Preliminary analysis of the Jimo coastal ecosystem with the ecopath model

The Jimo coast encompasses an area of 2157 km~2, and the ecosystem is valuable both socially and economically with regional fisheries substantially contributing to the value. A mass-balanced trophic model consisting of 15 functional ecological groups was developed for the coastal ecosystem using the Ecopath model in Ecopath with Ecosim(Ew E) software(version 6.4.3). The results of the model simulations indicated that the trophic levels of the functional groups varied between 1.0 and 3.76, and the total production of the system was estimated to be 5112.733 t km~(-2) yr~(-1) with a total energy transfer efficiency of 17.6%. The proportion of the total flow originating from detritus was estimated to be 48%, whereas that from primary producers was 52%, indicating that the grazing food chain dominated the energy flow. The ratio of total primary productivity to total respiration in the system was 3.78, and the connectivity index was 0.4. The fin cycling index and the mean path length of the energy flow were 4.92% and 2.57%, respectively, which indicated that the ecosystem exhibits relatively low maturity and stability. The mixed trophic impact(MTI) procedure suggested that the ecological groups at lower trophic levels dominated the feeding dynamics in the Jimo coastal ecosystem. Overfishing is thought to be the primary reason for the degeneration of the Jimo coastal ecosystem, resulting in a decline in the abundance of pelagic and demersal fish species and a subsequent shift to the predominance of lower-trophic-level functional groups. Finally, we offered some recommendations for improving current fishery management practices.     

南海区域渔船活动时空特征分析

近年来海洋资源的不断开发利用,使得海洋空间规划变得尤为重要,其中以渔业资源占主要比重。为了对渔业资源监测与规划提供辅助决策信息,本文通过对南海及周边国家2018年船舶自动识别系统（AIS）数据进行预处理,采用数理统计和GIS空间分析方法,实现了南海区域渔船活动强度时空特征分析。结果显示： ① 2018年南海及周边国家渔船以区域性分布为主,集中在中国和越南沿海岸100 km以内区域,在秋季11月捕捞活动频繁,全年渔船平均活动强度白天大于夜晚,16:00 PM 时达到最大渔船活动强度; ② 中国在广东省、广西省和海南省各主要港口渔船活动强度呈现聚集性点状分布,渔船活动强度多大于100,部分港口附近海域呈条带状分布,西沙群岛相较南海其他群岛渔船活动强度较大,除越南外其他周边国家靠近南海附近海域部分海湾和港口有聚集式分布,渔船活动强度都小于2; ③ 越南渔船区域性分布明显,在胡志明港口呈现稳定的块状聚集性分布,且一年四季活动强度变化趋势不大,近岸渔船活动强度保持在50~100,越南渔船在中国南海禁渔线内靠近海南省西南部有两处活动较强的块状分布区域,2018年全年在此区域活动频率占采样天数的87.71%,且平均每小时有7~10艘渔船在该海域活动,休渔期内平均每小时渔船数量大于5,给中国南海海域渔业资源造成巨大威胁。本文通过AIS数据研究分析渔船活动可为海洋空间规划与政府相关部门提供数据支撑。     

Coupling of an individual-based model of anchovy with lower trophic level and hydrodynamic models

Anchovy (Engraulis japonicus), a small pelagic fish and food of other economic fishes, is a key species in the Yellow Sea ecosystem. Understanding the mechanisms of its recruitment and biomass variation is important for the prediction and management of fishery resources. Coupled with a hydrodynamic model (POM) and a lower trophic level ecosystem model (NEMURO), an individual-based model of anchovy is developed to study the influence of physical environment on anchovy’s biomass variation. Seasonal variations of circulation, water temperature and mix-layer depth from POM are used as external forcing for NEMURO and the anchovy model. Biomasses of large zooplankton and predatory zooplankton which anchovy feeds on are output from NEMURO and are controlled by the consumption of anchovy on them. Survival fitness theory related to temperature and food is used to determine the swimming action of anchovy in the model. The simulation results agree well with observations and elucidate the influence of temperature in over-wintering migration and food in feeding migration.     

