The distributions of common minke whales observed in the East Sea in ten surveys in May of 2003, 2005, 2006, 2007, 2009, 2010, 2012, 2015, 2016 and 2020 were investigated using satellite sea surface temperature (SST) derived from the Moderate Resolution Imaging Spectrometer (MODIS). Most of the minke whales were observed in the waters off the Korean Peninsula at 36-38.5° N, which is expected as the highly productive coastal upwelling area. Yet, no minke whale was observed in 2006 when a relatively larger scale coastal upwelling occurred with SST at 11°C. In 2016 and 2020, the warm water higher than 17°C extended widely in the area, and the minke whales were observed in the offshore waters, deeper than 1,000 m. 87.5% of minke whales observed in May appeared in the SST from 13 to 16°C, and they seemed to avoid relatively high temperatures. This suggests that optimum habitat water temperature of minke whales in May is 13-16°C. The SST in the area had risen 1.67°C from 2003 to 2021, and it was remarkably higher than in other parts of the surrounding areas. The future temperature rising may change the route and timing of the migration of minke whales in the study area.

We examined the characteristics of egg and larval distributions and catch changes of anchovy in relation to abnormally high sea temperature in the South Sea of Korea in summer 2015 and 2016. The densities of anchovy eggs and larvae in the southern coastal region were lower in July-August 2016 than in July-August 2015. In particular, anchovy eggs and larvae (approximately 5 mm TL) were rarely observed in the coastal region in August 2016 due to the abnormally high SST (up to 28°C), which was above the optimum spawning temperature of anchovy. The catch of non-swimming stage (< 2 cm TL) larval anchovy was lower in July-August 2016 than in July-August 2015. The decreased catch of larval anchovy in July-August 2016 could be attributed to decreased spawning density in June-July 2016. In contrast, the catch of swimming stage (> 2 cm TL) anchovy was increased in July-August 2016. In the summer of 2016, prominent sea temperature near the southern coast of Korea and sea temperature higher than 30°C in the offshore region of the South Sea of Korea could greatly enhance the retention of swimming anchovies in the coastal fishing grounds.

A study for species composition and abundance of the fish assemblages in the coastal Sacheon Bay, Korea were conducted using monthly collection by a shrimp beam trawl from March 2015 to February 2016. The number of individuals, biomass and species diversity indices fluctuated with the station and month. Of all 73 species collected, the dominant species in terms of numbers were Liparis tanakae, Zoarces gillii, Amblychaeturichthys hexanema, Ricuzenius pinetorum and Pleuronichys cornutus. The peak number of fishes occurred in March and April, whereas the biomass of fishes was highest in April. The numbers and biomass of fishes were lower in February corresponding with the low temperature, and diversity indices were highest in June. Due to those seasonal difference in abundance of the dominant species, fish community were divided into three main groups. In addition, seasonal difference by station of fish community were devided into four main groups. Juvenile fishes of coastal Sacheon were presented during the study period. It presented that the study area served as an important role in spawning and nursery ground for fisheries resource.

진해만에서 출현하는 자어에 대한 계절별 군집 변동을 파악하기 위해 2015년과 2016년의 2월(겨울철), 5월(봄철), 8월(여름철), 그리고 11월(가을철)까지 계절별로 수행하였다. 조사기간 동안 출현한 자어는 종 수준까지 총 24과 28종이 출현하였다. 조사기간 동안 출현한 우점종은 청어(Clupea pallasii), 꼼치(Liparis tanakae), 돛양태과 sp. (Callionymidae sp.), 청보리멸(Sillago japonica), 세줄베도라치(Ernogrammus hexagrammus), 그리고 멸치(Engraulis japonica)로 나타났으며, 이들 6종은 조사기간 중 출현한 자어 전체 출현개체수의 77.6%를 차지하였다. 우점종 중 청어와 꼼치는 2015년과 2016년의 겨울철에 출현한 반면에 청보리멸은 여름철에 출현하였다. 종 다양도 지수는 2월과 8월에 높았고 5월에 낮게 나타났다. 조사기간 동안 출현한 자어의 출현개체수를 바탕으로 nMDS 분석을 실시한 결과 계절에 따른 4개의 그룹으로 구분되었다. 본 연구결과 진해만의 자어 군집은 계절에 따른 수온변화와 산란에 참여하는 어종에 따라서 변동하였으며, 잠도와 칠전도 북부해역에서 높은 출현량을 보여 이 지역이 진해만의 주요 산란장으로 이용되고 있음을 의미한다.

