• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.2
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• pp.106-116
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• 2001

A serious of studies on the fishing gear and system of the East Sea trawl fishery was carried out to improve the fishing efficiency and the working conditions. As the first step of these studies, the fishing gear and system of the traditional East Sea trawl were checked in order to solve the some problems, such as the poor sheering efficiency of net mouth, the inconvenient fishing system of the side trawl and etc. And then the fishing system was reorganized from the side trawl into the stern trawl by setting up the net drum system on the stern deck, and introduction of two types of new designed nets, one for mainly the midwater trawl and the other for the bottom trawl. The results of the field experiment on the modified system and nets can be summarized as follows : 1. the modified system was well worked and could save the man-labour by about 80%. 2. The sheering efficiency of the improved net, A type was improved to 20 m height and 30 m width in the net mouth, and that of B type net, to 10 m height and 33 m width, compared with 1.5 m height and 15 m width in the traditional net. 3. Catch efficiency of pink shrimp in A or B type net was better about 3 or 5 times than that of traditional net, and in B net, for herring and other bottom fishes is better about 2 times than that of the traditional net.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.3
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• pp.221-229
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• 1990

The horizontal distribution of squid gill-net fishing ground in the North Pacific Ocean was examined within the main fishing season, May to October, during 1986~1989. Data of sea surface temperature were selected from Technical Reports of National Fisheries Research Development Agency of Korea, Data Records of Hokkaido University, Deep-sea Training Reports of Korea Fishing Training centre, Fishing Operation Reports of Daelim Fisheries Co., Ltd., Oyang Fisheries Co., Ltd. and Dong-won Industrial Co., Ltd.. Data of catch were also collected from Deep-sea Training Reports of Korea Fishing Training Centre and Fishing Operation Report of three fisheries companies in Korea. The fishing ground was segmented in every 1 degree of latitude from $34^{\circ}N$ to $46^{\circ}N$ and 2 degree of longitude from $144^{\circ}E$ to $162^{\circ}W.$ The distribution and centeroid of fishing ground, fished and optimum surface temperature, catch per unit effort (CPUE) in the fishing ground were computed, based on the above data. The resulted obtained can be summarized as follows: 1. Range of fishing ground can be estimated as $35^{\circ}~40^{\circ}N,$ $178^{\circ}~166^{\circ}W$ in May, $36^{\circ}~41^{\circ}N,$ $178^{\circ}E~166^{\circ}W$ in June, $38^{\circ}~44^{\circ}N,$ $170^{\circ}E~170^{\circ}W$ in July, $39^{\circ}~44^{\circ}N,$ $144^{\circ}~180^{\circ}E$ in August, $39^{\circ}~44^{\circ}N,$ $144^{\circ}~170^{\circ}E$ in September and $40^{\circ}~44^{\circ}N,$ $144^{\circ}~154^{\circ}E$ in October. 2. Fishing ground in May, June and October is similarly distributed along longitude and latitude, but the range of the former is larger than that of the latter in July, August and September. Monthly centeroids of fishing sectors is estimated as #3888 in May, #3884 in June, #4078 in July, #4154 in August, #4146 in September and #4044 in October respectively. 3. Fished temperature and optimum and temperature are estimated as $14.0~18.5^{\circ}C$ and $15.0~16.0^{\circ}C$ in May, $13.5~18.5^{\circ}C$ and $14.5~16.0^{\circ}C$ in June, $14.0~20.0^{\circ}C$ and $14.5^{\circ}C,$ $19.0^{\circ}C$ in July, $16.0~21.5^{\circ}C$ and $18.0~20.0^{\circ}C$ in August, $14.5~22.0^{\circ}C$ and $17.0~18.5^{\circ}C$ in September, $14.0~18.0^{\circ}C$ and $16.0~17.0^{\circ}C$ in October. 4. Monthly mean CPUE which corresponds to the net weight of catch(kg) divided by the sheet number of operated gillnets is calcuted as 3.2, 4.5, 4.3, 5.1, 6.4 and 5.8 kg/sheet respectively. 5. Considering the monitoring program of the squid gill-net fishery in the North Pacific Ocean during 1989~1990, set by the Korean Government, 12 sectors may be restricted out of 21 fishing sectors in May, 7 out of 24 in June, 4 out of 25 in July. They are free from restriction hereafter August.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.9 no.1
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• pp.1-18
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• 1973

