• 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.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.3
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• pp.182-188
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• 2004

It has been, in general, known that the catching efficiency of a trammel net is better than that of a gill net because of the variability of catch species and size. In this stidy, A fishing gear test was carried out to analyze the catching efficiency of the gill net and the trammel net on the coast of Geomun-do of southern Korean waters and fish school aggregation was also investigated using a underwater video camera. CPUE of the gill net was 49.2% higher than the trammel net but fish species was 34.5% lower where there was no difference on the significance level of 5% by ANOVA test. Main catch species caught by the gill net were red seabream(Pagrus major) and triggerfish(Aluterus monoceros), skate ray(Raja Kenojei) and red seabream for the trammel net, and the average body length of red seabream was shorter than the trammel net. It was thought that the reason of higher catch in the gill net than the trammel net was a fish school which can be caught easily by gill net and the size of population was suitable for the gill net.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.41 no.3
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• pp.221-227
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• 2008

The black rockfish (Sebastes schlegeli) is an important commercial species in Korean fisheries. We used acoustic telemetry using coded ultrasonic transmitters to track the home ranges and homing routes of the black rockfish that inhabit in the Tongyeong marine ranching area. Twenty-four fish were released at five points. The distance from the capture point (C1) to the released point was 0 (R7), 0.2 (R1), 0.9 (R2), 1.3 (R3) and 1.9 (R4) km. Two of the three fish released at R1 (0.2 km) returned home in under 48hrs. Another was found 0.8km from C1. Two of the five fish released at R2 returned home, but it took over 250 days. None of the ten fish released at R3 and R4 returned home. Three of the ten fish moved 1.1-2.6 km from C1 and were found near a cage or a natural reef. Six fish were released at R7. The younger the fish, the wider was its movement range around the artificial reefs. Fish over 3 years old were likely to move less far.

• Economic and Environmental Geology
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• v.53 no.6
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• pp.729-742
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• 2020

In this study, we analyze seabottom conditions and characteristics integrated with topographic data, seafloor mosaic, underwater images and orthophoto(drone) of soft-hard bottom area around the Sib-Ri rock in the northern shore of the East Sea(Gyeongpo Beach, Gangneung). We obtained field survey data around the Sib-Ri rock(about 600 m × 600 m). The Sib-Ri rock is formed by two exposed rocks and surrounding reef. The artificial reef zone made by about 200 ~ 300 structures is shown the western area of the Sib-Ri rock. The underwater rock region is extended from the southwestern area of the exposed the Sib-Ri rock with 9 ~ 11 m depth range. The most broad rocky seabottom area is located in the southwestren area of the Sib-Ri rock with 10 ~ 13 m depth range. The study area were classified into 4 types of seabottom environment based on the analysis of bathymetric data, seafloor mosaics, composition of sediments and images(underwater and drone). The underwater rock zones(Type I) are the most distributed area around the Sib-Ri Rock(about 600 m × 600 m). The soft seabottom area made by sediments layer showed 2 types(Type II: gS(gravelly Sand), Type III: S(Sand)) in the areas between underwater rock zones and western part of the Sib-Ri rock(toward Gyeongpo Beach). The artificial reef zone with a lot of structures is located in the western part of the Sib-Ri rock. Marine algae(about 6 species), Phylum porifera(about 2 species), Phylum echinodermata(about 3 species), Phylum mollusca(about 3 species) and Phylum chordata(about 2 species) are dominant faunal group of underwater image analysis area(about 10 m × 10 m) in the northwestern part of the Sib-Ri rock. The habitat of Phylym mollusca(Lottia dorsuosa, Septifer virgatus) and Phylum arthropoda(Pollicipes mitella, Chthamalus challengeri hoek) appears in the intertidal zone of the Sib-Ri rock. And it is possible to estimate the range and distribution of the habitat based on the integrated study of orthphoto(drone) and bathymetry data. The integrated visualization and mapping techniques using seafloor mosaic images, sediments analysis, underwater images, orthophoto(drone) and topographic data can provide and contribute to figure out the seabottom conditions and characteristics in the shore of the East Sea.

• Strategy21
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• s.38
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• pp.287-320
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• 2015

On October 27, 2015, USS Lassen(DDG82), a 9,200 ton class Aegis destroyer of the United States Navy, began its operations within 12 nautical miles of Subi Reef, one of the seven artificial islands that China has built and claimed sovereignty over. The maneuver was joined by anti-submarine patrol airplanes such as P-8A and P-3. The White House press secretary mentioned that the President of the United States approved the operation. In response, China announced that it warned the US Navy ship about the 'illegal violation' by sending two destroyers(PLAN Lanzhou and Taizhou). This event represents a close call case where tension between the United States and China in the South China Sea might have been elevated to a conflict between the two navies. Moreover, considering that this happened only one month after Chinese president Xi's state visit to the United States, the event shows that the positions of the two countries have become starkly different to the extent that they are so hard to be reconciled. The United States' position is different from those of Vietnam and the Philippines. Countries like Vietnam and the Philippines have been directly involved in disputes with regard to sovereignty claims across the waters in the South China sea. As for the United States, being a third party in the disputes, it still cannot be a by-stander watching the whole waters in the region fall under the influence of China. Accordingly, the United States maintains that all countries bear the rights of innocent passage and military operations in the Exclusive Economic Zones(EEZ) as stipulated by the United Nations Convention on the Law of the Sea(UNCLOS). In contrast, China claims that, historically, the South China sea has been part of China's territorial waters, and that foreign countries are not allowed to conduct military operations within the waters. It strongly accuses that such military operations are illegal. Against this background, this paper tracks the different positions of the United States and China on the issues regarding the South China sea. It also carefully looks at the possibility that, in the process of dealing with the issues, the two countries may get into an armed conflict as the phrase 'Thucydides Trap' predicts.

