Acoustics are increasingly regarded as a remote-sensing tool that provides the basis for classifying and mapping ocean resources including seabed classification. It has long been understood that details about the character of the seabed (roughness, sediment type, grain-size distribution, porosity, and material density) are embedded in the acoustical echoes from the seabed. This study developed a sophisticated yet easy-to-use technique to discriminate seabed characteristics using a split beam echosounder. Acoustic survey was conducted in Tongyeong waters, South Korea in June 2018, and the verification of acoustic seabed classification was made by the Van Veen grab sampler. The acoustic scattering signals extracted the seabed hardness and roughness components as well as various seabed features. The seabed features were selected using the principal component analysis, and the seabed classification was performed by the K-means clustering. As a result, three seabed types such as sand, mud, and shell were discriminated. This preliminary study presented feasible application of a sounder to classify the seabed substrates. It can be further developed for characterizing marine habitats on a variety of spatial scales and studying the ecological characteristic of fishes near the habitats.

In order to investigate the behavioral characteristics of Pacific cod (Gadus macrocephalus) released at the entrance of Jinhae Bay, Korea, the direction and range of movement, swimming speed of the fish were measured with an acoustic telemetry techniques in winter, 2015. Three wild Pacific codes WC1 to WC3 (total length 66.0, 75.0, 76.0 cm; body weight 2.84, 2.79, 3.47 kg, respectively) were tagged with the acoustic transmitter. WC1 tagged with an acoustic transmitter internally by surgical method, WC2 and WC3, externally with the acoustic data logger and a micro data logger for recording audible sound waves including timer release unit. The movement routes of the tagged fish were measured more than five hours using VR100 receiver and a directional hydrophone. The directionality of the fish movement was tested by Rayleigh’s z-Test, the statistical analysis, and a statistical program SPSS. Three tagged fishes were individually released on the sea surface around the entrance to the Jinhae Bay on 10 to 24 January 2015. WC1 moved about 13.32 km with average swimming speed of 0.63 m/s for six hours. The average swimming depth and water depth of the seabed on the route of WC1 were 7.2 and 32.9 m, respectively. The movement range of WC2 and WC3 were 7.95 and 11.06 km, approximately, with average swimming speed of 0.44 and 0.58 m/s for 5.1 and 5.3 hours, respectively. The average swimming depth of WC2 and WC3 were 18.7 and 5.0 m, and the water depth on the route, 34.4 and 29.8 m, respectively. Three fishes WC1 to WC3 were shown significant directionality in the movement (p < 0.05). Movement mean angles of WC1 to WC3 were 77.7, 76.3 and 88.1°, respectively. There was no significant correlation between the movement direction of fish (WC1 and WC2) and the tidal currents during the experimental period (p >= 0.05). Consequently, three tagged fishes were commonly moved toward outside of the entrance and headed for eastward of the Korean Peninsula, approximately, after release. It may estimate positively that the tidal current speed may affect to the swimming speed of the Pacific cod during the spring tide than the neap tide.

The feeding habits of Pacific bluefin tuna, Thunnus orientalis were analyzed using samples by large purse seine fishery in Korean waters from 2012 to 2017. The number of samples was 1,274 and the fork-length (FL) ranged from 34.6 to 218.0 cm. According to %IRI, the Important main prey items of immature individuals (below 91.4 cm in FL) were Pisces, Cephalopoda and Euphausiacea and those of mature individuals were Cephalopoda and Pisces. T. orientalis showed ontogenetic changes in prey item that Pisces was dominated in size class of 30-89 cm (FL), Cephalopoda in 90-179 cm (FL), and Pisces above 180 cm. As for seasonal changes in prey item, Cephalopoda was dominant in spring and Pisces was dominant in summer, autumn and winter. %F, %N, %W and %IRI cluster analysis divided area into three groups: Group A was dominated by Pisces; Group B was dominated by Cephalopoda, and Group C was dominated by Euphausiacea.

This study was conducted in order to improve opening efficiency of the miniaturized small-scale net for anchovy boat seine gear to reduce the fleet size. Field experiment was performed to observe geometry of nets by catcher boats. When the distance between the two ships was 150, 300 and 450 m and the speed of towing nets was 0.6, 0.9, and 1.2 kt, the vertical opening and actual opening of each part of the miniaturized small-scale net was as follows: the front part of the wing net, 6.8-9.5 m, 45-63%; the middle part of the wing net, 16.1-30.7 m, 34-65%; the entrance of the inside wing net, 21.6-41.2 m, 44-84%; the square and bosom, 17.4-34.0 m, 38-75%; the entrance of the body net, 16.5-29.4 m, 36-64%; the entrance of the bag net, 14.5-21.9 m, 70-106%; the flapper, 6.7-7.7 m, 81-83%, and the end of the bag net, 8.6-10.9 m, 64-81%. The tension of towing nets was measured to be 2,734-6,812 kg approximately, which indicates that the fleet can tow nets with 350 hp, the standard engine horse power. The fishing operation time was shortened comparing to existent net with the large-scale buoy attachment operation. It was also possible to operate the ship without fish detecting boat.

