Abstract:With the unique geography and complex environment, the Northwest Pacific Ocean has nurtured extremely rich fishery resources, becoming a hotspot for global marine biodiversity conservation and fishery management. In order to more effectively identify and investigate the diversity of fish species, a local DNA barcodes database of common fish in Northwest Pacific Ocean was established. Based on the COⅠ gene sequences of fish, 307 samples of common fish were collected in Northwest Pacific Ocean from June to August 2023. These common fish belonged to 20 genera, 13 families, 7 orders, and 25 fish species. 77. 96% of COⅠ sequences can be compared to high similarity sequences in public database. The average interspecific genetic distance was 0. 233, and the average intraspecific genetic distance was 0. 003, and the interspecific genetic distance was 77. 67 times that of the intraspecific genetic distance, and it could form obvious bar code gap. The phylogenetic tree based on COⅠ gene sequences showed that fishes of the same genus first clustered into a single branch, then with fishes of the same family, and finally with fish of different families of the same order. In summary, the COⅠ gene has species specificity and can effectively distinguish common fish species in the Northwest Pacific Ocean. The initial establishment of the DNA barcode database of common fish is conducive to the monitoring and investigation of fish diversity in Northwest Pacific Ocean using environmental DNA technology, providing technical support for biodiversity conservation, resource management, and population dynamic monitoring in Northwest Pacific Ocean.

Abstract:Investigating the composition and functional analysis of the intestinal microbiome of wild leptocephalus larvae has significant scientific and practical value for predicting their nutritional needs and developing appropriate initial diet. The study identified the species of leptocephalus larvae captured during the 2022 and 2023 scientific expeditions of the "Songhang" research vessel in Western and Central Pacific Ocean using DNA barcoding technology. Additionally, 16S rDNA high-throughput sequencing was employed to sequence the intestinal samples of the leptocephalus larvae, aiming to analyze the intestinal microbial community structure and identify dominant microflora and their related functions. Results showed that 14 of 16 captured leptocephalus larvae were identified to the species level, including Ariosoma majus, Thalassenchelys coheni, Ariosoma megalops, Gnathophis longicauda, Ariosoma meeki, Muraenidae sp. KY17-483, and Gymnothorax zonipectis. The other two leptocephalus larvae were identified to the genus level, Gymnothorax and Gnathophis. Sequencing revealed that the dominant bacterial groups in the intestinal microbiota of pacific leptocephalus larvae were Proteobacteria, Bacteroidetes and Firmicutes. At the genus classification level, Psychrobacter and Acinetobacter exhibited relatively high abundance. However, there were some differences in the intestinal microbiota between different species and sampling sites. Furthermore, functional prediction analysis showed that intestinal microbiota involved in metabolism had the highest relative abundance, and functional pathways related to ‘amino acid transport and metabolism' were the most enriched. These data suggested that leptocephalus larvae have a higher demand for protein. Our results preliminarily elucidated the diverse composition of the intestinal microbiota in leptocephalus larvae, providing a reference for studying their feeding habits and the development of starter feeds during the artificial breeding of Japanese eels.

Abstract:This study used the Chub mackerel Scomber japonicus and Blue mackerel S. australasicus samples derived from both scientific survey and fishing vessels between 2020 and 2023, and analyzed the influence of species identification, different data sources and time variations on individual growth. The results revealed that the fattiness of samples from fishing vessels was slightly lower than that of scientific survey, and the body mass of samples from scientific survey grew faster. The length-body mass relationship showed that under the same fork length, the body mass of Blue mackerel was lighter than that of Chub mackerel. The range of condition factor was 1.886×10^-6-6.721×10^-5, with the exponent coefficient b mostly greater than 3. Heterogeneity analysis indicated that there were significant influence of data sources and years on the mackerels' growth, without significant growth difference between Chub mackerel and Blue mackerel in Northwest Pacific Ocean. Therefore, time-varying growth parameters and their uncertainties from different data sources of mackerels are strongly suggested to be considered during the stock assessment and fishery management which require life history traits. Additionally, species distinguishment between two mackerels could be given lower priority during data collection and management, but still deserve concern in the future research.