Tidal current observation in the southern Yellow Sea in the summers of 2001 and 2003

Direct current observations in the Yellow Sea interior are very scarce due to intense fishing and trawling activities. Most previous studies on tides in the area were based on coastal measurements or satellite altimeter sea levels and have not been rigorously compared with direct measurements. In this paper, tidal currents are studied with current profiles from three bottom-moored Sontek Acoustic Doppler Profilers （ADPs） deployed in the southern Yellow Sea in summer of 2001 and 2003. The measured current series were dominated by tidal currents. Maximum velocities are between 40-80 cm/s at the mooring stations. M2 current is the most dominant primary tidal constituent, while MS4 and M4 are the most significant shallow water tides with much smaller amplitudes than the primary tides.     

Observation of Currents in the Southern Yellow Sea in the Summers of 2001 and 2003

Long term current observations in the southern Yellow Sea are very scarce because of the intense fishing and trawling activities. Most of the previous studies on tides and circulation were not rigorously validated with direct current measurements. In this study, tidal and sub-tidal currents were examined using current profiles from three bottom-moored Sontek Acoustic Doppler Profilers （ADPs） deployed in the southern Yellow Sea in the summers of 2001 and 2003. The measured current time series were dominated by tidal currents. The maximum velocities were between 40-80 cm s^-1 at the mooring stations. The M2 current was the dominant primary tidal constituent, while the MS4 and M4 components produced the most significant shallow water tidal currents with much weaker amplitudes. The measured mean sub-tidal velocities were less than 5 cmsl. The mean flows in the lower layer implied that an anti-cyclonic circulation pattern might exist in the deeper central Yellow Sea. However, the previously expected cyclonic circulation pattern in the upper layer was not clearly shown by the observations.     

Natural mortality estimation and rational exploitation of purpleback flying squid Sthenoteuthis oualaniensis in the southern South China Sea

Based on the biological data of purpleback flying squid(Sthenoteuthis oualaniensis)collected by light falling-net in the southern South China Sea(SCS) during September to October 2012 and March to April 2013,growth and mortality of 'Medium' and 'Dwarf' forms of squid are derived using the Powell-Wetherall,ELEFAN methods and length-converted catch curves(FiSAT package).Given a lack of commercial exploitation,we assume total mortality to be due entirely to natural mortality.We estimate these squid have fast growth,with growth coefficients(k) ranging from 1.42 to 2.39,and high natural mortality(M),with estimates ranging from 1.61 to 2.92.To sustainably exploit these squid stocks,yield per recruitment based on growth and natural mortality was determined using the Beverton-Holt dynamic pool model.We demonstrate squid stocks could sustain high fishing mortality and low ages at first capture,with an optimal fishing mortality 3.0,with the optimal age at first capture increased to 0.4-0.6 years when fishing mortality approached optimal levels.On the basis of our analyses and estimates of stock biomass,we believe considerable potential exists to expand the squid fishery into the open SCS,relieving fishing pressure on coastal waters.     

Influence of the Physical Environment on the Migration and Distribution of Nibea albiflora in the Yellow Sea

This study investigates the migration and distribution of the warm-temperate fish Nibea albiflora. Their spawning migration and wintering migratory routes within in the Yellow Sea are described in detail. Considering the main physical features and environment of the Yellow Sea, it appears to be have one wintering ground and three migratory routes from the wintering ground to the spawning grounds. The fish begin to migrate from the wintering ground to the spawning grounds in the northwest region of the Yellow Sea in late March. The Yellow Sea has three spawning grounds. The first is located near the Yalu River on the Liaodong Peninsula and the second one is located in Rushan Bay of Shandong Peninsula. The third spawning ground is located in Haizhou Bay in the southern region of the Yellow Sea. This study found that the temperature of the Yellow Sea influences the migration of N. albiflora, and that the migratory routes coincide with the thermal fronts in the sea. Nutrients for juvenile fish are taken from the coastal upwelling area. Chlorophyll is a good environmental indicator of phytoplankton biomass and thereby provides the status of biological resources. Different types of sediment in near-shore zones are also of practical significance for the growth of fish. The study of the effects of marine environments on the migration of various fishes is not only significant to the fishing industry, but can also provide a scientific basis for the understanding of the ecological implications of the relevant physical processes.     

