• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2000.05a
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• pp.327-327
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• 2000

In the 1990's several economically important marine fisheries collapsed or showed signs of extreme hardship owing to overcapitalization and excessive fishing pressure on the resources. Public concern was raised and demands voiced for more prudent fishery management practices. The United Nations responded and developed international guidelines, such as the FAO Code of Conduct for Responsible Fishing and the UN Straddling Fish Socks and Highly Migratory Fish Stocks Agreement These guidelines task fishery managers to take prudent steps to ensure the long-term viability of fisheries and fishery resources. Included in the guidelines are two particular demands that will challenge stock assessment scientists in the new millennium. They are application of the precautionary approach and the inclusion of ecological considerations in assessments and management advice. High-lighted in the presentation are examples from the central-western Pacifi skipjack tuna fishery and the eastern Pacific thresher shark fishery where insufficien information is affecting stock assessments. The shortcomings are further linked t the new challenges of applying the precautionary approach, such as reference points, and ecological considerations, such as predator-prey and oceanographic-regime shift.(omitted)

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.55 no.3
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• pp.206-216
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• 2019

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.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.55 no.2
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• pp.95-104
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• 2019

This study is aimed to take a stock assessment of blackthroat seaperch Doederleinia seaperch regarding the fishing effort of large-powered Danish Seine Fishery and Southwest Sea Danish Seine Fishery. For the assessment, the state-space model was implemented and the standardized catch per unit effort (CPUE) of large powered Danish Seine Fishery and Southwest Sea Danish Seine Fishery which is necessary for the model was estimated with generalized linear model (GLM). The model was adequate for stock assessment because its r-square value was 0.99 and root mean square error (RMSE) value was 0.003. According to the model with 95% confidence interval, maximum sustainable yield (MSY) of Blackthroat seaperch is from 2,634 to 6,765 ton and carrying capacity (K) is between 33,180 and 62,820. Also, the catchability coefficient (q) is between 2.14E-06 and 3.95E-06 and intrinsic growth rate (r) is between 0.31 and 0.72.

• Ocean and Polar Research
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• v.24 no.4
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• pp.457-464
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• 2002

Distribution and stock assessment of mega-benthos living in the shallow hard bottom around Dokdo were studied in July,2000. Depth and topographical conditions have affected to the densities and biomass of benthic animals. In shallow area, less than 10 m depth, turbo shell Batillus cornutus, mussel, Mytilus corusucs were dominated and showed distinct patterns in vertical distribution. On the other hand, the area over 10m depth, it showed diverse pattern depending on topography. Turbo shell, mussel and sea cucumber Stichopus japonicus were dominated in terms of fishery resources, but abalones were rarely sampled. Stock assessment were estimated to be 6.54 M/T, 3.89 M/T and 8.92 M/T, respectively. Some parts of coastal hard bottom around Dokdo, such as the area between Dongdo and Seodo, seemed to play an Important role as nursery ground. Therefore, it is necessary to the environmental monitoring for coastal fishery managements aspects.

• Journal of Fisheries and Marine Sciences Education
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• v.18 no.1
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• pp.19-30
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• 2006

For fishery stock assessment and optimum sustainable yield of anchovy in Korea, surplus production(SP) models and a maximum entropy(ME) model are employed in this paper. For determining appropriate models, five traditional SP models-Schaefer model, Schnute model, Walters and Hilborn model, Fox model, and Clarke, Yoshimoto and Pooley (CYP) model- are tested for effort and catch data of anchovy that occupies 7% in the total fisheries landings of Korea. Only CYP model of five SP models fits statistically significant at the 10% level. Estimated intrinsic growth rates are similar in both CYP and ME models, while environmental carrying capacity of the ME model is quite greater than that of the CYP model. In addition, the estimated maximum sustainable yield(MSY), 213,287 tons in the ME model is slightly higher than that of CYP model (198,364 tons). Biomass for MSY in the ME model, however, is calculated 651,000 tons which is considerably greater than that of the CYP model (322,881 tons). It is meaningful in that two models are compared for noting some implications about any significant difference of stock assessment and their potential strength and weakness.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.60 no.3
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• pp.244-257
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• 2024

