This study analyzed the duct characteristics of hubless rim-driven propeller (RDP) used in underwater robots. In the previous study, flow visualization experiments were performed with an advancing ratio of 0.2 to 1. The vortex at the front of the duct increased in strength while maintaining its size as the advancing ratio decreased. Therefore, it is necessary to study the optimization of the duct shape. Conventional propeller thrusters use acceleration/deceleration ducts to increase their efficiency. However, unlike conventional propellers, it is impossible to apply to airfoil acceleration/deceleration ducts due to the RDP structure. In this study, duct wake flow characteristics, thrust force, and efficiency according to the duct shape of RDP were analyzed using numerical analysis techniques. Duct design is limited and six duct shapes were designed. As a result, an optimized duct shape was designed considering duct wake flow characteristics, thrust force, and efficiency. The shape that the outlet width of the RDP was kept constant until the end of the duct showed higher thrust force and efficiency.

Comparative fishing experiments were conducted in the eastern coastal waters near Uljin, Korea from 2002 to 2004, using the experimental trammel nets to estimate the selectivity for spinyhead sculpin Dasycottus setiger. The inner panels of the nets were made of nylon monofilament with four mesh sizes (82.2, 89.4, 104.8, and 120.2 mm) while its two outer panels were made of twisted nylon multifilament with a mesh size of 510 mm. The SELECT (Share Each Length’s Catch Total) procedure with maximum likelihood method was applied to obtain a master selection curve. The different functional models (normal, lognormal, bi-normal, and logistic model) were fitted to the catch data. The lognormal model with the fixed relative fishing intensity was chosen as the best-fitted selection curve through comparison of model deviance and AIC (Akaike’s Information Criterion). The optimum relative length (the ratio of fish total length to mesh size) with the maximum relative efficiency was obtained as 2.492.

Fishing pots are one of the important fishing gears in our coastal and offshore fisheries. In terms of a sustainable use of marine resources, there are concerns about the ghost fishing by lost pots. It is reported that 10 to 70% of the pots are abandoned or lost annually. This study is to compare the catching efficiency of drum type whelk pots that are made of biodegradable nets to those made of the ordinary nets, in the eastern coast of Korea. Five types of drum pots were used with combination of biodegradable nets and ordinary (PA, PE) nets applied to the main and funnel parts of the pots: pots with biodegradable nets (Bio+Bio); pots with PE net (PE+PE); pots with body and funnel made of biodegradable nets and PE nets respectively (Bio+PE); pots with body and funnel made of PE nets and PA nets respectively (PE+PA); pots with body and funnel made of PE nets and biodegradable net respectively (PE+Bio). Field experiments were conducted from June 18th, 2015 to August 7th, 2015 using a commercial fishing vessel in the Uljin waters on the eastern coast of Korea. Two fleets of pots with one hundred in each, 20 pots of each type, were casted for 8 to 15 days to analyze their catching efficiency. The catch of target species, whelks, was 202,563.0 g with catch rate of 38.7% of the total catch, while the bycatch was 320,709.7 g with the rate of 61.3% of the total catch. The catch of whelks was the highest in the Bio+PE pots (46,020.3 g), followed by the Bio+Bio pots (42,027.5 g), the PE+Bio pots (41,849.9 g) and the lowest being PE+PE pots (38,054.2 g). Compared to the conventional pots, the pots with biodegradable nets on the body or entrance part had slightly higher catch rate for both the target species and the bycatch. The PE+PE had the lowest catch rate. There is no significant difference in catch between the pots with biodegradable nets and the ordinary nets for the target species such as Buccinum opisthoplectum, Neptunea eulimata, Buccinum striatissimum. Consequently, using biodegradable nets for the conventional whelk pots can reduce ghost fishing by lost gears while keeping the performance of the pots.

