捕捞对长山群岛海域渔业生态系统的影响

为了评价捕捞对渔业生态系统的综合影响程度,建立渔业生态系统保护管理决策支持系统,本文基于状态、压力和生物群落响应PSR模型、利用层次分析法构建了捕捞对渔业生态系统的影响评价模型,包含渔船数量、捕捞压力指数、渔获量、底层鱼类比重、营养级、优势种单体重量、经济鱼类渔获量、多样性指数、均匀度指数3个层次9个指标,并选择1987—1988年和2006—2007年长山群岛游泳生物调查数据对其进行了定量评价。结果表明:近20年来,在捕捞强度不断增加的压力下,渔业生态系统的结构和功能发生显著变化,长寿命、高营养级的肉食性鱼类生物量下降明显,系统以短寿命、小型鱼类占优势;鱼类资源量、底层鱼类比重、营养级、优势种单体重量、经济鱼类渔获量、多样性指数、均匀度指数年退化率分别为4.75%、3.64%、0.31%、4.28%、2.32%、0.39%、1.14%;通过模型评价,渔业生态系统健康指数为0.34,低于评价等级Ⅲ级,说明近20年捕捞导致长山群岛渔业生态系统处于不健康状态。     

北部湾生态通道模型的构建

根据1997年～1999年在北部湾进行的渔业资源和生态环境调查数据,利用EwE软件构建北部湾生态系统的营养通道模型,模型由16个功能组构成,包括了哺乳动物和海鸟,每一组都代表在生态系统中具有相似地位的有机体,基本覆盖了北部湾生态系统能量流动的主要过程.模型分析表明,北部湾生态系统的能量流动主要以捕食食物链途径为主,其中无脊椎动物在能量从低级向高层次转换中起关键作用.各功能组的营养级范围为1.00～4.04,哺乳动物占据了最高营养层.生态网络分析表明,系统的能量流动主要有6级,来自初级生产者的能流效率为12.2%,来自碎屑的转换效率为12.3%,平均能量转换效率为12.2%.模型估算的可利用的生物量密度为8.7 t·km^-2,生态系统的生物生产量只占系统净初级生产力的1.81%.当前北部湾海洋生态系统处于不稳定状态.     

中国海域海洋生物的营养级指数变化特征

利用联合国粮农组织(FAO)1950-2011年渔获物捕捞量资料, 分析了我国海域(包括大陆海域、台湾海域、香港海域和澳门海域)129种渔获物的营养级指数变化特征。研究表明, 1950-1974年我国海洋营养级指数在3.45左右波动, 1975-1978年下降至3.35左右, 1982-1987年急剧下降到3.25并维持到1996年, 1997-2011年平稳回升至3.34。与全球海洋营养级指数相比, 1984年之前我国高于全球水平, 而1984年之后则低于全球水平。就生物类群而言, 鱼类对我国海洋营养级指数的贡献最大, 达73.1-85.8%; 甲壳动物次之, 为9.2-15.5%; 软体动物较小, 为3.3-11.6%; 其他无脊椎动物的贡献最小, 不超过1.8%。过度捕捞使我国部分渔获物由原来的长寿命、高营养级的底层鱼类变为现在的短寿命、低营养级的无脊椎动物和中上层鱼类。渔业捕捞许可管理制度、禁渔期和禁渔区制度、海洋捕捞产量“零增长”和“负增长”计划、增殖放流、扩大海洋保护区面积等措施的实施可能是我国海洋营养级指数回升的主要原因。     

基于营养通道模型的渤海生态系统结构十年变化比较

根据1982年和1992年渤海渔业资源和生态环境调查数据,应用EwE建模软件,构建了两个时期的营养通道模型,并比较分析了10a间渤海生态系统结构以及渔业资源的变化.模型包含鳀、黄鲫、蓝点马鲛、其它中上层鱼类、小黄鱼、花鲈、其它底层鱼类、底栖鱼类、浮游动物、浮游植物、碎屑等17个功能群, 基本覆盖了渤海生态系统能量流动的途径.分析结果表明,1992年渤海生态系统的总生物量比1982年有所下降;小型中上层鱼类成为渔业资源的主要成分,其生物量较1982年明显增加;由于低营养级层次渔获物数量的增加,渔获物平均营养级有所下降.从系统规模看1982年大于1992年.1982年到1992年的十年间, 引起渤海生态系统结构变化的主要原因是初级生产力的变化以及捕捞因素.1982年与1992年渤海生态系统均处于不成熟的发育期,仍有较高的剩余生产量有待利用,因此渔业资源恢复的物质基础是有保证的.     

