The influence of lipid-extraction on theδ^(13)C of mesopelagic and demersal fish in the South China Sea:modification and application of lipid normalization models

Mesopelagic fish,the most important daily vertically migrating community in the oceans,are characterized by high lipid content which may obscure the interpretation of stable isotopes analysis.Demersal fish,which are important consumers in the food web dominated by mesopelagic fish,also have a high lipid content.Here we collected 127 fish samples from the South China Sea and evaluated the effect of lipid contents on△δ^(13)C of mesopelagic and demersal fish.In lipid-extracted mesopelagic fish,the C/N content ratio(<5.5)shows a clear correlation withΔδ^(13)C(the offset of bulk and lipid-extractedδ^(13)C values),especially in non-migratory and semi-migratory species;these values were less correlation in demersal fish.Based on our results,we suggest that mesopelagic and demersal fish in different regions of the South China Sea should be studied separately using appropriate correction models and less fit for the traditional model.Moreover,the C/N content ratio should be used cautiously for establishing the lipid normalization model,especially for the fish in migratory mesopelagic fish and demersal fish.Our results also reveal that mesopelagic fish across nearby regions could be analyzed together.The new models described here can be applied in future studies of mesopelagic and demersal fish in the South China Sea.

Roles of fishing and climate change in long-term fish species succession and population dynamics in the outer Beibu Gulf,South China Sea

A prevailing,controversial hypothesis is that fishing pressure has played a greater role than climatic and environmental drivers,in changing fish species succession and biomass fluctuation in the South China Sea(SCS).Based on otter trawl survey data from 1959 to 2010 in the outer Beibu Gulf(OBG),northern SCS,large seasonal and interannual variation is reported for fish species composition,the proportional abundances of dominant taxa,and fish biomass.Generalized additive models are developed to quantify relationships between fish biomass and the external factors of fishing pressure and climate change.Fishing pressure proved to be the main driver of sharp declines in demersal fish stocks,with high-value species being replaced by low-value ones over time.Abrupt decreases in fish biomass during the years of 1993 and 1998 correspond to El Nino events,with climate change possibly the main driver of proportional representation of pelagic species in fisheries trawl catch.The need to differentiate impacts of fishing and environmental drivers on fish species with different life history strategies is stressed to better understand fish community dynamics.

Measurement of single-fish target strength in the South China Sea

We measured the target strength (TS) of three commercial fish species: whitespotted spinefoot (Siganus canaliculatus), black porgy (Acanthopagrus schlegelii), and creek red bream (Lutjanus argentimaculatus), in the South China Sea. The TS of caged or tethered fish (n=76 total) was measured using a Simrad EY60 portable scientific echosounder at 120 kHz. We evaluated the relationship between TS and total length (TL, cm) for the three species. This is the first attempt to use split-beam acoustics to measure single-fish TS in the South China Sea by Chinese researchers. Our results will improve the accuracy and precision of acoustic abundance estimates of commercially important species and further the development of underwater acoustic survey techniques in fisheries in the South China Sea.

Population parameters and dynamic pool models of commercial fishes in the Beibu Gulf, northern South China Sea

Length-frequency data of eight commercial fish species in the Beibu Gulf (Golf of Tonkin), northern South China Sea, were collected during 2006-2007. Length-weight relationships and growth and mortality parameters were analyzed using FiSAT II software. Five species had isometric growth, two species had negative allometric growth, and one species had positive allometric growth. Overall, the exploitation rates of the eight species were lower in 2006-2007 than in 1997-1999: for four species (Saurida tumbil, Saurida undosquamis, Argyrosomus macrocephalus, and Nemipterus virgatus) it was lower in 2006-2007 than in 1997-1999, for two species (Parargyrops edita and Trichiurus haumela) it remained the same, and for the other two species (Trachurus japonicus and Decapterus maruadsi) it was higher in 2006-2007 than in 1997-1999. The exploitation rates might have declined because of the decline in fishing intensity caused by high crude oil prices. The optimum exploitation rate, estimated using Beverton-Holt dynamic pool models, indicated that although fishes in the Beibu Gulf could sustain high exploitation rates, the under-size fishes at first capture resulted in low yields. To increase the yield per recruitment, it is more effective to increase the size at first capture than to control fishing effort.

