The change of fishing power index was analyzed to identify the development of the vessel and gear technology that may improve the fishing efficiency of the offshore conger eel pot fishery from 1980s to 2015. Gross tonnage per fishing vessel was rapidly increased annually. The standard of pot was maintained, but the number of pot used rapidly increased by using conger eel pot hauling devices, carrying and loading devices, main line hauler, casting devices and slide type pot. Fish finder system to identify fishing ground information and the conger eel pot hauling devices were modernized, and supply rate was also increased. Therefore, the relative fishing power index in the offshore conger eel pot fishery increased from 1.0 in 1980 to 1.3 in 1990, to 1.8 in 2000 and to 2.0 in 2015. The results are expected to contribute to reasonable fisheries stock management of the offshore conger eel pot fishery.

This study investigated the luring effect of the sardine bait, which is used to catch octopus with pot, as the preliminary study for the development of alternative bait for octopus pot. The soaking time for bait was divided into “5 days or less” and “11 days or longer” The number of times octopus entered the pot with bait and the empty pot was investigated under dark adaptation and light adaptation processes and the distribution of tank section was investigated under light adaptation process. The case of “11 days or longer” sardine soaking time showed higher rate of distribution in the section of pot with bait compared to the case of “5 days or less” In the case of “5 days or less” soaking time, the number of times the octopus entered the pot with bait was similar to that it entered the pot without it even during dark adaptation and light adaptation. However, in the case of “11 days or longer”, the octopus entered the pot with bait more quickly than the pot without bait and more frequently during dark adaptation hours. There were cases where the octopus did not enter any pot. In the case of “5 days or less”, with less decomposition of baits, the octopus entered the empty pot more during light adaptation process, and it appeared that the pot was used as a hideout.

Offshore trap fishery managers have payed in advance to attract excellent fishing crew in the minium grantee lay system. This practice can intensify competition among fishery management bodies and increase the burden of fishery manager about income tax and four social insurance programs. The purpose of this study is to identify the problems of advance payment practice in terms of fishery manager in offshore trap fishery. The main results of this study are as follows. First, under the TYPE 1 model, which is the current wage payment manner, there is a risk that fishery manager will not able to return the prepayment paid in advance when the income of fishery management bodies decrease. Second, the TYPE 2 or the TYPE 3 model which reduces or abolishes advance payment can alleviate the burden of fishery manager relative to the deduction of redemption amount, incentive to induce artificial expenses, income tax and four social insurance programs. In conclusion, advance payment practice in offshore trap fishery is placing a heavy burden on the fishery manager. In order to solve these problems in the future, we need to find solutions through similar case studies.

Fossil fuel combustion during fishing activities is a major contributor to climate changes in the fishing industry. The Tier1 methodology calculation and on-site continuous measurements of the greenhouse gas were carried out through the use of fuel by the coastal and offshore gillnet (blue crabs and yellow croaker) and trap (small octopus and red snow crab) fishing boats in Korea. The emission comparison results showed that the field measurements are similar to or slightly higher than the Tier1 estimates for coastal gillnet and trap. In offshore gillnet and trap fisheries, Tier1 estimate of greenhouse gases was about 1,644-13,875 kg CO2/L, which was more than the field measurement value. The CO2 emissions factor based on the fuel usage was 2.49-3.2 kg CO2/L for coastal fisheries and 1.46-2.24 kg CO2/L for offshore fisheries. Furthermore, GHG emissions per unit catch and the ratio of field measurement and Tier1 emission estimate were investigated. Since the total catch of coastal fish was relatively small, the emission per unit catch in coastal fisheries was four to eight times larger. The results of this study could be used to determine the baseline data for responding to changes in fisheries environment and reducing greenhouse gas emission.

Species composition and seasonal variation of aquatic organism at Baekryeong-do, Korea were investigated using pots in 2016. A total of 42 species, 90,050 individuals and 2,351,666 g of aquatic organism were collected. Among them, there were 12 species and 3,826 individuals of fish, 15 species and 51,237 individuals of crustaceans, 2 species and 54 individuals of cephalopods, 7 species and 33,981 individuals of gastropods, 2 species and 757 individuals of echinodea, 2 species and 187 individuals of shellfish, and 1 species and 8 individuals of holothuroidea. The dominant species in number of individuals were Pagurus ochotensis, Neptunea cuming, Cancer gibbosulus, and Buccinum yokomaruae, which accounted for 70.0% of the total number individuals collected. The dominant species in biomass were Neptunea cuming, Portunus trituberculatus, Cancer gibbosulus, and Pagurus ochotensis, which accounted for 65.3% of the total biomass collected.