Abstract:In order to explore the growth regularity of Scomber japonicus in Northwest Pacific Ocean, 210 samples collected by the "Songhang" from 2021 to 2022 used landmarks based on geometric morphometrics.Compared with other methods, the use of landmark methods can effectively reveal the phenotypic diversity of fish, reflect the changes in fish at different stages, and explore their individual growth regularity.The results showed that there were significant differences in the external morphology of S.japonicus across different fork length groups. Both principal component analysis and multivariate analysis of covariance showed that S. japonicus with smaller fork length had more distinct zones, with overlapping zones among the three different fork length groups. Different fork length groups had the same growth regularities.The growth rate of S.japonicus gradually decreased with increasing fork length. The thin-plate spline indicates that the smaller the fork length of S.japonicus, the smaller their abdomen and tail. The morphology of S.japonicus changes with the change of fork length. The conclusion is that the morphology of S.japonicus gradually changes with increasing fork length in Northwest Pacific Ocean.

Abstract:In order to better understand the nutritional niche changes during the ontogeny period of Ommastrephes bartramii and Onychoteuthis borealijaponicus,36 O.bartramii and 30 O.borealijaponicus samples were collected from "Songhang" fishery resources survey ship in 2021-2022, and stable isotopic analysis was conducted on their eye crystals. The results show that： the variation in individual δ¹³C and δ¹⁵N values for O. bartramii ranged from 0.10‰ to 1.68‰ and 0.79‰ to 7.51‰, respectively； and the variation in individual δ¹³C and δ¹⁵N values for O. borealijaponicus ranged from 0.15‰ to 1.20‰ and 0.81‰ to 7.05‰, respectively. The niche area change range for O. bartramii and O. borealijaponicus was 0.40‰²-5.85‰² and 0.27‰²-5.36‰², respectively. GAM model analysis showed that the δ¹³C and δ¹⁵N values of O. bartramii eye crystals had a significant correlation with crystal diameter, with deviation interpretation rates of 31.9% and 34.3%, respectively. Similarly, the δ¹³C and δ¹⁵N values of O. borealijaponicus eye crystals were significantly correlated with crystal diameter, with deviation interpretation rates of 12.9% and 19.4%, respectively. According to the analysis,O.bartramii and O.borealijaponicus feeding flexibility is responsible for the irregular change of δ¹³C and δ¹⁵N values with increasing carcass size. The larger magnitude of individual isotopic changes reflects the greater magnitude of baseline isotopic values in the Kuroshio-Oyashio transition zone in Northwest Pacific Ocean. Additional 83% of the O.bartramii samples and 80% of the O.borealijaponicus samples niche amplitude of δ¹³C was small,but niche amplitude of δ¹⁵N was larger,so the feeding level of O.bartramii and O.borealijaponicus in this area is different. The GAM model showed that individual growth and baseline values were factors affecting the tissue δ¹³C and δ¹⁵N values.

Abstract:In order to have a deep understanding of the role of ocean squid in Northwest Pacific Ocean food web, samples were collected during the comprehensive scientific survey launched by the Ministry of Agriculture and Rural Affairs in 2021 and 2022.Carbon and nitrogen stable isotope technology was used to analyze the muscle stable isotopes and nutritional niches of two cephalopod species, Ommastrephes bartramii and Onychoteuthis borealijaponicus, in Northwest Pacific Ocean. The results show that O.bartramii δ¹³C and δ¹⁵N values between sites were significantly different. O.borealijaponicus δ¹³C values between the two sites showed significant differences, while the δ¹⁵N values were not significant. Muscle δ¹³C and δ¹⁵N values between O.bartramii and O.borealijaponicus showed significant differences.During ontogeny,the δ¹³C and δ¹⁵N values of O.bartramii and O.borealijaponicus were not significantly associated with carcass length.The nutrient niche width of O.bartramii （SEAc=0.35‰²） is greater than that of O.borealijaponicus （SEAc=0.20‰²）, with a moderate overlap between the two squids （0.314）. The high niche overlap between males and females is 0.988 and 0.76, respectively.The analysis shows that the δ¹³C values of O.bartramii and O.borealijaponicus are influenced by SST and feeding effects, while the δ¹⁵N values are influenced by feeding effects. The utilization of food and habitat resources was highly similar in both female and male cephalopod groups.

