• Journal of Fisheries and Marine Sciences Education
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• v.5 no.2
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• pp.90-97
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• 1993

Pair trawling is one of the important fishing methods for Korean fisheries, and is working in the western sea of Korea - the Yellow Sea and the East China Sea. On the engine power of the trawlers, 72% of 190 pairs of trawlers were equipped with 450ps class engine, and 21% with 450~750ps and merely 7% with in 750ps class 1980. Thereafter the engine power has grown up, so that 450~750ps occupy 28% and 750ps or more 27% in 1992. Main objective fishes of pair trawling were traditionally flat fishes, so the fundamental shape of pair trawl net was a four - seam net, but by the gradual shortage of flat fishes, roundfishes has been noticed. So the six - seam net which performs high opening of net mouth has been used widely since 1985. In the six - seam net, the length of wing was not so short in the beginning but became short in the later instead of the net pendant elongated, and also the pendant was separated into three pieces according to the change of wing structure. Since the 1990's, the objective fishes has gradually been changed into pelagic fishes, the fishing technique is required to fit the behavior of fishes. So the midwater trawling or the multi -layer trawling became required.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.24 no.2
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• pp.78-82
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• 1988

Near sea trawlers of Korea sometimes catch pelagic fishes like file fish by using midwater trawl gear even though usually catch bottom fish. It is reasonable to use the specific otter board as well as specific net in bottom trawling and in midwater trawling respectively. But, the trawlers are so small ranging 100 to 120GT, 700 to 100ps that it is very complicated to use different otter board for bottom trawling and for midwater trawling. The otter board for bottom trawling. is also used for the midwater trawling without any change even though the net is changed into the specific one. Although the otter board in the midwater trawling should be lighter than that for bottom trawling, to use otter board for bottom trawling directly for the midwater trawling without any change makes the net easily touch the sea bed and also make the horizontal opening of the otter boards be limited owing to the length of warp in the southern sea of Korea, main fishing ground of midwater trawling, which is 100m or so in depth. That is why the otter board for the midwater trawling should be made lighter than that in the bottom trawling, even if temporary. The authors carried out an experiment to achieve this purpose by attaching a large styropol float on the top of the otter board. In this experiment, underwater weight of the otter board was 630kg and buoyancy of the float was 510kg. To determine the depth and horizontal opening of the otter board, two fish finder was used. A transmitter of 50KHz fish finder was set downward through the shoe plate of otter board to determine the elevation of otter board from the sea bed, and a transmitter of 200KHz fish finder was set sideways on the starboard otter board to be able to detect the distance between otter boards. The obtained results can be summarized as follows: 1. The actual towing speed in the experiment varied 1.1 to 1.8 m/sec. 2. The depth of otter board was within 41 to 25m with float on the top and 45 to 26m without float in case of the warp length 100m, whereas the depth 68-44m with float and 74-46m without float in case of the warp length 150m. This fact means that the depth with float was 9-4% shallower than that without float. 3. The horizontal opening between otter boards was within 34-41m with float and 30-38m without float in case of the warp length 100m, whereas the opening was 44-50m with float and 37-46m without float in case of the warp length 150m. This fact means the opening with float was 10% greater than that without float in case of the warp length 100m, and 15% greater in case of the warp length 150m. 4. The horizontal opening between wing tips by using the otter board with float was 1m greater than by without float in case of the warp length 100m, whereas the opening by with float was 2m greater than by without float in case of warp length 150m. From this fact, it can be estimated that the effective opening area of the net mouth by using the otter board with float could be made 10% greater than by without float in case of warp length 100m, whereas the area with float 20% greater than by without float in case of warp length 150m.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.5
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• pp.2674-2697
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• 2019

