• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.53 no.1
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• pp.60-66
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• 2017

This study researched the population of ecological characteristics of the goldeyes rockfish Sebasetes thompsoni sampled by gill net in the Ulleungdo area from February 2013 to February 2014 in order to assess the current stock status and provide scientific advice for management implementation. The instantaneous coefficient of total mortality (Z) was 0.78/year and the survival rate (S) was 0.459. The instantaneous coefficient of natural mortality (M) was 0.461/year. Based on the estimates of Z and M, the instantaneous coefficient of fishing mortality (F) was 0.318/year. The age at first capture ($t_c$) was 4.41/years. Current Yield-per-recruit (YPR) was 30.83 g, and fishing mortality at maximum YPR ($F_{max}$) and fishing mortality corresponding to 10% of the maximum slope in YPR curve ($F_{0.1}$) were 3.257/year and 0.673/year, respectively. $F_{35%}$ and $F_{40%}$, indicating fishing mortalities at 35% and 40% of maximum Spawning biomass-per-recruit (SBPR), were 0.619/year and 0.509/year, respectively. Based on the biological reference points, fishing mortality at overfished threshold yield ($F_{OTY}$) was calculated as 0.509/year. Current $SBPR/SBPR_{MSY}$ was 1.313 above 1.0, which means 'not overfishe,' while current $F/F_{OTY}$ was 0.629 below 1.0, which indicates 'not overfishing.' In conclusion, the current status of goldeyes rockfish was located in green zone (i.e., not overfished and not overfishing) according to the revised Kobe plot.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.23 no.6
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• pp.443-450
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• 1990

The virtual population analysis technique was applied to the silver croaker, Otolithes argenteus, stock based on length frequency composition, age-length key and nominal catches taken by the trawl fleet and fixed-stake nets in the Kuwait's waters during $1981\~1988$. One-year-old fish was dominant, whereas three-year-old and older fish were at a very low level. Fishing mortality was much higher in the age groups of 2 and 3 than in the others. A strong year-class occurred in 1980 and 1981. Population size of fishable stock markedly decreased from 1982 to 1985 and remained at a low level during $1986\~1987$. The effects of changes in fishing effort showed that an increase in fishing effort would not lead to benefits in yield and would comprise more young and fewer old fish, whereas a reduction in fishing effort to a certain level (by $20\~40\%$ ) from the fishing effort level on the average during $1981\~1988$ could bring some small advantage to the fishery consisting of fewer young and older fish.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.5
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• pp.499-506
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• 2012

We estimated the population size and fishing mortality of Pacific cod Gadus macrocephalus during the spawning season in waters off Woipo, Geoje Island, Korea, using a mark-recapture method. We marked and released 51 cod>50 cm in total length; six were recaptured by local fishermen during the period from December 15 to 31, 2009. The estimated population size was ca. 180,000 and the fishing mortality of the exploitable cod was 26%. Although we could assume a closed population due to the short survey period, we evaluated the uncertainty in the estimates by applying bootstrap resampling because the sample size was small. The estimated 95% confidence interval was 94,000-568,000 for the population size and 8-49% for fishing mortality. Our study demonstrated that the application of mark-recapture methods and bootstrap resampling can be useful in stock assessment for fisheries management in Korea, but requires a larger sample size, spatially extensive coverage, and sophisticated mark-recapture models based on a refined sampling design for reliable stock assessment and biological reference points in sustainable cod management.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.23 no.6
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• pp.475-483
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• 1990

An assessment of Kuwait's commercial fish stocks: hamoor (Epinephelus tauvina), zobaidy (Pampus argenteus), nakroor (Pomadasys argenteus) and sheiry (Lethrinus nebulosus), was conducted using length-frequency data, mean growth and mortality estimates obtained during 1981$\~$1988. The length-cohort analysis indicated that increases in fishing effort would not lead to long-term gains in yield of the stocks at the current estimate of natural mortality rate (M). At high M which was assumed arbitrarily, some benefit in yield could be obtained, especially for hamoor and sheiry. At low M, the yield of all stocks decreased with increased fishing effort. Increases in fishing effort resulted in significant dec-line in spawning stock size for all the stocks. Yield-per-recruit analysis indicated that, un-der low M assumption, a higher yield can be obtained for zobaidy and nakroor by reducing fishing effort. At moderate M, decreases in fishing effort brought gains in yield per recruit of the stocks, but it was not substantial compared with the present level of M. At high M, most of the stocks reached the maximum yield-per-recruit. Overall, increased fishing effort either will not be associated with large long-term gains in yield or, in some stocks, might cause a decline from the present level.

