• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.4
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• pp.251-262
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• 1994

The speed of vertical migration and the volume backscattering strength of the scattering layers during the evening and morning transitions between day and night were measured in November 1990-1992 in thermally stratified waters of the East China Sea. Acoustical measurements were carried out using a scientific echo-sounder operating at t재 frequencies of 25 and 100kHz, and using an echo-integration system connected with a micro-computer. Biological sampling was accomplished by bottom trawling to identify fish species recorded on the echo sounder, and the species and length compositions were determined. The values of scattering strength were allocated to group of fishes according to the fish traces on the echo recording paper and the species composition of trawl catches. The vertical velocities of migration derived from the changes in the depths and the values of peak scattering strength of the dense layer vertically migrating toward the bottom or toward the surface. The trawl data suggest that snailfish and fishing frog were the most abundant fishes in all research stations. As sunrise approached, the fish formed a strong concentration just above the thermocline. The the highest values of scattering strength in the entire water column appeared in the depth strata above the thermocline just before the begining of downward migration. As soon as the fish began to migrate downwards across the thermocline, the values of the scattering strength in the depth strata above the thermocline rapidly decreased, while the values for the scattering layer moving slowly toward the bottom gradually increased. During the 1992 surveys, the speed of the vertical migration was estimated to be 0.38m/min in the upward migration and 0.32m/min in the downward migration, respectively. That is the rate of vertical migration was slightly higher at dusk than at dawn. Similar migration patterns were observed on different stations and under different weather conditions during the surveys in 1990.

• Journal of Marine Bioscience and Biotechnology
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• v.12 no.1
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• pp.59-65
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• 2020

Fish, caught by bottom trawling in the middle of the Yellow sea (east of Korea), in the spring and summer of 2016 were assessed for species composition and fluctuation in their abundance. The fish were studied at four research stations (St.) and were found to be composed of 46 species, 31 families, and 14 orders. The dominant species caught were Engraulis japonicus, Larimichthys polyactis, Johnius grypotus, Liparis tanakae, and Larimicthys crocea. All the species were assessed for their numbers, richness, diversity, and dominance to gain a measure of the biodiversity. The highest number of individuals was recorded at St. 4 (50,053 individuals), while the lowest number of individuals was recorded at St. 1 (44,090 individuals). The evenness index was the highest at St. 2 (E = 0.65) and lowest at St. 3 (E = 0.62). The diversity index was the highest at St. 4 (H' = 2.31) and lowest at St. 3 (H' = 2.23). Furthermore, the dominance index was the highest at St. 3 (D = 54.9%) and lowest at St. 2 (D = 47.7%).

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.44 no.3
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• pp.239-249
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• 2008

Trawlers have to a sufficient towing force due to it's characteristics of the high performance. The newly constructed trawler with the conventional propellers shows the sufficient towing force, so that the propeller and engine are optimized. In the 1970s, many trawlers were imported from overseas by Korean fisheries industries. But the engine output degradation with year by year caused the trawlers to decrease the towing speed of the vessels. On the previous studies, the nozzle propeller had not so good efficiency with increasing of resistance in high-speed cruising operation over 15knots. But the trawling operation is just required the higher thrust and towing force, so that the nozzle propeller is very profitable for the it's effectiveness. A new nozzle propeller was designed for the 4,462G/T trawler, Dong-San, operated by Dongwon Industries Co., Ltd. to improve the towing speed, and the model tests were performed. The model ship and model propeller are preciously manufactured and used model tests in basin. The resistance test and propeller open water test were performed for the cases of the half and full loads. The required engine horse power and RPM were evaluated analytically by the speed-power curve, when the trawler was equipped with the nozzle propeller. The results of tests showed that the towing speed 4.85knots on the design load waterline requires the 200 engine RPM and 2,567ps in the delivered horsepower.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.1
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• pp.16-23
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• 1996

