Discarding juvenile fishes under girth 16 cm nearly equal to inner perimeter of codend mesh size collected by a cover net method in bottom trawl. The body size of the main five species (mackerel, horse mackerel, sea bream, melon seed and black throat seaperch) was measured for their body length, girth, weight, height and width and analyzed size selectivity. Frequency of penetrating fish as retention in a cover net was less than 40% of total number of juvenile discarding fish. The most of body length or girth of five species were significantly different between in the codend and in the cover net. The 50% selection girth in the cover net ranged 8-11 cm were smaller than those in the codend ranged 9-13 cm by the species respectively. The 50% selection body length was significantly related with the ratio of body height (H) by body width (W) both for in the codend or in the cover net while 50% selection girth was not significantly related with H/W. Furthermore 50% selection fish size by fish species between in the codend and in the cover net was not significantly different both in body length or girth. Therefore, the girth selectivity represented possibly as one unique value regarding fish body shape was considered as more useful method for multi-species catch in trawl.
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.
The small yellow croaker (Larimichthys polyactis) is one of the representative high-class fish species in Korea. The catch of small yellow croaker in adjacent water fisheries has been continuously decreasing from 59,226 tons in 2011 to 19,271 tons in 2016. The small yellow croaker is caught by gillnet, stow net and bottom trawl, among which about 55~65% is caught by gillnet. For the sustainable use of small yellow croaker, the fishing power of small yellow croaker drift gillnet is very important. Therefore, the change of fishing power index were analyzed to identify the development of the vessel and gear technology that may have improved the fishing efficiency of the small yellow croaker drift gillnet fishery from 1960s to 2010s. Gross tonnage and horse power per fishing vessel was increased annually. The mesh size was 75.0 mm in the 1960s, but reduced to 60.6 mm in the 1980s and to 51.0 mm in the 2000s. In the 1960s, it was hauled out by manpower. However, the net hauler were modernized and supply rate was also increased since 1970. Due to the mechanization of the net hauler, the number (length) of used net gradually increased from 1.5 km in the 1960s to 7.5 km in the mid-1980s and to 15 km in 2010. Colour fish finders and positioning system were introduced and utilized from the mid-1980s. Surveys on the supply and upgrading of fishing equipment utilized visiting research. Therefore, the relative fishing power index in the small yellow croaker drift gillnet fishery increased from 1.0 in 1980 to 0.8 in 1970, to 1.1 in 1990, to 1.6 in 2000 and to 1.9 in 2010. The results are expected to contribute to reasonable fisheries stock management of the small yellow croaker drift gillnet fishery.
This study is aimed to compare stock assessment models depending on how the models fit to observed data. Process-error model, Observation-error model, and Bayesian state-space model for the Korean Western coast fisheries were applied for comparison. Analytical results show that there is the least error between the estimated CPUE and the observed CPUE with the Bayesian state-space model; consequently, results of the Bayesian state-space model are the most reliable. According to the Bayesian State-space model, potential yield of fishery resources in the West Sea of Korea is estimated to be 231,949 tons per year. However, the results show that the fishery resources of West Sea have been decreasing since 1967. In addition, the amounts of stock in 2013 are assessed to be only 36% of the stock biomass at MSY level. Therefore, policy efforts are needed to recover the fishery resources of West Sea of Korea.
It was turned out by shrimp beam trawl monthly survey from March, 2015 to February, 2016 that different species composition and abundance of the fish assemblages in Sacheon Bay and coastal waters off Namhae, Korea were compared. As a result of monthly measured sea temperature and salinity of Sacheon Bay and coastal waters off Namhae, sea temperature of both areas was changed seasonally; however, differences in sea temperature occurred during certain periods depending on the region. Salinity was generally low in Sacheon Bay affected by fresh water, and both areas was low in summer and high in winter. A total of 73 species representing 37 families were collected in Sacheon Bay. The dominant fish species in terms of numbers and biomass were Liparis tanakae, 23,077 inds./km2, 332.1 kg/km2. A total of 91 fish species representing 49 families were collected in coastal waters off Namhae. The dominant fish species in terms of numbers were Leiognathus nuchalis, 139,683 inds./km2 and biomass were Chelidonichthys spinosus, 1,078.6 kg/km2. Analysis of dendrogram of the clustering showed that Sacheon Bay and coastal waters off Namhae were distinctive featured (global R = 0.691, p = 0.017). And except of summer season (July-October), there was a distinctive feature seasonally (global R = 0.844, p = 0.001). The fish species that appeared in common in both areas, where fish species caught in Sacheon Bay, an important inner bay,were smaller than those caught in coastal waters off Namhae appeared. It presented that Sacheon Bay plays a more important role in spawning and nursery ground for fisheries resource than coastal waters off Namhae, Korea.
