鄱阳湖物理生境特征及其对鱼类群落结构的影响

湖泊鱼类群落结构与物理生境特征密切相关。为了探究鱼类群落结构与物理生境特征之间的关系,在鄱阳湖设立17个采样点,通过采集鱼类样本研究其群落结构,并利用遥感技术分析样点物理生境特征（包括岸线分形维数、距离指数和高程值）及其空间区域差异。结果表明,依据17个采样位点的物理生境特征,鄱阳湖丰水期物理生境空间上可以划分为3个区域,分别为北方区、南方区和主湖区,但枯水期鄱阳湖生境没有显著的区域划分规律。丰水期鄱阳湖鱼类可以分为北方群、南方群和主湖区群3个类群,而枯水期鱼类组成没有明显规律。从功能类群上看,鄱阳湖鱼类以杂食性、湖泊定居性和偏好于底层以及中下层栖息的中小型鱼类为主。不同区域的鱼类功能群之间存在时间和空间上的变化,北方区和南方区鱼类功能群组成相似,主湖区与北方区和南方区存在差异。总体上,鱼类群落结构的时空变化和差异与物理生境特征具有良好的一致性;未来鄱阳湖鱼类的保护工作需要关注湖泊物理生境特征,不同区域应制定不同的保护措施。     

Flood pulse and the dynamics of fish assemblage structure from neotropical floodplain lakes

Abstract – The dynamics of fish assemblages from seven floodplain lakes of Salado River (Argentina) was monthly analysed during two contrasting hydrological seasons. Partial canonical correspondence analysis indicated that assemblage structure was predictably linked to environmental characteristics that varied along temporal and spatial scales. Species distributed differentially along an environmental gradient of temperature, hydrometric level, conductivity, macrophyte cover and transparency in relation to their sensory capabilities (following piscivory‐transparency‐morphometry model) and life history strategies. During high water season, assemblages were associated with temperature and hydrometric level, factors which varied mainly across temporal scales and exhibit a regional range of action. During low waters, assemblage structure correlated with macrophyte cover and transparency, factors that varied fundamentally on spatial scales and have local impact. These results indicate that the determinism of fish assemblages does not vary substantially between hydrometric periods, although the environmental variables affecting fish assemblages and their scale of action are clearly different.     

鱼类群落调控在浅水湖泊生态修复中的作用:以傀儡湖为例

鱼类是湖泊食物网中的重要消费者, 占据食物网多个营养级。通过食物网营养级联效应, 鱼类对湖泊生物群落结构和水环境可产生重要影响。本研究以长江中下游浅水湖泊——傀儡湖为例, 研究了基于不同饵料类群渔产潜力估算前提下食鱼性鱼类、滤食性鱼类、碎屑食性鱼类的组合放养技术, 并探讨了底层杂食性鱼类针对性捕捞的复合调控策略对傀儡湖鱼类群落结构、沉水植物群落和水质产生的影响, 旨在揭示鱼类群落调控在优化湖泊生态系统结构方面的重要作用, 为湖泊生态修复提供新的思路和手段。     

Large‐scale patterns of fish diversity and assemblage structure in the longest tropical river in Asia

Although the Mekong River is one of the world's 35 biodiversity hot spots, the large‐scale patterns of fish diversity and assemblage structure remain poorly addressed. This study aimed to investigate the fish distribution patterns in the Lower Mekong River (LMR) and to identify their environmental determinants. Daily fish catch data (i.e. from December 2000 to November 2001) at 38 sites distributed along the LMR were related to 15 physicochemical and 19 climatic variables. As a result, four different clusters were defined according to the similarity in assemblage composition and 80 indicator species were identified. While fish species richness was highest in the Mekong delta and lowest in the upper part of the LMR, the diversity index was highest in the middle part of the LMR and lowest in the delta. We found that fish assemblages changed along the environmental gradients and that the main drivers affecting the fish assemblage structure were the seasonal variation of temperature, precipitation, dissolved oxygen, pH and total phosphorus. Specifically, upstream assemblages were characterised by cyprinids and Pangasius catfish, well suited to low temperature, high dissolved oxygen and high pH. Fish assemblages in the delta were dominated by perch‐like fish and clupeids, more tolerant to high temperatures, and high levels of nutrients (nitrates and total phosphorus) and salinity. Overall, the patterns were consistent between seasons. Our study contributes to establishing the first holistic fish community study in the LMR.     

Influences of gear type and analytical methodology on fish assemblage characterisations in temperate lakes

A variety of gears and analytical methods can be used to characterise lentic fish assemblages; however, the combined influence of gear type and analysis can affect conclusions about assemblage patterns. Fish assemblages sampled with night electric fishing, gillnets and trapnets from 153 lakes were evaluated using summary indices of species composition, pairwise community similarity comparisons and multivariate ordination. For a given amount of effort, electric fishing had the highest species richness, while gillnets had higher diversity and evenness. Pairwise comparisons between gears revealed that (1) richness was positively correlated among all gears, (2) diversity and evenness were generally not correlated across gears and (3) electric fishing and trapnets captured more similar species than all other pairwise comparisons. Gear‐specific multivariate correlation and ordination revealed that gillnet and electric fishing samples more similarly characterised variation in assemblages among lakes, while trapnets characterised assemblages along different gradients of species composition. These results indicate that either electric fishing or trapnetting can be used when assessing shallow‐water assemblages for diversity or evenness, gillnets and either electric fishing or trapnets should be used for whole‐lake assessments, and either gillnets or electric fishing should be used when evaluating regionwide variation in lake assemblages.     

