• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.1
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• pp.16-25
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• 2015

Visual census and hydro-acoustic survey was carried out at Ulju small scale marine ranching area (MRA) to estimate demersal fish aggregations on September and November 2013. In this hydro-acoustic survey, the authors combined an image sonar with a scientific echo sounder to monitor an underwater situation and compare two acoustic data. Consequently, visual census survey was useful to estimate fish species composition for hydro-acoustic survey, because it is easy to identify aggregated fish species and overcome limits on a fishing depth and ability of an conventional fishing gear like a bottom gill-net or a fish trap at marine ranching area. Mean fish density was estimated as $0.757g/m^2$ on September and $0.219g/m^2$ on November and Fish abundance was finally calculated as 1.51ton (coefficient of variation, CV=13.1%) on September and 0.44ton (CV=47.7%) on November, respectively. Hydro-acoustic survey combined with the image sonar was useful to monitor fish aggregations and estimate fish stocks around artificial reefs at shallow coastal MRA. We were able to easily identify the underwater structures like an artificial reef and a fishing rope as well as fish aggregations from image sonar data. Therefore, the method was effective to separate unwanted echo signals in acoustic data of scientific echo sounder.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.6
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• pp.769-777
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• 2019

Low crested coastal structures such as detached breakwaters and submerged breakwaters (artificial reefs) have been commonly used as coastal protection measures. The armour units of these structures are unstable than those in non-overtopped structure cases. The stability of low crested structures armoured by rock has been suggested in existing studies. In this study, the stability of Tetrapods armour units on theses structures has been investigated using two-dimensional hydraulic model tests. The effect of wave steepness and freeboard on the armour stability on crest, front, and the rear slope has been investigated. Armour units were mostly damaged near the upper part of the seaward slope and the crest of the seaward side. From the experimental data, the new empirical formula for the stability coefficients of the Tetrapods was proposed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.1
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• pp.56-62
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• 2009

Feeding regimens was investigated for the growth and survival rate of juvenile Maroon clownfish (Premnas biaculeatus) in order to establish a seed production technique for this fish. Three types of feeding regimens were used, and growth and survival were highest under the following regimen: rotifer from day 0, Artemia from day 4, copepod from day 9 and artificial food from day 15, respectively (P<0.05). The average body lengths of the larvae were $6.76{\pm}0.55\;mm$, $7.63{\pm}0.50\;mm$ and $7.33{\pm}0.43\;mm$ in the Nannochloropsis oculata, Isochrysis galbana and control treatments conducted with 3 larvae/L, respectively (P<0.05). There were significant differences in larval growth between the treatments and controls conducted with 6 larvae/L and 9 larvae/L, respectively (P<0.05) but there was no significant difference between the N. oculata and I. galbana treatments (P>0.05). There were no significant differences in larval growth between the treatments at densities of 3-9 larvae/L (P>0.05). At highest density level, the larvae reared in I. galbana had the highest survival rate whereas survival was lowest in the control.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.2
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• pp.129-136
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• 2005

The movement ranges and diurnal behavior of the rockfish (Sebastes schlegeli) sonic tagged externally were measured by the acoustic telemetry in the marine ranching area of Tongyoung on 20 to 26 March and 4 October to 3 November, 2003. The results of study are as follows: 1. Two cage cultured fishes (body length: $30-34{\cal}cm$) were released the point where located approximately $250{\cal}m$ from the caught point on 30 March, 2003. They moved to the south $500{\cal}m$ away Sojangdudo and stayed within a $500{\cal}m$ radius of the position during the study. 2. Three wild fishes (body length: $28-32{\cal}cm$) were released around the caught point on 4 and 8 October, 2003. It was often measured that tagged fishes moved out the $500{\cal}m$ radius of released point for a week after release. After several days, the movement range tended to be reduced. Finally, they stayed within the $250{\cal}m$ radius of released point. 3. There was no significant difference of diurnal behavior of the rockfish between the cage cultured and the wild fishes. The movement range, however, for the night-time was a little wider than for the day-time.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.1
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• pp.1-8
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• 2014

In this study, a field monitoring on Namae beach erosion countermeasure in the east coast of Korea is conducted to verify its efficiency and effectiveness. The Namae Beach project has been carried out for six years with three years for planning and three years for actual construction. The planning phase of numerical model tests and investigations had been reported by Kim et al. (2008, 2011). The field monitoring confirms increase in the beach width after the submerged artificial reefs construction and is due to its wave energy dissipation effects. The field monitoring is performed at the seaward and landward of the countermeasures. The wave height reduction from the seaward side (depth h = 10.5 m) to the landward side (h = 3.7 m) of the reef is measured for wave transmission coefficient (Kt) analysis. The analysis shows 60% of deduction in wave energy due to the submerged artificial reefs.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.3
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• pp.283-291
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• 2014

This study assessed dominant fish species, and the characteristics and spatio-temporal distribution of fish schools using acoustic and catch data in the marine ranching area (MRA) of Yeosu in July and August 2013. Acoustic data were collected using a 200-kHz dual beam transducer, and catch data were analyzed through auction data generated by a set net installed in the MRA. More fish schools were detected by acoustic methods in July than in August. The temporal distribution of fish schools differed between July and August, but, many schools demonstrated a high mean volume scattering strength (SV) around artificial reefs. Additionally, the characteristics of fish schools detected by echograms and the species caught by set nets differed between July and August. The dominant fish species were Engraulis japonicus, Pampus argenteus, Scomberomorus niphonius, and Pampus echinogaster in July, and approximately 85% of the catch in August consisted of Scomberomorus niphonius. Therefore, hydro-acoustic tools are useful for estimating fish school characteristics in large areas over a short period. To determine species, it is important to conduct net sampling surveys during the acoustic surveys. However, if a database of fish school characteristics organized by species is constructed through continuous study, it could be possible to identify fish species through acoustic methods alone.

