Assessing electric fishing sampling effort to estimate stream fish assemblage attributes

The EU Water Framework Directive (WFD) obligates authorities to assess the ecological status of rivers. The sampling of the fish assemblage must be based on a reliable and cost‐effective monitoring programme, and it should be optimised to measure the ecological quality cost‐effectively. The efficiency of single‐pass versus three‐pass backpack electric fishing was measured to assess ecological status. The data included 295 electric fishing samplings from 137 rivers in Finland and a 5‐year data series from six small forest streams in mid‐eastern Finland. Compared with three‐pass electric fishing, single‐pass electric fishing in the same area increased the risk of missing rare fish species and species with low catchability. The concordance of the calculated fish metrics (e.g. proportion of tolerant and intolerant species) between one‐ and three‐pass measurements was, however, high, suggesting that single‐pass electric fishing was a suitable sampling procedure to evaluate ecological status. Increasing the area sampled by single‐pass removals stabilised the variances in the fish metrics and similarity indexes. It was concluded that in small streams electric fishing an area 24–27 times the stream width and in general a minimum of 300 m², but preferably more than 450 m², was adequate to estimate fish assemblage attributes reliably in boreal streams.     

Responses of fluvial fish assemblages to agriculture within the boreal zone

Abstract The effect of agriculture on fish assemblages was assessed using electric fishing data from 108 sites on 27 medium‐sized rivers running through organic soils in central and northern Finland. The intensity of agriculture was quantified as the percentage of the catchment area used for agriculture (range 0–31%). High correlations (r² = 0.68–0.86) were found between the intensity of agriculture and water quality parameters, especially total phosphorus, suspended solids and chemical oxygen demand. Densities of bullhead, Cottus gobio L., alpine bullhead, Cottus poecilopus Heckel, minnow, Phoxinus phoxinus (L.) and brown trout, Salmo trutta L., declined with increasing intensity of agriculture. Conversely, density of perch, Perca fluviatilis L., and roach, Rutilus rutilus (L.), increased with intensity of agriculture. A fish‐based index developed for the evaluation of the ecological integrity of rivers correlated negatively with the intensity of agriculture.     

An evaluation of the contribution of hatchery stocking on population density and biomass: a lesson from masu salmon juveniles within a Japanese river system

Stocking is an important management tool for enhancing fisheries resources, but its actual contribution to fisheries resources is controversial, taking into consideration both the positive and negative effects. This study compared density and biomass of hatchery (otolith thermal marked) and wild masu salmon parr between stocked and unstocked rivers to evaluate the contribution of stocking with hatchery‐reared fish. Density and biomass of all fish did not differ between stocked and unstocked rivers. Moreover, density and biomass of wild fish in the stocked rivers were lower than those of the unstocked rivers. Density and biomass of hatchery fish in a non‐natural reproducing river were similar with those of all fish in natural reproducing rivers. These results indicate that hatchery stocking does not have positive effects on population density or biomass but replaces wild fish with hatchery fish and that non‐natural reproducing areas are more suitable as stocking sites.     

Assessing biotic integrity in a Mediterranean watershed: development and evaluation of a fish-based index

Abstract  Biological indicators for Mediterranean rivers are poorly developed. This study evaluates the effectiveness of the Index of Biotic Integrity approach (IBI) with fish assemblages in the Guadiana catchment, a typical Mediterranean watershed in Southern Portugal. Reference sites were selected from a set of 95 sites, using a multivariate approach. Fifty-five candidate metrics were screened for range, responsiveness, precision and redundancy. Final metrics included: proportion of native fish, number of intolerant and intermediate species, number of invertivore native fish, number of phyto-lithophilic and polyphilic species, and catches of exotics. The IBI scores correlated with composite gradients of human impact and differed significantly between reference and non-reference sites. Application of the IBI to an independent validation set with 123 sites produced results congruent with the development set and repeatable assessments at 22 sites showed concordance in IBI scoring. This application highlights the effectiveness of the IBI approach even with fish assemblages of limited diversity and ecological specialisation as in Mediterranean streams.     