A New model to forecast fishing ground of Scomber japonicus in the Yellow Sea and East China Sea

The pelagic species is closely related to the marine environmental factors, and establishment of forecasting model of fishing ground with high accuracy is an important content for pelagic fishery. The chub mackerel（Scomber japonicus） in the Yellow Sea and East China Sea is an important fishing target for Chinese lighting purse seine fishery. Based on the fishery data from China＇s mainland large-type lighting purse seine fishery for chub mackerel during the period of 2003 to 2010 and the environmental data including sea surface temperature（SST）, gradient of the sea surface temperature（GSST）, sea surface height（SSH） and geostrophic velocity（GV）, we attempt to establish one new forecasting model of fishing ground based on boosted regression trees. In this study, the fishing areas with fishing effort is considered as one fishing ground, and the areas with no fishing ground are randomly selected from a background field, in which the fishing areas have no records in the logbooks. The performance of the forecasting model of fishing ground is evaluated with the testing data from the actual fishing data in 2011. The results show that the forecasting model of fishing ground has a high prediction performance, and the area under receiver operating curve（AUC） attains 0.897. The predicted fishing grounds are coincided with the actual fishing locations in 2011, and the movement route is also the same as the shift of fishing vessels, which indicates that this forecasting model based on the boosted regression trees can be used to effectively forecast the fishing ground of chub mackerel in the Yellow Sea and East China Sea.

A Preliminary Study on the Diversity of Fish Species and Marine Fish Faunas of the South China Sea

There are 3048 species of fish occurring in the China Seas (CS), of which at least 2321 species are found in the South China Sea (SCS), belonging to 35 orders, 236 families and 822 genera. The fish species diversity is analyzed in this paper based on biogeography, biostatistics, fishing methods, etc. It is found that the regional environment, especially biological factors, plays an important role in the distribution of faunas, and there are two fish faunas in the SCS, one in the north and another in the center and south. This regional division is of value for sustainable fishery production and efficient management of fishery resources.

Response of Spatio-temporal Distribution of Fishery Resources to Mairne Environment in the Northern South China Sea

[Objective] The paper was to investigate the spatio-temporal distribution of fishery resources in the northern South China Sea and to provide reference for scientific evaluation and effective protection of fishery resources in the northern South China Sea. [Methods] Based on monitoring data and satellite remote sensing data [including Sea Surface Temperature(SST), Chlorophyll a concentration(Chl a) and Sea Surface Wind(SSW)] in winter(January to February) and summer(August to September) in the northern South China Sea, the relationship between spatio-temporal distribution of fishery resources and marine environment was investigated by using Generalized Linear Models(GLM), fishing ground gravity and correlation analysis. [Results] The suitable SST and Chl a of light falling-net fishing ground in winter were 17-23°C and 0.2-0.6 mg/m3, respectively. The suitable SST and Chl a in summer were approximately 28°C and 0.2-1.0 mg/m3. Standardized Catch Per Unit Effort(SCPUE) was higher in summer(2-4) and lower in winter(1-3). From winter to summer, the fishing ground gravity migrated to the east about 1 °E. [Conclusion] The spatio-temporal distribution of fishery resources is related to eastern Hainan-western Guangdong upwelling and the coastal flow, caused by the monsoon in the northern South China Sea, and the major catch species of light falling-net.

Distribution characteristics of zooplankton biomass in the East China Sea

On the basis of the data of oceanographic survey in the East China Sea in four seasons during 1997-2000 (23°30'~33°00'N, 118°30'-128°E), the variation of total biomass and diet biomass of zooplankton and their spatial-temporal distribution and relationship with the fishing ground of Engraulis japonicus are approached and analyzed. The results show that the average biomass is 65.32 mg/m3 in four seasons, autumn (86.18 mg/m3) being greater than summer (69.18 mg/m3) greater than spring (55.67 mg/m3) greater than winter (50.33 mg/m3). The average value of diet zooplankton biomass is 40.9 mg/m3. The trends of horizontal distribution both in the total biomass and the diet biomass of zooplankton are similar. The high biomass region (250-500 mg/m3) is very limited, only accounting for 1% of the investigation area. Seasonal variation of the biomass is very remarkable in the west and north parts of East China Sea coastal waters ( 29°30'N,125°E). The horizontal distribution of diet zooplankton depends on the abundance distribution of crustacean. The distribution of diet zooplankton is related to the fishing ground of Engraulis japonicus and the high-density area of young fish and larval. In spring, the central fishing ground of Engraulis japonicus (>100 kg/h) and the high-density area of young fish and larval (>100 individuals per net) are located at the same place of high-density (100-250 mg/m3)area of diet zooplankton in the middle-southern part of East China Sea or the edge of its waters.

