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Assessing the stock status of two commercially important flounder species in the East Sea of Korea using multiple length-based methods
No full textThe blackfin flounder (Glyptocephalus stelleri) and pointhead floundeer (Cleisthenes pinetroum) are the commercially important flounder species in the Korean East Sea. In this study, we utilitzed three length-based methods known as TropFishR, length-based spawning potential ratio (LBSPR), and length-based Bayesian biomass (LBB) to assess the stock status these two flounder species. Length and weight data for a total of 4715 blackfin flounder from August 2011 to December 2023 and 1947 pointhead flounder from march 2015 to December 2023 were collected from two landing sites (Hupo and Ayajin) in the East Sea of Korea. Both flounder species exhibit postive allometric growth patterns based on the length-weight relationship with b (slope) values of 3.39 and 3.40 for G.stelleri and C.pinetorum, respectively. The estimated growth parameters, growth co-efficient (k), and asymptotic length (L∞) using the ELEFAN-GA method were 42.27 cm and 0.16 year-1 for for G.stelleri, and 43.44 cm and 0.20 year-1 for C.pinetorum. The estimated total mortality based on the length-converted catch curve (LCC) was Z=0.92 year-1 and 1.19 year-1 for G.stelleri and C.pinetorum, respectively. The exploitation rates (E) for both of the species were higher than the optimum rate of 0.5, i.e. 0.66 year-1 for G.stelleri and 0.69 year-1 for C.pinetorum. This indicates that both species are in an overexploited condition. The results of the LBSPR showed that both flounder species are experiencing recruitment overfishing due to very low spawning potential ratio: 0.23 for G.stelleri and 0.19 for C.pinetorum, this is because the majority of the samples were below the size at first maturity (Lm50) of 24.09 cm for G.stelleri and 24.67 cm for C.pinetorum. The fishing mortality to the natural mortality ratio (F/M) for G.stelleri was estimated at 2.25, while for C.pinetorum it was 2.84, both excedding the reference point of 1. The current biomass with respect to virgin biomass (B/Bo) was 0.15% and 0.12% for G.stelleri and C.pinetorum. For both species, the current biomass was lower than the reference point of 0.50. The current fishing mortality was 36% and 61.44% higher than the reference point of F0.4 for G.stelleri and C.pinetorum, respectively.2
Trophic Ecology of Three Flounder Species in the East Sea of Korea Based on Stable Isotopes and Stomach Contents Analyzes
No full textThree flounder species Cleisthenes pinetorum , Glyptocephalus stelleri , and Hippoglossoides dubius are common flatfish along the eastern coast of Korea, constituting a significant portion of the fishery catch. This study investigates their trophic ecology through combined stomach content and stable isotope analyses from Hupo and Ayajin regions. A total of 845 stomachs were examined, of which 651 contained prey items. Two hundred sixty one muscle tissue samples were analyzed for stable isotope analysis to mea sure carbon ( δ13C) and nitrogen ( δ15N) isotopes. The dietary data were quantified using frequency of occurrence (%F) and weight percentage (%W). Isotopic niches and niche overlap were assessed using the SIBER and nicheROver packages in R. The stomach content analysis identified 18 prey tax a for C. pinetorum, 25 for G. stelleri , and 16 for H. dubius . In terms of weight contribution, small sized C. pinetorum mainly consumed euphausiids regardless of region (Hupo and Ayajin), but their diets showed ontogenetic shift from euphausiids to teleosts in Hupo region. In the diets of G. stelleri, polychaetes and euphausiids constituted dominant food resources in both regions while their mature group fed more on euphausiids in Ayain and sea cucumbers in Hupo. In Hupo, i mmature Hippoglossoides dubius primarily fed on brittle stars and euphausiids, while mature individuals shifted their diet to brittle stars and teleosts. Stable isotope analysis revealed three flounder specie exhibited distinct ontogenetic and spatial vari ations in niche sizes. In Ayajin, immature Cleisthenes pinetorum exhibited broader isotopic niches than mature individuals, whereas mature Glyptocephalus stelleri showed broader niches than immature individuals. In Hupo, mature Cleisthenes pinetorum and Glyptocephalus stelleri had broader niches than their younger individuals. Conversely, mature Hippoglossoides dubius had narrower isotopic niches compared to their younger individuals. These findings provide insights into the feeding habits and trophic ecolo gy of these three flounder species in Korean East Sea.1
