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.

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.

Squid is one of the important fisheries resources in Korea. Therefore, squid has been designated and managed as a target species of total allowable catch (TAC) since 2007, but the catch amount is gradually decreasing. The analysis was conducted to identify the change of relative fishing power index to develop the vessel and gear technology that may have improved the fishing efficiency of the offshore squid jigging fishery from 1960s to 2010s. Gross tonnage per fishing vessel increased with the increase in size until 1990, but then gradually decreased to 41.0 tons in 2000 and 37.1 tons in 2010. The illuminating power (energy consumption) by fishing lamps increased to 180 kW in 2005 and stabilized to 120 kW in 2015. Jigging machine started to be supplied to fishing vessels from the early 1970s, and fish finders began to be supplied in the early 1980s and gradually increased. Therefore, the relative fishing power index in the offshore squid jigging fishery increased from 1.0 in 1980 to 1.1 in 1990, to 3.5 in 2000 and to 2.5 in 2010, but the increment rate slowed down gradually. The results are expected to contribute to reasonable fisheries stock management.

The reproduction characteristics of hagfish Eptatretus burgeri were examined using individuals caught in the South Sea of Korea. The spawning season and size at minimum sexual maturity of this species were characterized based on a gonad-somatic index (GSI) and monthly variation egg size (long axis). From monthly variation of GSI, the spawning season was estimated to be from August to September. Developing eggs larger than 10 mm were found in March, and the largest egg size was found in July. The first spawning length was 34.2 cm TL. Batch fecundity ranged from 13 to 117 eggs for hagfish sized from 34.2 cm TL to 77.0 cm TL, respectively, and increased linearly with total length.

The purpose of this study is to estimate potential yield (PY) for Korean west coast fisheries using the holistic production method (HPM). HPM involves the use of surplus production models to apply input data of catch and standardized fishing efforts. HPM compared the estimated parameters of the surplus production from four different models: the Fox model, CYP model, ASPIC model, and maximum entropy model. The PY estimates ranged from 174,232 metric tons (mt) using the CYP model to 238,088 mt using the maximum entropy model. The highest coefficient of determination (R2), the lowest root mean square error (RMSE), and the lowest Theil’s U statistic (U) for Korean west coast fisheries were obtained from the maximum entropy model. The maximum entropy model showed relatively better fits of data, indicating that the maximum entropy model is statistically more stable and accurate than other models. The estimate from the maximum entropy model is regarded as a more reasonable estimate of PY. The quality of input data should be improved for the future study of PY to obtain more reliable estimates.

매오징어 Watasenia scintillans 유생분포양상을 알아보기 위해 2015년 8, 9, 11월 R/V 탐구 21호로 동해 남서부연안 28개 정점 에 대해 CTD관측 및 IKMT(망목: 500 μm)를 사용하여 저층(최대 수심 100 m)에서 표층까지 경사채집을 실시한 결과, 채집된 매오징어 유생의 개체수는 총 238개체로 외투장(ML) 범위는 0.6 ~ 18.5 였다. 조사기간 중 8월이 9월과 11월보다 유생의 출현정점 수, 출현개체 수, 유생분포밀도에서 현저히 높았다. 특히 8월에 냉수괴가 분포하는 포항 ~평해까지의 동해연안에서 가장 높은 밀도를 보였다. 유생이 채집된 정점의 연직수온분포에서 매오징어의 부화수온(6 ~ 16 )은 주로 40 ~ 180 m의 수심에 위치하였다.

Lots of fishery stocks are overexploited and the overcapacity exists in Korean fishing fleets. One of the reasons is technological development, which increases the efficiency of the vessels continuously. The analysis was conducted to identify the change of fishing power index to develop the vessel and gear technology that may have improved the fishing efficiency of the offshore large powered purse seine fishery from 1960s to 2010s. Gross tonnage and horse power per fishing vessel was increased annually. Fishing gear material was changed to the knotless webbing to settle faster. Fishing equipments was modernized and supply rate was also increased. Therefore the relative fishing power index in the offshore large powered purse seine fishery increased from 0.4 in 1970 to 1.0 in 1980, to 1.5 in 2000 and to 1.6 in 2010, but the rate of increase slowed down gradually. The results are expected to contribute to reasonable fishery stock management.