Abstract:Sardinops melanostictus is mainly distributed in Northwest Pacific Ocean, which is significantly affected by climate change. The carbon and nitrogen stable isotope ratios of the muscles of Japanese sardines from the Northwest Pacific Ocean were measured based on samples taken by the ocean-going fishery resources survey ship “Songhang” in the high seas of the Northwest Pacific Ocean between June and July 2021. The GAM model was then used to examine the effects of both biotic （body length） and abiotic（Latitude, sea surface temperature, offshore distance, chlorophyll-a） factors on the stable nitrogen isotopes； The differences in the trophic niche among sex and body length groups were also analyzed in Japanese sardines in Northwest Pacific Ocean. The results showed that there was no significant difference in muscle δ¹³C and δ¹⁵N between males and females during La Niña years. However, both δ¹³C and δ¹⁵N differed among body length groups. The GAM model's results showed that as body length increases, both δ¹³C and δ¹⁵N exhibited a trend of first decreasing and then increasing； δ¹³C also exhibits this trend with increasing latitude； δ¹⁵N exhibits a negative correlation with both offshore distance and chlorophyll-a. The overlap rate between female and male niche is generally high, with a similar niche width between females and males ranging from 100 to 160 mm. The width of the ecological niche varied across the length groups, and its position changed with growth. However, compared to males, females have substantially broader niches, ranging from 161 to 220 mm. In contrast to usual years, the La Niña year's readings for δ¹³C and δ¹⁵N are all low. The study demonstrates that the feeding ecology of Japanese sardines in Northwest Pacific Ocean varies depending on sex and body length, and that changes in the marine environmental elements under La Niña events affected the feeding ecology of Japanese sardines.

Abstract:In order to understand the feeding habits of Ommastrephes bartramii and explore its position in the food web and ecological function, we analyzed the food composition of 15 Ommastrephes bartramii samples which were collected in the high sea of Northwest Pacific Ocean using high-throughput sequencing.The results showed that there were 646 980 high-quality sequences in 15 samples, a total of 624 operational taxonomic units （OTUs） were obtained through cluster analysis. A total of 65 food species, belonging to 6 phyla, 11 classes, 22 orders, 37 families and 51 genera, were detected by screening and comparison.Ommastrephes bartramii fed mainly on cephalopods, fishes, and a variety of zooplanktons （including Euphausiid, Ostracod, Medusae, etc.）. The dominant prey species included Sardinops sagax, Onychoteuthis borealijaponica, Gonatopsis borealis, Watasenia scintillans, Notoscopelus caudispinosus, etc. In conclusion, the feeding range of Ommastrephes bartramii was wide, and the food species were related to the natural preys in the sea area. Furthermore, Ommastrephes bartramii showed different feeding preferences among different mantle length groups. The analysis of the whole composition of stomach contents of Ommastrephes bartramii plays an important role in digging out the relationship between feeding and life history, such as growth, migration and reproduction. This provides a scientific basis for the sustainable development and conservation of Ommastrephes bartramii resources from the perspective of ecosystem.

Abstract:The Kuroshio-Oyashio confluence region of the Northwest Pacific Ocean is one of the most productive fishing areas, which is rich of fish resources. In order to understand the biodiversity of fish communities in the confluence region and to protect and exploit fishery resources properly,we used environmental DNA （eDNA） to analyze the fish diversity in the Kurishio-Oyashio confluence region during the summer. A total of 51 species of marine fishes （22 orders,30 families and 44 genera） were detected among 22 water sampling stations using high-throughput sequencing analysis. The Myctophidae family was the richest in species, comprising 33.33% of the detected fish species. In addition, the primary species with higher relative abundance were Stenobrachius nannochir, Gonostoma atlanticum, Notoscopelus japonicus, Sardinops melanostictus, Takifugu poecilonotus, Ceratoscopelus warmingii, Hexagrammos agrammus, Scomber japonicus, Nematalosa japonica and Diaphus kuroshio. The alpha diversity among stations was obviously different, and there were higher biodiversity in low-latitude sections than that of high-latitude sections. Redundancy analysis showed that the content of dissolved oxygen was the main environment factor impacting the fish species composition. The results indicated that eDNA can be a useful method for monitoring fish diversity and spatial distribution in the Kuroshio-Oyashio confluence region.