The annual production of silver croaker (Argyrosomus argentatus) in Korean towed fishing gears has been increased in recent five years. In 2017, the annual production of silver croaker in metric ton was increased 99.2% compared to 2013. However, the research for silver croaker has been focused on ecology in Korea. There has not been enough research in terms of fishing gears. Therefore, the research for retention probability for towed gears was conducted on covered codend method from June, 2016 to July, 2018. During the experiments, the total catch of silver croaker was 1,563. The geometry of the experimental trawl gear was controlled by trawl monitoring system; net height was 3.3 m, distance of trawldoors was 59.8 m and distance of wing net was 17.3 m. The selection curve for silver croaker was estimated by a logit model. The analysis was applied with the confidence interval to reduce uncertainty of the estimation. The l50 was 13.87 cm and its selection range was 2.71 cm. P-value was estimated at 0.99. The mesh size for silver croaker in towed gears needs to be adjusted by considering its minimum maturity length, stakeholder’s interests and fisheries regulations.

Basic reproductive biology of the daggertooth pike conger, Muraenesox cinereus were investigated based on the samples from August 2015 to December 2017 in Korean waters. A total of 2,328 samples was collected (1,593 females and 735 males) during the study period. The mean anal lengths (AL) were 33.5 ± 9.2 cm in females and 26.2 ± 7.3 cm in males respectively. The females were larger than males in AL (p < 0.05). Sex ratio was 2.2:1 in female to male (p < 0.05). The gonadosomatic index (GSI) varied monthly. GSI of female reached the maximum in July 2016 and June 2017 and the minimum in October 2016 and September 2017 respectively. The spawning period was from June to October. The size at sexual maturity (L50) of females was estimated at 24.9 cm in AL (63.5 cm in TL).

In this study, a motion control problem for the vessels towed by tugboats or towing ships on the sea is considered. The towed vessel looks like the barge ship, which is used for many purposes. In these vessels, basically, the power propulsion system is not installed but just towed by a towing vessel such as tugboats with ropes and wires. It means that the motions of towed vessel are basically dependent on the tracking route of towing boat. Therefore, in some cases, undesirable and unpredictable motions may be made by environmental factors such as wave, wind attack and so on. As a result, a collision accident with others may occur during maneuvering situation. Based on these facts, the authors try to encourage the steering performance of the towed vessel by using controllable rudders without any propulsion system. In this study, especially, a controllable vessel with three rudders is considered, and a mathematical model is induced for the future study. The model is described as surge, sway motion and inertia moment by following the general representation method for the surface ship.

In order to manage and rebuild fishery resources, the fishing effort should be controlled effectively. Especially in the setting up of the proper level of fishing efforts, economic standards as well as biological standards must be carefully considered to promote the sustainable and economically viable development of fisheries. This study is aimed to estimate optimal fishing effort of giant octopus by combo fishing which uses longline in Gangwon with statistical data. The result showed that current fishing effort is 28% higher than EMEY. Unit fishing cost for each voyage will be 27% lower and unit fishing profit will be 17% higher than the current situation when the fishing effort meets EMEY. Although current fishing effort is similar to the EMSY, current catching is 16% higher than MSY and 22% higher than MEY.

We conducted a questionnaire survey to analyze the current status of the coastal composite fisheries, as well as the improvement point in designing a new type coastal composite fishing boat suitable for Korean fishing environments from April to August 2017. The questionnaire composed of 20 questions about the features of the coastal composite fishing boat and fishing work. The survey sites were selected to cover all parts of the country by considering the geographical position. The significance testing for the response results was accessed by  test and ANOVA. The results revealed that more than half (59.1%) of the fishermen operated one day per voyage and operating alone topped with 22.5% in the number of crews, followed by 2 persons (20.3%) and 5 persons (22.1%). The navigation devices had a high rate of installation and GPS plotter ranked first in the devices. In addition, fish finder ranked first in fishing equipment, followed by net hauler. The most inconvenient work that they felt during the fishing operation was fish handing at 49.8% and other general fishing works like setting and hauling line, deck cleaning accounted for about 25%. The hardest work was the accident by ropes wrapped around propeller and the engine trouble came in second. The most inconvenient facilities to the present design of fishing boat was wheelhouse (76.7%), followed by fish hold (38.5%), and deck (35.1%). Furthermore, inconvenient points related to the movement of fishing gear, noise and vibration of engine, slippery deck and small fish hold exceeded 50%.

Fossil fuel combustion during fishing activities is a major contributor to climate changes in the fishing industry. The Tier1 methodology calculation and on-site continuous measurements of the greenhouse gas were carried out through the use of fuel by the coastal and offshore gillnet (blue crabs and yellow croaker) and trap (small octopus and red snow crab) fishing boats in Korea. The emission comparison results showed that the field measurements are similar to or slightly higher than the Tier1 estimates for coastal gillnet and trap. In offshore gillnet and trap fisheries, Tier1 estimate of greenhouse gases was about 1,644-13,875 kg CO2/L, which was more than the field measurement value. The CO2 emissions factor based on the fuel usage was 2.49-3.2 kg CO2/L for coastal fisheries and 1.46-2.24 kg CO2/L for offshore fisheries. Furthermore, GHG emissions per unit catch and the ratio of field measurement and Tier1 emission estimate were investigated. Since the total catch of coastal fish was relatively small, the emission per unit catch in coastal fisheries was four to eight times larger. The results of this study could be used to determine the baseline data for responding to changes in fisheries environment and reducing greenhouse gas emission.

