Chan-Moon Choi

Characteristics of lost fishing gear distribution on the sea bed around gillnet fishing ground for yellow croaker in the near sea of Jeju, Korea

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Catch fluctuation of the rectangular set net according to the tide age in the coastal waters of Jeju

The fundamental data on the catch fluctuation in the rectangular set net according to the tide age weredeveloped based on the catches recorded from the year 1986 to 2004 in the coastal waters of Hamdeok, Jeju.Total catch by the rectangular set net had a deep connection with the tide age. In particular, duringincreasing tide, total catch were reduced gradually from the neap tide to the high tide. As it turned out, theslope of total catch declined by degree and showed a correlation coefficient of determination of 0.76. On thecontrary, in the case of decreasing tide, there was little sign of rise in total catch. In particular, large catchseemed to occur at the next tide to the neap tide. In the relation between the catch and the tide age, the levelof the correlation coefficient chosen at p0.05 decreased in the order rabbitfish(0.84) and horsemackerel( 0.71), while the significance of other dominant species were not selected.Key words : Tide age, Neap tide, High tide, Catch fluctuation, Set net

Hearing Ability of Conger eel Conger myriaster caught in the Coast of jeju Island

In order to obtain the fundamental data about the behavior of conger by underwater audible sound, this experiment was carried out to investigate the hearing ability of Conger eel Conger myriaster which was in the coast of Jeju Island by heartbeat conditioning method using pure tones coupled with a delayed electric shock. The audible range of conger eel extended from 50Hz to 300Hz with a peak sensitivity at 80Hz including less sensitivity over 200Hz. The mean auditory thresholds of conger eel at the frequencies of 50Hz, 80Hz, 100Hz, 200Hz and 300Hz were 105dB, 92dB, 96dB, 128dB and 140dB, respectively. The positive response of conger eel was not evident after the sound projection of over 200Hz. At the results, the sensitive frequency range of conger eel is narrow in spite of swim bladder. Auditory masking was determined for Conger eel by using masking stimuli with the spectrum level range of about 60~70dB (0dB re ). According to white noise level, the auditory thresholds increased as compared with thresholds in a quiet background noise including critical ratio at 68dB of white noise from minimum 26dB to maximum 30dB at test frequencies of 80Hz and 100Hz. The noise spectrum level at the start of masking was distributed at the range of about 68dB within 80~100Hz.

The tendency and the effectiveness of policy in marine accident occurring in the sea around Jeju island

The objective of this paper is to aid in basic directions for the countermeasure against marine accidents by using the statistical data of Jeju Coast Guard from 1983 to 2012. Marine accidents of about 600~1,000 vessels was reported in all the waters around South Korea from 2000 to 2008. From 2009, these accidents increased rapidly and reached 1,600~2,000 vessels. Although marine accidents of longline fishing vessels did not show a big change prior to 1993, the number have increased steadily until 2007. This is considered a tendency that appears when longline vessels, using the Port of Sungsanpo as a base and operating in fishing grounds in the East China Sea, are converted to long-term fishing from short-term fishing for reasons such as cost reduction due to the sudden rise of oil prices and the performance improvement of the fishing vessels. The number of vessels in marine accidents decreased gradually from 1999 to 2002 and for nearly 7 years from 2002 to 2008, the annual average of marine accidents stayed at 97 vessels. This is seemed to be the result of a change in the policy of either the central or local government and largely associated with changes in the way of statistical processing. This tendency is resulted in lower number of the accidents due to careless navigation which can be viewed as a human error than the number of marine accidents due to poor maintenance as a cause of mechanical failure in the same period. The increase rate in the marine accidents of Jeju Island-based fishing vessels is greater than that of other area-based fishing vessels among the fishing vessels operating in coastal and near sea around Jeju Island each year.

Hearing Ability of Redlip croaker Pseudosciaena polyactis cultured in the Coastal Sea of Jeju

The purpose of this paper is to improve the availability of underwater sound by the fundamental data on the hearing ability of Redlip croaker Pseudosciaena polyactis, which is cultured according to the cultivation technology, recently. The auditory thresholds of Redlip croaker were determined at 6 frequencies from 80Hz to 800Hz by heartbeat conditioning method using pure tones coupled with a delayed electric shock. The audible range of the Redlip croaker extended from 80Hz to 800Hz with the best sensitive frequency range including little difference in hearing ability from 80Hz to 500Hz. In addition, the auditory thresholds over 800Hz increased rapidly. The mean auditory thresholds of the Redlip croaker at the test frequencies from 80Hz to 800Hz were 90.7dB, 93.4dB, 92.9dB, 94.4dB, 95.5dB and 108dB, respectively. Auditory masking for the redlip croaker was measured using masking stimuli with the spectrum level range of about 66, 71, 75dB (0dB re 1PaHz ). According to white noise level, the auditory thresholds increased as compared with thresholds in a quiet background noise. The Auditory masking by the white noise spectrum level was stared over about 70dB within 80~500Hz. Critical ratio ranged from minimum 20.7dB to maximum 25.5dB at test frequencies of 80Hz~500Hz.