• Ocean and Polar Research
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• v.29 no.1
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• pp.81-86
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• 2007

Abandoned fishing nets served Little Tern(Sterna albifrons) chicks as cover on a sandy island on Ganwol Lake, Hongsung-gun, Chungcheongnam-do, Korea. Chicks were incidently caught in $2.5cm{\times}2.5cm$ mesh sized nets and died of dehydration and exhaustion. Three adults died when they were caught by abandoned fishing net during parental care period in $2.5cm{\times}2.5cm$ mesh sized nets. Whereas $0.7cm{\times}0.7cm$ mesh sized nets did not affect the chicks' or adults' survival. Overlapped nets with several layers were more dangerous for chicks than were spread nets with a single layer. Dead chicks and adults were found to have been entangled by wing and neck. In this study, wing and nape(head+bill) of dead chicks were longer than those of live chicks. To improve the survival rate of Little Tern chicks at Ganwol Lake, abandoned fishing nets must be removed before the breeding season.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.6
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• pp.901-907
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• 2014

We investigated the population ecology of blackthroat seaperch, Doederleinia berycoides, from samples collected in the southern seas of Korea from January to December, 2006. Population ecological parameters included survival rate, the instantaneous coefficient of natural and fishing mortality, and age at first capture. The survival rate (S) of blackthroat seaperch was estimated as 0.4966 using the catch curve method. The instantaneous coefficient of total mortality (Z) was 0.8598/year. The instantaneous coefficient of natural mortality (M) was estimated as 0.4694/year. From the estimates of Z and M, the instantaneous coefficient of fishing mortality (F) was calculated as 0.3904/year. The age at first capture ($t_c$), based on the Pauly method, was 2.87 years.

• The Korean Journal of Malacology
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• v.24 no.3
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• pp.189-197
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• 2008

In order to develop the sustainable ecological management, short-necked clams, Ruditapes philippinarum, were collected from Yoengi coast in Tongyoeng, Korea. The growth of the clam was estimated as: $L_f=68.08{\cdot}(1-e^{-0.145(t+0.324)})$ from ring radius composition of shell. Instantaneous co-efficiency of total mortality and natural mortality were calculated as: 0.991/year and 0.494/year, respectively. The age of the clams from the first capture was estimated to be 3.28. The total biomass was estimated to be 212 MT in the fisheries area (6.4 ha). Applied by these parameters, the annual recruit biomass and the current yield per recruit were calculated to be 649.5 individual/$m^2$ and $0.7\;g/m^2$, respectively. The current fishing intensity was much lower for maximum sustainable yield and acceptable biological catch. Although higher yield per recruit could be achieved by increasing fishing intensity, it is favorable to retain the current fishing intensity because of the unique fishing attitude on Yeongi coast in Tongyoeng, Korea.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.6
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• pp.942-953
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• 2020

Achieving optimal sustainable yields (i.e., avoiding overfishing and maximizing fishery harvest at the same time) is one of the main objectives in fisheries management. Generally, management reference points (MRPs) such as fishing mortalities (Fmsy, F0.1, Fx%) have been suggested for the purpose. In this study, we intended to suggest MRPs for Korea chub mackerel Scomber japonicus stock, using a stochastic catch-at-age model (SCAA) and evaluate whether the current fishing intensity on the stock is appropriate. We used length frequency and catch-per-unit-effort data on the Korea chub mackerel stock collected from the large purse-seine fishery, and yields landed by all fisheries from years 2000 - 2019. We calculated yield per recruit and spawning potential ratio, and projected spawning stock biomass (SSB) under different fishing mortality, assuming annual recruitments were solely controlled by environmental effects (i.e., steepness of 1.0). Some of our major findings and suggestions were that the overfishing threshold would be F46%; i.e., the fishing mortality in the terminal year, 2019 was 0.257/year, which corresponded to F46%.

• Fisheries and Aquatic Sciences
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• v.27 no.4
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• pp.207-212
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• 2024

The study was conducted at Lake Hayq, one of the lakes of Wollo, Ethiopia. Data were collected at the landing sites for 365 days (June 8, 2022 to June 7, 2023). The basic information gathered in the fishing part of the Lake was Nile tilapia caught by fishermen, the total number of tilapia and the increase in fishing effort. The aim of the research was to estimate the size of the Nile tilapia population and the fishing mortality rate in length groups for Nile tilapia stocks occurring in the lake. A Jones length-based cohort analysis model was used to estimate Nile tilapia population. The estimated Nile tilapia population was over 46.8 Million tilapia per year. The model estimates that more than 13.3 million 8-10 cm Nile tilapia are caught in fisheries each year.

• Fisheries and Aquatic Sciences
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• v.27 no.4
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• pp.256-264
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• 2024

Small pelagic fish populations have long been exploited by various fishing gears in the Natuna Sea, and since the 1970s, purse seine exploitation has expanded to offshore fishing grounds. Various small pelagic fish species are exploited from these waters including spotted sardinella (Amblygaster sirm). This research was conducted for 22 months, from March 2019 to December 2020. The fish sample was taken from the purse seine fleet's catch in the fisheries management area (FMA) 711 Natuna Sea and Karimata Strait, which was brought to Pemangkat fishing port in the West Kalimantan Province, Indonesia. This paper aims to determine the exploitation status of spotted sardinella in the Natuna Sea as a recommendation material for management policies. The methods used in this analysis are estimated age, cohort, population parameters, and spawning potential ratio of spotted sardinella. The results show three primary cohorts of spotted sardinella in the Natuna Sea, with ages ranging from 9 months to 3.1 years and a maximum attainable age (longevity) of 4.3 years. The asymptotic value (L_∞) is 21.79 cmFL in length, with a growth rate (K) of 0.65 per year. The natural mortality rate (M) was 1.19, the total mortality rate (Z) was 2.19, and the fishing mortality rate (F) was 0.99. The exploitation rate (E) was 0.45 and the stock status was still in a sustainable condition. Therefore, the sardinella fisheries can be developed using a precautionary approach and focus on the ecosystem sustainability of FMA 711.