• Fisheries and Aquatic Sciences
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• v.17 no.2
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• pp.223-227
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• 2014

The present study examined whether light emitted by long-afterglow phosphorescent pigments (LumiNova) would stimulate gonadal development in fish during the nonbreeding season. Pellets containing LumiNova powder (treatment group) were prepared and placed on the calvaria of specimens of the sapphire devil Chrysiptera cyanea, a reef-associated damselfish that requires long days for gonadal recrudescence. A pellet without LumiNova powder was placed on the calvaria of the control fish (control group). Fish were reared at $26^{\circ}C$ under a light-dark cycle (12 h photophase, 12 h scotophase; LD 12:12) for 4 weeks. No difference in the gonadosomatic index (GSI) or ovarian histology was observed among the control, sham-operation, and treatment groups 1 week after the start of the experiment. After 4 weeks, the GSI of the control and sham-operation groups remained at low levels, and ovaries contained immature oocytes at the perinucleolus stage. In contrast, the treatment group exhibited significantly higher values of GSI as well as developed ovaries with fully vitellogenic oocytes. These results demonstrated that long-day conditions were produced by light emitted from the LumiNova pellets, thus stimulating ovarian development in the damselfish. Therefore, long-afterglow phosphorescent pigments can be used as an alternative to standard light sources for purposes of artificial stimulation of gonadal development in fish.

• Fisheries and Aquatic Sciences
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• v.1 no.1
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• pp.129-146
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• 1998

Fatty acid compositions of seventy-two species of Korean fish muscle, 59 species of sea water fish and 13 species of fresh water fish, were studied. Polyunsaturated fatty acid (PUFA) was the richest fatty acid group in all fish samples, accounting for $38.0\pm10.3\%$ of total fatty acids. Monounsaturated fatty acids $(MUFA,\;31.4\pm9.67\%)$ and saturated fatty acids $(SFA, 30.5\pm3.81\%)$ showed a similar level. There was a positive correlation between the total lipid content and MUFA (r=0.7788, p<0.001) and a negative correlation between the total lipid content and PUFA (r= -0.7786, p<0.001) while there was no correlation between the total lipid content and SFA. The proportion of n-3 PUFA and n-6 PUFA was $29.7\pm8.73\%$ and $6,48\pm3.70\%$, respectively, in all fish samples. The n-3 PUFA was rich in sea water fish while n-6 PUFA was rich in fresh water fish. The migratory fish contained the highest level of the n-3 PUFA $(1.82\pm1.01g/100g\;muscle)$, followed by the fresh water fish $(1.09\pm1.04g/100g\;muscle)$, the reef fish $(0.90\pm0.60g/100g\;muscle)$ and the demersal fish $(0.77\pm0.38g/100g\;muscle)$. There was a positive correlation between the total lipid and n-3 PUFA content, $y=0.2083\times+0.05 (r=0.9352,\;p<0.0010)$.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2036-2041
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• 2005

The underwater multi-agent technology has many potential for the various activities related to ocean development/conservation in the near future. For example, in such fields as water pollution investigation, aquaculture control, or coral reef research, we feel a growing need for a system that realizes underwater continuous monitoring in the wide rang e. In this case, the target monitoring area will be sliced planar hierarchically toward the depth as monitoring layers, and many AUVs arranged on each layer track the given trajectory and gather various environmental information continuously, with communicating each other in the layer or with other layers. To realize those systems we need to develop AUV multi-agent technologies. So we are now building basic systems for basin experiment for the development of AUV multi-agent behavior. We must experience many situations and problems to be solved for the development of its elemental technologies by using real systems as well as our computer simulations. In this paper we introduce our concept of the experiment in the near future and the hardware/software design of our two types of handy AUVs and ultrasound ranging/communication system for that experiment. One AUV is designed using a 17inches-diameter glass sphere with DOS/V and RT-Linux based subsystems, which is intended to use not only in the basin but also in the calm real sea. The other AUV is designed for the basin experiment using a 7inches-diameter acrylic sphere with low-cost embedded system with SH-2 based subsystems. The basin experiment to verify the basic AUV facilities and ultrasound ranging for position detection was carried out.

• Journal of Ocean Engineering and Technology
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• v.24 no.1
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• pp.106-115
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• 2010

This study described the stability of riprap, which was examined by a two-dimensional physical model of a scattered riprap submarine breakwater. Artificial reef structures made of scattered riprap are used like artificial intertidal zone structures as waterfront seaside structures. To prevent topography change in such an artificial intertidal zone the energy is reduced at the scattered riprap submarine breakwater by intercepting high waves. The breaking waves are converted into flow on the front surface slope of the submarine breakwater, which follows the upper part of the artificial intertidal zone. Because of this phenomenon of resisting water flow, it is very important to calculate the required weight of the riprap to maintain its stability. The results of a physical model can be abstracted as shown below. First, distribute the wave breaking types occurring on the front surface slope of the submarine breakwater and arrange it in relation to the movement of riprap. Second, using the hydraulic phenomenon that occurs at the depth of the scattered riprap submarine breakwater, propose a calculation formula for the velocity distribution showing the influence on the stability of the riprap. Third, propose and compare values, which can be obtained by experiments and calculations for riprap stability on the front surface of the artificial intertidal zone. Fourth, calculate the required weight for riprap stability.