The largehead hairtail (Trichiurus japonicus) is the most productive fish caught in China. In order to understand the seasonal distribution of T. japonicus in the East China Sea and the central and southern parts of the Yellow Sea, three species distribution models were used in this study, namely the random-forest model, K-nearest-neighbor algorithm, and gradient-ascending decision-tree model, based on the data of trawling surveys in the East China Sea and central and southern parts of the Yellow Sea from 2008 to 2009. Combined with a variance inflation factor and cross-check, a distribution model of T. japonicus was screened and constructed to analyze the influence of environmental factors on the distribution of T. japonicus in the East China Sea and central and southern parts of the Yellow Sea. The results showed that the random-forest model had the advantages of fitting effect and prediction ability among the three models. The analysis of this model showed that the water depth, bottom water temperature, and surface salinity had a great influence on the habitat distribution of T. japonicus. The relative resources of T. japonicus increased with the increase of bottom water temperature, reached the maximum at 23.8 °C, and first increased and then decreased with the increase of water depth and surface salinity, reaching the maximum when water depth is 72 m and surface salinity is 31.2%. This study also used the random-forest model to predict the spatial distribution of T. japonicus in the central and southern waters of the East China Sea and south-central Yellow Sea from 2008 to 2009, and the results showed that the predicted results were close to the actual situation. The research results can provide a reference for the exploitation and protection of T. japonicus resources in the East China Sea and the south-central Yellow Sea.

Growth, mortality parameters and exploitation of the swimming crab Portunus trituberculatus (Miers, 1876) in the East China Sea

Based on the field survey and reference data of the sea area of the Zhongjieshan Islands from 2021 to 2022, the Ecopath model was used to analyze the energy flow structure of the marine ecosystem of the sea area of the Zhongjieshan Islands; the energy structure of the marine ecosystem was divided into 21 functional groups, and its nutrient structure, energy flow, and total system characteristics were analyzed. The results show that the credibility of the model is 0.414, which is at a medium level. The trophic level of each functional group of the ecosystem in the sea area of Zhongjieshan Islands was 1–3.48, the energy flow structure of the system was mainly concentrated in the first five grades, and the trophic level was relatively simple, with the average energy transfer efficiency of the system being 8.11%, the energy flow range being 2.81–13.04%, the energy transfer efficiency of the primary producers of the system being 7.25%, and the energy conversion efficiency of the system debris being 9.12%. The total system throughput was 2125.96 t·km⁻²; The analysis of the overall characteristics of the ecosystem showed that the system connectance index and the system omnivory index were 0.45 and 0.24, respectively, while the Finn’s cycling index was 8.24, the Finn’s mean path length of the system was 2.72, and the total primary production/total respiration was 1.71. In this study, the marine ecosystem model of the sea area of the Zhongjieshan Islands was studied to understand the trophic structure and ecosystem status of the sea area, which is conducive to the sustainable utilization and scientific management of fishery resources in the sea area.

Trichiurus japonicus is the most productive fish caught in our country. In order to understand the seasonal distribution of Trichiurus japonicus in the central and southern parts of the East China Sea and Yellow Sea, three species distribution models were adopted, namely Random Forest Model, K-nearest neighbor algorithm and gradient ascending decision Tree model, based on the data of trawling surveys in the central and southern parts of the East China Sea and Yellow Sea from 2008 to 2009. Combined with variance inflation factor and cross-check, the distribution model of Trichiurus japonicus was screened and constructed to analyze the influence of environmental factors on the distribution of Trichiurus japonicus in the central and southern parts of the East China Sea and the Yellow Sea. The results showed that the random forest model had the advantages of fitting effect and prediction ability among the three models. The analysis of this model showed that the water depth, bottom water temperature and surface salinity had a great influence on the habitat distribution of Trichiurus japonicus. The relative resources of Trichiurus japonicus increased with the increase of bottom water temperature and reached the maximum at 23.8℃, and first increased and then decreased with the increase of water depth and surface salinity, reaching the maximum at 72 m and 31.2‰, respectively. The random forest model was used to predict the spatial distribution of Trichiurus japonicus in the East China Sea and the central and southern Yellow Sea during 2008-2009, and the results showed that the predicted results were close to the actual situation. The research results can provide reference for the exploitation and protection of Trichiurus japonicus resources in the East China Sea and the central and southern Yellow Sea.

Fulgoraria rupestris is a predatory marine gastropod belonging to Neogastropoda and possessing considerable taxonomic significance. However, research on this species remains limited. We acquired the complete mitochondrial genome of F. rupestris through second-generation sequencing and conducted an analysis of its genome structural features. The mitochondrial genome of F. rupestris spans a total length of 16,223 bp and encompasses 37 genes (13 protein-coding genes (PCGs), 22 transfer RNAs, and 2 ribosomal RNAs). Notably, most tRNAs exhibit the typical cloverleaf structure, but there is an absence of the Dihydrouridine (DHU) arm in the trnS1 and trnS2 genes. The A + T content is 68.67%, indicating a pronounced AT bias. Additionally, we conducted a selection pressure analysis on the mitochondrial genomes of four species within Volutidae, revealing that all PCGs are subjected to purifying selection. In comparison to other species within Neogastropoda, F. rupestris shares an identical gene arrangement. Additionally, based on mitochondrial genome sequences of the 13 PCGs from 50 species within Neogastropoda, we constructed a phylogenetic tree. The phylogenetic tree indicates F. rupestris forms a clade with species within the family Volutidae (Cymbium olla, Neptuneopsis gilchristi, and Melo melo). This study serves as a valuable reference for future research on F. rupestris, offering insights for the upcoming phylogenetic and taxonomic classification within Neogastropoda. Furthermore, the findings provide valuable information for the development of genetic resources in this context.

The marine region of the Zhongjieshan Islands is an essential component and location for enhancement and release in Zhoushan Fishing Ground. The scientific assessment of the target species' ecological carrying capacity serves as the foundation for augmentation and release efforts. Based on data from the 2021-2022 survey of biological resources in the waters of Zhongjieshan islands, the Ecopath model was built to analyze the trophic structure, energy flow, and overall characteristics of the ecosystem, as well as the ecological carrying capacity of the main enhancement and releasing species, Larimichthys crocea and Sepiella maindroni. The ecosystem's functional groups had trophic levels ranging from 1 to 3.48, with an average energy transfer efficiency of 8.11% and total flow of 2125.905 t·km-2. The ratio of total primary output to total respiration is 1.713. Zhongjieshan Islands' ecosystem was currently at an embryonic stage. The ecological carrying capacity of Larimichthys crocea and Sepiella maindroni was calculated to be 0.2325 t·km-2 and 0.1617 t·km-2, separately or individually. Larimichthys crocea and Sepiella maindroni showed enormous potential for development and release. The findings offered essential data for ecological studies on the waters of Zhongjieshan Islands, as well as a reference for enhancement and release efforts in this area.