Influence of the physical environment on the migration and distribution of <Emphasis Type="Italic">Nibea albiflora</Emphasis> in the Yellow Sea

This study investigates the migration and distribution of the warm-temperate fish Nibea albiflora. Their spawning migration and wintering migratory routes within in the Yellow Sea are described in detail. Considering the main physical features and environment of the Yellow Sea, it appears to be have one wintering ground and three migratory routes from the wintering ground to the spawning grounds. The fish begin to migrate from the wintering ground to the spawning grounds in the northwest region of the Yellow Sea in late March. The Yellow Sea has three spawning grounds. The first is located near the Yalu River on the Liaodong Peninsula and the second one is located in Rushan Bay of Shandong Peninsula. The third spawning ground is located in Haizhou Bay in the southern region of the Yellow Sea. This study found that the temperature of the Yellow Sea influences the migration of N. albiflora, and that the migratory routes coincide with the thermal fronts in the sea. Nutrients for juvenile fish are taken from the coastal upwelling area. Chlorophyll is a good environmental indicator of phytoplankton biomass and thereby provides the status of biological resources. Different types of sediment in near-shore zones are also of practical significance for the growth of fish. The study of the effects of marine environments on the migration of various fishes is not only significant to the fishing industry, but can also provide a scientific basis for the understanding of the ecological implications of the relevant physical processes.     

Current status of small yellow croaker resources in the southern Yellow Sea and the East China Sea

We used data from bottom trawl surveys to study the factors influencing the abundance of small yellow croaker, Larimichthys polyactis, in the southern Yellow Sea (SYS) and the East China Sea (ECS). The resource density index (RDI) was generally higher in summer and autumn than in spring and winter. RDIs were also significantly greater in the SYS than in the ECS in summer and autumn. The bottom water salinity and depth of spatial distribution of small yellow croaker was similar between the two areas in summer, but different in other seasons. Regression analysis suggested that environmental factors such as bottom water temperature, salinity, and depth influenced the RDIs in summer in these areas. Growth condition factor (GCF) in the two areas varied monthly and the croaker in the SYS grew more slowly than those in the ECS. This was likely due to the low bottom temperature of the Yellow Sea Cold Water Mass in summer and autumn or to higher human fishing pressure in the ECS. To ensure sustainable utilization of the croaker stocks in these regions, we recommend reducing the fishing intensity, increasing the cod-end mesh size, and improving the protection of juveniles.     

Age,growth,and mortality rate of the yellow goosefish Lophius litulon(Jordan,1902) in the Yellow Sea

With the decline in the most fisheries resources in the Yellow Sea,the yellow goosefish Lophius litulon has increased in commercial and ecological importance in recent years.We studied the length distribution,length-weight relationship,age composition,growth pattern,mortality,and exploitation rates of the yellow goosefish in the Yellow Sea.Total length(TL) of females and males ranged from 173 to582 mm and 178 to 500 mm,respectively.The length-weight relationships were also estimated for females and males.Age classes from 2 to 4 years predominated in the samples.The von Bertalanffy growth function(VB GF),estimated based on non-linear least-squares methodology,showed significant differences between sexes.Females attained a greater estimated asymptotic total length(765 mm TL) compared to males(579 mm TL).The VBGF did not differ significantly between stocks of the northern Yellow Sea and the southern Yellow Sea.Estimated natural instantaneous mortality rate(M) ranged from 0.25/a to 0.33/abased on four age-and length-based methods.Total instantaneous mortality rate(Z) of total samples calculated by the age-based catch curve method was 0.591/a and the average fishing mortality(F) was 0.30/a.Estimated exploitation rate(E) was approximately 0.5,indicating that the population of L.litulon in the Yellow Sea may be sustainable.These results provide a reference for the present status of L.litulon and information for the management.     