In this paper, numerical modeling is conducted to analyze the tension of an anchor line by varying the size and drag coefficient of a buoy when the trapnet is influenced by the wave and the current simultaneously. A mass-spring model was used to analyze the behavior of trapnet underwater under the influence of waves and current. In the simulation of numerical model, wave height of 3, 4, 5 and 6 m, a period of 4.4 s, and the flow speed of 0.7 m/s were used for the wave and current condition. The drag coefficients of buoy were 0.8, 0.4 and 0.2, respectively. The size of buoy was 100, 50 and 25% based on the cylindrical buoy (0.0311 ㎥) used for swimming crab trap. The drag coefficient of the trapnet, the main model for numerical analysis, was obtained by a circular water channel experiment using a 6-component load cell. As a result of the simulation, the tension of the anchor line decreased proportional to buoy’s drag coefficient and size; the higher the wave height, the greater the decrease rate of the tension. When the buoy drag coefficient and size decreased to one fourth, the tension of the anchor line decreased to a half and the tension of the anchor line was lower than the holding power of the anchor even at 6 m of wave height. Therefore, reducing the buoy drag coefficient and size appropriately reduces the trapnet load from the wave, which also reduces the possibility of trapnet loss.

The species composition and variation in abundance of fishery resources near Oenarodo, Go-heung Peninsula, Korea, were investigated by gill net, trap net, and longline in May, July, and October 2015 and 2016. During the study period, the total catch included 14 species in the gill net, 11 species in the trap net, and 4 species in the longline. The dominant species were Portunus trituberculatus and Raja pulchrain the gill net, Charybdis japonicaand and Octopus vulgarisin in the trap net, and Muraenesox cinereusin in the longline. The Catch Per Unit Effort (CPUE) per individual and per weight in the gill net were similar in May and July of 2015 and 2016. In October 2015, the CPUE per individual was 2.1 ind./h and the CPUE per weight was 505 g/h higher than the results in 2016, but there was no significant difference in the total CPUE between 2015 and 2016. In the trap net, the CPUE per weight was similar in both 2015 and 2016, but the CPUE per individual was 2.7 ind./h higher in October 2015 than in October 2016 and the total CPUE was not significantly different from 2015 to 2016. The CPUE per individual and weight in the longline were significantly higher in July and October 2015 than in the same months of 2016, but the total CPUE in 2015 and 2016 did not show a significant difference.

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.

In order to obtain scientific information for the conservation of Utricularia japonica Makino, rare plant species, we investigated life history, phenology, growth and distribution in the east coastal region of Korea. Seven habitats of U. japonica were confirmed in this study. Turion of U. japonica rests overwinter at the bottom and ripens at the water surface and then usually germinate and sprout when the water warms in spring. A single shoot grown from turion divided into several shoots. Shoot decomposition started in October and formed a new turion at the end of the decomposed shoot. Flowering period was from early July to late October. Percentage of flowering ramets was significantly low as 6.3%. U. japonica showed the fastest growth rate from April to July, the maximum growth in August and the highest biomass in October. U. japonica tended to be concentrated in larger ramets in the water depth of 50 cm~150 cm in Cheonjin lake. The main factors affecting the growth of U. japonica were water temperature and turbidity. The establishment and growth of U. japonica in Cheonjin lake were determined by responses to water temperature with seasonal change and to light conditions caused by the different plants. These conditions affect the temporal and spatial distribution of U. japonica and population change. The findings of this study would be helpful to provide the basic information needed for the conservation and restoration of U. japonica.

This study was conducted to analyze fishing capacity and bycatch by mesh size and entrance size of spring net pot conductedby water tank and field experiment. The water tank experiments were conducted by using traps with mesh size of 22 mm and entrance size of 120 mm and 140 mm, respectively in the water tank of NIFS. The field experiment was conducted using 5 kinds of spring net pot with mesh sizes of 20 mm, 22 mm, 35 mm and entrance size of 120 mm, 130 mm, 140 mm, 360 mm by coastal trap fishery vessel operating around the area of Geoje island. In the result of water tank experiments, the catch of conger eel was 1.5 times higher when using trap with entrance size of 140 mm than that of 120 mm. In the field experiment, when using same mesh size, the larger the entrance size, the higher amount of conger eel catch, bycatch and number of bycatch species. When using the same entrance size, the larger the mesh size, the lower amount of conger eel catch and number of bycatch species, whereas the amount of bycatch showed increasing trend.

Morotoge shrimp Pandalopsis japonica is caught by pot and others in the eastern coastal waters of Korea. Comparative fishing experiments were carried out in the eastern coast of Korea, using the dome–shaped pots with different five mesh sizes (17.1, 24.8, 35.3, 39.8, and 48.3 mm) in order to estimate the mesh selectivity of the pot for the morotoge shrimp, Pandalopsis japonica. The SELECT (Share Each Length’s Catch Total) analysis method was applied to the catch data. The master selection curve of the pot for the shrimp was estimated to be s(R) = exp(15.770R–10.573)/[1+exp(15.770R–10.753)], where R is the ratio of carapace length to mesh size. From the selection curves, the carapace lengths of 50% retention were 11.6, 17.0, 23.9, and 34.1 mm for 17, 25, 35, and 50 mm mesh–size pot, respectively. It means that the pots of larger mesh size allow more shrimp of small size to escape.