Search Results (11)

Marine mammal Bycatch Reduction Devices (BRDs) can result in the escape of target fish species. In the present study, a modified single-layer codend configuration developed from previous studies was evaluated using BRDs with guide net angles of 30° and 45°. Catch was collected separately from the codend and the BRD cover to estimate catch loss rates and characteristics. For caught species, catch loss rates based on the number and weight of individuals were 9% and 13% for herring with the 30° guide net and 16% and 18% with the 45° guide net, respectively. For Korean pomfret, catch loss rates were 24% and 23% at 30° and 4% at 45°. These results suggest that further modification of BRD is necessary. In contrast, catch loss rates of mackerel with the 30° guide net reached 56%, whereas hairtail showed loss rates of 60% and 65% with the 45° guide net. Underwater observations indicated that catch loss was influenced by swimming behavior and entanglement with the guide net. Despite the modification of the codend to a single layer, the present study still observed high catch loss rates. However, no bycatch of marine mammals occurred during the experimental operations. Full article

Guide-net marine mammal bycatch reduction devices (BRDs) are intended to reduce protected species interactions in trawl fisheries, but their use may also cause catch loss of commercial fish and cephalopods. We restructured June and September 2024 sea trial records into a final six-taxon BRD/COD modeling dataset containing 5641 individual records from 24 unique haul clusters. Logistic GLM, random forest, and XGBoost models were evaluated using haul-grouped cross-validation, and random forest SHAP and permutation analyses were used as exploratory variable contribution diagnostics. Model discrimination was modest and split-sensitive, but Brier score and accuracy were interpreted cautiously because the catch loss prevalence was 0.163 and trivial baselines were strong. Body length and headline height were the leading non-species contributors, while nominal guide-net angle remained a relevant design variable but ranked below several biological, tow condition, and realized gear geometry variables. Additional haul-clustered GEE sensitivity analyses treated nominal guide-net angle as a two-level categorical factor (30°/45°). Across four GEE specifications, the 45° angle term was consistently positive, but confidence intervals were wide, p-values were not significant, and the full species-adjusted model showed suspected quasi-separation in the hairtail term. These results indicate that nominal angle contribution cannot be cleanly isolated from species composition and realized gear geometry in this field dataset. We therefore interpret guide-net angle as an exploratory predictive contributor rather than as a causal factor of catch loss. Full article

Small-scale fisheries constitute the backbone of coastal livelihoods in Indonesia, yet comprehensive socio-economic data remain limited for effective management. This study characterizes the operational and socioeconomic patterns of multi-gear artisanal fisheries in the Pangandaran coastal waters of West Java, Indonesia. A cross-sectional survey of 136 fishers across 14 coastal communities was conducted using structured questionnaires covering socio-demographic characteristics, fishing operations, and catch composition. Complete economic data were available for 125 fishermen, while multivariate analyses used n = 105 due to listwise deletion of cases with missing predictor variables. Fishermen averaged 46.9 years of age with 25.8 ± 11.6 years of fishing experience. Mean monthly income was IDR 5.80 million (SD = 7.51, 95% CI: 4.47–7.13 million, approximately USD 387). Gillnet was the dominant fishing gear (73.5% of fishermen), followed by hook-and-line (14.7%). A total of 57 fish species were recorded, dominated by hairtail Trichiurus spp. (61.0% occurrence). Statistical analyses revealed weak relationships between conventional demographic and operational variables and income. Although crew number showed a statistically significant association with income (p = 0.039), its effect size was small, and the overall regression model was not significant, with very low explanatory power (R² = 0.038). These results indicate that income variability is largely driven by unmeasured and context-specific factors rather than observable fishing characteristics. These findings provide baseline socio-economic data essential for developing community-specific management interventions in Pangandaran waters. Full article

This study examined the spatial distribution and environmental determinants of hairtail (Trichiurus lepturus) catch volumes in the southern coastal waters of South Korea, employing a Spatial Durbin Model (SDM) based on grid-level data collected from 2020 to 2022. Key explanatory variables included chlorophyll-a concentration, dissolved oxygen, salinity, sea surface temperature, and fishing effort. Spatial autocorrelation was confirmed through Moran’s I test, justifying the application of a spatial econometric framework. Among the environmental factors, salinity exhibited the strongest positive direct effect on catch volumes, whereas dissolved oxygen consistently showed a negative effect. Chlorophyll-a concentration exhibited significant positive effects both within local grids and in neighboring areas. Sea surface temperature also had a modest but significant direct effect on catch volumes. Additionally, higher fishing effort was associated with increased catch volumes, emphasizing the spatial impact of human activities on fishery resources. These findings reveal that hairtail tend to aggregate in high-salinity, low-oxygen environments and respond to seasonal oceanographic variations. Overall, the results highlight the value of spatial econometric models in fisheries research by revealing how environmental and anthropogenic factors influence fish catch through both direct and indirect effects. The spatial framework offers deeper insight into the mechanisms driving hairtail distribution, particularly in ecologically complex regions like the Jeju Strait. Full article