Estimating the budgets of nutrients for phytoplankton bloom in the central Yellow Sea using a modified lower tropic ecosystem model

A modified lower trophic ecosystem model (NEMURO) is coupled with a three-dimensional hydrodynamic model for an application in the central Yellow Sea. The model is used to simulate the horizontal distributions and annual cycles of chlorophyll-a and nutrients with results consistent with historical observations. Generally, during the winter background and spring bloom periods, the exchange with neighboring waters constitutes the primary sources of nutrients. Howerver, during the winter background period, the input of silicate from the layer deeper than 50 m is the most important source that contributes up to 60% to the total sources. During the spring bloom period, the transport across the thermocline makes significant contribution to the input of phosphate and silicate. During the post spring bloom period, the relative contribution of relevant processes varies for different nutrients. For ammonium, atmospheric deposition, excretion of zooplankton and decomposition of particulate and dissolved nitrogen make similar contributions. For phosphate and silicate, the dominant input is the transport across the thermocline, accounting for 62% and 68% of the total sources, respectively. The N/P ratio averaged annually and over the whole southern Yellow Sea is up to 51.8, indicating the potential of P limitation in this region. The important influence of large scale sea water circulation is revealed by both the estimated fluxes and the corresponding N/P ratio of nutrients across a section linking the northeastern bank of the Changjiang River and Cheju Island. During the winter background period, the input of nitrate, ammonium, phosphate and silicate by the Yellow Sea Warm Current is estimated to be 4.6×10¹⁰, 2.3×10¹⁰, 2.0×10⁹ and 1.2×10¹⁰ mol, respectively.     

浅谈南海渔业管理对策

南海渔业资源衰退的主要原因是捕捞过度和海洋生态环境破坏。由于海洋生态过程是动力学过程,很多生态因素的变化会相应引起生态过程的变化,同时生态动力学过程的因素又是多方面的,因此南海渔业资源的管理和生产方式应该从过去的开发型管理向着管理型管理方向转变。这种管理方式涉及面较广,必须实施从渔业资源管理、渔业水域管理、渔业水域周围环境管理到加强对渔船与船员管理、捕养并重、健全法制、强化治政队伍与执法力量配置以及开展国际渔业合作等管理措施。     

Distribution and migration of the common squidTodarodes pacificus in the Yellow Sea

Study of the distribution and migration of the common squid,Todarodes pacificus Steenstrup,basedon the index of important fishing ground(P) and fisheries statistics on the Yellow Sea and northern EastChina Sea during 1980—1991 showed that:1.Its catch in the fishing period(June to November) is 91.77% of the annual yield.The fishingground distributes over the northem and middle Yel1ow Sea and adjacent area of the Changjiang Estuary.2. It over-winters in the northem East China Sea and waters adjacent to Goto Island from De-cember to February and spawns in waters near Haijiao Is1and and west of Kyushu. The main stock mi-grates along 123°30′E to the ChangJiang Estuary, Haizhou Bay. offsea from Shidao to Qingdao,mideastern Yellow Sea, and offsea Weihai and Haiyang Island succesively for feeding after April. The sur-plus stock migrates again to the wintering ground in December.3.The favorable feeding temperature is 6-23℃(optimum of l3-20℃ in the Changjiang Estua-ry and 7-13℃ in the northern and middle Yel     

Microbial ecological associations in the surface sediments of Bohai Strait

Microbial communities play key roles in the marine ecosystem. Despite a few studies on marine microbial communities in deep straits, ecological associations among microbial communities in the sediments of shallow straits have not been fully investigated. The Bohai Strait in northern China(average depth less than 20 m) separates the Bohai Sea from the Yellow Sea and has organic-rich sediments. In this study, in the summer of 2014, six stations across the strait were selected to explore the taxonomic composition of microbial communities and their ecological associations. The four most abundant classes were Gammaproteobacteria, Deltaproteobacteria, Bacilli and Flavobacteriia. Temperature, total carbon, depth, nitrate, fishery breeding and cold water masses influenced the microbial communities, as suggested by representational dif ference and composition analyses. Network analysis of microbial associations revealed that key families included Flavobacteriaceae, Pirellulaceae and Piscirickettsiaceae. Our findings suggest that the families with high phylogenetic diversity are key populations in the microbial association network that ensure the stability of microbial ecosystems. Our study contributes to a better understanding of microbial ecology in complex hydrological environments.     