For regulating the depth of midwater trawl nets towed at the optimum constant speed, the changes in the shape of warps caused by adding a weight on an arbitrary point of the warp of catenary shape is studied. The shape of a warp may be approximated by a catenary. The resultant inferences under this assumption were experimented. Accordingly feasibilities for the application of the result of this study to the midwater trawl nets were also discussed. A series of experiments for basic midwater trawl gear models in water tank and a couple of experiments of a commercial scale gears at sea which involve the properly designed depth control devices having a variable attitude horizontal wing were carried out. The results are summarized as follows: 1. According to the dimension analysis the depth y of a midwater trawl net is introduced by $$y=kLf(\frac{W_r}{R_r},\;\frac{W_o}{R_o},\;\frac{W_n}{R_n})$$) where k is a constant, L the warp length, f the function, and $W_r,\;W_o$ and $W_n$ the apparent weights of warp, otter board and the net, respectively, 2. When a boat is towing a body of apparent weight $W_n$ and its drag $D_n$ by means of a warp whose length L and apparent weight $W_r$ per unit length, the depth y of the body is given by the following equation, provided that the shape of a warp is a catenary and drag of the warp is neglected in comparison with the drag of the body: $$y=\frac{1}{W_r}\{\sqrt{{D_n^2}+{(W_n+W_rL)^2}}-\sqrt{{D_n^2+W_n}^2\}$$ 3. The changes ${\Delta}y$ of the depth of the midwater trawl net caused by changing the warp length or adding a weight ${\Delta}W_n$_n to the net, are given by the following equations: $${\Delta}y{\approx}\frac{W_n+W_{r}L}{\sqrt{D_n^2+(W_n+W_{r}L)^2}}{\Delta}L$$ $${\Delta}y{\approx}\frac{1}{W_r}\{\frac{W_n+W_rL}{\sqrt{D_n^2+(W_n+W_{r}L)^2}}-{\frac{W_n}{\sqrt{D_n^2+W_n^2}}\}{\Delta}W_n$$ 4. A change ${\Delta}y$ of the depth of the midwater trawl net by adding a weight $W_s$ to an arbitrary point of the warp takes an equation of the form $${\Delta}y=\frac{1}{W_r}\{(T_{ur}'-T_{ur})-T_u'-T_u)\}$$ Where $$T_{ur}^l=\sqrt{T_u^2+(W_s+W_{r}L)^2+2T_u(W_s+W_{r}L)sin{\theta}_u$$ $$T_{ur}=\sqrt{T_u^2+(W_{r}L)^2+2T_uW_{r}L\;sin{\theta}_u$$ $$T_{u}^l=\sqrt{T_u^2+W_s^2+2T_uW_{s}\;sin{\theta}_u$$ and $T_u$ represents the tension at the point on the warp, ${\theta}_u$ the angle between the direction of $T_u$ and horizontal axis, $T_u^2$ the tension at that point when a weights $W_s$ adds to the point where $T_u$ is acted on. 5. If otter boards were constructed lighter and adequate weights were added at their bottom to stabilize them, even they were the same shapes as those of bottom trawls, they were definitely applicable to the midwater trawl gears as the result of the experiments. 6. As the results of water tank tests the relationship between net height of H cm velocity of v m/sec, and that between hydrodynamic resistance of R kg and the velocity of a model net as shown in figure 6 are respectively given by $$H=8+\frac{10}{0.4+v}$$ $$R=3+9v^2$$ 7. It was found that the cross-wing type depth control devices were more stable in operation than that of the H-wing type as the results of the experiments at sea. 8. The hydrodynamic resistance of the net gear in midwater trawling is so large, and regarded as nearly the drag, that sweeping depth of the gear was very stable in spite of types of the depth control devices. 9. An area of the horizontal wing of the H-wing type depth control device was $1.2{\times}2.4m^2$. A midwater trawl net of 2 ton hydrodynamic resistance was connected to the devices and towed with the velocity of 2.3 kts. Under these conditions the depth change of about 20m of the trawl net was obtained by controlling an angle or attack of $30^{\circ}$.