• Fisheries and Aquatic Sciences
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• v.17 no.1
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• pp.145-153
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• 2014

The motion of the otter board on a trawl can affect the motion of trawl nets, and the motion of the codend can affect fish selectivity. Preliminary measurements of the tilt of bottom trawl gear were carried out to compare the tilts of the otter board and codend. The tilt of the otter board was measured by Vector and tilt at 1.5 m anterior to the end of the codend, and the middle upper panel was measured with a micro-DST-tilt logger. Tilt data such as yaw, pitch, and roll were analyzed by the fast Fourier transformation method and global wavelet and event analyses for the period or amplitude. The mean period ${\pm}$ standard deviation of the tilt in the otter board, $(5-6){\pm}2s$, was similar to the period of the codend, $(4-6){\pm}(2-3)s$, whereas the amplitude of the codend was greater than that of the otter board. The yaw and pitch periods were not significantly different between the otter board and codend, but roll was different. Furthermore, the tilt period frequencies of the otter board and codend were not significantly different. Accordingly, the tilt motion of the codend was mostly related to the tilt of the otter board.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.1
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• pp.26-34
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• 2015

The angle of attack of a cambered otter board in a bottom trawl was estimated using a three-dimensional semi-analytic treatment of a towing cable (warp) system that was applied to the field experiments of a bottom trawl obtained by the Scanmar system. The equilibrium condition of the horizontal component and vertical component of forces was used to the three forces acting on the otter board in the horizontal plane. Those forces were the force on the warp at the bracket, hydrodynamic lift and drag forces on the otter board and the force on the hand rope attached just behind the otter board. Also the equilibrium of moment about the front edge of the otter board was used to find out the angle of attack of the cambered otter board. When the warp length was 120m and 180m long and the towing speed was between 1.23 and 1.90 m/s, the estimated angle of attack of the cambered otter board was ranged between $26.1^{\circ}$ and $29.6^{\circ}$, respectively, though the maximum lift force was at the angle of attack $22.6^{\circ}$. The angle of attack of the otter board was tended to increase weakly with the longer length of warp (180 m) at the same towing speed in the experiment.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.4
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• pp.41-48
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• 1986

To investigate the midwater trawl gear available for the Korean near sea trawlers, the authors carried out a field experiment on the attitude and the opening efficiency of the otter board with the Pusan 404 (160GT, 750ps), a training ship of National Fisheries University of Pusan. The experimental trawl gear was designed to be operable by the ship and the otter board was made of single iron plate with 12% camber ratio. The special-prepared potentiometric angle detector was used for determining the attitude, and the 50 KHz fish finder for the opening between the otter boards. The results obtained can be summarized as follows: 1. The angle of attack varied by moving the towing point on the towing plate of the otter board. It showed 33 to 36 degrees when the point was set at the outmost position, 25 to 31 degrees at the middle position and 19 to 30 degrees at the inmost position, with a decreasing tendency according to the increase of towing speed in each cases. 2. The heel of the otter board always occured inwards, increasing slightly according to the increase of towing speed. 3. The tilt of the otter board always occured outwards, increasing slightly according to the move of the towing point inwards, and decreasing slightly according to the increase of towing speed. 4. The opening between otter boards showed the largest value when the towing point was set at the outmost position.

• Journal of Fisheries and Marine Sciences Education
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• v.16 no.1
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• pp.124-141
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• 2004

This study focuses on the off-shore trawl fishery, specifically on its restructuring and new regulations governing its operation since the 1990s. This fishery has an important role in terms of fishing capacity and production amount and is dependent on close diplomatic relations with adjacent fishing countries. The off-shore trawl fishery has been shrinking since the 1990s. In addition to a decrease in stock and an increase in imports, there are vessel buyback programs and a decrease in fishing grounds related to a tri-lateral agreement among Korea, China and Japan which have sped up the shrinking of the fishery. In this processing, costs exceed the increase of revenue. Excess investments in fishing gear and salary for crews have lowered profits in this fishery. Considering the above, the off-shore otter trawl fishery should stop increases in production and restructure the fishery by coordinating fishing gear restrictions and fishing areas, and down-sizing management capacity.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.4
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• pp.49-55
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• 1986

