.3ml/kg/h at $25^{\circ}C$ in indoor experiment. It seemed that mass mortality of Halocynthia roretzi in summer was caused by metabolism disorder due to insufficient oxygen level influenced by the high water temperature and the high density of Halocynthia roretzi, which results in the paucity of oxygen especially in 2 years groups.

• Atmosphere
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• v.17 no.1
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• pp.45-53
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• 2007

In order to investigate the impacts of heat wave on human health, cluster analysis of meteorological elements (e.g., temperature, dewpoint, sea level pressure, visibility, cloud amount, and wind components) for identifying offensive synoptic air masses is employed. Meteorological data at Seoul during the past 30 years are used. The daily death data at Seoul are also employed. Occurrence frequency of heat waves which is defined by daily maximum temperature greater than the threshold temperature (i.e., $31.2^{\circ}C$) was analyzed. The result shows that the frequency and duration of heat waves at Seoul are increasing during the past 30 years. In addition, the increasing trend of the frequency and duration clearly appears in late spring and early autumn as well as summer. Factor analysis shows that 65.1% of the total variance can be explained by 4 components which are linearly independent. Eight clusters (or synoptic air masses) were classified and found to be optimal for representing the summertime air masses at Seoul, Korea. The results exhibit that cluster-mean values of meteorological variables of an offensive air mass (or cluster) are closely correlated with the observed and standardized deaths.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.56 no.4
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• pp.407-418
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• 2020

Mass mortality of mariculture fish due to high summer temperatures is a major issue in the mariculture industry in many coastal waters of Korea, yet measures to mitigate the impact are generally limited. We injected a micro-bubble of liquefied oxygen into the bottom of rockfish cages (about 6-8 m deep) in order to maximize the dispersal of micro-bubbled seawater and reduce fish mortality. The injection of low-temperature oxygen in micro-bubbles lowered the water temperature at the injection area by as much as 1℃ and increased dissolved oxygen concentration by 0.5 ppm. In early August, following a week with persistent high water temperature (above 28.5℃), there was an increase in fish mortality despite the micro-bubble system, which resulted in approximately 7% death of the total introduced fish population. However, this mortality appeared to be much lower than mortality reported in a neighboring mariculture facility (approximately 50% mortality). We also estimated the volume that can be recirculated with pumped seawater using a micro-bubble system. We suggest that this approach of injecting liquefied oxygen through a micro-bubble system may reduce fish mortality during high temperature periods.

• Journal of environmental and Sanitary engineering
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• v.18 no.4
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• pp.24-35
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• 2003

Recent epidemiologic studies revealed that the concentration of air pollutants and fine particulated matter have some effects on health status and are associated with increased mortality and morbidity. The purpose of this study was to characterize background mass concentration of fine particle (PM2.5) and metallic composition from September 2001 to August 2002 in comparison with a medium city, Asan and metropolitan city, Seoul. Conclusively, proper management for fine particles was required in a medium city, Asan, considering the concentrations of metallic elements in fine particles in Asan were relatively higher than those in Seoul. The results were as followed. 1. Average mass concentrations of fine particles in Asan and Seoul were 37.70(${\pm}18.41{\;}{\mu}g/\textrm{m}^3$) and 5.83(${\pm}38.50$) ${\mu}g/\textrm{m}^3$, respectively. When the weather conditions were classified as normal and yellow-sand, measured average mass concentrations of fine particles in yellow-sand weather condition was significantly higher than those of normal weather condition in both cities (p<0.05). 2. Depending on seasons, measured average mass concentrations of fine particles in Asan and Seoul in spring were 47.76(${\pm}19.07$) ${\mu}g/\textrm{m}^3$m and 61.53 (${\pm}4.37$) ${\mu}g/\textrm{m}^3$, respectively. In summer, the average mass concentrations of fine particles in Asan and Seoul were 29.44(${\pm}9.85$) ${\mu}g/\textrm{m}^3$ and 25.42(${\pm}8.10$) ${\mu}g/\textrm{m}^3$, respectively. Especially, the concentration was the highest in spring and the lowest in summer among four seasons. 3. Average concentrations of manganese(Mn), iron(Fe), chromium(Cr), cadmium(Cd), lead(Pb) and silicon(Si) in fine particles in Asan were significantly higher in Seoul (p<0.05). Average concentration of Si in fine particle in Asan was statistically higher than that of Seoul during yellow -sand condition (p<0.05). 4. Considering the characterization of four seasons, average Pb concentration of fine particle in Asan is significantly higher than that of Seoul in spring(p<0.01). In summer, average Mn and Cr concentrations of fine particle in Asan is higher than those of Seoul (p<0.05). Average Mn, Fe. Cr and Si concentrations in fall (p<0.05), and average Mn, Fe, Cr, Pb, and Si concentrations in winter (p<0.05) in Asan were higher than those of Seoul, respectively. 5. Mass concentrations of each Mn, Fe, Cd and Si in fine particles were significantly correlated with both cities. In normal weather condition, Mn, Cu and Si concentrations are statistically significant in Asan, while Mn, Fe, Cu and Si concentrations are statistically significant in Seoul. Mn, Fe and Si concentrations in both cities were statistically significant during yellow-sand weather.

• Korean Journal of Poultry Science
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• v.14 no.2
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• pp.125-135
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• 1987

Total 720 brown layers were fed 9 rations differing in metabolizable energy (2500, 2700 and 2900 kcal/kg) and crude protein (13, 15 and 17%) levels for a period of 12 weeks in order to study the effects of dietary energy and protein levels on the performance of brwon layer in summer. As metabolizable energy level increased from 2500 to 2900Kcal/kg of feed egg production, daily feed and protein intake were decreased, but daily energy intake, energy requirement and feed cost per kilogram of egg mass were increased. There were no significant difference in egg weight, feed conversion and motality among dietary energy levels. On the other hand, as dietary Protein level increased from 13 to 17% egg Production, egg weight, daily protein intake and protein requirement per kilogram of egg mass were increased, but feed and energy requirement and feed cost per kilogram or egg mass were decreased. However daily feed intake and mortality were not affected by dietary protein level.

• Journal of fish pathology
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• v.4 no.2
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• pp.87-94
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• 1991

In the late summer of 1990 and 1991, mass mortality occured among cage-cultured grouper, Epinephelus septemfasciatus in south cost of Korea. The moribund fish didn't feed and became pale or dark chestnut colour and irregularly swimmed due to the loss of equilibrium, finally the diseased fish fell down side away on the bottom or the surface of cage showing the bent of body and died. The diseased fish showed the extensive hemorrahge in brain, the swelling of spleen and bile duct as the specific syptoms of internal organs. So the gill, skin and other organs of the diseased fish were examined for the presence of pathogenic parasites and bacteria. The parasitic Trichodina sp. were detected only from the gill lamella of the diseased fish, but these parasites seemed to be not a direct causative agents that induced the gross mortality of the cultured grouper. because these parasites were also observed in normal grouper, yellowtail, red seabream and rock bream co-cultured with the diseased grouper in same or near cages. In the viral examination, although isolation of the causative agent by the use of estabilshed cell Lines, RTG-2 and CHSE-214, was not succeed, the normal grouper inoculated intramuscularly with the filtered homogenate of the organs of the diseased fish showed the same external and internal signs with the naturally infected grouper. They died within a week. By using the naturally and the artificially infected fishes, electron microscopic observation revealed numerous hexagonal or polygonal particles in the cytoplasm of liver cells. Based on the these results, we suggest that the mass mortality of the cultured grouper would be occurred by the infection of a viral agent.