基于渔船AIS数据的南海北部海洋渔业捕捞强度空间特征挖掘

高精度渔业捕捞强度数据是开展捕捞限额管理的前提与关键,也是海洋渔业资源可持续发展的重要保障。因此,本文以挖掘海洋渔业捕捞强度空间特征为出发点,选用2018年2、4、9和11月典型季节的中国籍6364艘渔船1.8亿条高时空粒度AIS数据。运用专家知识经验、空间统计及数据挖掘分析方法,以广西南岸北部湾渔场、广东沿岸和环海南岛周边海域为研究区域,对渔业捕捞强度空间特征展开了细致的挖掘与分析。结果表明：① 广东、广西两省（以下简称“两广”）沿岸海域渔业高强度捕捞主要呈现“团块”向外扩张汇聚成“条带”或“更大团块”的特征,而环海南岛周边主要呈现“团块状”特征;② 受渔业从业人员、渔业作业船舶数量、海洋渔场及海域环境影响,“两广”沿岸近海海域捕捞强度明显高于环海南岛周边海域; ③ 高强度捕捞区域主要集中于近岸30~50 km范围内,且近海捕捞强度高于远海区域,归因于研究区内中小型作业渔船占比较高,达50.9%;④ 渔业捕捞活动受农历传统春节及休渔期等政策因素的影响,春节期间的渔业捕捞强度是所选数据覆盖时间范围中最低的,并且休渔期后（9月）渔业捕捞强度明显高于休渔期前（4月）;⑤ 研究区海岸附近的大型渔港对近岸海域的高强度捕捞具有一定的辐射带动效应。本研究通过对高时空粒度的AIS数据进行处理、分析及深度挖掘,可为近岸海洋渔业捕捞强度探析提供重要数据支撑,服务于海洋渔业可持续发展。     

Biomarker evidence for paleoenvironmental changes in the southern Yellow Sea over the last 8200 years

Previous studies have indicated that the Yellow Sea underwent significant environmental changes during the Holocene, but many questions remain concerning the timing of the establishment of the modern circulation system, which would have major implications for the Yellow Sea ecosystem and carbon cycle. In this study, marine and terrestrial biomarkers were analyzed in Core YE-2 from a muddy area in the southern Yellow Sea to reconstruct Holocene environmental and phytoplankton community change. The content of three individual marine phytoplankton biomarkers (alkenones, brassicasterol and dinosterol) all display a similar trend, and their total contents during the early Holocene (362 ng/g) were lower than those during the mid-late Holocene (991 ng/g). On the other hand, the contents of terrestrial biomarkers (C27+C29+C31n-alkanes) during the early Holocene (1 661 ng/g) were about three times higher than those during the mid-late Holocene (499 ng/g). Our biomarker results suggest that the modern circulation system of the Yellow Sea was established by 5-6 ka, and resulted in higher marine productivity and lower terrestrial organic matter inputs. Biomarker ratios were used to estimate shifts in phytoplankton community structure in response to mid-Holocene (5-6 ka) environmental changes in the Yellow Sea, revealing a transition from a dinoflagellate-diatom dominant community structure during the early Holocene to a coccolithophore-dominant community structure during the mid-late Holocene.     

基于AIS的海上渔船捕捞活动聚集区提取方法研究

船舶自动识别系统(Automatic Identification System, AIS)不仅是海上交通监管的有效工具,也为研究海上交通运输及其相关产业活动特征提供了一种良好的数据源。基于海上渔船AIS数据,本研究利用高斯混合模型(Gaussian Mixed Model,GMM)识别渔船捕捞活动状态,提出一种将核密度估计(Kernel Density Estimation,KDE)与热点分析(Hot Spot Analysis, HSA)相融合用于渔船捕捞活动聚集区提取的方法。结果显示：与单一KDE或HSA方法相比,二者相融合的方法将KDE的距离衰减效应与HSA统计指数相结合,在渔船捕捞活动聚集区提取中的应用效果较好、效率较高;采用该融合方法,基于2018年9—12月AIS数据,实现对渤海海峡周边海域渔船捕捞活动聚集区的提取,发现不同月份,渔船捕捞活动聚集区的分布范围和空间形态特征具有一定差异性,烟威近岸海域和渤海海峡是主要的捕捞活动聚集区,其结果可为该海域捕捞活动管理和海洋生态保护提供技术方法和决策支持。     