Contrasting changes in freshwater fish assemblages and food webs follow modification of tropical waterways

Fresh waters are increasingly threatened by flow modification. Knowledge about the impacts of flow modification is incomplete, especially in the tropics where ecological studies are only starting to emerge in recent years. Using presence/absence data dated approximately four decades apart (~1966 to ~2010) from 10 tropical rivers, we assessed the changes in freshwater fish assemblage and food web after flow modification. The sites were surveyed with methods best suited to habitat conditions (e.g., tray/push netting for low‐order forest streams, visual surveys for canalised rivers and net casting for impounded rivers). With the presence/absence data, we derived and compared six measures of fish assemblage and food web structure: species richness, proportion of native species, overall functional diversity, native functional diversity, food web complexity and maximum trophic level. We found that changes in community assemblage and food web structure were not generalisable across modification regimes. In canalised sites, species richness and maximum trophic levels were lower in the second time period while the opposite was true for impounded sites. However, proportion of native species was consistently lower in the second time period across modification regimes. Changes in fish assemblages and food webs appear to be driven by species turnover. We recorded 79 cases of site‐specific extirpation and 117 cases of site‐specific establishment. Our data further suggest that turnover in assemblage is again contingent on flow‐modification regime. While the process was stochastic in canalised rivers, benthopelagic species were more likely to be extirpated from impounded rivers where species lost were replaced by predominantly alien fish taxa.     

大连湾海域鱼类的群落结构研究

采用大连湾海域四季底拖网调查数据(2006年夏、冬季和2007年春、秋季),对其鱼类群落结构进行研究,并利用多样性指数法和丰度/生物量比较法(ABC曲线)评价鱼类群落受外界扰动的程度。研究结果表明,该海域四季共采集鱼类31种,隶属于10目24科31属,鱼类区系组成在适温性上以暖温性鱼类为主,在栖息水层上以底层鱼类为主。夏季鱼类生物量(43.16kg/h)和生物数量(950个/h)均明显高于其他3个季节。四季共有优势种为大泷六线鱼和许氏平鲉。鱼类群落多样性指数季节变化范围分别为物种丰富度指数0.76~2.16、多样性指数0.63~1.96、物种均匀度指数0.36~0.91。各季节间生物量和丰度组成的Bray-Curtis相似性均较高。多样性指数法和丰度/生物量曲线法对鱼类群落受外界扰动评价结果一致,均表明鱼类群落受到中度扰动,且秋冬季高于春夏季。本研究可为大连湾海湾生态系统健康评价和生态修复提供科学依据。     

Processes of collating a European fisheries database to meet the objectives of the European Union Water Framework Directive

Abstract  FIsh Database of European Streams, a common database for the FAME project, was merged using existing data on electric fishing and environmental data. FIsh Database of European Stream is a relational database with eight tables. Metrics based on classification of fish species into guilds were calculated, and provided in separate tables. FIsh Database of European Stream contained information about 150 freshwater fish species, from 12 countries, 17 ecoregions, 40 main river regions, 2651 rivers and 8228 sites. Examples of data coverage and use are given. Relationships between environmental variables were illustrated using principal component analysis, which resulted in three environmental components – latitude, size and altitude. Environmental component scores were correlated with fish metrics used in the European Fish Index. Results exemplify how fish guilds reflect gradients in environmental variation. Benefits and problems concerning standardisation and data availability at the global level are discussed.     

Patterns of diel activity and species richness in young and small fishes of European streams: a review of 20 years of point abundance sampling by electrofishing

Originally developed to assess the relative abundance of ≥1+ fishes in large rivers, point abundance sampling by electrofishing (PASE) was adapted for 0+ fishes in the mid‐1980s. Being both economical and widely applicable, PASE for 0+ fish has become a commonly used sampling approach in Europe, but its use for estimating 0+ fish density and species richness has attracted particular concern because of size and species selectivity. As such, this review is both timely and necessary. It summarizes the development of PASE and evaluates its various applications: studies of 0+ fish community composition, relative abundance and density, species richness (S), population size structure, larval and juvenile growth dynamics, microhabitat use, diel dynamics of species–species and species–microhabitat interactions, and the analysis of data emanating from PASE databases. The use and potential misuse of replicate sampling in estimates of S are examined, with PASE data from various European rivers re‐analysed to assess geographical patterns in 0+ fish S. Comparisons of PASE and other approaches for estimating 0+ fish density and species richness have all demonstrated PASE to be cost‐effective and relatively reliable, but sampling accuracy and precision do decrease as fishes enter the juvenile period of development.     