Identity authentication is a crucial line of defense for network security, and passwords are still the mainstream of identity authentication. So far trawling password attacking has been extensively studied, but the research related with personal information is always sporadic. Probabilistic context-free grammar (PCFG) and Markov chain-based models perform greatly well in trawling guessing. In this paper we propose a systematic targeted attacking model based on structure partition and string reorganization by migrating the above two models to targeted attacking, denoted as TG-SPSR. In structure partition phase, besides dividing passwords to basic structure similar to PCFG, we additionally define a trajectory-based keyboard pattern in the basic grammar and introduce index bits to accurately characterize the position of special characters. Moreover, we also construct a BiLSTM recurrent neural network classifier to characterize the behavior of password reuse and modification after defining nine kinds of modification rules. Extensive experimental results indicate that in online attacking, TG-SPSR outperforms traditional trawling attacking algorithms by average about 275%, and respectively outperforms its foremost counterparts, Personal-PCFG, TarGuess-I, by about 70% and 19%; In offline attacking, TG-SPSR outperforms traditional trawling attacking algorithms by average about 90%, outperforms Personal-PCFG and TarGuess-I by 85% and 30%, respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.45 no.4
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• pp.223-233
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• 2009

It has been considered that fishing areas for shrimp beam trawl have been in ruin because Korean local governments have permitted trawling into the areas limited by the fisheries local regulations from 1994. Physical and biological effects of the trawling were investigated in the study. Physical effects were investigated by optical methods such as trawling tracking by side scan sonar and comparing the gear both before and after trawling. Biological aspects were investigated by grab sampling of benthic animals, concentration of trace metals in sediment and a flux evaluation of ${NH_4}^+,\;{PO_4}^-,\;and\;SiO_2$ by coring. The fishing activity had physical impacts on the seabed but these recovered naturally in less than fourty days naturally, which increased the benthic biodiversity, increases the trace metal concentration of and nutrient flux into the seawater, especially phosphate and silicate. This method and these results can help in further studies looking for disturbances by fishing.

• Journal of Species Research
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• v.11 no.3
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• pp.188-193
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• 2022

Araeosoma owstoni Mortensen, 1904, a newly recorded sea urchin, was collected from the Korea Strait by trawling during a research expedition in April 2017. The specimen was damaged and was severely peeled off on the aboral side during trawling. However, a test and the surface of the oral side of the sample were well preserved, allowing us to successfully identify it. The species was distinguished by the large and flexible test, the tiny apical section, and the interambulacra width which is twice of the ambulacra. Pedicellaria tridentate and triphyllous were presents, but tetradactyle pedicellaria was absent due to severe peeling on the aboral side. Moreover, a length of 1,212 bp sequence from mitochondrial COI gene was obtained and this sequence covered the general DNA barcoding region. The mean of interspecific divergence within A. owstoni from Korea and other eight species of Araeosoma from the GenBank was 6.8%. This value indicated that our species was clearly distinguishable from the others. Thus, the first Araeosoma species occurring in South Korea is presented in this study.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.4
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• pp.91-98
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• 2000

The present study is the first attempt involving quantification of the different types of debris found on the seabed of Chinhae Bay in the South Sea of Korea. Eleven cruises were undertaken to collect marine debris samples by bottom trawling from February in 1998 to January in 1999. The tows were conducted over a period of 60-90 min, and eight types of debris were counted: plastic, fishing gear, metallic objects, wood, rubber or leather, glass, textile and the others. Results are obtained based on the number and weight of the objects classified as per eight categories and station for a trawling period. The results of this study are that the number and weight of debris found per unit of swept area (1 hectare) were surveyed as 27.8(1,612 in total) and 3,130 g(193,820 g in total), and plastic and fishing gear have the most composition of marine debris by number, on the other hand, metallic objects and fishing gear have the most composition of marine debris by weight.