Uncertainties in Stock Assessment and the Precautionary Management Suggestions for the Anchovy （Engraulisjaponicus） Stock in the Yellow Sea

Anchovy(Engraulis japonicus) is an abundant fish species in the Yellow Sea,and its natural stock is decreasing rapidly in recent years. Based on the stock-recruitment(SR) data from 1987 to 2002 published in Zhao et al.(2003),the criterion BIC(Bayesian Information Criterion) is applied to selecting a suitable model from six normal and lognormal error structured SR statisti-cal models,the age-structured model is used to calculate the biological reference points(BRPs),and the precision of the SR parame-ters and BRPs are calculated using bootstrap method. The results indicate that the anchovy fishery resource in the Yellow Sea is in an over-fished state. The precaution management principle requires that the fishery should be closed immediately.     

Importance of kelp-derived organic carbon to the scallop <Emphasis Type="Italic">Chlamys farreri</Emphasis> in an integrated multi-trophic aquaculture system

Bivalves and seaweeds are important cleaners that are widely used in integrated multi-trophic aquaculture (IMTA) systems. A beneficial relationship between seaweed and bivalve in the seaweed-based IMTA system has been confirmed, but the trophic importance of seaweed-derived particulate organic materials to the co-cultured bivalve is still unclear. We evaluated the trophic importance of the kelp Saccharina japonica to the co-cultured scallop Chlamys farreri in a typical IMTA farm in Sungo Bay (Weihai, North China). The dynamics of detritus carbon in the water were monitored during the culturing period. The proportion of kelp-derived organic matter in the diet of the co-cultured scallop was assessed via the stable carbon isotope method. Results showed that the detritus carbon in the water ranged from 75.52 to 265.19 μg/L, which was 25.6% to 73.8% of total particulate organic carbon (TPOC) during the study period. The amount of detritus carbon and its proportion in the TPOC changed throughout the culture cycle of the kelp. Stable carbon isotope analysis showed that the cultured scallop obtained 14.1% to 42.8% of its tissue carbon from the kelp, and that the percentages were closely correlated with the proportion of detritus carbon in the water (F =0.993, P= 0.003). Evaluation showed that for 17 000 tons (wet weight) of annual scallop production, the kelp contributed about 139.3 tons of carbon (535.8 tons of dry mass). This confirms that cultured kelp plays a similar trophic role in IMTA systems as it does in a natural kelp bed. It is a major contributor to the detritus pool and supplies a vital food source to filter-feeding scallops in the IMTA system, especially during winter and early spring when phytoplankton are scarce.     

Monthly variation in the fat content of anchovy (Engraulis japonicus) in the Yellow Sea: implications for acoustic abundance estimation

Anchovy is a key species in the Yellow Sea ecosystem. An accurate estimate of anchovy abundance is vital for the management of the anchovy stock and measurement of the ecosystem response to changes in anchovy abundance. However, the acoustic fish abundance estimate may be biased by 30%?C40% if the fat-content induced target strength variation is not taken into account. We measured the monthly variation in the fat content of anchovy (Engraulis japonicus) in the Yellow Sea, and evaluated the potential effect of variation in fat content on the acoustic assessment of anchovy abundance. The fat content of anchovy varied seasonally, with two maxima and two minima in a year. The highest fat content (14.75%) was measured in the pre-spawning period in May, and the lowest fat content (2.48%) was measured during the post-spawning period in October. Fat content appeared to correlate with water content, but not body size. Assuming that the target strength is decreased by 0.2dB for every 1% increase in fat content, the seasonal difference in the target strength of anchovy may be as high as 2.45 dB. Given this, the acoustic abundance estimate may be biased by between 43% and 76%. Our results highlight the need for more information on the changes in fat content of fishes whose abundance is estimated by acoustic surveys.