Properties of aggregation and spatial distribution of fish were examined based on three lines in the South Sea of Korea using three frequencies (18, 38, and 120 kHz) of a scientific echosounder. The vertical distribution of fish was displayed using acoustic biomass namely nautical area scattering coefficient (NASC). As a result, at 120 kHz high NASC showed from water surface to 20 meters in deep while at 18 and 38 kHz very high NASC presented in 70 ~ 90 meters in depth, especially at line 3. Among three lines, the line 2 had lowest NASC. The horizontal distribution of fish using three frequencies together exhibited high NASC between the eastern South Sea and center of South Sea. In especial, NASC (801 ~ 1,920 m2/n·mile2) was observed along coastal waters from Busan to Tongyeong, Geoje, and Namhae. In regard with the property of aggregation of fish schools, the volume back-scattering strength (SV) of three lines presented close each other, however, the range of SV in the line 2 was shortest (-53.5 ~ -43.4 dB). The average distributional depth was deep in the order of L3 (32.8 ± 9.0 m), L1 (45.2 ± 9.5m), L2 (49.7 ± 5.6 m). The average altitude was high in the order of L3 (13.4 ± 10.3 m), L1 (17.0 ± 12.6 m), L2 (56.7 ± 5.6 m). The average length, thickness, and area were large in the order of L1, L3, and L2. This means that small sized fish schools were distributed near water surface in the line 2 while relatively large and similar sized fish aggregations between line 1 and line 3 appeared however, fish schools at line 3 had lower distributional depth and smaller compared to those at line 1. Acoustic data were visualized for demonstrating the entire circumstances of survey area. Additionally, there was no correlation between acoustic and trawl results.

The survey was conducted to investigate biomass and distribution of fisheries resources using a quantitative echo sounder and a fixed gillnet around Marado coast of Jeju to obtain the scientific basic data for dispute resolution with a large purse seine fishery and coastal fishing and policy establishment of reasonable fisheries resources. Hydroacoustic surveys were conducted six times (November 28~29, 2015 (night), February 23~24, 2016 (night) and March 3~4, 2016 (night/day), March 30~31, 2016 (night/day)) using a quantitative echo sounder. The pelagic fish densities were relatively higher around Marado in November 2015, February 2016 and March 3~4, 2016. However, demersal fish densities were relatively higher in Jeju coastal waters on March 30~31, 2016. Catch data using fixed gill net were used to calculate biomass. Based on the hydroacoustic data, fish length-weight function and target strength information of dominant fish, the biomass of fishes were estimated as follow: 5.64 ton CV = 70.2% at night on November 28-29 2015, 7.14 ton CV = 35.8% of pelagic fish and 530.77 ton CV = 34.6% of demersal fishes at night on February 23-24 2016, 2.34 ton CV = 56.7% of pelagic fish and 571.93 ton CV = 40.3% of demersal fish at daytime, 1.39 ton CV = 48.4% of pelagic fish and 194.59 ton CV = 54.3% of demersal fish at night on March 3~4 2016, 0.37 ton CV = 72.9% of pelagic fish and 338.79 ton CV = 99.7% of demersal fish at daytime, 0.24 ton CV = 21.3% of pelagic fish and 68.61 ton CV = 53.8% of demersal fish at night on March 30~31 2016.

An acoustic and trawl pilot survey using a small vessel was conducted in Jinhae bay of the South Sea of South Korea on April 13~14, May 11~13 and June 8~10, 2015. During the survey, acoustic data was collected and bottom trawls were conducted at the same time. First, various noises were eliminated by using the Park method based on the Wang method(Wang et al., 2015; Park et al., 2015), the species compositions and catch rate from each bottom trawl were observed, and spatial distribution of fishery resources in the water column and their nautical area scattering coefficient (NASC) were investigated through acoustic data. During the entire survey period, 12 orders, 33 families and 41 species were caught. The most caught species in April, May and June were Okamejei kenojei, Zoarces gilli and Pholis nebulosa, respectively. Fish schools were observed near the line of net mouth height in April. Numerous weak scatters were presented on the echograms in May and June. Many fish schools appeared in between the water surface and 20 m deep in May. The NASC value from entire water columns was the lowest in April (35.9 m2/n･mile2) and highest in June (1541.3 m2/n･mile2).