Spinyhead sculpin Dasycottus setiger, a species of cold water fish, is distributed along the eastern coastal waters of Korea. A series of fishing experiments was carried out in the waters near Uljin from June, 2002 to November, 2004, using the experimental monofilament gill nets of different mesh sizes (82.2, 89.4, 104.8, and 120.2 ㎜) to describe the selectivity of the gill net for the fish. The SELECT (Share Each Length’s Catch Total) analysis with maximum likelihood method was applied to fit the different functional models (normal, lognormal, and bi-normal models) for selection curves to the catch data. The bi-normal model with the fixed relative fishing intensity was selected as the best-fit selection curve by AIC (Akaike’s Information Criterion) comparison. For the best-fit selection curve, the optimum relative length (the ratio of fish total length to mesh size) with the maximum efficiency and the selection range (R50%,large - R50%, small) of 50% retention were obtained as 2.363 and 0.851, respectively. The ratios of body girth to mesh perimeter at 100% retention where the selection curve of each mesh size represented the optimum total length were calculated as the range of 0.86 ~ 0.87.

This study investigated luring distributions by water layer of common squid which were targeted by angling fishing vessels equipped with LED and metal-halide lamps using a scientific echosounder with a 120 kHz frequency in order to develop energy-effective underwater fish aggregation devices. In the analysis, angles of a transducer were changed from 0° to 45° and were rotated every 10° horizontally. It was shown that common squid were densely distributed from the surface to 40 m and they were also distributed in directions of 10°∼+30°, -30°∼-60°, and -120°∼-130°with the head of vessel as the center. Comparative results of angles of transducer on acoustical densities of common squid distributing in 21~40 m water depth showed an average 101.8 m2/nm2 in vertical direction of 0°, 12.3 m2/nm2 in angle of 30°, and 42.4 m2/nm2 in angle of 45°, respectively. It implied that more considerations on acoustic scattering strength by incidence angle direction of the transducer and swimming oriental angle direction of common squid would be required.

The species composition and distribution of catches by dredge gear in the Yeongil Bay, Korea were investigated on aseasonal basis from February to November, 2015. Total catches consisted of 44 species and 35 families. They were 13 species of fish, 10 species of crustacea, 5 species of echinodermata, 5 species of gastropoda, 4 species of cephalopoda and 3 species of bivalvia. Major catch species was shellfish and had seasonal variations in catch. In spring and winter, the catch of ark shell (Scapharca broughtonii) was increased. Adversely, the catch of admas venus clam (Callithaca adamsi) increased in sunmmer and autumn. Species diversity indices was high as the value of 1.99 in spring, and low to the value of 0.34 in summer. In addition, multi dimentional scaling (MDS) indices also was high in spring as the value of 1.99. In summer, the index was low as the value of 0.34. Similarity analysis based on species data was transformed by fourth root. With the result of cluster analysis and MDS analysis, species was divided into two groups. The first group as Group A consists of winter and spring species and another was Group B made of species in summer and winter.

Experiments for catch and cluster analysis on the catch by gillnet for the Pacific herring were conducted using traditional nylon net (PA) and developing biodegradable net (PBS) with different monofilaments of #2 (=0.23 mm) and #3 (=0.28 mm) in diameter between 2011 and 2012, and of #2, #2.5 and #3 in 2013 in the eastern coastal waters of Samcheok, Korea. The total catch during the experiments was 3,337kg in weight and 16,757 individuals in number. Though the catch ratio of the Pacific herring in 2011 and 2012 was 97.4% and 98.7%, respectively, that of the Pacific herring in 2013 was 73.6% as the biggest and followed by goldeye rockfish (8.6%), black edged sculpin (8.4%), atka mackerel (7.2%) and Alaska cod (1.0%). The ANOVA analysis on the total catch in relation to net material showed that there was not statistically significant difference at the 5% level between nylon net (PA) and biodegradable net (PBS) (p=0.91). With the cluster analysis on the catch in relation to net material (PA, PBS) and twine thick (#2, #3), it showed the influence of net material on the catch was greater than that of twine diameter in this experiment. From the test of homogeneity on the catch by the gillnet with PA and PBS in which several species were caught in 2013, there was not statistically significant homogeneity in relation to net material (p<0.005). That meant the traditional gillnet of nylon (PA) was more efficient than the biodegradable (PBS) gillnet to catch several kinds of fish, however the PBS gillnet was better than the PA gillnet to catch the target Pacific herring.