基于生态通道模型的长江口水域生态系统结构与能量流动分析

利用Ecopath with Ecosim在前期研究的基础上构建了3个时期(2000年秋、2006年秋、2012年秋)长江口水域生态系统的生态通道模型,分析对比了三峡工程蓄水前中后期,长江口水域生态系统结构与能量流动特征。模型将长江口水域生态系统划分为鱼类、虾类、蟹类、头足类、底栖动物、浮游动物、浮游植物、碎屑等17个功能组,基本覆盖了长江口生态系统能量流动的主要途径。模型结果分析表明:蓄水前中后期,长江口水域生态系统各功能组营养级组成和分布相近,但由于长江口渔业过度捕捞,蓄水中后期多数功能组的生态营养转换率被动提高。长江口渔获物的组成未发生明显变化,但渔获物的平均营养级降低,渔获量减少。蓄水中后期,生态系统中牧食食物链的重要性增加,碎屑食物链的重要性降低,这与蓄水之后长江入海径流改变、泥沙量减少、陆源污染增加关系密切。结果表明,蓄水前中后期,生态系统均处于不成熟阶段,蓄水后生态系统总生物量、初级生产量及流向碎屑的能量呈降低趋势,但系统的净效率和再循环率升高。     

基于生态通道模型的北部湾渔业管理策略的评价

北部湾位于南海17°00′-21°45′N,105°40′-110°10′E,为中越两国共同管辖的天然半封闭海湾。根据1997-1999年在北部湾进行的渔业资源和生态环境调查数据,利用EwE软件构建了北部湾生态系统的营养通道模型（Ecopath）。在此基础上,以30a为周期,利用Ecosim中的“渔业管理者”模拟了不同管理策略（经济效益最大化、社会效益最大化、生态效益最大化以及综合考虑三者的最佳管理）对北部湾捕捞结构的影响。结果表明：以经济利益最大化为管理策略时会提高所有渔具的捕捞努力量,除了拖网下降43.2%之外;以社会利益最大化为管理策略时模型要求极大地增加小型渔业,尤其是混合渔业的捕捞努力量将上升3.34倍;而以生态稳定性最大化为管理目标时,模型要求所有渔业的捕捞努力量都必须降低甚至停止。以经济和社会利益最大化为管理目标对不同的vulnerability（V＇s）值的反应敏感,高营养级种类减少而低营养级种增加,其中社会利益最大化时系统的营养级最低（2.78）;而生态稳定性和综合管理目标最大化则对不同的敏感度的反应较为一致。综合考虑经济、社会和生态效应的最佳管理策略能满足渔业和保育目标的平衡,有望成为最佳的管理策略。由此可见,多鱼种捕捞策略的模拟是个复杂的任务,目标功能有时互相冲突,而且易受到初始模型条件的影响。     

基于Ecopath模型的太湖生态系统结构与功能分析

根据2008—2009年太湖湖区水生生物调查的结果及主要水生动物摄食生态学已发表资料,应用Ecopath with Ecosim 6.1软件构建了太湖生态系统的食物网模型,初步分析了太湖生态系统功能与结构特征.模型由初级生产者、主要鱼类及无脊椎动物和有机碎屑等20个功能组组成.结果表明： 太湖生态系统的能流主要分布在4个营养级上,顶级捕食者鲌鱼营养级最高.食物网存在两条主要的营养传递途径,即碎屑食物链和牧食食物链,且碎屑食物链占比较大;营养级I的利用效率低下,大量初级生产力未能流入更高的营养层次,造成生态系统下层的营养流动“阻塞”.对系统总体特征分析发现,反映系统成熟度的指标,包括较高的净初级生产力(NPP)和净初级生产力/呼吸(NPP/R),以及较低的连接指数(CI)、系统杂食指数(SOI)和Finn循环指数(FCI)等,都揭示了太湖“幼态化”的生态系统现状;混合营养分析和关键种筛选结果显示,高强度的渔业捕捞活动对系统负影响显著,而顶级捕食者的下行效应显著下降.
     