Species composition in the coastal waters off Ulleungdo of Korea were examined based on catches bimonthly collected by trammel net in 2013. A total of 711 individuals and 181.9 Kg were caught and catches were composed of 4 classes 15 orders 27 families 52 species including 44 Pisces, 4 Gastropoda, 3 Cephalopoda, and 1 Echinodermata. The dominant species in biomass were File fish (Thamnaconus modestus), Atka mackerel (Pleurogrammus azonus), and Greenling (Hexagrammos otakii). Data were summarized using hierarchical cluster analysis (HCA) and detrended correspondence analysis (DCA) to examine similarity in species composition for each month, and community structure in Ulleungdo was divided into two groups. Community structures in February, April and December with low temperature and well-mixed surface water were distinguished from those in June, August and October with high temperature and strong stratification, which could be attributed to temporal changes in dominant species. Atka mackerel and Spear squid mainly caught in February and April, disappearing in June, August and October, and File fish outburst was shown in October. Because the water off Ulleungdo has been under low human pressure, it could be a good case study to elucidate effects of climate change on community structure and ecosystem in the East sea. Continuous surveys and further studies are required to demonstrate migration route and distribution of dominant species and long-term changes in community structure in the water of Ulleungdo.

To examine species composition, abundance and biomass of fishes in the northwestern East Sea of Russian EEZ, trawl survey were conducted at 31 sampling stations from 2006 to 2008. Also, trawl survey were conducted at 21 sampling stations in the southwestern East Sea of Korean EEZ from 2006 to 2008. A total of 67 fishes were collected in the northwestern East Sea of Russian EEZ, a total of 39 fishes were collected in the southwestern East Sea of Korean EEZ. Among them, a total of 53 fishes were collected in the northwestern East Sea of Russian EEZ only, and a total of 25 fishes were collected in the southwestern East Sea of Korean EEZ only. Mean abundance per area which caught by trawl survey in the northwestern East Sea ranged from a high of 116,478 inds./km2 in 2008 to a low of 19,737 inds./km2 in 2006. And mean abundance per area in the southwestern East Sea ranged from a high of 89,129 inds./km2 in 2006 to a low of 8,234 inds./km2 in 2008. Mean biomass per area which caught by trawl survey in the northwestern East Sea ranged from a high of 11,333 kg/km2 in 2008 to a low of 2,439 kg/km2 in 2006. And mean biomass per area in the southwestern East Sea ranged from a high of 6,273 kg/km2 in 2006 to a low of 1,062 kg/km2 in 2008. Cluster analysis, based on a Bray–Curtis similarity matrix of fourth root transformed data of number of species and individuals per area, showed division into three different groups by depth in the northwestern and southwestern East Sea.

This study was performed to estimate biomass and provide management guidance through population ecological characteristics, including growth parameters, instantaneous coefficients of natural and fishing mortalities, and age at first capture of the starry flounder, Platichthys stellatus and olive flounder, Paralichthys olivaceus of Korea. For describing growth of this species, a von Bertalanffy growth model was adopted. The von Bertalanffy growth parameters estimated from a non-linear regression for starry flounder were L∞=48.25 cm, K=0.16/yr, and t0=-1.48, respectively and those for olive flounder were L∞=86.46 cm, K=0.26/yr, and t0=-0.29, respectively. Biomass of Platichthys stellatus was estimated by direct biomass estimation method was 2.6 M/T, that was estimated by indirect method was 13.4 M/Tt. Those of Paralichthys olivaceus were estimated as 10.1 M/T, 19.3 M/T, respectively. An yield per recruit analysis showed that the current yield per recruit on Platichthys stellatus was about 48.2 g with F=0.646/yr and the age at first capture (tc) 1.35yr, that on Paralichthys olivaceus was about 167.6 g with F=1.121/yr and the age at first capture (tc) 1yr.

Maturity and spawning of the giant Pacific octopus, Octopus dofleini was investigated based on the samples collected in the coast of Gangwondo, East Sea, from January to December in 2009. Individuals of mature stage had a higher occurrence rate from February toMay, and gonadosomatic index (GSI) also showed a higher value from February toMay than the other months. For that reason, the spawning period was estimated from February to May with the main spawning period from March to May. The total number of eggs in the fecundity (F) ranged from 9,045 in 11.0 kg (TW) to 148,682 in 16.5 kg (TW), which was proportional to total weight (TW), and the relationship between total weight and fecundity was F=0.185×TW2.238 (R2=0.389). The total weight at 50% group maturity (TW0.5) of female was estimated to be 12.2 kg.