Abstract:Zooplankton is an important link between primary producers and lower trophic level organisms in the marine food web, and is an important biological basis for the formation of fishing grounds. Based on the zooplankton samples collected by the fishery resources survey vessel “Songhang” of Shanghai Ocean University during the comprehensive scientific survey of fishery resources in the high seas of the Northwest Pacific Ocean from June to August in 2021 and 2022, the zooplankton samples were analyzed in terms of their species composition, distributional characteristics, and their relationship with the environment. The results showed that a total of 174 zooplankton species were collected in the surveyed area over the two years, belonging to 10 groups. Copepoda and planktonic larvae were the most abundant zooplankton, with 95 and 22 species identified respectively, accounting for 54.6% and 12.6% of the total number of species, followed by Scyphozoa, with 18 species identified, and Ostracoda, Tunicata, Chaetognatha, Euphausiacea, and Gastropoda with 11, 9, 6, 4 and 3 species respectively. Additionally, two species each of Polychaeta, Amphipoda, and Cladocera were identified.The dominant genes （species） included seven categories：Clausocalanus sp., Oncaea sp., Paracalanus sp., Calocalanus sp., Oithona plumifera, Oithona decipiens and Metridinidae larvae. The species diversity and dominant genes （species） composition were similar in both years. The mean zooplankton abundance in 2021 was 732.89 ind./m³, lower than that in 2022 （1 418.88 ind./m³）.The Shannon-Wiener index in 2021 was 1.57-3.16, the Evenness index was 0.54-0.91, and the abundance index was 0.84-3.36. All three indices were higher than those in 2022, which ranged from 0.66 to 2.92, 0.26 to 0.94, and 0.77 to 3.11, respectively.GAM analyses showed that zooplankton abundance was significantly and negatively correlated with the sea-surface salinity and the water temperature in the 200 m layer,and the analyses suggested that the Kuroshio current and the Oyashio also had a certain effect on the temporal and spatial distributions of the abundance. The results of this study will provide basic information for the study of zooplankton in the high seas of the Northwest Pacific Ocean.

Abstract:Lanternfishes are the most abundant species of mesopelagic fish in the ocean, playing an important role in connecting the epipelagic and mesopelagic marine food webs. Due to their global distribution, diel vertical migration, and low trophic position, they may be highly susceptible to ingest microplastics. In this study, Notoscopelus resplendens and Symbolophorus californiensis from the Northwest Pacific Ocean were used to compare and analyze potential interspecific differences in the abundance and physicochemical characteristics of microplastics in their intestines. The results showed that both lanternfish species in Northwest Pacific Ocean exhibited a high detection rate of microplastic pollution. The abundance of microplastics in the intestine of S. californiensis and N. resplendens were （0.83 ±0.90） items/individual [（6.54 ±8.33） items/g] and （1.17 ±1.27） items/individual [（11.33 ±14.06） items/g], respectively. However, no significant difference was found in abundance and size of microplastics detected in S. californiensis and N. resplendens. The shape was primarily composed of fiber （accounting for ≥80.00%）. However, there were variations in the chemical composition of microplastics. Polyethylene terephthalate （PET） accounted for 36.00% and polyacrylamide （PAM） accounted for 24.00% of microplastics found in the intestines of S. californiensis, while cellophane （CP） constituted 54.29% and PET constituted 31.43% of MPs found in the intestines of N. resplendens. The microplastic pollution characteristics of lanternfish species may be influenced by accidental ingestion, nutrient transfer, and the water layers in their habitat. These findings contribute to a better understanding of the current status of microplastic pollution among lanternfish species in the same marine area, providing essential data for further exploration of the ecological effects of microplastics on mesopelagic fish in the ocean.

Abstract:In order to investigate the relationship between the surface distribution of fish larvae and juveniles and environmental factors in the Philippine Sea in summer, surface horizontal trawl surveys were conducted with large larvae and juvenile fish nets （diameter 1.3 m, mesh 0.5 mm） at 50 sampling stations in the Philippine Sea （11°N-19°N, 129°E-138°E） during the summer of 2022. A total of 38 159 fish larvae and juveniles, belonging to 14 orders, 21 families, and 56 species were collected. The dominant species in the daytime collection were Thunnus albacares and Encrasicholina punctifer, while the dominant species in the nighttime collection was Encrasicholina punctifer, so the co-dominant species was Encrasicholina punctifer, which accounted for 97.05% of the total number of samples collected. The total mean density of fish larvae and juveniles at each station was 292.43 ind./1 000 m³, with a mean density of 17.61 ind./1 000 m³ collected during the daytime and 526.54 ind./1 000 m³ collected during the nighttime, indicating significant differences in diel distribution. The stations with higher densities were mainly located in the sea near 15°N, and all sample were collected at night. Canonical correlation analysis showed that the environmental factors affecting the distribution of fish larvae and juveniles were, in descending order, sea surface salinity, sea surface temperature, and dissolved oxygen. The distribution of the dominant species Encrasicholina punctifer was mainly influenced by sea surface salinity and dissolved oxygen. The study shows that the fish larvae and juveniles in the Philippine Sea have a rich species composition with uneven surface distribution and significant differences in diel distribution. This study can provide a scientific basis for the assessment, conservation and utilization of fishery resources in the Philippine Sea.