This study is aimed to analyze the hydrodynamic characteristics of the cage net in the circulating water channel. It visualized wake flows using a PIV (paricle imaging velocimetry) and analyzed the flow velocity distribution. In addition, the vorticity and turbulence intensity were analyzed from the wake flow distribution and compared changes by flow velocity. Results showed that the average turbulence intensity in the circulating water channel was very stable showing less than 1% in the range between 0.2 and 0.8 m/s. The drag coefficient affecting to the netting was estimated to be 1.35. The flow decreasing rate of the wake in the middle of the netting was 2.1% at the range of 0.2 m/s and it was constant at 6.6―6.9% over the range of 0.4 m/s irrespective of velocity increases. Finally, the change of turbulence intensity by netting and knot mesh could be confirmed. These results can be utilized as a basic information for the future research of flow characteristics by fishing nets and meshes.

We investigated biomass, diatom species and fucoxanthin contents as cell growth, fatty acid and amino acid contents as nutritional composition of diatoms attached on plate to confirm effects of light emitting diodes (LEDs) due to block off natural light. In the single LED irradiation, biomass showed significantly higher to 30.0±6.48mg/m2 in white LED than that of others (P<0.05). The dominate diatom species was Navicula cancellata. Their lipid contents showed significantly higher to 112.9±19.23ug/mg dry matter (DM) in control than that of others LEDs. But eicosapetaenoic acid (EPA) contents showed significantly higher to 3.3±0.62ug/mg DM than others, but not significantly differed with natural control light treatment (P<0.05). And total protein contents are higher in control and blue LED light than that of others, but essential amino acid contents showed significantly higher to 3.2±4.8% in control (P<0.05). In mixing light with natural and LED light, biomass showed 2.6±0.22mg/m2 in blue LED (P<0.05). Fatty acids contents were not significantly differed with all treatments. Amino acid contents showed to 11.0±0.33ug/mg DM in white LED (P<0.05), but not significantly differed with others LED lights (P>0.05). Therefore, we could suggest that irradiation of blue LED in natural light very benefit to diatom culture for larvae of sea cucumber and abalone and do on.

The dredge gear is dragged along the bottom of the sea to catch targeted edible bottom dwelling species. Species composition and ecological index of the catches of dredge were estimated around Gangneung coastal fishing ground by dredge with different mesh size and tooth space from July to December 2013. Eight different types of dredge including four different tooth space (24.7 mm, 29.9 mm, 34.9 mm, 40.1 mm) and four different mesh size(15.5 mm, 32.7 mm, 51.1 mm, 060.0 mm) were used in the experiment. During the experiment, total catches were collected 31 species as sipunculida 1 species, mollusca 13 species, annelida 3 species, arthropoda 8 species, echinodermata 4 species and others 2 species. The dominant genus were mollusca and echinodermata while the dominant species were Megangulus venulosus, Pseudocardium sachalinensis, Schaphechinus brevis. The richness index was ranged 1.29-1.72, evenness index was 0.6-0.65 and diversity index was 1.65-1.83 according to the tooth space and mesh size of dredge. Richness index, diversity index were high at tooth space 34.9 mm dredge and ecological index showed decreasing tendency with the increasing of mesh size of dredge. Cluster and MDS analysis, based on a Bray-Curtis and similarity matrix of fourth root transformed data of number of species and wet weight, showed division into four different groups as four different tooth space (Group A), four different mesh size Group B (51.1 mm, 60.0 mm), Group C (32.7 mm) and Group D (15.5 mm).