Species composition and yearly variation of fish eggs and larval fishes were investigated from 2014 to 2016. During the study period, the fish eggs were identified as belonging to 14 taxa. The dominant species of fish eggs were Leiognathus nuchalis, Engraulis japonicus, and Konosirus punctatus. These three species accounted for 97.4% of the total number of individuals collected. The collected larval fishes were identified into 37 taxa, 22 families, and seven orders. The dominant species of larval fish were Leiognathus nuchalis, and Gobiidae fishes. These three species accounted for 85.4% of the total number of individuals collected. The diversity index of the larval fishes was the highest in 2014 (H’ = 1.60) and the lowest in 2015 (H’ = 1.15). The evenness index was the highest in 2016 (J = 0.51) and the lowest in 2015 (J = 0.39). The dominance index was the highest in 2015 (D = 83.5%) and the lowest in 2016 (D = 70.9%). In addition, the economically important species in this area were Engraulis japonicus, Konosirus punctatus, Hippocampus coronatus, Sebastes schlegelii, Acanthopagrus schlegeli, and Cynoglossus joyneri.
The ichthyoplanktons were sampled by Bongo net to study the distribution of the eggs and larvae in the West coastal waters of Korea during the study period (February, May, August and October of 2017). Collected fish eggs were divided into Engraulis japonicus and unidentified species. The most dominant species, Engraulis japonicus accounted for 79.52% of the total fish egg, which was followed by unidentified species (20.48%). The total of 36 taxa in fish larvae were identified based on morphological and molecular characteristics. Fish larvae were dominant by Gobiidae species. 48.30% of the total catch in abundance, which was followed by Engraulis japonicus (31.86%). These two taxa composed 80.16% of the total collected fish larvae. The seasonal diversity index of species from the collected fish larvae in the West coastal waters in 2017 was 0.625-1.883 and the evenness index was 0.380-0.865. In addition, dominance index was 0.618-0.920 and richness was 0.573-3.189.
In order to understand the tidal current and mean flow at the west channel of Yeoja Bay in the South Sea of Korea, numerical model experiments and vorticity analysis were carried out. The currents flow north at flood and south at ebb respectively and have the reversing form in the west channel. Topographical eddies are found in the surroundings of Dunbyong Island in the east of the channel. The flood currents flow from the waters near Naro Islands through the west channel and the coastal waters near Geumo Islands through the east channel. The ebb currents from the Yeoja Bay flow out along the west and the east channels separately. The south of Nang Island have weak flows because the island is located in the rear of main tidal stream. Currents are converged at ebb and diverged at flood in the northwest of Jeokgum Island. Tidal current ellipses show reversing form in the west channel but a kind of rotational form in the east channel. As the results of tide induced mean flows, cyclonic and anticyclonic topographical eddies at the northern tip but eddies with opposite spin at the southern tip are found in the west channel of Yeoja Bay. The topographical eddies around the islands and narrow channels are created from the vorticity formed at the land shore by the friction between tidal currents and the west channel.
The aim of this study is to analyze the relationship between international oil price as a fuel cost in overseas fisheries and skipjack tuna price as a part of main products in overseas fisheries using monthly time series data from 2008 to 2017. The study also tried to analyze the change of fishing profits by fuel cost. For a time series analysis, this study conducted both the unit-root test for stability of data and the Johansen cointegration test for long-term equilibrium relations among variables. In addition, it used not only the Granger causality test to examine interactions among variables, but also the Vector Auto Regressive (VAR) model to estimate statistical impacts among variables used in the model. Results of this study are as follows. First, each data on variables was not found to be stationary from the ADF unit-root test and long-term equilibrium relations among variables were not found from a Johansen cointegration test. Second, the Granger causality test showed that the international oil prices would directly cause changes in skipjack tuna prices. Third, the VAR model indicated that the posterior t-2 period change of international oil price would have an statistically significant effect on changes of skipjack tuna prices. Finally, fishing profits from skipjack would be decreased by 0.06% if the fuel cost increases by 1%.
The authors has predicted the maneuvering characteristics of a fishing vessel in deep water using Kijima's empirical formula in a previous study. Since the Kijima’s empirical formula was developed by a regression analysis of merchant vessels which have dimensions ( , , etc.) that are different from those of fishing vessels, it was possible to make a prediction approximately even with inaccurate estimation. In this study, the authors estimated the turning-motion characteristics of a model ship of fisheries training ship in shallow water based on the results of its previous study. The turning-motion characteristics of the model ship in shallow water was found out through quantitative analysis according to the water depth to ship draft ratio . In conclusion, the turning-motion characteristics of the model ship had significant changes immediately after an , and this result will be helpful for sailing in shallow water.