• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.4
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• pp.21-31
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• 1986

The author investigated the relation between the catches of tuna species and the distribution of horizontal mean temperature at the Jepth of 10m and of vertical temperture sections in the different fishing grounds, using the date of catches in 1980, showing a relative good ones during six years from 1975 to 1980, and of oceanographic observations. Yellowfin and bigeye are mainly caught in South Equatorial Current regions including equatorial upwelling region in 5$^{\circ}$N to 5$^{\circ}$S, and albacore is mainly caught in Subtropical region in 20$^{\circ}$5 to 40$^{\circ}$5. The good fishing grounds of yellowfin and bigeye are made in the depth layer of 100 m to 250 m and temperature of 15$^{\circ}$C to 26$^{\circ}$C having a smooth gradient of thermocline in the Central Pacific between 180$^{\circ}$ and 1500W. But albacore is caught well in which the temperature of thermocline ranges from 100e to 25$^{\circ}$C and its gradient very smoothly. Approaching to the American Continent, the catches of yellowfin and big eye decrease because the thermocline becomes shallower and steeper at Eastern Pacific Region between 1500 and 800W.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.4
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• pp.360-369
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• 1987

The relationship between the catches of tuna and hydrographic conditions in South-East Pacific region (latitude $5^{\circ}N-12^{\circ}S$, longitude $135^{\circ}W-115^{\circ}W$) was investigated by using the catch data of tuna and Digital Bathythermograph (DBT) data from December 9, 1980 to April 2, 1981. The results are as follows : The study area were located in South Eguatorial Current regions including equatorial upwelling regions in $5^{\circ}N\;to\;12^{\circ}S$. The horizontal mean temperature at the depth of 10m on the first quarter months in the study area was about $25^{\circ}C$C and the salinity of those fishing areas ranged from 34.8 to $35.0\%_{\circ}$. Yellowfin tuna and bigeye tuna were mainly caught in SW vertical temperature profile type, which the depth of thermocline ranged from loom to 300m, and temperature difference of thermocline was about $12^{\circ}C$. The deeper the depth of thermocline, the more the catches of tuna. While albacore tuna was caught well in SS vertical temperature profile type which the temperature of thermocline ranged from $9^{\circ}\;to\;26^{\circ}C$ and its gradient was very smooth. The depth of 1 ml/l surface of dissoved oxygen content ranged from loom to 200m in the South-East Pacific between longitude $140^{\circ}W-100^{\circ}W$, but it was shallower than 100 m near the North-South American continent. The catches of bigeye tuna were larger than those of yellowfin tuna in South Equatorial Current region. As approaching to the South and North American continent, the catches of yellowfin tuna and bigeye tuna decreased because the thermocline becomes shallower and steeper and the depth of the 1 m1/1 surface of dissolved oxygen content became shallower.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.2 no.2
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• pp.161-172
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• 1969

Ten experimental tuna long line fishing operations were performed with the long lines A and B, in combination casting orders of BA and AB. The long line B differs from A in its additional main line length per basket and its greater depth of submersion (Table 1). The BA casting order results in an AB hauling order, so that the long line B is casted at an earlier time of a day and fishes for a longer period than A line (fig. 2). The number of fish caught was divided into subclasses in order to be subjected to $x^2-tests$ (Table 2). The first series of $x^2-tests$ were calculated using the hooking rates of two subclasses with other factors pooled (Table 3). The second series of $x^2-tests$ were calculated to obtain the interactions between two subclasses when other factors differed (Table 4). Attention was paid to the extremely small interactions as well as to the large interactions in order to find out whether a factor functions in the same way or in a contradictory way when the other factors involved differ. The test result is summarized in Table 5. The relationship between the hook casting time (relative to the sunrise time) and the hooking rates reveals the feeding behavior of particular species (fig. 3) A high hooking rate for yellowfin tuna shown in the period from one hour before sunrise to the moment of sunrise suggests that they feed actively in that period. Their poor hooking rate on earlier casted hooks suggests that they do not feed well under conditions of darkness and that they feed best while the hooks are sinking. Furthermore it is likely that yellowfin tuna maintain a shallow depth in the daytime, for the $x^2$ interaction between the line casting order BA and AB shows their persistant preferance of the long line A regardless of line casting order. Bigeye tuna show their feeding behavior under conditions of darkness, and show a preference for the sea's deeper layer. Alepisaurus borealis (Gill) show their feeding behavior under conditions of darkness more significantly than the bigeye tuna and their preferance for deep layers is also more significant. Marlins (mainly Makaria mazara) show a feeding behavior which is similar to the yellowfin tuna. The author emphasizes that certain variations of the hooking rates in relation to the line easting time were caused by an inadequate fishing depth as well as by the fish preference for a particular feeding time. When the part of the line casted in pre-dawn hours and hauled in the pre-sunset hours show a significantly lower hooking rate than other parts of the line, then it is concluded that tile hooks settled in a sea layer too deep for feeding.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.58 no.4
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• pp.317-325
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• 2022