The maturation and spawning of black scraper, Thamnaconus modestus were studied using samples collected monthly from March, 2015 to February, 2016 in the coastal waters off Middle East Sea, Korea. The gonadosomatic index (GSI) of female was the highest in June. The spawning periods lasted from March to September based on histological observation of female gonad development. The percentage of sexually mature females estimated from a logistic function was over 50% for the size group 18.02 cm (total length, TL). The size of eggs spawned was between 0.40 to 0.58 mm. Fecundity varied between 185,648 and 9,747,250 eggs. The relationship between the fecundity and TL of the fish was expressed in the fecundity equation as F = 0.0297TL5.4835.

We examined monthly changes in the rate of fishes by-caught by gape net with wings and their immature ratio in thecoast of Yeosu and Jindo Island, Korea. A minus correlation between bycatch rate, the ratio of fishes except for anchovy, Engraulis japonicus, to all fishes collected by gape net with wings, and individuals of the collected anchovy was significantly observed, implying that as the anchovy catch decreased and the bycatch rate increased. Immature ratios by the dominant bycatch species during the study is the following; Leiognathus nuchalis was 72.7~99.0%, Sphyraena pinguis was 84.0%, Sardinella zunasi was 90.0%, others (Leptocephalus, Trichiurus lepturus, Ammodytes personatus, Sphyraena pinguis, Trachurus japonicas, Mugil cephalus and Erisphex pottii) were 100.0%. In order to decrease the high bycatch rates of immature fishes in spring and autumn, our study suggested increasing of codend mesh size and developing suitable bycatch reduction devices in a gape net with wings.

The feeding habits of the Pacific bluefin tuna, Thunnus orientalis were examined based on the stomach contents of 330 specimens caught by offshore large purse seine fishery in the southern sea of Korea, 2011. The size of Pacific bluefin tuna used in this study ranged from 34.1 to 67.3 cm in fork length (FL). The percentage of empty stomachs was 41.8%. The main prey items were Pisces and Cephalopoda based on percentage IRI (index of relative importance). The main fish preys were Trachurus japonicus, Bregmaceros japonicus, Engraulis japonicus, and Cephalopoda were Todarodes pacificus, Loligo edulis, Watasenia scintillans. T. orientalis showed ontogenetic change in diet composition. Although Pisces dominated the diet of all length classes the portion of Cephalopoda was relatively higher in size between 40 and 50 cm other than length classes. In terms of seasonal variation in feeding habits, Pisces was the main prey group in all seasons, but Cephalopoda was also frequently consumed during spring and autumn based on %IRI.

This study was carried out to compare the regional fishing gears and catches of the gape net with wings used in Jeonnam, Korea. The total length of the gear used in Yeosu, Wando and Jindo was 107.0m, 64.0m, 52.8m, and the size of codend was 4.3mm. 7.8mm. 9.8mm, respectively. The total number of bycatch species from anchovy (Engraulis japonicus) catches in Yeosu, Wando, and Jindo during the survey period were 21, 13, and 13 species. A total of individuals of anchovy accounted for over 90% out of total catches in all survey areas. The proportion of anchovy individuals was constantly high up to October in Yeosu, but it showed a sharp reduction to 18% in October in Wando with the increase of the individuals of Kammal thryssa (Thryssa kammalensis) and Big eyed herring (Sardinella zunasi). In Jindo, individuals of anchovy occupied over 99.8% out of total catches up to August. Since August, the number of individuals of Big eyed herring (Sardinella zunasi), Kammal thryssa (Thryssa kammalensis), and Slimy (Leiognathus nuchalis) has increased while the number of anchovy individuals were decreased.