The National Institute of Fisheries Science in Korea is developing marine mammal bycatch reduction devices (BRDs) for midwater trawl gear. In this study, we tested two BRD-type guide nets (inclined net panel) with 30° and 45° tilt angles to prevent marine mammals from reaching the codend and facilitating their escape from the net. Fishing operations were conducted along the east and south coasts of South Korea, and cameras were installed in front of the BRDs to monitor their performance. The catch loss of herring with the 30° guide net was 13% and 11% in number and weight. The catch loss of hairtail was 53% and 51% in number and weight with the 30° guide net. Mackerel showed a 97% catch loss in number and weight with the 45° guide net. The 30° guide net resulted in lower catch loss for rudderfish and jack mackerel compared to the 45° guide net. The jellyfish discard rate of the BRD was 5% and 7% in number and weight with the 30° guide net and 12% and 11% with the 45° guide net, indicating that the 30° guide net was more effective at discarding jellyfish. Mesh selectivity was not strongly related to target species body length. Full article

Accurate catch data are essential for effective fisheries management. This study reconstructs the historical recreational catch of hairtail (Trichiurus lepturus) in Korean waters by incorporating unreported catches to improve stock assessment accuracy. Using a Bayesian state-space surplus production model, we conducted a multi-fishery stock assessment by integrating abundance indices from eight major fisheries. The multigear mean standardization (MGMS) method was applied to derive standardized CPUE indices for each fishery, providing a more comprehensive evaluation of stock trends. The results indicate that excluding recreational catches and multiple CPUE indices may lead to biased stock assessments of hairtail in Korean waters. Models using an integrated CPUE index (SMSC) yielded higher MSY and biomass estimates, suggesting a more optimistic stock condition, whereas fishery-specific CPUE models (MSC) provided more precautionary estimates. The Kobe plot analysis indicates recent stock recovery, but continued monitoring and adaptive management are required to ensure long-term sustainability. This study highlights the importance of integrating recreational catch data and multi-fishery approaches in stock assessments, particularly under data-limited conditions, to enhance resource management and policy decision-making. Full article

Climate change is a major challenge affecting marine environments, making it essential to understand species distribution responses in both time and space for effective conservation strategies. Meanwhile, varying responses of species to climate change may lead to changes in interspecific relationships and future spatial distributions. This study assessed spatial and temporal distributions of four trophically dependent species of economic importance in the China seas, including largehead hairtail (Trichiurus lepturus), Spanish mackerel (Scomberomorus niphonius), chub mackerel (Scomber japonicus), and anchovy (Engraulis japonicus). By incorporating fishery-dependent survey data and environmental variables, we developed a spatio-temporal mixed-effects model to analyze the distributional correlations among these species and predicted their distributions by the end of the century under different climate change scenarios. The results showed that the selected environmental factors influenced encounter probability and catch rates differently. Predictions for the end of the century under representative concentration pathways (RCPs) 2.6 and RCP8.5 suggested significant shifts in population densities, with species like T. lepturus and S. niphonius experiencing reduced densities and altered spatial patterns, while E. japonicus may benefit from climate change. The center of gravity for most species was projected to shift northward by the year 2050, with notable variations under RCP8.5. Additionally, spatial overlap among species was expected to decrease significantly by the year 2100, indicating increasing divergence in their distributions. This study underscores the effects of climate change on species habitat distribution and offers a scientific basis for future habitat protection. Full article

The northeastern waters of Guishan Island constitute one of the crucial fishing grounds for coastal trawl fishery in Taiwan and have been exploited for many decades. To construct the marine ecosystem and to examine the interactions among trophic levels of fisheries resources in the waters of Guishan Island, historical catch, catch composition, biological information, fishing effort, environmental data such as sea surface temperature, salinity, and nutrients were analyzed using Ecopath with Ecosim. The results indicated that the longline and drift net fisheries have a very minor incidental catch of cetaceans, with a fishing mortality (F) of 0.01 year⁻¹ and an exploitation rate (E) of 0.03. The F and E were 0.308 year⁻¹ and 0.617 for small skates and rays, and were 0.261 year⁻¹ and 0.580, respectively, for small sharks. The F and E of the dolphinfish, Coryphaena hippurus, an important pelagic species, were 0.411 year⁻¹ and 0.245, respectively. Fisheries had negative impact on major commercial species except the dolphinfish and the oil fish, Lepidocybium spp., which benefited from the reduction of their predators or competitors. The keystone species of the Guishan Island marine ecosystem is phytoplankton, which has the lowest trophic level and great biomass, and is an important energy source of the ecosystem. The influences of zooplankton and anchovy rank as second and third, respectively, with regard to the keystone species in the ecosystem due to their great biomass. Regarding the biomass of less abundant species, carangids had the highest influence followed by hairtail due to their feeding habits. The results of simulations using Ecosim indicated that the hairtail, small sharks, skates and rays, mackerels, and marine eels will benefit if fishing efforts are reduced by 30%. On the other hand, the biomass of phytoplankton, zooplankton, demersal benthivores, and shrimps will decrease due to the increase in the biomass of their predators. Full article