Korean tuna purse seine fishery in the Western and Central Pacific Ocean (WCPO) began to operate in earnest in the early 1980s. Since then, the total catch has shown an increasing trend and the target species are skipjack tuna (Katsuwonus pelamis), yellowfin tuna (Thunnus albacare) and bigeye tuna (Thunnus obesus). Based on the operational data of Korean tuna purse seine fishery from 2016 to 2020, the catch rates of target species (skipjack and yellowfin tunas) were analyzed by operation time for set types (free school and FAD sets). In the case of the free school sets, they were usually made from sunrise to sunset, and the catch rate was high before and after sunrise for skipjack tuna and before sunset for yellowfin tuna. On the other hand, for the FAD sets, more than 90% of them were made just before sunrise, and there were few operations during the daytime. The purpose of this study is to examine whether there are differences in the catch rate of skipjack and yellowfin tunas by operation time and by school type for Korean tuna purse seine fishery in the WCPO, which could be helpful in understanding its fishing characteristics and providing useful information for developing the stock indices of the target species.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.56 no.4
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• pp.363-372
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• 2023

This study was developed to prepare hamburger steak (HS), wantang soup (WS), and tomato soup (TS) for senior-friendly seafood's (SFS) using bigeye tuna Thunnus obesus, and to investigate their quality characteristics. All data were presented in the order of HS, WS, and TS. The hardness values were 298.9×1.0³, 47.1×1.0³ and 14.9 ×1.0³ N/m², respectively. The viscosity of TS was 2,856 mPa·s. The protein contents were 13.8, 11.7, and 9.7 g/100 g, respectively. The fat-soluble vitamins content were as follows: vitamin A 21.88, 5.03, and 23.72 ㎍RAE/100 g; vitamin D 1.15, ND, and 1.81 ㎍/100 g, respectively. The water soluble vitamins contents were as follows: vitamin C 47.22, 32.83 and 37.01 mg/100 g; vitamin B₂ 0.17, 0.11 and 0.10 mg/100 g; vitamin B₃ 34.87, 34.76 and 54.62 mgNE/100 g. The Ca contents were 15.9, 16.8, 28.9 mg/100 g, and the K contents were 383.8, 167.4, and 300.0 mg/100 g, respectively. The dietary fiber was 0.04, 0.07 and 0.08 g/100 g, respectively. Escherichia coli was not detected in any of the products. These results suggest that the products should be classified as follows, based on their appropriateness as SFS: HS, WS and TS.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.45 no.1
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• pp.22-33
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• 2009

Ecological risk assessment(ERA), developed in Australia, can be used to estimate the risk of target, bycatch and protected species from the effects of fishing using limited data for stock assessment. In this study, we employed the ERA approach to estimate risks to tunas, billfishes, sharks, sea turtles and other species by the Korean tuna longline fishery in the Western and Central Pacific Ocean using productivity and susceptibility analyses of the ERA based on low(<1.30), medium(1.30-1.84) and high risk(>1.84). Albacore, bigeye, yellowfin, skipjack and bluefin tunas were generally evaluated in the medium risk. The susceptibility of tuna species, however, had higher risks than the productivity. Billfishes were also at medium risk, while sharks were at high risk by the tuna longline fishery. The risk of productivity was generally high, because most sharks caught by the tuna longline fishery have high longevities, i.e., over 10 years, including ovoviviparous species. Susceptibility, which is related with the selection of fishing gear, was also high, because the longline fishery has no gear modifications to prevent bycatch of protected species. Not only target tuna species were influenced by the tuna longline fishery in the Western and Central Pacific Ocean, but also nontarget species, such as pomfret, mackerels rays, sea turtle were done. Ecosystem-based fishery assessment tools, such as productivity and susceptibility analysis(PSA), have the ability to provide broad scientific advice to the policy makers and stakeholders.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.15 no.4
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• pp.312-316
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• 1982