The annual and monthly fluctuation in the species composition and the catch abundance of dominant species were analyzed using the daily sales slip catch data by a set net in the offshore waters off Dolsan Island in Yeosu from March 2004 to December 2011. Mean catch from 2004 to 2011 is 372M/T and the maximum and the minimum catch are 526 M/T in 2005 and 27 2M/T in 2009, respectively. The dominant species were Engraulis japonicus mainly in spring and Scomberomorous niphonius in Autumn and therefore the set net catch that is dominated by S. niphonius's catch was much higher in autumn than in spring. Through comparative analyses for the environmental factors to the annual catch fluctuation, it is revealed that the water temperature variation affected the recruitment property of S. niphonius to the fishing ground but the effect of typhoon on the catch fluctuation was not distinct. Furthermore, the big blooming event of jellyfish, particularly Nemopilema nomurai, that occurred in 2009 showed a tendency of faster appearance and later extinction until December. The occurring characteristic of N. nomurai became a direct cause that brought about the lowest total catch in 2009 since the dominant species catch of the set net fishery was concentrated mostly in Autumn.

A preliminary study on species composition of a Korean purse seine catch landed at cannery was conducted in April 2011. In the cannery, all tuna catch are sliding through a sorting grid panel that filters and drops fish in the buckets by size class (above 9kg, 3.4-9kg, 1.8-3.4kg, 1.4-1.8kg and below 1.4kg). In cannery processing, species sorting was made for skipjack tuna and yellowfin tuna only from catches greater than 3.4kg during filtering but not for bigeye tuna because of difficulties in species identification between bigeye tuna and yellowfin tuna under frozen state. As no species identification was carried out for catch groups less than 3.4kg in the cannery process, this study focused on sorting out skipjack tuna and yellowfin tuna from these groups and then identifying bigeye tuna from all size groups of yellowfin tuna. Using the mixture rate of species obtained from the samples taken, species composition of the landed catch was estimated. As results, cannery research showed 95% for skipjack tuna, 3% for yellowfin tuna and 2% for bigeye tuna in species composition, while vessel logbook data represented 96%, 3% and 1% for skipjack tuna, yellowfin tuna and bigeye tuna, respectively. The proportion of bigeye tuna identified in the cannery was slightly higher than shown in logbook data by 1%.

The forming of fishing ground and the population ecological characteristics of yellowtail, Seriola quinqueradiata, in the coastal waters off Gim-nyeong of Jeju Island were investigated. The stock of yellowtail, Seriola quinqueradiata, between Jeju Island and coastal areas of the East Sea is probably the same. Water temperature probably is a major factor for controlling distribution of yellowtails in deeper, offshore areas off Jeju Island. However, the major factor that determines aggregation of yellowtails in coastal areas of Jeju Island, especially off Gim-nyeong is probably strong tidal currents driven by distribution of yellowtails rather than hydrological conditions such as Yellowtails collected off Jeju Island were from 1 to 4yrs old and about 50% of them were 1-yr old, probably indicating overfishing. Jack mackerel was the major prey item for yellowtails off Gim-nyeong from October to March, suggesting concurrence of the two species.

This study examined the maturation and main spawning season of Japanese spear lobsters, Linuparus tirgonus(Von Siebold) captured around Jeju island from January to September, 2008. Carapace length(CL), body weight(BW) and gonad weight(GW) were measured. Gonadosomatic index(GSI) and sex ratio were calculated. In female group, CL showed the highest value in June and decreased after August. GW showed a peak in July and decreased rapidly after August. The mean gonadosomatic Index(GSI) reached a maximum value between June and August. Number of egg ranged from 143,360 to 189,504.