• Journal of the Korean Society of Safety
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• v.33 no.6
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• pp.15-21
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• 2018

Ships may collide with reefs or other objects during operation, when arriving or departing ports. The hull plate may be damaged due to the contact with other ships. The total number of domestic powered fishing vessels has decreased, but that of FRP fishing vessels has increased by 0.7% and the ratio of FRP fishing vessels to the total fishing vessels increased to 96%. Recently, fishing vessels has been used as fishing boats for income of non-fishermen as well as fishermen. Therefore, safety management for repair and maintenance is necessary. The penetration of moisture and moisture in the composite material such as FRP may deteriorate the mechanical properties and the salt (NaCl) component of the damaged portion may cause a relatively high deterioration in material strength. The gel coat painting is the final stage of repairs ans maintenance of FRP fishing vessels. The thickness criteria in the domestic and foreign gel coat is 0.3~0.762 mm. The joint specimens, which was immersed in seawater for 120 days, were compared with those without seawater immersion. As a result, the tensile strength was 83 ~ 121.8% and the flexural strength was 83 ~ 113% compared with the specimens without seawater immersion. According to the previous study the tensile strength decreased by more than 29% and the flexural strength decreased by more than 50% when the composite material was immersed in seawater for 1,083 hours without coating. As a result, it was found that the gel coat with 0.5 mm thickness is very effective in preventing the strength decrease of the composite material.

• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.75-81
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• 2021

Artificial Coral Reefs (ACRs) have been introduced to help solve coastal erosion problems, but their feasibility has not been assessed with field data. This study conducted a feasibility analysis of ACRs on their erosion mitigation effects by performing a case study of Cheonjin-Bongpo beach, South Korea. A numerical-physical combined analysis was carried out using a SWAN model simulation and physical model test with a scale of 1/25 based on field observations of Cheonjin-Bongpo beach. Both Dean's parameter and the surf-scaling parameter were applied to comparative analysis between the absence and presence conditions of the ACR. The results for this combined method indicate that ACR attenuates the wave height significantly (59~71%). Furthermore, ACR helps decrease the mass flux (~50%), undertow (~80%), and maximum wave set up (~61%). The decreases in Dean's parameter (~66%) and the surf-scaling parameter suggest that the wave properties changed from the dissipative type to the reflective type even under high wave conditions. Consequently, an ACR can enhance shoreline stability.

• Korean Journal of Remote Sensing
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• v.37 no.3
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• pp.615-625
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• 2021

The coastal areas around Palau Island and Tonga Island, near the Pacific equator, consist of coral reefs, mangrove and seaweed. In particular, understanding the optical properties of sea surface water in coral reef habitats helps improve the accuracy of remote sensing based habitat mapping and identify tropical ecosystem characteristics. Here, we collected spectral characteristics of sea surface water of Palau Island and Tonga Island and analyzed the concentration of suspended matters, absorption coefficient, and remote sensing reflectance to understand the seawater characteristics of the coral reef habitats. Based on the results of the suspended matter concentration analysis, we developed and verified an empirical algorithm to derive the concentration from satellite data using remote sensing reflectance of three bands, 555, 625, 660 nm, showed a high determinant coefficient, 0.98. In conclusion, coral reef habitats in tropical regions are characterized by CASE-I water in terms of the marine optics with oligotrophic properties, and require monitoring using continuous collection and analysis of field data.

• Journal of Practical Agriculture & Fisheries Research
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• v.17 no.1
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• pp.45-56
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• 2015

The distribution of seaweed was examined in Jeonnam archipelago marine ranching area, the coastal of geumo-do, Yosu. Abundance and distribution of seaweed in dropping site of artificial reef were sampled at 6 station at October 2007. Seaweed community were investigated with quadrat method at line-transect by scientific SCUBA divers. as a result, 30 species in total, 4 green, 9 brown and 15 red seaweed were identified. Range of seaweed biomass in all sampling stations were about 1,600~4,000 g/m². At intertidal zone, appearance of individuals and dominance rate were showed higher than below the subtidal line and at depth from 4m to 6m, individuals, dominance rate and biomass were represented low level. characteristic of water in marine ranching area is turbidity and also compensation depth is low. For that reason, individuals of seaweed community were smaller from depth of 4 meters. Therefore, when equip the artificial reef for preparation of seaweed beds need consider that equipment periods(early spring; before releasing marine seaweed spore) and suitable water depth(3~6m).