Experiment was set up to analyze bycatch and discards situation including snow crap Chionoecetes opilio of whelk trap. Four types of trap were used: drum type trap with PE net; drum type trap with PBS net; cylinder type trap with PE net; and cylinder type net with PBS net. Three funnels were attached in drum type trap and two funnels were used in cylinder type trap. A fleet of traps was consisted with one hundred traps. 25 traps of each type were set on a line in repeated sequence. Field experiments were conducted with 6 fishing operations in the Uljin waters, East Sea in July 2014. Catch of target whelks were 173,261 g and catch rate was 48.7% of total catch, while bycatch were 182,571 g, 51.3% of tatal catch. The catch rate of bycatch was 2.6% higher than that of target catch. Bycatch weight of snow crap was the highest as 142,987 g and formed about 40.2% of total catch, followed giant octopus, Enteroctopus dofleini, 31,762 g (8.9%). Bycatch rate of cylinder type trap was 2.3 times higher than that of drum type trap. Discard rate (discard/(discard+landing)) was 43.6%. Discard rate was the highest at cylinder type trap with PBS net as 63.1%, followed cylinder type trap with PE net as 47.9%, drum type trap with PE net as 33.4%, the lowest at drum type trap with PBS net as 22.1%.

This study is aimed to analyze the three-dimensional underwater irradiance using an optical simulation software and to clarify the propriety and operation method under considering luminous intensity distribution of the luring lamp and penetrability in the seawater, when we use the light diffuser type 300W high powered LED and the metal halide lamp (MHL) on a coastal squid jigging vessel in the 10-ton class, simultaneously. For their attenuation characteristics of each wavelength in relation to the sea, LED lamp was to be effective in the 1.9-fold at 50 m depth and 2.1-fold at 80 m for underwater irradiance more than MHL according to the power consumption. In addition, the underwater irradiance distribution using the LED and MHL combination was rather increased even when reducing total power usage up to 20% depending on the simulation with changing the configuration and lighting angle of the lamp. These results can be utilized as an evaluation method of the operation and performance of the LED lamp according to adjusting its arrangement and lighting angle.

The marine microalgae Chaetoceros calcitrans was cultured under a fluorescent lamp (CON) and light-emitting diodes (LEDs) of various wavelengths (blue, LB; red, LR; green, LG; white, LW); changes in growth, fucoxanthin, chlorophyll-a, amino acid and fatty acid profiles were investigated. LR-exposed cultures exhibited the highest specific growth rate (SGR) (0.34), whereas LG-exposed cultures showed the lowest SGR (0.26). After cultivation for 10 days, the maximum dry cell weight (g/L) of LR-exposed cultures was significantly higher than that of those exposed to other light conditions (LR≥ CON>LB≥LW≥LG). Eicosapentaenoic acid (EPA) levels were significantly higher in CON-exposed cultures compared to those exposed to LW (P<0.05), with no marked difference compared to those exposed to LB, LR and LG (P>0.05). The fucoxanthin content was highest in LB-exposed cultures (6.3µg/mL), whereas LW showed the lowest (3.6µg/mL; P<0.05). Chlorophyll-a content was highest in cultures exposed to LB compared to other light sources. These results suggest consistent differences in growth and biochemical composition after exposure to light of different wavelengths.

Finely-striate buccinum Buccinum striatissimum, a species of whelks, is caught mainly by pot in the eastern coastal waters of Korea. In order to determine the size selectivity of pot for the species, comparative fishing experiments were conducted near Yeongil Bay from June to September in 2003 using the dome-shaped pots with different five mesh sizes (17.1, 24.8, 35.3, 39.8, and 48.3 mm). The parameters of logistic equation were estimated by the SELECT (Share Each Length’s Catch Total) method based on a multinomial distribution. The model with the estimated split parameter was found to fit the catch data best. The master selection curve was estimated to be s (R)=exp (13.044R－16.438)/[1 + exp (13.044R－16.438)], where R is the ratio of shell height to mesh size. The relative shell height of 50% retention was 1.260, and the selection range was 0.168. Enlargement in mesh size of the pot allows more small-sized whelks to escape.