Inter-specific Differences in Otolith Shapes and Body Morphometrics Among Co occurring Three Flounder Species in the East Sea of Korea
No full textAssessing body and otolith morphology is crucial for studying fish populations, particularly in distinguishing similar species. This study examined the body morphometrics and otolith shapes of three flounder species Cleisthenes pinetorum, Glyptocephalus stelleri , and Hippoglossoides dubius collected from the East Sea off Korean coast between 2023 and 2024. A total of 191 specimens were analyzed for body morphometrics, including 90 Cleisthenes pinetorum , 66 Glyptocephalus stelleri , and 35 Hippoglossoides dubius . Additionally, otoliths of 669 specimens were examined for otolith shape analyses, inlcuding 230 C. pinetorum, 335 G. stelleri, and 104 H. dubius. Eight body morphometric traits, five otolith size indices, and ei ght otolith shape indices were measured. Multivariate analysis was used to compare the clusters of the three species, and average otolith shapes were visualized using wavelet coefficients in the shapeR package. In terms of body morphometry, C. pinetorum ex hibits the largest mouth height, head length, and post orbital length, while G. stelleri shows the smallest mouth height and post orbital length. Otolith shape analyses revealed significant inter specific differences, particularly in the anterior, dorsal, and posterior regions of otolith. A canonical
analysis of principal components (CAP) performed on wavelet coefficients confirmed the complete separation of otolith shapes among the species, with CAP1 explaining 93.7% of the variation. Linear discriminant analysis (LDA) of body morphometrics also showed clear separation, with LD1 accounting for 89.88% of the variation. Cleisthenes pinetorum had larger and heavier otoliths in terms of length, area, perimeter, width, and otolith weight. Otoliths of G. steller i were rounder and more rectangular, while those of H. dubius were more elongated. This study is the first to compare otolith and body morphology of these three flounder species in the East Sea of Korea. The results of this study will aid in developing fisheries management practices for the fisheries in Korean East Sea.1
대마난류권역에서 수온 상승에 따른 자치어의 분포 변동 및 특성
No full text본 연구는 한반도 주변해 대마난류권역에서 어류유생(자치어)의 분포특성을 밝히기 위하여 2021년부터 2023년까지 고수온기와 저수온기에 위도별 4개 정점에서 RN80 네트를 이용하여 자 치어를 채집하였다. 채집된 자치어는 현장에서 95% 에탄올에 고정하여 실험실로 운반하였고, 해부현미경을 활용하여 종 동정 및 계수를 실시하였다. 형태동정이 어려운 경우 분자동정을 실시하였다. 자치어로 밝혀진 어종의 산란종 시기 및 기후대별 분포 특성에 따라 온대(Temperate), 아열대(Subtropical), 열대(Tropical), 아한대(Boreal)로 구분하였고 미확인 종은 기타(Other)로 구분하였다. 연구기간 동안 총 9목 36과 75분류군에 속하는 자치어가 채집되었고, 멸치(Engraulis japonicus), 자리돔(Chromis notata), 가막베도라치(Enneapterygius etheostomus), 청베도라치(Parablennius yatabei)가 연구해역에서 우점하는 종으로 파악되었다. 시기별, 위도별 자치어 우점종을 살펴보면, 고수온기에 울릉도에서 멸치가 48.9%, 자리돔이 26.0%로 우점하였고, 울진에서 청베도라치(Parablennius yatabei)가 38.2%, 앞동갈베도라치(Omobranchus elegans)가 12.4%로 우점하였다. 거제에서는 청베도라치가 70.2%, 청보리멸(Sillago japonica)이 15.3%로 우점하였고 제주도에서는 후악치과(Opistognathidae sp.) 어류가 45.5%, 줄도화돔(Apogon semilineatus)이 18.4%로 우점하였다. 저수온기는 울릉도에서 멸치가 28.4%, 가막베도라치가 19.7%로 우점하였고, 울진에서 참가자미가 53.3%, 볼락(Sebastes inermis)이 18.4%로 우점하였다. 거제에서는 쏨뱅이 (Sebastiscus marmoratus)가 21.2%, 고등어(Scomber japonicus) 12.6%로 우점하였고 제주도에서는 쏨뱅이 59.1%, 볼락과 멸치가 각각 11.4%로 우점하였다. 시기별 기후대 출현종수를 살펴보면, 제주도에서 저수온기에 온대(37.5%), 아열대(37.5%), 열대(12.5%) 어종 순으로 나타났지만, 고수온기에는 온대(25.0%) 및 아열대(12.5%) 어종은 감소하고, 열대(50.0%) 어종은 증가하였다. 거제에서는 저수온기와 고수온기에 온대, 아열대, 열대 어종 순으로 나타났지만, 계절별 큰 차이는 없었다. 울진에서는 저수온기 온대(76.9%) 어종이 가장 많이 출현하였지만, 고수온기에 아열대(52.9%) 및 열대(5.9%) 어종이 증가하였다. 울릉도에서도 저수온기에 온대 46.2%, 아열대 15.4%, 열대 7.7%로 나타났고, 고수온기에 온대 44.4%, 아열대 22.2%, 열대 22.2%로 나타나, 고수온기에 아열대 및 열대 어종의 출현이 증가하였다. 전반적으로 저수온기에서 고수온기로 갈수록, 그리고 제주도와 울릉도에서 열대 및 아열대 출현 종수가 증가하고 온대 종수가 감소하는 경향을 보였다. 본 연구결과는 수온 상승과 같은 한반도 주변 해역의 환경변화에 따라 생태계 변동 특성을 파악하고, 수산자원과 밀접한 연관이 있는 자치어에 대한 지속적인 모니터링을 통하여 한반도 주변해 아열대화 경향을 파악할 수 있는 자료로 활용될 것이다.2