Analysis of basic productivity of fishing vessels registered on Aewol port in the Jeju island

In order to propose basic references for the policy making of fishing vessel fishery by Jeju Special Self-Governing Province, we have obtained the basic productivity through analyzing operating days and catches of 16 sample fishing vessels registered in Aewol port, the north of Jeju island in the year of 2011. In addition, to compare with the basic productivity of southern sea area in the Jeju island, that of 7 sample fishing vessels registered in Kangjung port was used. Around Aewol port, average operating days during the main catch period from July to October were over 15 days a month. A average daily catch of fishing vessels was minimum 21.0 kg in May and reached to maximum 54.5 kg in December, showing U-shaped catch pattern through the year. The trend formula of the average daily productivity (y) depending on a tonnage (x) of fishing vessels around Aewol port was described by the equation, y

Efficiency of wave absorption by the porous of "Taewoo" of Jeju in regular seaway

In an effort to find the optimum porous of Taewoo through the mathematical model 2 dimensional tank water experiment among the approached to a problem related to ocean engineering, this study analyzed the porosity by dividing it into 9 cases. As the wave penetrates through the longitudinal porous of the Taewoo model, it was found that there is a wave energy loss because of the phenomenon of the separation of the porous due to the eddy. Looking into the general tendency based on the wave-height meter (probe) data, it was found that the shorter wavelength and higher frequency area, the more reflection coefficients increased, but in contrast, the longer wavelength and lower frequency area, the transmission coefficients showed the increasing trend and energy dissipation was in a similar way with reflection coefficients. In addition, it was found that the bigger the porosity was, the narrower distribution range of reflection coefficients was, and the more its average value decreased. On the other hand the transmission coefficients in direct opposition to reflection was found to show the wider range and the more gradual increase in the average value as porosity was the bigger around the average value. In contrast, energy dissipation rate was found to increase linearly as porosity increased the more around the porosity of 0.2518 but it decreased gradually around the peak point. Through the above results, it is judged that the porous of optimum in the longitudinal direction of the Taewoo model perforated plate was about 2.6cm because it was found that the porosity which produced the lowest reflection and transmission coefficient and the highest energy dissipation. As a result of comparing this to the case where there was no porosity at all, it showed the function of wave absorbing about 31.60%.

Hearing Ability of Bambooleaf wrasse Pseudolabrus japonicus caught in the coast of Jeju

Abstract In order to improve the availability of underwater sound by the fundamental data on the hearing ability, the auditory thresholds for the bambooleaf wrasse pseudolabrus japonicus were determined at 80Hz, 100Hz, 200Hz, 300Hz, 500Hz and 800Hz by heartbeat conditioning method using pure tones coupled with a delayed electric shock. The audible range of the bambooleaf wrasse extended from 80Hz to 800Hz with the best sensitivity around 100Hz and 200Hz. In addition, the auditory thresholds over 300Hz increased rapidly. The mean auditory thresholds of the bambooleaf wrasse at the test frequencies, 80Hz, 100Hz, 200Hz, 300Hz, 500Hz and 800Hz were 100dB, 95.1dB, 94.8dB, 109dB, 121dB and 125dB, respectively. Auditory critical ratios for the bambooleaf wrasse were measured using masking stimuli with the spectrum level range of about 70, 74, 78dB (0dB re 1    ). According to white noise level, the auditory thresholds increased as compared with thresholds in a quiet background noise. The Auditory masking by the white noise spectrum level was stared over about 60dB within 80~300Hz. Critical ratios to be measured at frequencies from 80Hz to 300Hz were minimum 33dB and maximum 39dB. Key words : Bambooleaf wrasse, Hearing Ability, Underwater Audible Sound, Auditory threshold, Critical ratioCorresponding author : 064-754-3491 leech@jejunu.ac.kr

Effects for reduction of roll motion by the control of steering gear

Reduction of ship ′s rolling is the most important performance requirement for improving the safety of thecrew on board and preventing damage to cargo as well as improving the comfort of the ride . It is acommonexperience for mariners , to see that steering with a rudder generally induces rolling of the ship , though theoriginal aim of the rudder is to keep the ship ′s heading to the required course . At the first stage , when arudder is steered , usually aship heels in an inward direction , due to the roll moment acting on the rudder . Atthe next stage in steering , the main heel may change to an outward . This coupling between rudder and rollmotion has become an attractive problem from the point of view of roll stabilization using the rudder ,because it is a natural in sight that if the rudder action is skillfully related to the change of roll as well as tothe course deviation , the roll can be reduced to acertain degree . The main aim of this paper is to discuss theresults of the actual full-scale sea trials carried out on steer gear No .1 and No .1 ·2, the individual quarter -master and to make clear their statistical properties , using the actual data which included measurement ofroll angle , roll rate and the comparative tests were carried out immediately after each other , in order tominimize any statistical variation in sea conditions . It can be concluded that the steer gear No . 1 ·2 reducedthe roll motion on average by about 21% in comparison with the No .1 and confirmed the some difference asper aability of quarter -master ′smaneuver .Keywords: Roll stabilization reduction , Steering gear , Rudder , Roll angle , quarter -master ′smaneuver

A study for rolling reduction of fishing boat by utilizing u-type fish-hold

In this study it will be discussed how to solve the problem of discomfort from rolling motion on the fishing boats. Most discomfort is caused by the short cycle of rolling due to the light weight of the boats. The light weight is due to the FRP material which dries a boat. A way to improve the feeling of boarding by using fish hold was researched. The experiment was done on experimental fishing boat made by FRP in Jeju. An existing fish hold was designed and manufactured through the rolling test and that was used for a marine experiment. The rolling condition of the U-tank boat ideally designed was compared to that of an existing fishing boat using the same conditions. The experiments were carried out two times on the stop engine in the outward Sehwa fishing port, which the experimental data had analysed for effects of rolling reduction to compare the U - tank with the of exiting fish hold. The results were confirmed that the U-boat tank in the roll period and GoM were more safe than the existing fish hold and the average amplitude and significant of rolling angles were decreased relatively.