Study on spatial and temporal distribution of planktonic amphipoda in the East China Sea

Quantitative distribution of planktonic amphipoda in the East China Sea is analyzed and the relation with environmental factors and mackerel and scad fishing grounds is studied. The result shows that the characteristic of biomass is great seasonal and interannual variety during the passing three decades. The distribution of planktonic amphipoda basically reflects the movement, decay and intensification of the different water systems in the survey area.

Connectivity of fish assemblages along the mangrove-seagrasscoral reef continuum in Wenchang, China

Understanding the connectivity of fish among different typical habitats is important for conducting ecosystembased management, particularly when designing marine protected areas(MPA) or setting MPA networks. To clarify of connectivity among mangrove, seagrass beds, and coral reef habitats in Wenchang, Hainan Province,China, the fish community structure was studied in wet and dry seasons of 2018. Gill nets were placed across the three habitat types, and the number of species, individuals, and body size of individual fish were recorded. In total, 3 815 individuals belonging to 154 species of 57 families were collected. The highest number of individuals and species was documented in mangroves(117 species, 2 623 individuals), followed by coral reefs(61 species,438 individuals) and seagrass beds(46 species, 754 individuals). The similarity tests revealed highly significant differences among the three habitats. Approximately 23.4% species used two habitats and 11.0% species used three habitats. A significant difference(p<0.05) in habitat use among eight species(Mugil cephalus, Gerres oblongus, Siganus fuscescens, Terapon jarbua, Sillago maculata, Upeneus tragula, Lutjanus russellii, and Monacanthus chinensis) was detected, with a clear ontogenetic shift in habitat use from mangrove or seagrass beds to coral reefs. The similarity indices suggested that fish assemblages can be divided into three large groups namely coral, seagrass, and mangrove habitat types. This study demonstrated that connectivity exists between mangrove–seagrass–coral reef continuum in Wenchang area;therefore, we recommend that fish connectivity should be considered when designing MPAs or MPA network where possible.

How Did Vinh Moc Village, Located near Vietnam DMZ, Protect Their Villagers from United States Air Force Bombardment during the Vietnam War?

The buried village is Vinh Moc where more than 1200 Vietnamese, including soldiers, who lived underground during the Vietnam War (1965 to 1972) were hand dug into red basalt bedrock. The Vinh Moc Village was strategically located on the border of North Vietnam and South Vietnam approximately 14 km north of the DMZ and along the shoreline of the South China Sea. During the Vietnam War, the US Air Force heavily bombed Vinh Moc. The North Vietnamese Army (NVA) had an important military base on nearby Con Co Island. Brave civil volunteers from Vinh Moc would make the 28 km dangerous journey to the island, disguised as fishermen, to deliver supplies to the soldiers stationed there. The people who remained at Vinh Moc dug tunnels into red basalt hills in order to survive this onslaught. The American forces assessed the villagers of Vinh Moc were supplying food and armaments to the NVA garrison on the island of Con Co, which was in turn hindering the American bombers on their way to bomb Hanoi. The US military objective was to force the villagers of Vinh Moc to leave the area. The villagers initially dug the tunnels to a 10 m depth but the American forces designed bombs that burrowed down 10 m before exploding. The soil tunnels were then deepened to 30 m to provide safety for the soldiers and civilians working there during the intense US Air Force bombing. The primary objective of the research study was to determine how the soils and parent material of Vinh Moc Village, protected their villagers from the United States Air Force bombardment during the Vietnam War. In addition, the natural parent material at both the Vinh Moc and Cu Chi were assessed to determine why the tunnels were so resilient. The Cu Chi and Iron Triangle soil tunnels were dug by hand in the Old Alluvium soils and parent material where iron in solution precipitated and became the soil binding material. The Vinh Moc tunnels were hand dug in porous, red basalt (bedrock) hills where the consolidated rock structure itself provided the required binding material. Neither site needed support beams to hold up the ceilings.