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.58 no.2
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• pp.106-112
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• 2022

As a series of basic research to draw the pilot design measures for developing the habitat apparatus of Sulculus diversicolor supertexta inhabiting the coastal area of Jeju island, this study conducted a water tank experiment to understand the habitat marine environment of Sulculus diversicolor supertexta and the preference of habitat space focusing on the research fisheries performing the discharge of marine products. In the composition degree of marine algae in both fisheries, Donggwi-ri showed the highest gulfweed (79.3%) as brown algae and there were some coralline algae (17.2%) as red algae. Hansu-ri yielded the highest gulfweed (48.1%) as brown algae, which was followed by sea lettuce (10.4%) as green algae. In the preference of habitat space, the shelter angles 40° showed the highest adhesion as number of 82.9, which was followed by 60° and 70° as 69.2 and 68.2 respectively (P<0.05) by reviewing the environmental characteristics of habit of Salculus diversicolor supertexta in the coastal fishery of Jeju Island, when considering the adhesion rate in each of five shelters with different angles. In the future, there should be continuous research and monitoring for designing the fish shelters suitable for the coastal fisheries of Jeju island, and it would be also necessary to add the field-centered sustainable concrete research.

• Korean Journal of Ichthyology
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• v.22 no.3
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• pp.168-178
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• 2010

Fish assemblages associated with rock reef and non-rock reef were studied using specimens collected at three sites in Geomun Island waters of the Southern Sea, Korea, in February, May, August and October, 2006. Two survey methods for the study were followed: collection by a gill net, and video observation by scuba diving. The gill-net survey was conducted during the night, the scuba-diving observations were conducted during the day. From the gill-net survey, a total of 40 species, 380 inds. and 71,426.9 g was caught at the three sites. The dominant species was Trachurus japonicus; other species were Raja kenojei, Dasyatis akajei, Stephanolepis cirrhifer, Narke japonica, Pagrus major, Sebastes inermis, and Sphyraena pinguis. At the rock-reef site, a total of 26 species, 264 inds. and 46,776.7 g was caught by gill net, and the dominant species was T. japonicus. A total of 17 species, 45 inds., 10,535.1 g was caught at the flat-bottom 1 site, and 19 species, 71 inds. and 14,115.1 g were caught at the flat-bottom 2 site. The scuba-diving survey resulted in 13 species and 1,749 inds. observed at the three sites through the survey period. The main observed fishes were rock-dwelling species such as Chromis notatus, Microcanthus strigatus, S. cirrhifer, Ditrema temmincki, Evistias acutriostris, Girella punctata, Halichoeres poecilopterus, Hexagrammos agrammus, Prionurus scalprum, Sebastes inermis, and Semicossyphus reticulatus. Seven species and 1,739 inds. observed at the rock-reef site comprised 99.4% of the inds. of the three sites. Therefore, the fish community in Geomun Island waters included many rock-reef. species, but a few were migratory species like T. japonicus and Scomber japonicus. The abundance of fish at the rock-reef site was high in comparison with those at two non-rock reefs. The dominant species were very different between the day and the night, although rock-reef species comprised the main part of the fish community. We conclude that the high abundance of fish in Geomun Island waters is most closely related to physical structure, such as rock reefs, which is the main habitat of many fishes.