Species composition and seasonal variation of aquatic organism at Baekryeong-do, Korea were investigated using pots in 2016. A total of 42 species, 90,050 individuals and 2,351,666 g of aquatic organism were collected. Among them, there were 12 species and 3,826 individuals of fish, 15 species and 51,237 individuals of crustaceans, 2 species and 54 individuals of cephalopods, 7 species and 33,981 individuals of gastropods, 2 species and 757 individuals of echinodea, 2 species and 187 individuals of shellfish, and 1 species and 8 individuals of holothuroidea. The dominant species in number of individuals were Pagurus ochotensis, Neptunea cuming, Cancer gibbosulus, and Buccinum yokomaruae, which accounted for 70.0% of the total number individuals collected. The dominant species in biomass were Neptunea cuming, Portunus trituberculatus, Cancer gibbosulus, and Pagurus ochotensis, which accounted for 65.3% of the total biomass collected.

Maturity and spawning of the pointhead flounder, Hippoglossoides pinetorum were investigated on the basis of samples collected in the coastal waters off Gangwon-do, East Sea from January 2012 to December 2013. The average total length of H. pinetorum was 25.0 cm and 21.9 cm for females and males, respectively. The spawning period was from May to July according to monthly changes gonadosomatic index (GSI) and maturity stages. The spawning period in Gangwon-do was delayed relatively to that in Gyeongbuk-do. The mature egg diameter ranged between 300-700 ㎛. The relationship between TL and fecundity (F) was F = 63.574 TL - 1471.3 (R2=0.7603), that is, the larger total length, the more fecundity H. pinetorum had. We estimated that the TLs at 50% group maturity were 25.6 cm for females and 19.9 cm for males. The spawning ecology by sea area should be considered efficient resource management for H. pinetorum. Furthermore, it is necessary to study more on the relationships among growth, maturity and water temperature variations in the East Sea.

The ichthyoplanktons were sampled to study distribution of the ichthyoplankton in coastal waters of Nanji-Island in August and November 2015 and January and May 2016. During the study, fish eggs of eight different species were collected. Engraulis japonicus was the most dominant species which accounted 44.80%. Sebastes schlegeli comprised 31.39% of the total larvae and juveniles. The diversity index of species per month of the collected juveniles at Nanji Island from 2015 to 2016 was 0.598-1.770 and the evenness index was 0.432-0.761. In case of dominance index was 0.619-0.897 against the evenness index. The analyzed species diversity index by the each station was 0.818-1.945 and the dominance index was 0.492-0.897 against the species diversity index. The months of August and May exhibited similar results. In addition, the community structure was very similar in state 2 and state 3.

The objective of this study was to quantitatively evaluate the influence of the netting hanging ratio on fishing performance of gillnet. A total of six tests was carried out using three kinds of gillnets with different horizontal hanging ratios (0.3, 0.5 and 0.7) on the basis commercial gillnet of mesh size of 60 mm used in Yeosu Dolsan. As a result of the test fishing operation, catches of the net with hanging ratio 0.3 and the shortest float length was 1.34 times larger than the net with hanging ratio 0.7. The caught species in experimental testes was lager in the net with hanging ratio 0.3 than the net with hanging ratio 0.7. The catch rate per unit area (CPUE) is on the silver croaker with the largest catches in tests as follows. The net with hanging ratio 0.3 net was 89.45 g/m2, hanging ratio 0.5 net was 41.63 g/m2, and hanging ratio 0.7 net was 24.50 g/m2. The net with hanging ratio 0.3 (float line length of 45 m) exhibited the largest CPUE value.

In this study, the conventional cylinder-shaped lower bar on the canvas was modified and its performance was tested to improve the opening force of the stow net on anchor. The improved new lower bar used in the test is consisted of 13 flat bars with a length of 1.8 m, a width of 0.075 m and a thickness of 4 mm, and a pipe with a length of 2.0 m and a diameter of 50 mm. A stow net with the improved lower bar and a stow net with an existing lower bar were installed underwater and their trajectories for 21 hours were examined. To confirm their trajectories, GPS loggers were attached to the buoys on the left and right canvases and the buoy of the hauling rope. As a result of the test, the rotation of the gear with the improved bar was smoother than that with the existing bar. As a result of comparing the changes in the interval of the buoys attached to the canvas after the low and high tide, the buoy spacing of the gear with the improved bar is wider than that of the conventional gear; moreover, the larger the interval, the smoother the rotation of the fishing gear was. Therefore, it is considered that using the improved lower bar can enhance the performance of the stow net.