In this study, we conducted field surveys to investigate and analyze species and length composition of catch from gape net with wings being set in two areas - Masari, Supomri - located in southern part of Jin-do for understanding fishing characteristics of gape net with wings fishery from March to September of 2011. And with those results, we attempted to propose fishery management strategy to harvest fisheries resources continuously. Catch obtained from field surveys comprised total 78 species, which accounted for 53 species of fish, 20 species of crustacean, 4 species of cephalopod and one of polychaete. As to species composition in weight, it showed that there was 88.5% for pisces, 9.0% for cephalopoda and 2.5% for crustacea. As to catch specifics by area, there was 36 species (596,891 individual, 456,551g) of pisces, 17 species (35,815 individual, 12,909g) of crustacea and 3 species (2,876 individual, 3,004g) of cephalopoda in Masari area. In Supumri area, there was 41 species (396,898 individual, 281,457g) of pisces, 15 species (16,113 individual, 7,772g) of crustacea and 4 species (6,792 individual, 72,329g) of cephalopoda and one polychaeta (36 individual, 11g). Catch of anchovy by month recorded on high level on June, July, September in both areas. When considering size composition by month, it was found that new populations recruit to these fishing grounds on June and September. Most of bycatch species including hairtail (Trichiurus lepturus), dotted gizzard shad (Konosirus punctatus), conger eel (Leptocephalous), Pacific sandlance (Ammodytes personatus), horse mackerel (Trachurus japonicus) were juvenile, and grass puffer (Takifugu niphobles), Kammal thryssa (Thryssa kammalensis), Japanese sardinella (Sardinella zunasi) were also small in size. As a result, it is considered that gape net with wings fishery which is likely to catch juvenile needs to be set fishing prohibit period for conserving above stocks during the period excluding main fishing periods of anchovy or fisheries management such as expanding mesh size for preventing juvenile catch.

제주연안선 부근에 밀집된 육상양식장 배출구 주변 4개 해역(애월리, 행원리, 표선리, 일과리)에서 수질환경의 시공간적 변화에 영향을 미치는 요인을 파악하기 위해 2010년 2월부터 2011년 12월까지 격월로 총 12회 조사하였다. 주성분 분석 결과 조사해역에서 연중 영양염의 분포는 염분과의 관련성 없이 배출구로부터 공급되는 물질에 의해 영양염의 농도가 조절되어, 연안에서 외해역으로 갈수록 농도구배가 감소하는 특징을 나타냈다. 특히 용존무기질소의 경우는 배출구와 인접한 해역에서는 부영양상태로 인에 비해 질소가 과잉되고 있었다. 유기물의 분포는 담수유입량이 증가하는 고수온기에 증가하는 경향을 보였다. 식물플랑크톤의 생물량 변화는 애월 및 행원해역은 담수유입과 관련된 기상요인(기온 및 강우), 표선 및 일과는 영양염의 인위적 공급요인(양식장 배출수)에 의한 영향을 주로 받는 것으로 나타났다. 특히, 배출구로부터 직선거리 약 300 m 및 수심 10 m이내 해역의 표ㆍ저층에서는 고영양염 농도 분포가 지속되고 있어, 부영양화 과정에서 발생하는 문제를 직ㆍ간접적으로 받을 수 있는 가능성을 나타냈다. 육상양식장의 운영 시 취수지점이 배출수의 영향을 받는 지점에 위치할 경우 사육수질의 문제가 발생할 수 있다.

The feeding habits of Sebastiscus marmoratus collected from the Western Coastal Waters of Jeju Island between June 2008 and July 2009 were studied based on examination of the stomach contents. A total 254 individuals of S. marmoratus ranged from 13.2 to 29.6cm (mean 20.7cm) in Standard length (SL). S. marmoratus consumed mainly teleosts such as Chromis notata and Sebastes inermis. Its diet also includes shrimps and crabs. The individuals smaller than 15cm SL consumed mainly shrimps, but on the other hand the individuals larger than 25cm SL consumed mainly fishes. The proportion of fish consumption increased with increasing size of S. marmoratus.