Spatial distribution characteristics, volume backscattering strength and species composition of midwater trawling catch was analyzed biological and acoustical characteristics of anchovy shoal, using a high resolution echo - sounder at the south region of East sea of Korea. 1) In the survey site A of Lat.35$^{\circ}$55'N, Long.129$^{\circ}$45'E, the anchovy shoal of small to middle size with the horizontal range of 10~25m and large size with the horizontal range of 40~50m were distributed together. However in the survey site B of Lat.35$^{\circ}$38'N, Long.129$^{\circ}$40'E, the anchovy shoal was observed to be mainly small size which about 78% of the detected shoal. Another was that the anchovy shoal with the vertical range of 2~8m occupied about 68.6% in the survey site A and that of 6~12m occupied about 42.5% in the survey site B. The mainly the site A and B were found to be 10~50m super (2), 64.5% and 20~80m super (2), 66%, respectively. 2) The volume backscattering strength in the site A and B were observed to be -44.0~ -28.0dB, respectively. In the site A, the backscattering strength of -40.0~ -30.0dB was analyzed about 41.4%. 3) Most of total anchovy shoal was concentrated in the water layer of 50~100m in depth with 15.3~18.5$^{\circ}C$, 34.0~34.3$\textperthousand$ in the survey site A and 14.2~16.4$^{\circ}C$, 34.1~34.2$\textperthousand$ in the survey site B. 4) Mean total length(TL) and body weight(BW) of anchovy in the survey site A were 9.9cm and 4.4g respectively, with TL-BW relationship of BW=0.0007T$L^3.65$super (3.85). In site B, mean total length(TL) and body weight(BW) were 11.2cm and 8.7g, with TL-BW relationship of BW=0.0023T$L^3.36$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.1
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• pp.7-15
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• 1996

Full scale experiment was carried out in the southern sea of Korea to compare some important factors tested in the model experiment. The results obtained can be summarized as follows ; 1. The changing aspect of mouth performance of the full scale net was almost coincided with the results obtained by the model experiment. The vertical opening(H) and the opening area(S) can be expressed as a function of the towing velocity(V) as H=48.78. $e^0.38V$(unit: m, k't) S= 1,443 .$e^-0.25V$(unit: $m^2V$, k't) 2. The changing aspect of working depth of the full scale net was almost coincided with the results obtained by the model experiment. The depth(D) can be expressed as a function of the towing velocity(V) and the warp length(L) as D=92.49.$V^1.37$(unit: m, k't, L= 150m) D= 12.07+0.32. L (unit: m, V=2k't) [)= - 7.90+0.22 . L (unit: m, V=3k't) 3. Some problems were found to operate A - type full scale net by common bottom pair trawlers. The problems can be summarized as follows; (1) Entangling of wing and square head ropes while net casting.(2) Man power needed and time spent for net hauling by common bottom trawlers increased considerably.( 3) Tearing of nettings caused by over -load of tension and entangling of net pendant while net hauling. To solve these problems, the trawlers are favorable to be equipped with variable pitch propeller and llet drum. While the net is favorable to be constructed with trifurcated net pendant in stead of quadrifurcated net pendant used at present.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.48 no.3
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• pp.242-255
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• 2012

The Nemopilema nomurai a very large jellyfish that has been found in the East China Sea and is now are migrating to Korea and Japan. To investigate the occurrence of N. nomurai based on the changing marine environment of the East China Sea, we conducted field survey in the early summer from 2006-2008. We observed the marine environment using CTD and the occurrence of N. nomurai using FMT and bottom trawling. We caught the most N. nomurai in 2007 and the fewest in 2008 and environment factors influencing its are more sensitive temperature than salinity. Large quantities of N. nomurai with a small bell diameter were caught in 2007 and large individuals with a significant bell diameter were caught in 2008. This appeared which between the catch and bell diameter of N. nomurai had (-) correlation (R=-0.988, p=0.098). Meanwhile, the spatial distribution of N. nomurai concentrations in lower salinity mixed seawater inflow in Changjiang Diluted Water.