Experiments were conducted to assess the selectivity of diamond mesh codends in capturing largehead hairtail (Trichiurus lepturus) in the demersal trawl fishery of the Beibu Gulf, located in the South China Sea. The selectivity experiments involved four codends with different mesh sizes (30, 35, 40, and 45 mm), and the covered codend method was employed. Catch data were analyzed using the maximum likelihood method, with both Logistic and Richards curves fitted to the data, and the abundance–biomass comparison (ABC) curve method was used to analyze the impact of codend on fishery resources. Model deviance was compared with the degree of freedom to choose the best fit curve. The Logistic curves gave a better fit for the codends with 30 and 40 mm mesh sizes, while the Richards curves had a better fit for the codends with 35 and 45 mm mesh sizes, respectively. The 50% retention lengths (L₅₀) and selection ranges (SR) were determined for 30 mm (L₅₀: 11.40 cm; SR: 3.81 cm), 35 mm (L₅₀: 11.65 cm; SR: 3.98 cm), 40 mm (L₅₀: 12.92 cm; SR: 5.30 cm), and 45 mm (L₅₀: 13.28 cm; SR: 4.14 cm) mesh codends. The results indicated that the present minimum mesh size, 40 mm diamond mesh, did not match with minimum landing size of largerhead hairtail, 190 mm anal. length. Based on the observed linear relationship between L₅₀ and mesh opening, it was determined that the diamond mesh codend should be adjusted to a larger mesh opening of approximately 72.47 mm in order to achieve an L₅₀ value of 190 mm. The ABC curve characteristics indicate that the fish community structure in the Beibu Gulf in the South China Sea is in a severely disturbed state. This study suggests that the square mesh codend and T90 codend (diamond mesh netting turned by 90 degrees) should be tested and compared with the diamond mesh codend, to obtain the optimal configuration and mesh size of the codend for demersal trawl fishery in the Beibu Gulf in the South China Sea. Full article

Hairtail (Scombriformes: Trichiuridae) have always ranked first in single-species production in Chinese marine fishery. However, due to the confusion of species identification, in official statistics, data on hairtail production and economic value are a combination of all the different species of Trichiuridae. In this study, based on sampling along China’s coastal areas, the composition and distribution of common hairtail species, as well as their age, growth, and trophic traits, are discussed. Six species of four genera and two subfamilies were identified, and largehead hairtail (Trichiurus japonicus) and Savalai hairtail (Lepturacanthus savala) were the most important populations that constituted catch production. The growth parameter b could be divided into two groups, with values in species mostly inhabiting northern parts of Chinese seas higher than those in southern parts. Most individuals were 1–2 years of age, suggesting species sexual precocity and individual miniaturization under multiple stresses. Species of Trichiuridae are at the top of the food web and play a bottom-up role in regulating the trophic dynamics of marine food webs. Largehead hairtail showed the highest stability and the greatest impact on the stability of the trophic structure. Despite temporary resource maintenance under fishery-induced evolution, the effective recovery and reasonable utilization of hairtail resources are still the main focuses of attention for Chinese marine fishery. Full article

The East China Sea population of hairtail (Trichiurus lepturus, also known as T. japonicus) is a commercially important element of Chinese fisheries. Hairtail has long been widely exploited. Due to overfishing, however, its production declined over the years. One of solutions to this dilemma is to institute reasonable fishery policies. Generally, skillful short-term and long-term prediction of fish catch is a central tool for guiding the development of fishery policy. Accurate predictions require a comprehensive understanding of the relationship between fluctuations in fish catch and variability in both fishing effort and marine environmental conditions. To investigate the combined impact of fishing effort and marine environments on hairtail catch and to develop models to predict hairtail catch, we applied empirical dynamic modeling (EDM) to data on East China Sea fisheries, including hairtail catch, fishing effort, and marine environmental factors. EDM is an equation-free approach that enables the investigation of various complex systems. We constructed all possible multivariate EDM models to investigate the potential mechanisms affecting hairtail catch. Our analysis demonstrates that all key environmental factors (salinity, summer monsoon, sea surface temperature, precipitation, and power dissipation index of tropical cyclones) have an impact on nutrient supply, which we suggest is the central factor influencing hairtail catch. Finally, our comparison of EDM models with parametric models demonstrates that EDM models overwhelmingly outperform parametric models in analysis of these complex interactions. Full article