• Development and Reproduction
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• v.15 no.2
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• pp.121-131
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• 2011

The aim of this study was to investigate the egg development and the color change of Amphiprion melanopus, by the live food and thyroid hormone. After fertilizing, it took 168 h until hatching. The size of hatching larvae were $3.5{\pm}0.3$ mm, and some individuals had small yolk sac. As reaching the particular age, they underwent the color change (metamorphosis) - Days after hatching (DAH) 10: black, DAH 15~20: the 3 white stripes appear, DAH 30: the dorsal & the caudal white stripe begin to disappear. DAH 90: body color become red and orange, adult: cinnamon body color and a white stripe on head. - The group fed enriched Artemia with Tigriopus japonicus grew the faster than with only Artemia. The fin coloration of the one fed the only T. japonicus has a vivid red and orange color. $T_3$-treated group (4 ppm) grew the faster than the others (0, 2, 6 ppm). The size of the 6 ppm group was the smallest. The results suggest T. japonicus can be used as a supplement with rotifer and Artemia for the juvenile development and coloration. $T_3$ is considered to be involved in the metamorphosis and color formation of Amphipirion sp.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.3
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• pp.174-180
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• 2001

Dusky spinefoot, Siganus fuscescens live primarily in shore reefs with sea weeds, like around Jeju Island in Korean south sea. Therefore they are caught much by set net in the coast of Jeju Island. We carried out measurements of the dorsal aspect target strengths of Dusky spinefoot in order to study the influences of swim bladder for fishes. and have obtained some desired results though not sufficiently complete as comparison with target strengths of fishes before and after the air gas in the swim bladder of fish is taken off by an injector. The appropriate equations share the common form TS = A + 20 log L. TS = B + 20/3 log W where TS is the average dorsal aspect target strength in decibels. L is the fish total length in centimeters. W is the fish total weight in grams, and the coefficient A and B are determined by a least mean squares regression analysis. The results obtained before the air gas in the swim bladder of fish is taken off are TS = -63.16 + 20 log L TS = -50.50 + 20/3 low W and, the results obtained after the air gas in the swim bladder of fish is taken off are TS = -65.29 + 20 log L TS = -52.62 + 20/3 log W As above result, the differences of target strengths before and after the air gas is taken off from swim bladder are 2.12-2.13 dB, but the maximum difference of target strengths of both cases averaged according to the fish aspects from $-45^\circ$ to $45^\circ$ is 5.87 dB, and the average difference of them is 2.01 dB.

• Geophysics and Geophysical Exploration
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• v.9 no.2
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• pp.163-170
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• 2006

The shortage of proven hydrocarbon reserves has resulted in exploration progressing from the offshore into progressively deeper water of the continental shelf. Despite the success of seismic acquisition at ever greater depths, there are marine geological terrenes in which the interpretation of seismic data is difficult, such regions dominated by scattering or high reflectivity that is characteristic of carbonate reefs, volcanic cover and submarine permafrost. A marine controlled-source electromagnetic (CSEM) method has recently been applied to the oil and gas exploration thanks to its high-resistivity characteristics of the hydrocarbon. In particular, this method produces better results in terms of sensitivity under the deep water environment rather than the shallow water. Only in the last five years has the relevance of CSEM been recognized by oil companies who now use it to help them make exploration drilling decisions. Initial results are most promising and several contractors now offer magnetotelluric and CSEM services.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.6
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• pp.602-610
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• 2008

A beach has such functions as disaster prevention, providing an amenity place, attracting people and maintaining the coastal ecosystem. Already well known that a beach provides an amenity place, it has also been ascertained through various examples that a sand beach performs a very important function to maintain the coastal ecosystem as well. However, Beach erosion began to occur in Korea in the 1990's and posed a social problem in the late 1990's. Nowadays, along the shorelines of Korea's many beaches, about 400 beaches have reported erosion. This study demonstrate the Disaster Overall Prevention System for Beach Erosion and it's application. The Disaster Overall Prevention System for Beach Erosion is a coastal management system established for managing the implementation of long-term countermeasures to protect eroded beaches effectively in this study. Especially, the economic feasibility test and adaptive management for sustainable mitigation included in DOPS. The coastal prevention work applied to Namae beach is carried out by Disaster Overall Prevention System. Consequently, beach nourishment is proposed as a main countermeasure. Also, submerged artificial reefs and groin integrating artificial rock are proposed as secondary countermeasures for beach erosion. This resulted to be the optimal beach erosion countermeasure from DOPS, considering the economic and environmental conditions of the study area.