基于底栖动物的东江上游生态健康状况评价

大型底栖动物是评价水生态健康状况最常用的生物类群。为系统评价东江流域上游生态健康水平,以底栖动物为指示生物,2013年11月对东江上游的重要支流—鱼潭江、浰江、车田水、小庙水、彭寨水、沙洲水、罗浮水和黄麻布水进行采样调查,通过计算底栖动物的Shannon-Wiener多样性指数(H′)、Pielou均匀度指数(J)、Margalef丰富度指数(D)和BMWP(Biological Monitoring Working Party)指数,评估了8条支流的生态健康状况。结果显示,东江流域上游共采集到底栖动物109属种,隶属5门、9纲、55科,其中水生昆虫为主要类群,占总物种数的72.4%,EPT类群采集到18属种。研究区域的生物多样性指数较高,物种组成丰富,就不同水体而言,浰江的种类最丰富,小庙水种类数最少,各个支流均以水生昆虫类群占优势。底栖动物平均密度为2362个/m²,平均生物量为39.1 g/m²。河蚬(Corbicula fluminea)为第一优势种,出现率90%,第二和第三优势种分别为涡虫纲一种(Turbellaria sp.)和四节蜉属一种(Baetis sp.)。BMWP指数作为应用广泛的生物评价指数,对河流生态健康的指示作用最强,可达到快速准确的效果。研究表明,东江上游8条支流的生态健康状况总体较好,其中5条河流为极清洁。     

南昌市13个湖泊的鱼类群落结构及其物种多样性特征

为了解南昌市面积1 km2以上湖泊的鱼类群落结构及其物种多样性特征,探究影响湖泊鱼类群落结构空间分布的环境因子,于2019-2020年在南昌市13个湖泊进行了鱼类资源调查。结果显示,采集到的39种鱼类隶属5目、9科、33属;优势种以鲫（Carassius auratus）、?（Hemiculter leucisclus）为主;不同湖泊的鱼类群落结构被划分为3个类群,与湖泊功能定位密切相关。鱼类Shannon-Wiener多样性指数值平均值为2.15,丰富度指数平均值为2.97,均匀度指数平均值为0.92,Shannon-Wiener多样性指数、丰富度指数与湖泊面积、水深、pH和透明度存在显著的相关性。冗余分析（RDA）表明,水深、pH、总氮和氨氮是引起鱼类群落结构在南昌市不同湖泊间差异的主要影响因子,人为活动干扰可能对调查区域内湖泊的鱼类群落结构和生物多样性特征施加影响。     

Ecological traits of fish assemblages from Mediterranean Europe and their responses to human disturbance

Abstract  Mediterranean river systems are characterised by more diverse fish assemblages and regional ecological processes compared with the rest of Europe. A data set from Mediterranean France, Iberia and Greece (∼2000 sites) was used to describe the characteristics of fish assemblages, explore their responses to anthropogenic disturbance and analyse the implications for river quality assessment. There was a southwards decline in species richness per site, but endemicity and proportion of alien species increased. Sites in the eastern Mediterranean had higher endemicity, lower site richness and lower number of alien species than sites in western Mediterranean Europe. Assemblage composition differed between Mediterranean sub-regions, but was dominated by three major fish types: a salmonid fish type common throughout the study area and two cyprinid-dominated fish types (in some sub-regions, Salmo trutta L. is present but not numerically dominant), corresponding to a gradient in hydrological and temperature regimes. Metric responses to perturbation were compared with those found at the European (larger scale) and basin (smaller scale) levels. Overall metric response was weaker in this Mediterranean application. The best responses to human pressure were usually obtained with abundance-based metrics and included the contribution of naturalised alien species. Some widespread alien species contributed to the response to anthropogenic alteration (notably Cyprinus carpio L. and Lepomis gibbosus (L.)).     

Spatial organisation of fish assemblages in the Chishui River,the last free‐flowing tributary of the upper Yangtze River,China

The Chishui River is the last free‐flowing tributary of the upper Yangtze River, China, which has an important role in fish conservation. This study aimed to explore the spatial organisation of fish assemblages in this river. Field sampling was conducted biannually between 2015 and 2017 at 41 sites from its headwater and downstream. One hundred and twenty‐two fish species were captured, including 34 endemic, 15 threatened and six exotic species. Fish assemblages varied significantly along the longitudinal gradient. Based on cluster and ordination analyses, 41 sampling sites could be divided into five site‐groups, corresponding to the headwater, upstream, midstream, downstream and the Xishui‐branch, respectively. The splitting of fish assemblages was consistent with the geographical divisions. However, fish species changed gradually along the longitudinal gradient rather than abruptly, which was consistent with the River Continuum Concept (RCC). In the headwaters and upstream, fish assemblages were mainly dominated by cold‐water and rheophilic species, while in the lower stretches, fish assemblages were dominated by warm‐water and limnophilic species. According to null models, fish assemblages were significantly nonrandomly structured at the basin scale, but randomly structured at the regional scale. This study is an important step in understanding the assembly rules of fish assemblages in this free‐flowing river and provides useful information for future fish conservation and ecological restoration.     