广西北部湾近岸生态系统风险评价

根据2009年9月广西北部湾近岸的海洋生态调查资料,利用地理信息系统的空间分析功能,从海水水质、营养水平、生物量和初级生产力水平、生物多样性和生态系统缓冲容量5个方面分析了秋季广西北部湾近岸海域环境现状,并进一步利用生态风险综合指数对广西北部湾海洋生态风险进行了评价.结果表明:2009年秋季,广西北部湾近岸海域生态环境质量较好,大部分生态系统风险指标等级均处于“中低”或“较低”水平,整体处于低风险状态.生态风险综合指数结果显示,广西北部湾海域生态风险分布具有明显的空间异质性,离岸水域生态系统的风险综合指数较低,越靠近港湾内,风险状态等级越高.     

福田红树林湿地生态系统EWE模型构建

以福田红树林湿地生态系统为研究对象,将其生物组成分为红树植物、底栖动物、浮游植物、浮游动物、鸟类和碎屑等15个功能组,运用Ecopath with Ecosim(EWE)软件,构建了福田红树林湿地生态系统的EWE模型,探讨了红树林湿地生态系统的状态、特征及不同物种之间的营养关系,并评价红树林湿地生态系统当前的健康状况。分析表明,福田红树林湿地生态系统能流的最主要来源是碎屑,能流主要在营养级Ⅰ到Ⅳ之间流动,转化效率最高发生在第Ⅰ和第Ⅱ营养级之间(28.8%),总体转化效率为11.2%,且系统对营养级Ⅱ的利用最为充分。处于低营养级的功能组在系统能量传递的过程中起着非常关键的作用,并且对整个系统的影响强烈。生态系统总体特征参数生物量/总流量(TB/TT)、连接指数(CI)和系统杂食性指数(SOI)分别为0.163、0.123和0.018,综合分析表明,福田红树林湿地生态系统目前有退化的趋势。     

基于Ecopath模型分析分水江水库生态系统结构和功能

根据2008-2009年浙江分水江水库渔业资源和生态环境调查数据,采用Ecopath with Ecosim软件构建了分水江水库的物质平衡Ecopath模型.模型构成包括鲢、鳙、鳊、花〖HT5,7〗鱼〖KG-*3〗〖HT5,6〗骨〖HT5F〗、翘嘴鲌、鲴类、其他鱼类、寡毛类、水生昆虫、浮游动物、浮游植物、有机碎屑等14个功能组,较好地模拟了分水江的水库生态系统.结果表明： 分水江水库生态系统包含5个营养级,且营养物质流动主要发生在前3个营养级.牧食食物链和碎屑食物链是系统中的主要能流,但是食物网结构较简单,容易受到外界干扰的影响.转移效率在低营养级较低,表明系统的能量利用较低,过多的营养物质储存在系统中可能导致富营养化的发生.较低的联结指数、系统杂食性系数、Finn氏循环指数以及Finn氏平均路径长度值都表明该生态系统处于不稳定状态,而生产量/总呼吸和生产量/生物量的值较高,说明此生态系统的初级生产力远高于其呼吸量,系统处于生态发育前期.分水江水库由于发育历史较短,仍处于由不成熟向成熟发育的过程中.     

Using an Ecosystem Modeling Approach to Explore Possible Ecosystem Impacts of Fishing in the Beibu Gulf,Northern South China Sea

Using the Ecopath with Ecosim software, a trophic structure model of the Beibu Gulf was constructed to explore the energy flows and provide a snapshot of the ecosystem operations. Input data were mainly from the trawl survey data collected from October 1998 to September 1999 and related literatures. The impacts of various fishing pressure on the biomass were examined by simulation at different fishing mortality rates. The model consists of 20 functional groups (boxes), each representing organisms with a similar role in the food web, and only covers the major trophic flows in the Beibu Gulf ecosystem. It was found that the food web of the Beibu Gulf was dominated by the primary producers path, and phytoplankton was the primary producer mostly used as a food source. The fractional trophic levels ranged from 1.0 to 4.02, and the marine mammals occupied the highest trophic level. Using network analysis, the ecosystem network was mapped into a linear food chain, and six discrete trophic levels were found with a mean transfer efficiency of 11.2%. The Finn cycling index was 9.73%. The path length was 1.821. The omnivory index was 0.197. The ecosystem had some degree of instability due to exploitation and other human activities, according to Odum’s theory of ecosystem development. A 10-year simulation was performed for each fishery scenario. The fishing mortality rate was found to have a strong impact on the biomass. By keeping the fishing mortality rate at the current level for all fishing sectors, scenario 1 had a drastic decrease in the large fish groups. The biomass of the small and medium pelagic fish would increase to some extent. The biomass of the small and low trophic level species, jellyfish, prawns and benthic crustaceans would be stable. The total biomass of the fishery resources would have a 10% decrease from the current biomass after 10 years. In contrast, the reduced fishing mortality rate induced the recovery of biomass (scenarios 2–4). In scenario 2, the biomass of the large demersal fish and the large pelagic fish would increase to over 16 times and 10 times, respectively, of their current level. In scenario 4, the biomass of the large pelagic fish would increase to over 3 times of its current level. The total biomass of the fish groups, especially the high trophic level groups, would become significantly higher after 10 years, which illustrates the contribution on biomass recovery by relaxing the fishing pressure. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Author contributions: Xiaoping Jia designed research; Zuozhi Chen and Yongsong Qiu performed research; Zuozhi Chen, Yongsong Qiu, and Shannan Xu analyzed data; and Zuozhi Chen and Shannan Xu wrote the article.     