Abstract:To compensate for the lack of sub-surface environmental data of the fishing ground, this experiment analyzed the vertical temperature and salinity structure at the fishing points using the gradient-dependent optimal interpolation and Argo profiles in the Kuroshio-Oyashio Confluence region.The reliability of the constructed results was verified by theoretical testing and comparison with in-situ observation. The results showed that the maximum root mean square errors of the temperature and salinity were less than 1 ℃ and 0.4 compared to Argo profiles. Furthermore, the absolute deviation of temperature and salinity from the "Songhang" survey data is less than 0.25 ℃ and 0.27, respectively.Analysis discussed the vertical temperature and salinity structure and the relationship with the squid CPUE.The results indicated the suitable temperatures for squid at the 5m were 16 ℃ and 14 ℃ in August and October 2018. And the suitable temperatures decreased to 9-12 ℃ at the depth of 50m.The statistical relationship between temperature and squid CPUE conforms to an exponential function under a certain curvature. Additionally, it was observed that there are significant thermoclines at the fishing points. The greater the variation in thermocline intensity, the greater the randomness of the squid CPUE. When the thermocline intensity at the fishing points is around 0.4 ℃/m, the squid CPUE is relatively stable. Regardless of the month, higher CPCEs are located in low-salinity areas.This study provides a new approach for establishing long-time-series and quasi-real-time environmental data of fishing ground. That will offer the necessary data support for deep research on fishery dynamic mechanisms.

Abstract:The Chub mackerel （Scomber japonicus） in Northwest Pacific Ocean holds significant economic value. It is important to better manage its resources by understanding its suitable habitat distribution. This study transformed acoustic data collected from the high seas fishery survey during the summer of 2021 into acoustic index suitable for habitat modeling. By integrating satellite remote sensing data on sea surface temperature （SST）, sea surface salinity （SSS）, sea surface height （SSH）, and chlorophyll a mass concentration （Chl. a）, this study analyzed the relationship between suitable habitat and marine environmental factors. The ranges of environmental factors corresponding to suitable habitat were analyzed. Habitat suitability index models were established using both arithmetic mean method and geometric mean method. Their performance was compared through 500 iterations of cross-validation, and the suitable habitat distribution map was developed. The results indicated that the suitable ranges for SST, SSS, SSH, and Chl. a were respectively 22.51-25.09 ℃, 34.09-34.65, 0.48-1.14 m, and 0.13-0.23 mg/m³. The model developed using the arithmetic mean method performed superiorly in terms of regression slope, R² and AIC, proving more appropriate for modeling suitable habitat for Chub mackerel. Suitable habitat was primarily concentrated south of 38°N, near the Kuroshio current.

Abstract:To investigate the energy storage capabilities of species in Northwest Pacific Ocean, this study utilized fish and squid as case study, and the samples were collected by "Songhang" distant water fishery research vessel. The technique of tissue energy density determination was applied to measure the energy density of soma tissue of fish and squid, and the mixed-effects models were used to analyze the effective relationships between soma tissue energy density and marine environmental variables. The results showed that the soma tissue energy density of fish was greater than that of squid, with tissue energy density measured at （23.50±2.80） kJ/g for fish and （19.67±1.16） kJ/g for squid. Among the fish, Ceratoscopelus townsendi had the highest soma tissue energy density, with a mean value of （28.75±0.96） kJ/g, while Hyperoglyphe japonicus had the lowest soma tissue energy density, at （20.37±1.04） kJ/g. Regarding the squids, the highest soma tissue energy density was found in Eucleoteuthis luminosa [（20.07±0.39） kJ/g], and the lowest density was in Onychoteuthis borealijaponicus [（18.42±0.22） kJ/g]. Both fish and squid in higher latitude areas exhibited higher energy density in their soma tissues, which was significantly correlated with the interaction of latitude×longitude. In addition, they had greater soma tissue energy density in areas where the sea surface height was 0 m, and showed an increase trend when the net primary production was larger than 12 mg/（m³·d）. However, their soma tissue energy density decreased with increasing sea surface temperature. This study indicates that there is latitudinal trend in the distribution of soma tissue energy density of fish and squid in Northwest Pacific Ocean, where the sea surface height, sea surface temperature and net primary production have significant effects on the energy accumulation per unit of soma tissue of fish and squid. The study puts forward our understanding of the environmental adaptability of marine species, and warrants future research on the marine ecosystem stability in Northwest Pacific Ocean.