Assessing the stock status of pointhead flounder (Cleisthenes pinetorum) and blackfin flounder (Glyptocephalus stelleri) in the East Sea of Korea using length-based methods
No full textPointhead flounder (Cleisthenes pinetorum) and blackfin flounder (Glyptocephalus stelleri) are key commercial species distributed in the East Sea off the Korean coast. Evaluating the stock status of commercial fish is essential for sustainable fisheries management, as it informs conservation efforts and resource allocation. This study evaluated the stock status of these two flounder species using three length-based assessment methods: TropFishR, length-based spawning potential ratio (LBSPR), and length-based Bayesian Biomass (LBB). Length and weight data from 1947 pointhead flounders and 4715 blackfin flounders were collected in the eastern waters of Korea. Both species exhibited positive allometric growth patterns, with b values of 3.40 and 3.39, respectively. Among the growth parameters estimated via the ELEFAN-GA method, the asymptotic length was 43.44 and 42.27 cm, and the growth coefficient was 0.20 and 0.16 year⁻¹ for pointhead and blackfin flounder, respectively, while the total mortality derived from the length-converted catch curve for the two species was 1.19 year⁻¹ and 0.92 year⁻¹ , respectively. Both species showed exploitation rates above the optimal value of 0.5 (0.69 for pointhead flounder and 0.66 for blackfin flounder), which indicated overexploitation. The LBSPR results revealed low spawning potential ratios of 0.19 for the former and 0.23 for the latter, which indicated recruitment overfishing. Furthermore, growth overfishing was also evident, as most samples were below the length at first maturity, i.e., 24.67 cm for pointhead flounder and 24.09 cm for blackfin flounder. The ratio of fishing mortality to natural mortality was 2.87 and 2.25, respectively, exceeding the reference point of 1 for both species, while that of current biomass to virgin biomass was 0.12 and 0.15, respectively, both below the reference point of 0.50. The current fishing mortality rates were 61.44 % and 36.06 % higher than the reference point F₀.₄ for pointhead flounder and blackfin flounder, respectively.11Nsciescopu
Assessment of Exploited Stock and Management Implications of Kingfish (Scomberomorus commerson) in the Omani Waters
No full textThe high demand and economic value of kingfish (Scomberomorus commerson) have led to intensive fishing of this species in the Omani waters. The increased fishing pressure has made the fishery vulnerable; hence, information on the current stock status is essential for the sustainability of the kingfish stock. Three length-based stock assessment approaches (TropFishR, spawning potential ratio, and Bayesian biomass method) were used to estimate growth, mortality, exploitation, spawning potential capacity, and relative biomass in relation to maximum sustainable yield (MSY). Asymptotic length (L∞) was 186.31 cm, and the growth coefficient (K) was 0.15 yr−1 for S. commerson. Fishing mortality was 0.45 yr−1, which was higher than natural mortality (M = 0.18 yr−1) and optimal fishing mortalities (F40% = 0.15 yr−1). The exploitation rate (E) was found to be 0.71 yr−1, higher than the optimum exploitation (E = 0.50), indicating a total overfishing of 42% of the S. commerson in Oman waters. The current length at first capture (Lc50 = 74.38 cm) was significantly smaller than the length at first maturity (Lm50 = 91.25 cm), indicating growth overfishing. The current spawning potential ratio (SPR) was 10%, which was significantly below the reference point (SPR = 20%), indicating that the stock was severely overfished. Biomass was critically low (B/Bo = 0.17), and lower than the reference point of 0.20. Additionally, the current biomass was 44% of Bmsy (B/Bmsy = 0.44), which is significantly lower than the reference point of 1, indicating that the stock biomass was below the maximum sustainable yield level, suggesting recruitment overfishing. Stock indicators revealed that the fishery was primarily targeting immature/juvenile fish, as well as older and larger fish, which indicated stocks were both growth- and recruitment-overfished. Therefore, carrying out commercial fishing for an optimum size range (118 to 144 cm) and reducing fishing pressure to a sustainable level (F = M, 0.18 yr−1) would sustain a healthy stock biomass of kingfish in Omani waters.11Ysciescopu