Fishery-induced changes in a marine ecosystem: insight from models of the Gulf of Thailand

Two mass-balance trophic models are constructed to describe the Gulf of Thailand ecosystem (10–50 m depth): one model pertains to the initial phase of fisheries development, and the other to when the resources were severely depleted. The two phases are compared, and changes brought about by fishing discussed. A dynamic simulation model, Ecosim, is then used successfully to reproduce the 1980 state of the fishery based on the 1963 model and the development in catches. In addition the 1980 model is used to predict how the ecosystem groups may bounce back following marked reduction in fishing pressure. Finally, the 1963 model is used to study alternative scenarios for how the fisheries development could take place, notably the effect of exploiting only the resources of larger species. The study validates that the Ecosim model can be used to predict ecosystem level changes following changes in fishing pressure, therefore fishing induced changes can to a large extent explain the changes in ecosystem pools and fluxes observed over time.     

The trophic role of lutjanid fish and impacts of their fisheries in two ecosystems in the Gulf of Mexico

The trophic role of snappers was evaluated on the continental shelves of the south-western Gulf of Mexico and the Yucatan in the south-eastern Gulf of Mexico. Mass-balanced, steady-state trophic models of the two ecosystems were constructed with Ecopath and perturbations were simulated in the ecosystems with Ecosim by increasing fishing mortality. Impacts were measured by changes in biomass of snappers and other groups, and in some indices of stability: persistence, recovery time and resilience. The snapper populations differed between ecosystems. The western Gulf of Mexico system appeared more complex and more stable than the Continental Shelf of Yucatan. Although overall stability indices between ecosystem suggested a similar structure and function, there were clear differences at a group level. Correlation of stability attributes between groups suggested differences in the role of snappers between the ecosystems suggesting that each stock should be managed individually.     

Changes in the trophic interactions and the community structure of Lake Taihu (China) ecosystem from the 1960s to 1990s

As the third largest freshwater lake in China, Lake Taihu has suffered from overfishing, eutrophication, and physical disturbance over the last several decades. Evaluating and quantifying changes in the ecosystem can help us better understand and develop hypotheses to explain the dynamics of the ecosystem. In this study, trophic interactions and community structure of commercial fisheries species of Lake Taihu ecosystem were analyzed and compared for three time periods (1961–1965, 1981–1987, and 1991–1995) using the Ecopath with Ecosim model with the aim of evaluating the changes in the population dynamics and ecosystem development mechanism spanning the period from the 1960s to 1990s. The results show that the biomass of large predators decreased over the three decades, while the biomass of small species increased. Increases in the P/B ratios and fishing mortality levels observed for species groups reveal rapidly intensifying fishery stress over the three decades. The fisheries operated at the highest trophic level during the 1980s, and there are some indications of “fishing down the food web” in this ecosystem between the 1980s and the 1990s. Drawing upon Odum’s theory of ecosystem maturity, the structured, web-like ecosystem of the 1960s developed into a highly mature system during the 1980s; yet, in the 1990s, this structure became less complex and the system’s maturity fell to its lowest observed level. During this period, the successional development of the system occurred in reverse.     