Considering the negative impact of IUU fishing on fishery resources and fishery management, a revised approach for estimating risks of the ecosystem-based fisheries assessment (EBFA) of Zhang et al. (2011) was developed that incorporates three components of the IUU (illegal, unreported and unregulated) fishing as penalties. In this study, we introduced ways to develop indicators of IUU fishing suitable for the Korean fishery and apply them to ecosystem-based resource assessment. The indicator for the illegal fishing component was set as the fishing without licenses or permits, and that for the unreported fishing component was set as unreported fishing activities. Indicators for the unregulated fishing component were set as fishing operated by illegal fishing gear, illegal fish capture, fishing operations in prohibited fishing area, and fishing with restrict permits. IUU fishing significantly impacts the stock of target species. Therefore, in this study, the influence of IUU fishing is included in the Species Risk Index (SRI) at the species level, and weights are assigned based on the ratio of the stock, as $SRI={{\sum\limits_j}{\lambda}_j{\cdot}ORI/{\sum\limits_j}{\lambda}_j}+P_f(B_i/B)$. The revised ecosystem-based fisheries assessment method, which considers the impact of IUU fishing, was applied to major fisheries on the south coast of Korea. It is necessary to reduce the non-reporting rate through the expansion of the TAC system and improve the accuracy of statistical compilation. To this end, the electronic fishing reporting system, which is being implemented on all vessels in Korean distant water fishing vessels, should be introduced to the coastal and offshore fisheries as well.

• The Journal of Fisheries Business Administration
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• v.47 no.3
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• pp.15-33
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• 2016

This study aims to analyze effectiveness of the resource use under the total allowable catch system (TACs) of Comb pen shell, a species among TAC targeting ones through its stock assessment based on the surplus production model such as the Clark Yoshimoto Pooley (CYP) model. Particularly, this study is separated into five analysis periods in order to understand changes in Comb pen shell resource and its efficient use after TAC system implemented in 2001. The results of this study are as follows. First, five sustainable yield curves (SYCs) and exponential growth functions (EGFs) produced by the surplus production model based on Gompertz growth function to compare before and after implementation of the Korean TAC system show that the TAC system has generated a positive stock rebuilding effect for Comb pen shell caught by the diver fishery since 2001. Secondly, five profits based on differences between the sustainable total revenue (STR) and the total cost (TC) with respect to fishing efforts present that the TAC system has increased efficiency of resource use of Comb pen shell caught by the diver fishery after implementation of the Korean TAC system. In conclusion, the Korean TAC system has increased efficiency of resource use as well as has led a positive stock rebuilding effect for Comb pen shell.

• 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.54 no.5
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• pp.769-781
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• 2021

Given data about the annual fishery yield of the common squid Todarodes pacificus, and the catch-per-unit-effort (CPUE) data from multiple fisheries from 2000-2018, we applied a Bayesian state - space assessment model for the squid population. One of our objectives was to do a stock assessment, simultaneously incorporating CPUE data from the following three fisheries, (i) large trawl, (ii) jigger, and (iii) large purse seine, which comprised on average a year about 65% of all fisheries, allowing possible correlations to be reflected. Other objectives were to consider both observation and process errors and to apply objective priors of parameters. The estimated annual exploitable biomass was in the range of 3.50×10⁵ to 1.22×10⁶ MT, the estimated intrinsic growth rate was 1.02, and the estimated carrying capacity was 1,151,259 MT. Comparison with available results from stock assessment of independently analyzed single fisheries revealed a large difference from the estimated values, suggesting that stock assessment based on multiple fisheries should be performed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.2
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• pp.183-188
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• 2022

It is a difficult task to estimate parameters in even a simple stock assessment model such as a surplus production model, using only data about temporal catch-per-unit-effort (CPUE) (or survey index) and fishery yields. Such difficulty is exacerbated when time-varying parameters are treated as random effects (aka state variables). To overcome the difficulty, previous studies incorporated somewhat subjective assumptions (e.g., B₁=K) or informative priors of parameters. A key is how to build an objective joint prior of parameters, reducing subjectivity. Given the limited data on temporal CPUEs and fishery yields from 1999-2020 for common squid Todarodes pacificus, we built a joint prior of only two parameters, intrinsic growth rate (r) and carrying capacity (K), based on the resilience level of the population (Froese et al., 2017), and used a Bayesian state-space production assessment model. We used template model builder (TMB), a R package for implementing the assessment model, and estimating all parameters in the model. The predicted annual biomass was in the range of 0.76×10⁶ to 4.06×10⁶ MT, the estimated MSY was 0.13×10⁶ MT, the estimated r was 0.24, and the estimated K was 2.10×10⁶ MT.