With an object to obtain an indication on the efficiency of the saury baits for tuna longline, frequencies of the saury heads found in the tuna stomachs were analysed by the equations developed from tile binomial distribution. Four factors were introduced into the equations : The hooking rate, p; rate of not being hooked q; rate of the effective baits retained in the stomachs of the captured tuna r; and the rate of tile previously taken baits retained in the tuna stomachs, t. The best estimates of $\frac{p}{p+q^t}$ and r are empirically obtained as follows. Yellowfin tuna: $\frac{p}{p+q^t}$=0.789, r=0.598 Bigeye tuna: $\frac{p}{p+q^t}$=0.810 r=0.608, Albacore tun : $\frac{p}{p+q^t}$=0.838, r=0.621.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.2
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• pp.149-161
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• 2016

Fishing characteristics of Korean tuna purse seine fishery in the Pacific Ocean were investigated using logbook data compiled from captain onboard and the statistical data from 1980 to 2014. Changes in fishing ground and correlation between marine environmental factors and fishing patterns were investigated using Oceanographic index. The proportion of unassociated set was higher than that of associated set. The catch proportion of yellowfin was higher in the unassociated set, while that of skipjack and bigeye was higher in the associated set. Due to vessels, fishing gears and Korean captains' high-level of skills in fishing technology optimized for the unassociated set and preference of large fishes, especially large yellowfin tuna, it showed unique fishing characteristics focusing on the unassociated set. As for fishing distributions of Korean tuna purse seine fishery and impacts of oceanographic conditions on the fishery, the main fishing ground was concentrated on the area of $5^{\circ}N{\sim}10^{\circ}S$, $140^{\circ}E{\sim}180^{\circ}$ through the decades. When stronger El-nino occurred, the range of fishing ground tended to expand and main fishing ground moved to the eastern part of western and central Pacific Ocean. During this season, yellowfin tuna had high CPUE and catch proportion of yellowfin tuna in the eastern part also increased. As for the proportion of fishing effort by set type, proportion of log associated set was high during El-nino season while that of FAD associated set was high during La-nina season.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.56 no.4
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• pp.299-315
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• 2020

Tuna fisheries were applied to an integrated ecosystem-based fishery risk assessment method using indexes of target species status, inhabited species in a target ecosystem, habitat quality and socio-economic benefit of affected fisheries. This study suggested more effective and efficient management measures to break away from traditional management methods, such as limitation of catch and fishing effort. The results presented that the objective risk index (ORI_S) on sustainability of bigeye and yellowfin tunas by purse seine fishery was estimated high due to the high catch ratio of small fishes. The ORIs of biodiversity (ORI_B) and habitat quality (ORI_H) of purse seine fishery were also estimated at a high level from using fish-aggregating devices (FAD). However, due to skipjack tuna's high catches, the ORI of socio-economic benefit (ORI_E) was estimated at a very low level. Due to the high bycatch rate, ORI_B was high, and ORI_S and ORI_H were evaluated at a low level in longline fishery. Due to strengthern of fishing restrictions and increase of fishing costs, the ORI_E was assessed to be very high. The ecosystem risk index (ERI) for two tuna fisheries was assessed low, but the overall FAD management by purse seine fishery is necessary at the ecosystem level.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.56 no.4
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• pp.277-291
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• 2020

In order to understand characteristics on bycatch of Korean tuna purse seine fishery, especially operations associated with Fish Aggregating Device (FAD) in the Indian Ocean, we conducted analyses related to bycatch by school association type (unassociated school, FAD associated school and log associated school) using the data collected by scientific observers from 2016 to 2018. The FAD used by Korean tuna purse seine fishery in the Indian Ocean was a drifting FAD, which belongs to non-entangling FADs according to the category proposed by the International Seafood Sustainability Foundation (ISSF). The target species of Korean tuna purse seine fishery are skipjack, yellowfin and bigeye tunas, accounting for 99% of the total catch. The ratio of bycatch was 0.97% in total catch and the discard accounted for less than 1%, indicating that most catch was retained on board. In terms of bycatch ratio by school association type, it accounted for 0.12% for unassociated school, 1.09% for FAD associated school and 1.25% for log associated school. As for the catch proportion of shark species by school association type, it accounted for 0.01% for unassociated school, 0.11% for FAD associated school and 0.10% for log associated school, which showed that unassociated school type was the lowest to affect bycatch of non-target and shark species. Given the proportion of bycatch compositions, however, it is considered that FAD associated school of Korean tuna purse seine fishery has less caught bycatch species of non-target and shark, compared to other fleets operating in the Indian Ocean.