Top–down control by great blue herons Ardea herodias regulates seagrass‐associated epifauna

Top predators can influence the structure and function of plant and animal communities. In coastal marine systems, fish, shark and mammal population declines are major drivers of recent ecosystem‐level change. Cascading effects of predatory wading birds, however, are less understood, even though wading bird populations have declined in many regions. We quantified the effects of predation by the piscivorous great blue heron Ardea herodias fannini on fish, invertebrates and epiphytes living in eelgrass Zostera marina. We found that herons forage on benthic fish in seagrass meadows, and foraging intensity increased from late spring until midsummer. When we experimentally excluded herons, benthic fish abundance increased, and the invertebrate assemblage shifted to more shrimp‐dominated assemblages while grazing gammarid amphipod abundance declined. These shifts were associated with reduced epiphyte abundance when herons were excluded, reflecting a four‐level trophic cascade and mediated by shifts in the grazer assemblage. In summary, we found that a piscivorous wading bird species exerts top down control in a subtidal seagrass ecosystem. Losses and recovery of wading birds could have ecosystem‐level ecological consequences that may need to be considered in the context of concern for overfishing and predator recovery in marine coastal management.     

An ecological model of the artificial ecosystem (northern Hangzhou Bay,China): analysis of ecosystem structure and fishing impacts

The artificial ecosystem is a large-scale enclosure in northern Hangzhou Bay, China. Using the Ecopath with Ecosim software, a trophic structure model is constructed for 2006–2007 to characterize the food web structure, functioning, and describing the ecosystem impacts of fishing. Input information for the model were gathered from published and unpublished reports and from our own estimates during the period 2006–2007. Pedigree work and simple sensitivity analysis were carried out to evaluate the quality and the uncertainty of the model. Results show that the food web in the enclosed sea area was dominated by a detritus pathway. The trophic levels of the groups varied from 1.00 for primary producers and detritus to 3.90 for piscivorous fish in the artificial system. Using network analysis, the system network was mapped into a linear food chain, and five discrete trophic levels were found with a mean transfer efficiency of 9.8% from detritus, 9.4% from primary producer within the ecosystem. The geometric mean of the trophic transfer efficiencies was 9.5%. Detritus contributed 57% of the total energy flux, and the other 43% came from primary producers. The ecosystem maturity indices-TPP/TR (total primary production/total respiration), FCI (Finn cycling index), A (ascendancy) and TB/TDET were 2.672, 25%, 31.5%, and 0.013, respectively, showing that the artificial system is at developmental stage according to Odum’s theory of ecosystem development. The ‘Keystoneness’ result indicates that herbivorous zooplankton was identified as keystone species in this system. Furthermore, a simple dynamical simulation was preformed for varying fishing mortality over 10 years. The biomass of most fish groups has a small increase when the fishing mortality at current level. Increasing fishing mortality by twofold resulted in a marked decrease in biomass of piscivorous fish accompanied by an increase in that of other fish groups, notable zooplanktivorous fish. Generally, this study represents the first attempt to evaluate the food web structure and the potential effects of fisheries in the artificial coastal ecosystem. It is concluded that this model is a potential tool for use in the management of the artificial ecosystem in northern Hangzhou Bay.     

Ecological role and historical trends of large pelagic predators in a subtropical marine ecosystem of the South Atlantic

Large pelagic predators occupy high positions in food webs and could control lower trophic level species by direct and indirect ecological interactions. In this study we aimed to test the hypotheses: (1) pelagic predators are keystone species, and their removals could trigger impacts on the food chain; (2) higher landings of pelagic predators could trigger fishing impacts with time leading to a drop in the mean trophic level of catches; and (3) recovery in the pelagic predators populations, especially for sharks, could be achieved with fishing effort reduction. We performed a food web approach using an Ecopath with Ecosim model to represent the Southeastern and Southern Brazil, a subtropical marine ecosystem, in 2001. We then calibrated the baseline model using catch and fishing effort time series from 2001 to 2012. Afterwards, we simulated the impact of fishing effort changes on species and assessed the ecological impacts on the pelagic community from 2012 to 2025. Results showed that the model was well fitted to landing data for the majority of groups. The pelagic predators species were classified as keystone species impacting mainly on pelagic community. The ecosystem was resilient and fisheries seem sustainable at that time. However, the temporal simulation, from 2001 to 2012, revealed declines in the biomass of three sharks, tuna and billfish groups. It was possible observe declines in the mean trophic level of the catch and in the mean total length of landings. Longline fisheries particularly affected the sharks, billfish and swordfish, while hammerhead sharks were mostly impacted by gillnet fishery. Model simulations showed that large sharks’ biomasses could be recovered or maintained only after strong fishing effort reduction.