The authors carried out an experiment to determine the horizontal opening of the mid water trawl gear, which is the same as was used in the foreward experiment concerned to the attitude and opening efficiency of otter board. The trawl net .used in the experiment was designed to have a square sectional four-seamed body with two three-sepenlted wings. Each wing tip was rigged with a net pendant of 70 m long and the fore ends of the pendants were directly jointed to the otter pendant without inserting hand rope, and a front weight of 200 kg weigh was rigged with in front of the lowest wing tip. To determine the opening between otter boards ani between wing tips, two 50 KHz fish finders were set sideways on the otter board and on the port middle wing tip so as to detect the distance froa the finders to the starboard otter board and to the wing tip respectively, and the informations were transmitted to the indicators onboard the ship through water-tight cables. The results obtained can be summarized as follows: 1. The openings between otter borads were 43-45 m in case of the warp 100 m, 53-55 m in the war;> 150 m and 54-59 m in the warp 200 m. It was increased in linear according to the increase of towin; speed in the range of 1. 1-1. 8 mlscc. 2. The determined values of the openings between otter boards were greater than the estimated values. which were calculated by the opening between warps at the gallows of the ship and the length of tt~ warp, assuming that the warps from the top rollers to the otter boards were straight. The rates of the determined values to the estimated values were 1. 23-11. 0 in case of the warp 100 m, 1. 23-1. 12 in the warp 150 m and 1. 23-1. 15 in the warp 200 m respectively. The rates were almost the same at the slow towing speed of 1. 3 mlscc or so, then the higher the speed, the less the rate, and the longer the warp, the greater the rate. 3. The rates of the openings between otter boards to the total length of net pendant and the net (excluded cod end) showed 43-43% in case of the warp 150-200 m. It was a little smaller than th~ standard. which is 50%. in the common bottom trawl. 4. The determined openings between wing tips were 18-19 m in case of the warp 100m, 21-22 m in the warp 150 rn, They showed that the higher the speed, the greater the openings even though its range was no more than 1 m or so. 5. The rates of openings between otter boards to th~ openings betwee:l wing tips were almost invariably 38%. 6. The rates of openigs b2tween otter boards to the lenth of h~ad rope were 60-65% in cas': of th~ warp lOa-150m. It were much larg2r than th~ standard. which is 50%. in the common botto:n trawl.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.3
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• pp.238-244
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• 2001

A method of estimating the fluid drag of a fishing gear and otter board spread in a midwater trawl on full scale was described by implementing a three-dimensional semi-analytic treatment of the towing cable (warp) of a trawl system with the field experiments obtained with the SCANMAR system. The shape of hand rope, bridle and float(or ground) rope attached behind otter boards in a horizontal plane was assumed to be of form $y_r=Ax_r^B$. The distance between otter boards (otter board spread) obtained by the three dimensional analysis of a towing cable must be equal to that obtained by the functional equation of the shape of ropes behind otter boards, The angle of attack of ropes which can be obtained from the functional equation enables one to estimate the fluid drag of trawl net (net drag) by subtracting the fluid drag of the hand rope and bridles from the drag component of the tension of hand rope attached just behind the otter boards.

• Korean Journal of Ichthyology
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• v.23 no.3
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• pp.187-197
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• 2011

Fish species composition and size frequency distribution of major species were analyzed using seasonal samples collected by an otter trawl in the coastal water off Uljin and Hupo in 2002. Fish collected during the study were 20 species, 1,927 individuals and 53,969 g off Uljin, and 23 species, 2,762 individuals and 146,550 g off Hupo. Liparis tessellatus, Glyptocephalus stelleri and Cleisthenes pinetorum were predominated in abundance, and these 3 species were accounted for 70.9% in the number of individuals and 83.8% in biomass off Uljin, and 90.3% and 70.9% off Hupo, respectively. In the Korean coastal water of the East Sea, the migrating pelagic fish were predominated in catch by set net or gill net, and species composition varied greatly by season. Meanwhile, the fish collected by an otter trawl in the coastal water off Uljin and Hupo were dominated by the resident demersal fishes and did not show any clear seasonal trend in species composition. Collected G. stelleri and C. pinetorum were mainly composed of young fish, and size data as depth indicated that they moved into deeper shelf as they grew.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.5
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• pp.739-748
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• 1998

Demersal fishery resources were collected by an otter trawl in May, August and November 1996 at 9 stations off Youngkwang. And they were compared with the data obtained by a stow net, Of 73 species identified, assemblages were consisted of $63.0\%$ in fish, $14\%$ in shrimps, $14\%$ in crabs, $5\%$ in cephalopods and $3\%$ in gastropods. Johnius grypotus, Palaemon gravieri, Crangon hakodatei, Cynoglossus joyneri, Collichthys niveatus predominated in abundance, consisting of $64.4\%$ in the number of individuals. Catch by an otter trawl consisted mainly of demersal fishery resources, while catch by a stow net consisted mainly of pelagic fishery resources.

• Korean Journal of Ichthyology
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• v.21 no.4
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• pp.299-306
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• 2009

Fish fauna in the eastern Yellow Sea was determined using samples collected by an otter trawl from September 1999 to November 2001. The fish consisted of 97 species belonging to 80 genera and 50 families. The major taxa were the Perciformes (40 spp.), Pleuronectiformes (17 spp.), Scorpaeniformes (11 spp.) and Clupeiformes (10 spp.). Larimichthys polyactis, Engraulis japonicus, Liparis tanakai, Pampus echinogaster, Lophius lituron and Collichthys niveatus were predominated in abundance in the study area. The composition of the fish fauna has changed during the last three decades.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.4
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• pp.429-436
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• 2017

The seasonal and interannual variations in fish assemblages in the coastal waters off Gijang were examined with an otter trawl from 2015 to 2016. A total of 59 fish species was collected during the study period. The dominant species were Caelorinchus multispinulosus, Clupea pallasii pallasii and Chelidonichthys spinosus. Seasonal changes in fish assemblages appeared to be distinct in the study area. The fish assemblages in summer and autumn were clearly distinguishable from those in other seasons, and the largest numbers of species and individuals were captured in winter and summer, respectively. Because fish assemblages are closely related to changes in water temperature, long-term changes in water temperature can have a significant impact on the productivity of offshore fisheries by changing fish species composition, habitat migration, and growth rate of fish.