Abstract:The meso/bathypelagic organisms in the ocean serve as a crucial link between the epipelagic and bathypelagic food webs, playing an indispensable role in upholding the stability of the structure and function of the ocean ecosystem. Research on microplastic pollution in the meso/bathypelagic zone is limited due to the challenges associated with sample collection. Longnose lancetfish Alepisaurus ferox possesses a unique digestive mechanism and serves as an effective biological accumulator. This study quantitatively analyzed the abundance and physicochemical characteristics of microplastics in meso/bathypelagic species preserved within the stomachs of longnose lancetfish using laser infrared imaging spectroscopy. A total of 146 microplastics were found in the intestines of 7 species of meso/bathypelagic fish and cephalopods, with a detection rate of 85.71%. The average abundance was （10.43±12.12） items/individual, while the size ranged from 20.34 to 309.89 μm with an average size of （47.36±43.41） μm. The majority of microplastics were granules （59.58%） or fragments （36.30%）, with acrylic copolymer being the predominant polymer composition at 60.27%. This study demonstrates the feasibility of using longnose lancetfish as a biological sampler to investigate microplastic pollution in the meso/bathypelagic organisms for the first time. The results of this study are highly significant for analyzing microplastic pollution and its potential ecological risks in ocean ecosystems.

Abstract:In order to understand the active mesoscale processes in the Kuroshio extension （KE） region, and reveal the three-dimensional structure of mesoscale eddies in this region, as well as the contributions of mesoscale eddies to water mass redistribution and ocean-atmosphere interactions, based on shipboard observations and satellite remote sensing data, this study investigates the three-dimensional structural characteristics of a typical eddy dipole composed of cyclonic eddy （CE） and an anticyclonic eddy （AE） distributed on the north and south sides of the KE axis, respectively, during June-July 2022. Results show that the CE has a southward cross-frontal motion dominated by shear forcing, while the AE remains relatively stable. The "cold tongue" structure of the CE gradually diminishes due to sea surface warming and heat diffusion from the KE axis, with the AE exhibiting a "reverse eddy sea surface temperature anomaly" structure due to the entrainment of cold water carried by the CE. The vertical multi-cores of internal temperature and salinity anomalies in the eddy dipole are related to the vertical redistribution of water masses with different characteristics. The AE's internal flow field is strongly baroclinic, with around 50% of it having a Richardson number less than the critical value of 0.25, indicating a tendency for turbulent mixing. The upper layer of the CE is barotropic, hindering substantial diapycnal mixing. This study helps to enhance understanding of the eddy dipole characteristics and internal structure of eddies in the KE region, providing information for further research on eddy dynamics.

Abstract:To comprehensively examine the hook depth distribution and influencing factors of tuna longline fishing in Western and Central Pacific Ocean, data collected aboard the vessel "Songhang" from August to October 2021 were analyzed. A combination of Support Vector Regression （SVR） and Generalized Additive Model （GAM） was employed to investigat the distribution of hook depths across different operational parameters and environmental variables. The objective was to elucidate the impact of each factor on hook depth. The results showed that： （1） Among the calculated values of hook depth, Hook No.1 had the smallest value at （130.03±3.32） m, while Hook No.8 had the largest value at （363.25±36.52） m. Regarding the measured values, Hook No.1 had the smallest depth at （130.81±17.94） m, whereas Hook No.7 exhibited the largest depth at （329.91±54.37） m. （2） The SVR model exhibited varying goodness of fit, with Hook No.1 displaying the lowest （R²=0.38） and Hook No.6 demonstrating the highest （R²=0.77） overall fit. The mean squared error （MSE） for training data was smallest for Hook No.6 （0.138） and largest for Hook No.8 （0.309）, while for testing data, it was smallest for Hook No.4 （0.086） and largest for Hook No.5 （0.282）. （3） GAM analysis reveals that water layer average velocities at 0-64 m and 128-192 m, as well as the casting speed, exhibit the highest correlations with hook depth across all hooks. Following these, water layer average velocities at 64-128 m, 192-256 m, and 256-320 m, along with vessel speed, show significant correlations. However, water layer average velocity at 320-384 m and wind speed demonstrate no significant correlations with hook depth. （4） The average differences between predicted hook depths by SVR and GAM models and the actual measured values are 1.75% and 6.38%, respectively. The predictions from the SVR model align well with the measured values, showing consistent trends with the variation in hook positions, thus demonstrating good agreement. The results of this study will contribute to understanding the distribution pattern of tuna longline fishing hooks in operation, and provide a basic reference for optimizing the performance of longline.