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.     

The critical importance of an undammed river segment to the reproductive cycle of a migratory Neotropical fish

Biotelemetry, ichthyoplankton and genetic data can provide detailed information about the migratory dynamics and reproductive cycle of freshwater fishes. However, few studies have combined these techniques in Neotropical systems. The objective of this study was to examine the migratory and reproductive dynamics of Prochilodus costatus in the São Francisco River watershed, south‐east Brazil, by comparing the ecological importance of two rivers to the species, an undammed segment of the São Francisco River and a dammed segment of one of its main tributaries, the Pará River. In total, 215 fish were radio‐tagged over three years (2014–16). Eggs and larvae were sampled at seven locations and analysed by PCR to identify Prochilodus spp. ichthyoplankton. Most radio‐tagged individuals (97%) used the undammed segment of the São Francisco River as spawning migration route, even those captured and released in the Pará River. Fish migrated to spawn from late September to late November with the arrival of the rains and returned to feeding sites from December to May after spawning. The highest densities of fish eggs and larvae were recorded in the upper reaches of the São Francisco River during months of peak river discharge. Returning fish showed high fidelity to sites occupied before spawning migration. Fish spent roughly 71% of the year at feeding sites, 25% at spawning sites and 4% moving between them. This study provides novel information about the migratory dynamics of Neotropical fishes and underscores the key role of undammed river segments for the conservation of Neotropical migratory fish species.     

Riverine connectivity,upstream influences,and multi‐taxa representation in a conservation area network for the fishes of Michigan,USA

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Release of critically endangered crocodiles: Development and application of a food web approach to determine suitability of release habitat

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岱衢洋产卵场鱼卵、仔稚鱼群落结构及其与环境因子的关系

为了解岱衢洋海域鱼卵、仔稚鱼的群落结构及其与环境因子的关系,本团队分别在2010年5月—2012年2月春、夏、秋和冬季,利用大型浮游生物网在此海域开展了8个航次调查。共采集到鱼卵1 042粒,仔稚鱼2 055尾,隶属于10目19科37种。鱼卵优势种为扁舵鲣和小带鱼等;仔稚鱼的优势种为鰉、鳀和中华小公鱼等。调查海域鱼卵的平均密度是8.40粒/100 m3,仔稚鱼的平均密度是14.85尾/100 m3。单因素方差分析结果显示,2010年和2011年春、夏季4个季节之间丰富度指数(D)、均匀度指数(J′)和多样性指数(H′)均存在极显著差异。鱼卵、仔稚鱼资源密度分布不均匀,春、夏季较高,冬季最低,大体呈现南高北低的趋势。Pearson相关性结果分析得出,与鱼卵、仔稚鱼关系最密切的环境因子为温度、盐度和海水悬浮物。研究表明,春、夏季是岱衢洋海域鱼类产卵的重要时期,该海域是鳀、扁舵鲣、中华小公鱼等中上层鱼类的重要产卵场和育幼场。     

Using flow guilds of freshwater fish in an adaptive management framework to simplify environmental flow delivery for semi‐arid riverine systems

Freshwater rivers have been substantially altered by development and flow regulation. Altered hydrological regimes have affected a range of biota, but impacts are often most obvious on freshwater fish. Flow largely influences the range of physical habitat available to fish at various life history stages. Biological rhythms are therefore often linked to flow and optimized so that opportunities for spawning, growth and dispersal are synchronized. Assuming that flow therefore becomes the main factor which structures freshwater fish communities, the use of species specific biological information should be able to inform adaptive flow delivery strategies from the river reach to catchment scale. A test of this assertion was performed as a case study of native fish within the Edward‐Wakool River system (New South Wales, Australia). Fish within the system were assigned to one of four groups based on biological similarity. Aspects of reproductive and movement ecology were then reviewed to generate optimal flow release strategies for each group. Life expectancy and hydrological constraints were then investigated and used to develop a possible 10‐year flow delivery program that could generate ecological outcomes within a strategic adaptive management framework that considered potential impacts on third parties. The approach could be used to develop flow characteristics to benefit biota in any watercourse provided enough data are available to link potential outcomes with flow delivery.