• Fisheries and Aquatic Sciences
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• v.12 no.2
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• pp.152-161
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• 2009

The largehead hairtail (Trichiurus lepturus) is one of the most common fisheries stocks in the East China Sea and the Yellow Sea. The species is caught using a variety of fishing tools, such as a stow net or a long line, as well as jigging and trawling. Scientific investigations have been conducted throughout the world to enable evidence-based estimations for the management and protection of the main fisheries biomass. For example, inshore and offshore hydro acoustic surveys are performed annually using bottom- and mid-water trawls around the Korean Peninsula. However, to date, no acoustic survey has been conducted to estimate fish size distribution, which is necessary to construct a data bank of target strength (TS) relative to fish species, length (L), and frequency. This study describes the frequency and length dependence of TS among fishes in Korean waters for the purpose of constructing such a TS data bank. TS measurements of the largehead hairtail were carried out in a water tank (L 5 m$\times$width 6 m$\times$ height 5 m) at frequencies of 50, 75, 120, and 200 kHz, using a tethering method. The average TS patterns were measured as a function of tilt angle, ranging from $-45^{\circ}$ (head down) to $+45^{\circ}$ (head up) every $0.2^{\circ}$. The length conversion constant ($b_{20}$) was estimated under the assumption that TS is proportional to the square of the length. In addition, in situ TS measurements on live largehead hairtails were performed using a split beam echo sounder.

• Journal of Fisheries and Marine Sciences Education
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• v.6 no.1
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• pp.11-19
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• 1994

The North Pacific midwater trawling which is one of the important fishing methods for Korean fishing industry is working in the Bering Sea and the sea near Kamchaka Peninsula. The catch by Korean midwater trawlers had been recorded about 300 thousands $^{M/_T}$ a year. Six types of midwater trawl net-ordinary midwater trawl net, super-V trawl net, super mesh trawl net, rope trawl net, super plus trawl net and kite trawl net-have been widely used by large trawlers above 1,500gt in size since 1982. Regarding the fishing efficiency, the super plus trawl net and kite trawl net were acknowledged as higher than other nets. Maximum mesh size of super-plus trawl net and kite trawl net ranges about 20m, whereas the length of net about 150m, and high-tech polyethylene is used as the material of rope part. The problems involved in the North Pacific midwater trawl net may be summarized as follows ; (1) The dimension of fishing gear is too big compared with the towing power of trawler. (2) The mesh size of the rope part is too big compared with that of the common netting part. (3) The net is often torn out in the connecting position of the rope part and the netting part. (4) The net is not matched with the trawler and the otter board in many trawlers, so the shape of the trawl gear in the water is instable. (5) The fish school located near head rope, ground rope and side rope in the net recorder is not caught in practice because of the net instability.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.3
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• pp.375-386
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• 2015

The study aims at a selective effect of the Grid and Window net in the shrimp beam trawl. The experimental trawling of the Proto type, Grid type and Grid and Window net type was performed in a sea area of Geo-je and Tong-yeong from Mar, 2006 to Apr, 2010. The obtained results are as follows; Catch per unit area (Number) of the Proto type net and Grid type net were $0.18/m^2$, $0.23/m^2$, respectively. The Grid type demonstrated 2.4% lower bycatch rate than the proto type (6.6% vs 4.2%, respectively). In addition, in terms of total weight, the bycatch rate of Grid type was 7.6% lower than the proto type (50.2% vs 42.6%, respectively). In the comparison of shrimp catch, the Proto type demonstrated better haul outcome ($0.02case/m^2$) than the Grid & Window type ($0.02case/m^2$). The Grid & Window net type demonstrated 16.4% lower bycatch rate than the Proto type (32.2% vs 48.6%, respectively). In addition, in terms of total weight, the bycatch rate of Grid & Window net type was 8.3% lower than the Proto type (85.9% vs 94.2% respectively).

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.2
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• pp.111-120
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• 2016

Acoustic surveys using a scientific echosounder and trawl surveys were concurrently carried out in between Geoje and Tongyeong of the South Sea by season. The anchovy schools were identified by trawling in each station and used for frequency response analysis. Frequency responses of anchovy schools by season and species composition ratio were examined using multi-frequencies (18, 38, 70, 120 and 200 kHz). The frequency response r(f), is one of the acoustic characteristics which means the volume back-scattering strength ratio between a reference frequency and other frequencies. In spring, the r(f) of anchovy schools decreased with increased frequency, with the exception of 120kHz. While, in winter, the r(f) continuously decreased inversely proportional to the increase in frequency. Frequency response of anchovy schools presented a distinctive difference between spring and winter, however it did not different in spife of different species composition ratios in schools.