• Fisheries and Aquatic Sciences
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• v.25 no.9
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• pp.473-488
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• 2022

To have a better understanding of the impact of the PETRONAS oil and gas platform on commercial fisheries activities, Universiti Malaysia Terengganu (UMT) examined two approaches which are data collection from satellite and data collection from fishermen and anglers. By profiling the anglers who utilize reefed oil and gas structures for fishing, it can determine if the design and location of the reef platforms will benefit or negatively impacts those anglers and fisherman. Furthermore, this assessment will be contributing to the knowledge regarding the value of offshore oil and gas platforms as fisheries resources. Collectively, the apparent fishing activity data included, combined with the findings in the reefing viability index will help to inform PETRONAS's future decommissioning decisions and may help determine if the design and proposed locations for future rigs-to-reefs candidates would benefit commercial fishing groups, further qualifying them as appropriate artificial reef candidates. The method applied in this study is approaching by using a data satellite known as Google's Global Fishing Watch technology, which is one of the applications to measure commercial fishing efforts around the globe. The apparent commercial fishing effort around the selected twelve PETRONAS platforms was analyzed from January 2012 to December 2018. Using the data collection from fishermen which is the total estimation of commercial fish value cost (in Malaysia ringgit, MYR [RM]) in Peninsular Malaysia Asset, Sabah Asset, and Sarawak Operation region. The data were extracted every month from 2016 to 2018 from the National Oceanic and Atmospheric Administration database. Most of the selected platforms that show a high frequency of vessels around the year are platform KP-A, platform BG-A and platform PL-B. The estimated values of commercial fishes varied between platforms, with ranged from RM 10,209.92 to RM 89,023.78. Thus, platforms with high commercial fish value are selected for reefing in-situ and will serve multi-purposes and benefit the locals as well as the country. The current study has successfully assessed the potential reefing area of the Malaysian offshore environment with greater representativeness and this paper focused on its potential as a new fishing ground.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.67-72
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• 2022

Concrete prevents corrosion of reinforcing bars due to its strong alkalinity. However, in the sea, strong alkali components with a pH of 12 to 13 are eluted, which adversely affects the ecological environment and growth of marine organisms. In this study, the mechanical properties and durability of the low alkali mortar were evaluated for the development of a low alkali mortar for the 3D printed artificial reefs. As a result of evaluation of strength characteristics, the α-35 mixture, which were produced with fly ash, silica fume and α-hemihydrate gypsum, satisfied the strength requirement 27 MPa in terms of compressive strength. As a result of pH measurement, it was found that mixing with alpha-type hemihydrate gypsum resulted in minimizing pH due to the the formation of calcium sulfate instead of calcium hydroxide production. As a result of the chloride ion penetration resistance test, the α-35 mixture exhibited the best performance, 3844C. As a result of measuring the length change over time, the α-35 mixture showed the shrinkage 33.5% less compared to the Plain mix.

• Korean Journal of Environment and Ecology
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• v.30 no.1
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• pp.104-109
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• 2016

In Korea, the government has invested the installation of artificial reefs (ARs) which deploying to enhance the restoration of marine environment and productivity on the coastal area at the part of 222,627ha, from 1971 to 2014 for 44 years. The number of ARs are gradually increasing, while their comparison and corelation analysis were not much studied. Therefore, this study is to analyse temporal variation of ARs which composed of concrete named the Horn triangle reefs were deployed at Pohang, Jangkil-ri, a depth of 5 to 7m, in 2003, was monitored 4 times from 2009 to 2011. In results, the biodiversity investigated that the dominant species was Mollusca Omphalius pfeifferi except in 2009. The different species mainly depend on spatial-temporal variation. In this type of study can be used to the R&D, management and government policy of ARs as well improving marine environment.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.46 no.3
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• pp.239-247
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• 2010

Species of fish such as striped beakperch, bluefin searobin and konoshiro gizzard shad are commercially very important due to their high demand in the Korean market. When estimating acoustically the abundance of stocks for these species, it is of crucial importance to know the target strength (TS) to the length dependence. In relation to these needs, the TS experiments were conducted on three different species in an acrylic salt water tank using two split-beam echo sounders of 70 and 120 kHz. The TS for these three species under the controlled condition was simultaneously measured with the swimming movement by a DVR system and analyzed as a function of fish length (L) and frequency (or wavelength $\lambda$). The equation of the form TS=a log (L)+b log ($\lambda$)+c was derived for their TS-length dependence. The best fit regression of TS on fork length for striped beakperch was estimated as TS=35.67 log (L, m) -15.67 log ($\lambda$, m) -46.69 ($r^2$=0.78). Furthermore, the best fit regression of TS on fork length for konoshiro gizzard shad was shown to be TS=25.85 log (L, m) -5.85 log ($\lambda$, m) -32.22 ($r^2$=0.51). The averaged TS for 12 bluefin searobins with a mean length of 24.36cm at 70 kHz was analyzed to be -41.55dB. In addition, the averaged tilt angle obtained simultaneously by a DVR system with TS measurements for 27 konoshiro gizzard shads swimming within an acrylic salt water tank was estimated at $-2.7^{\circ}$.

• 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.