Abstract:This study aimed to develop a multi-objective distant-water fisheries survey scheme that balances survey cost and effectiveness. Based on the survey data from 2021 to 2023 in Northwest Pacific Ocean, the relative abundance distribution of Scomber australasicus, Scomber japonicus, Sardinops melanostictus was simulated using Kriging interpolation, and assume relative resource as their ‘true' values. The effectiveness of the Simple random sampling （Design 1）, Systematic sampling （Design 2）, Stratified random sampling based on stratum area size allocation method （Design 3）, and Stratified random sampling based on fishery resource biomass allocation method （Design 4） was assessed through computer simulation. Two indicators, Relative estimation error （REE） and Relative bias （RB） were used to evaluate the accuracy of the assessment effects, and the number of sampling stations was selected using the Accuracy change rate （ACR）. The results showed that the estimation accuracy of the four sampling designs were different. In general, Design 4 had the highest accuracy, followed by Design 3, Design 2 and Design 1. The REE values of target species abundance index estimation of Design2 fluctuated with the increasing number of sampling stations. Design 4 exhibited higher accuracy in estimating the abundance index of S. japonicus, S. melanostictus and the total fishery resources. However, Design 4 demonstrated an overestimation in estimating the abundance index of Chub mackerel. Using Design 4 for simulated sampling, and considering all objectives, the optimal number of sampling stations could be set at 28. In conclusion, the Stratified sampling method （Design 4） can be prioritized as the survey station design approach for the Northwest Pacific Ocean fishery resource survey.

Abstract:Cephalopods are widely distributed in the world's oceans and are among the most important species in the marine ecosystem due to their short life cycle, fast growth rate and extremely rich biomass. Like other marine organisms, cephalopods are at risk of being infected by parasites, often acting as either intermediate or final hosts for different species of parasites. Due to the unique life cycle of parasites, their life cycle can run through the entire or partial life cycle of the host, greatly affecting the growth and survival of cephalopods. Currently, research on parasites in cephalopods mainly focuses on species composition, life history, infection status, and other aspects. This article summarizes the current research status of parasitic infections in cephalopod marine animals.The results show that the main parasites infecting cephalopods are Dicyemida, Cestoda and Nematoda. Dicyemida parasitize cephalopods characteristically, with maturation and reproduction taking place exclusively in the kidneys of cephalopods. Available statistics show that there are 149 species of Dicyemida infecting cephalopods, mainly found within the Sea of Japan, with fewer species found at lower latitudes. Cephalopods, as intermediate hosts, are also susceptible to infection by Cestoda larvae and have a high infection rate. Cestoda mainly parasitize the digestive tract of cephalopods. Due to the large size, stretching, and mobility of Cestoda larvae, they are prone to cause mechanical damage to the host. Nematodes are another common parasites infecting cephalopods, and are primarily ingested as third-stage larvae of Nematodes, which mostly parasitize the stomach and cecum. Nematodes are among the most abundant and common species of cephalopod parasitic infections, and can have significant pathological effects on the host. Other types of parasites can also affect the physiological characteristics of cephalopods to a certain extent. Research on parasites in cephalopods is still in its early stages. Therefore, future research should focus on accelerating the establishment of an open database of parasites in cephalopods, expanding and sharing information on parasite species. It is also important to deeply explore the life processes of parasitic species in cephalopods to further understand their impact on host growth.Additionally, using parasites in cephalopods to divide population composition can provide new ideas for the sustainable development and utilization of cephalopod fisheries.