论南海渔文化的特征与价值——以海南为考察中心

渔文化是中华优秀传统文化的重要组成部分。南海渔文化资源丰富,有鲜明的特色,具有很高的理论价值和开发利用潜力。应旗帜鲜明地提出南海渔文化的概念,大力推进南海渔文化理论研究,揭示南海渔文化的精神价值,丰富南海渔文化的时代内涵,发掘南海渔文化资源优势,促进南海渔文化的保护、传承与发展,更好地服务于海南社会经济发展。

基于结构方程模型分析海洋环境因子对南海鸢乌贼的影响

为探究鸢乌贼(Sthenoteuthis oualaniensis)资源变化与海洋环境因子的关系,基于2019—2020年南海围网捕捞鸢乌贼的电子渔捞日志数据,首先分析了鸢乌贼资源的月间变动特征,之后利用结构方程模型解析海洋环境因子对其资源时空分布的影响。结果表明:围网月间的平均单位捕捞努力量渔获量(Catch per unit effort,CPUE)变化趋势基本一致,年平均CPUE则为2020年大于2019年。南海鸢乌贼渔汛期为3—4月,高产区域集中在112°E—117°E、8°N—12°N,渔汛期CPUE呈现向东和向北偏移的趋势。海洋环境对鸢乌贼资源分布的综合影响系数为0.38,而海表盐度和光合有效辐射在海洋环境上的载荷量分别为0.87和0.82,两者是影响鸢乌贼资源分布的重要环境因子。所用结构方程模型为量化海洋环境因子与鸢乌贼资源分布之间的复杂关系提供了新的研究思路,可为鸢乌贼资源可持续利用和管理提供参考依据。

Cenozoic Propagated Rifting in the Dangerous Grounds in Response to the Episodic Seafloor Spreading of the South China Sea

The southern continental margin of the South China Sea has documented multiphase continental rifting corresponding to the propagation of seafloor spreading.Here we investigate three multi-channel seismic reflection profiles across different segments of the Dangerous Grounds with a NE-SW direction.Stratigraphic correlation reveals that the Cenozoic tectono-stratigraphic framework in the Dangerous Grounds is featured with diachronous rifting,which records the successive spreading of East Subbasin and Southwest Subbasin,South China Sea.By reconstructing the tectono-sedimentary evolution history in different segments,we combine the quantification of the brittle extension,tectonic subsidence,as well as the crustal thinning.Results provide evidence that the extensional stress migrated from northeast to southwest with the progressive propagation of the seafloor spreading in the oceanic basin.Besides,the impact of the tectonic propagation persists even after the cessation of seafloor spreading,evidenced by a longer stretching duration in the West-Dangerous Grounds than that in the eastern area.Moreover,a temporary syn-rift subsidence delay synchronously to the spreading of the adjacent oceanic basin is observed along the southern margin.This observation proves the secondary mantle convection during the seafloor spreading in the southern continental margin,which is related to the propagating rift.

南海区拖网渔业发展趋势及其对渔业资源的影响

拖网是南海区海洋渔业生产最重要的渔具,拖网渔业在南海区海洋渔业生产中占主导地位。南海区拖网渔船数量从1986年的6730艘增长至2003年的14599艘,随后减少,2010年后基本维持在9000艘左右;其总吨位在212864~876045 t波动,呈显著上升趋势;而总功率从1986年的440438 kW上升至2005年的1735173 kW,之后呈下降趋势。1986—2020年单船平均吨位和功率均呈显著上升趋势。拖网渔船产量在59.24×10^(4)~181.66×10^(4)t之间波动,占南海区总捕捞产量的38.35%~62.96%,呈逐年下降趋势;单位功率和单位吨位的产量分别在0.72~1.40 t和1.18~3.90 t之间波动,1999年最高,之后呈下降趋势。根据8种重要经济鱼类幼鱼占比统计结果,1992—2020年底拖网渔获物中幼鱼生物量占比均值为24.35%~84.28%,数量占比均值为40.09%~89.84%,其中白姑鱼(Pennahia argentata)、带鱼(Trichiurus japonicus)和竹荚鱼(Trachurus japonicus)幼鱼比例最高。鉴于拖网渔业选择性不强,对幼鱼资源及海洋环境影响较大,建议逐步压减拖网渔船规模,严格执行网目尺寸和可捕规格制度,引导渔民使用资源节约型、环境友好型的作业方式,以利于近海渔业资源养护和可持续利用。

Record of a juvenile Omura's whale live stranded in Hainan Island:Evidence of a potential breeding ground in the South China Sea?

On January 12,2011,a very young juvenile Bryde's-like baleen whale was found stranded alive on the east coast of Hainan Island,in the South China Sea.Unfortunately,it died the next morning.This baleen whale showed some unique external morphology and skull features of the Omura's whale(Balaenoptera omurai).Subsequently,it was genetically identified as an Omura's whale using two different mitochondrial DNA markers.This study documents the first confirmed live stranding of a juvenile Omura's whale on Hainan Island,China.Our findings expand the known distribution range of this species in Chinese waters and may indicate that waters around Hainan Island in the South China Sea could be a potential breeding ground for the Omura's whale.