• The Journal of Fisheries Business Administration
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• v.45 no.1
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• pp.63-77
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• 2014

This study is to estimate the recent changes in total factor productivity of 15 Korean adjacent water fisheries based on Malmquist productivity indices. The study adopted both input and output oriented productivity measures utilizing a hyperbola distance function. In addition to this point, the study also calculated the 95% confidence interval for the various components of the productivities in order to access the statistical significance of estimates using 2000 times of re-sampling process through the smoothed bootstraping. The results of the study showed us that there was 18% reduction in the overall total factor productivity during the study period from 2007 to 2011, which turned out to be 5% of annual decrease in productivity. The study found that the main reason of this decrease in total productivity is about 22% downward shift of a fisheries production function due to recent conditions of a devastated fishing ground. When we evaluated the statistical significance of changes in technical efficiency combining both pure technical and scale efficiency based on the 95% confidence intervals, we could not find any evidence of changes in those components of total factor productivity. When we accessed the productivity of the each of 15 adjacent water fisheries methods, only the large danish seine fisheries showed us about 7% increase in productivity. Even though the large trawling and the large tow-boat trawling revealed no changes in productivity, all of the other 12 fisheries suffered the decreases in productivities.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.1
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• pp.1-6
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• 1996

Towing tension of the model nets were determined by the load cell(O~20kg, 20DBBP) in front of W$T_mA$ = 1.57 . $V^1.86$ (unit: kg, mlsec) $T_mB$= 1.58 . $V^1.90$ 2. The towing tension of the full scale net was almost coincided with the results obtained by the model experiment. The towing tension(T) can be expressed as a function of the towing veJocity(V) as T=479$V^1.75$(unit: kg, k't)

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.3
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• pp.183-190
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• 1993

A cooperative Korea-Japan investigation for the demersal fisheries resources of the East China Sea carried out by using the training ship Oshoro Maru belong to Hok-kaido University, Japan, during 1-8 November, 1991. The research vessel sampled 15 stations with demersal trawls on the East China Sea, and 1,364 nautical miles of track line were surveyed hydroacoustically. The hydroacoustic observations were taken with a scientific echo sounder operating at two frequencies of 25 kHz and 100 kHz, and a microcomputer-based echo integrator. Fish samples were collected by demersal trawling, and temperature, salinity and dissolved oxygen were measured with a CTD system. The target strength of fish school was estimated from the relationship between mean scattering strength and catches caught by demersal trawling. The results obtained can be summarized as follows: 1. The mean backscattering strength for 15 layers occupied by demersal trawls at 25 kHz ranged from -70.4 dB to -59.1 dB. Then the catch per one hour ranged from 8.2 to 587.5 kg/hour. 2. The mean backscattering strength for the entire layer between transducer and seabed in the survey area of the East China Sea at 25 kHz and 100 kHz were -68.0 dB and -73.1 dB, respectively. 3. The mean fish-school target strength per one kilogram at 25 kHz and 100 kHz were -28.3 dB/kg, and -30.4 dB/kg, respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.2
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• pp.85-94
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• 2001

The vertical distribution and activity patterns of fishes during the evening and morning transitions were investigated acoustically and by pelagic trawling on October 2-10, 1997 in the Korean Eastern Sea. The acoustic data were collected from four stations with a scientific echo sounder operating at a frequency of 38 kHz, and the echogram was used to analyze the diel vertical migration of fish. Biological sampling was accomplished by pelagic trawling to identify fish species recorded on the echograms, and the species and length compositions were investigated. Vertical profiles of water temperature, salinity at the trawl station were taken with a CTD system and were related to the diel movement and the depth distribution of fish. During the day, one group of fish mainly distributed above the depth layer of 50 m, the other group was at deeper water, approximately 250 m, but began to migrate toward the surface before sunset with a time difference. During the night, they were dispersed between the surface and the depth of 125 m. Just prior to sunrise, the scattering layer was divided with 2 groups and began to migrate downwards, respectively. Several trials of pelagic trawling for scattering layers suggest that the most dominant scatterer in the survey area of this study was Japanese flying squid, Todarodes pacificus..