Assessment of Exploited Stock and Management Implications of Tiger Tooth Croaker (Otolithes ruber) in Coastal Waters of Makran, Pakistan
No full textPakistan’s marine fishing industry is crucial to the country’s economy, generating employment opportunities and foreign revenue. It produces 80% of the country’s total fish production. Otolithes ruber is a commercially important fish on the Makran coast of Pakistan, contributing significantly to the region’s croaker fisheries. This study is the first to apply three length-based approaches for assessing the stock status of O. ruber in the Makran coast: (1) TropFishR to estimate the mortality, growth parameters, and current exploitation status, reference points based on the yield per recruitment model, (2) the length-based Bayesian biomass method (LBB) to calculate stock biomass, and (3) the length-based spawning potential ratio (LBSPR) to estimate the spawning potential ratio. The length–weight relationship of Otolithes ruber was a positive allometric pattern (b = 3.28; R2 = 0.94). Growth parameters for Otolithes ruber were L∞ = 55.47 cm, K = 0.50 year−1. The calculated total mortality rate (Z), natural mortality (M), and fishing mortality (F) were 2.27 year−1, 0.67 year−1, and 1.6 year−1, respectively. The exploitation rate (E) was 0.70, indicating severe overexploitation. The current length at first capture (Lc50) = 27.37 cm was lower than that at first maturity (Lm50) = 30.75 cm, indicating growth overfishing. The current spawning potential ratio (8%) was lower than the optimal value (40%), indicating recruitment overfishing. The current biomass, concerning virgin biomass B/Bo, was also 8%, resulting in a 92% stock decline. We recommend reducing the exploitation pressure by limiting the commercial catch to an optimum length range of 34.5–42.2 cm and reducing fishing pressure by 40% to ensure sustainable fishery management
Stomach content and stable isotope analyses provide evidence trophic niche partitioning among three commercial fish species in the Yellow Sea, Korea
No full textFood resources and trophic niche partitioning among co-occurring three commercial fish species, bartail flathead (Platycephalus indicus), ocellate spot skate (Okamejei kenojei) and yellow croaker (Larimichthys polyactis) inhabiting the southwestern waters off Korea were
examined based on stomach content and stable isotope analyses. The diets of bartail flathead consisted mainly of teleosts and carid shrimps, while carid shrimps and prawns were primary prey items for ocellate spot skate. On the other hand, yellow croaker mainly consumed carid shrimps and euphausiids. nMDS and PERMANOVA results revealed significant differences in dietary composition among the three species, implying a partitioning of food resources. Carbon (δ13C) and nitrogen (δ15N) stable isotope values further demonstrated that the three species have significantly different trophic positions, with δ13C and δ15N values being the highest for bartail flathead and the lowest for yellow croaker. Among prey taxa consumed by the three species, the increased contribution of euphausiids with lower δ13C and δ15N values resulted in a decreased trophic level of yellow croaker, while higher consumption of teleosts in the diets of bartail flathead contributed
increase in trophic position. Combined stomach contents and isotopic analyses provide a more comprehensive understanding of how fish diets and trophic positions vary with changes in the type and amount of prey resources. These results could contribute to the understanding of trophic relationships among fish species inhabiting the Yellow Sea, Korea.1
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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