Spatial distribution patterns of fish egg and larval assemblages in the lower reach of the Yangtze River: Potential implications for conservation and management

1. River fish diversity is threatened by anthropogenic environmental alteration to landscapes. The early life-history stages of fish play an important role in maintaining diversity and population recruitment and can be heavily influenced by landscape patterns. Information on temporal and spatial distribution patterns of fish eggs and larvae is also important for biodiversity conservation and management of fish resources.
2. The Yangtze River possesses a high diversity of fishes, including many commercially important species. The economy along the lower reach of the river is well developed, and most of the area is experiencing high pressure from human impacts. This section of the Yangtze River connects with the largest freshwater lake in China at the upstream end and flows into the estuary at the downstream end. These two landscape features are likely to have a significant impact upon the spatial distributions of fish egg and larval assemblages.
3. Environmental variables, fish eggs, and larval assemblages were sampled in three locations, at Hukou, Anqing, and Jingjiang, in the lower reach of the Yangtze River. The results suggest that the higher number of species and greater abundance in upstream sites reflect the critical function of connectivity of Poyang Lake with the river for fish recruitment in the lower Yangtze. The delayed bloom of larval fish, occurrence of estuarine species, and a lower species number and abundance of freshwater fish downstream reflect the influence of tidal intrusion from the estuary.
4. This study highlights the value of maintaining natural river–lakes connectivity in the Yangtze River as a conservation measure. The connected river–lake system should be designated as a priority area for fish resource protection in the lower reach of the Yangtze River. We recommend further measures to break down barriers between the river and other lakes and to restore the natural lateral connectivity of the floodplain ecosystem.

     

鄱阳湖湖口的水位特性及其对水环境的影响

水位作为重要的湖泊水文因子，对湖泊水动力过程、化学过程和生态过程具有重要的影响。通过2007～2008年鄱阳湖湖口的水位、水环境实测数据，分析了湖口的水位及水体各环境因子的变化特征，阐述了各水环境因子对水位变化的响应关系，并建立了水位与各水环境因子的回归方程。结果表明：湖口的水位及各水环境因子均呈现季节性变化，湖口水位与长江（九江站）水位呈直线正相关；湖口的水位变化对其水体各环境因子均存在明显的影响，其中水体透明度随水位上升而增大，悬浮物、溶解氧、高锰酸盐指数、氮化物和磷化物浓度随水位上升而下降。     

Big floods,big knowledge gap: Food web dynamics in a variable river system

While flow regime is widely recognised as an over‐arching feature structuring aquatic ecosystems, the influence of flood events on feeding habits in fish assemblages inhabiting variable environments remains largely unknown. In this study, we investigated how diets of a fish assemblage changed in response to fluctuations in hydrology in a highly variable, wet‐dry tropical Australian river. We compared dietary habits, trophic guilds and intra‐ and interspecific dietary overlap and diet breadth across different seasons. Wet‐season floods acted as major geomorphic and ecological perturbations that exerted substantial effects on the trophic dynamics of the terapontid assemblage, particularly through the removal of in‐stream plant production and detritus. Forced by major shifts in food source availability due to seasonal flooding, fishes responded to these perturbations by marked changes in diet, with significant guild switching following wet‐season floods. Rather than the predictable, gradual, changes in consumer–resource interactions associated with the gentler seasonal flood pulse evident in other tropical river systems, study results instead emphasised rapid and profound changes to species' diets and trophic interactions following abrupt flood pulses. These sudden shifts in food sources may also explain some of the lack of clarity in discrimination of specific carbon sources or species' trophic levels evident in isotopic food web studies from the region. Results indicate that the effects of flood pulses on assemblage trophic interactions may differ among ecosystem types and across the broad potential scale of hydrological disturbance mediated by flood events.     

Fishing down or fishing up in Chinese freshwater lakes

Changes in mean trophic level (MTL) of catches have been widely used to reflect the impact of industrial fisheries on aquatic ecosystems because this measure represents the relative abundance of fished species across the trophic level spectrum. In this study, fisheries data from six important freshwater lakes at the middle‐lower Yangtze River and Huaihe River reach of Southern China from 1949 to 2009 were used to evaluate changes in catch MTL. After fishery markets opened at 1985, fish catches increased significantly in all the lakes. Lakes Poyang and Dongting, which were dominated by omnivores and connected to the Yangtze River, showed no significant change in catch MTL before and after 1985. Catch MTL in lakes Taihu and Hongze increased significantly due to an increase in the proportion of pelagic zooplanktivorous. Catches in Lake Chaohu were dominated by zooplankton‐feeding lake anchovy, Coilia ectenes Temminck & Schlegel and icefish, Neosalanx taihuensis Chen, while Lake Donghu was dominated by phytoplanktivorous carps. Due to low biodiversity, catch MTL of these two lakes showed no significant change before and after 1985. Both fisheries‐based and human activities‐based drivers influenced the structure and catch MTL of fisheries in Chinese freshwater lakes.