基于北斗船位数据的南海外海灯光罩网渔船作业特征研究

灯光罩网是中国南海外海主要捕捞作业方式之一。为加强对南海外海灯光罩网渔船生产监测和渔船捕捞活动的有效管理,根据2017年2—5月南海外海灯光罩网渔船北斗船位数据,分析定位时间、经纬度等特征,结合作业时间、等深线等采用多层过滤法判断渔船作业状态;通过阈值筛选渔船作业的位置和时间,采用过滤窗修正法对船位点状态进行修正,计算渔船作业时长,并与渔民实际记录的纸质捕捞日志进行对比分析。结果表明:北斗船位数据提取结果和渔民实际记录的结果误差较小,航次准确率为100%,航次天数准确率为94.30%;相同作业日期准确率为92.72%;作业时长总平均绝对误差为1.12 h,平均相对误差为2.1%,具有较好的一致性。研究设计的灯光罩网渔船状态判断、作业位置确定、作业时长提取和捕捞努力量计算方法可为灯光罩网作业分析和其捕捞强度量化提供新思路。

琼州渔民开辟南海渔业航路之历史原因考述

明清时期,渔民群体社会地位低下,生产模式具有向外开拓的冒险导向。南海渔业航路的形成,与明清之际东南沿海地区的复杂基层社会环境密切相关。严厉的海禁政策、沉重的赋税与猖獗的海盗活动,迫使琼州渔民前往西沙、南沙谋生。更路簿中所载始发于南沙岛礁南部的外洋航路,是渔民为出售渔货而开辟的。琼州渔民作为南海渔业航路的开拓者,为更路簿文本的形成积累了重要的实践经验。

南海区大型灯光罩网渔场渔期和渔获组成分析

根据2005年8月～2010年5月"琼文昌33180"渔船的生产监测记录,分析了南海区大型灯光罩网渔业的渔场渔期分布和主要渔获组成。结果显示,鸢乌贼(Sthenoteuthis oualaniensis)、鲹科(Carangidae)、带鱼(Trichiu-rus japonicus)、枪乌贼(Loligo)和舵鲣(Auxis)等为主要渔获种类,分别占总产量的40.94%、21.92%、13.56%、10.17%和6.21%;作业渔场可分为西、中沙邻近深水海域(Ⅰ区)、珠江口外大陆架海域(Ⅱ区)、北部湾大陆架海域(Ⅲ区)3个区域;Ⅰ区主捕鸢乌贼(91.10%),大型金枪鱼类也占0.83%的比例;Ⅱ区主捕鲹科(42.88%)、枪乌贼(20.34%)和带鱼(14.52%);Ⅲ区主捕带鱼(45.06%)、鲹科(22.16%)和枪乌贼(14.58%)。3月～5月主要在Ⅰ区生产,8月～9月和12月～翌年2月主要在Ⅱ区生产,10月～11月主要在Ⅲ区生产。外海(Ⅰ区)作业天数的年度波动较大,建议调整罩网外海休渔制度。

南海新建钢质罩网渔船渔获组成及渔场分析

根据2012年8月-2014年6月＂粤电渔42212＂渔船的生产数据,分析了南海区大型钢质灯光罩网渔船的渔获组成和渔场渔期。结果显示,主要渔获种类为鸢乌贼（Sthenoteuthis oualaniensis）、鲹科（Carangidae）、鲭科（Scombrida）、枪乌贼（Loliginidae）和带鱼（Trichiurus japonicus）,分别占总渔获产量的69.8%、12.6%、7.3%、3.9%和3.5%。作业渔场可分为近海陆架区和外海深水区,其中陆架区渔获种类相对较多,包括科、枪乌贼、带鱼、鲭科等;而深水区渔获以鸢乌贼为主,其他种类相对较少。近海陆架区作业月份为8月至翌年2月,每月作业1-20 d,平均作业10 d,渔获率为370.5-3 670.0 kg·d^-1,平均渔获率1 152.0 kg·d^-1。深水区作业集中在2月-6月,每月作业1-30 d,平均作业13 d,渔获率为1 000-10 190 kg·d^-1,平均渔获率4 071.3 kg·d^-1。相对于近海陆架区,灯光罩网渔业在外海深水区渔获效率更高、产量更大,在现有资源条件下应大力发展大型钢质灯光罩网渔船,积极开发南海外海渔业资源。