Fish assemblages in Atlantic Forest streams: the relative influence of local and catchment environments on taxonomic and functional species

Streams are under environmental pressures acting at different scales that influence the ecological organisation of their fish assemblages. However, the relative influence of the different scale‐related variables on assemblage composition and function is poorly understood. We evaluated the importance of local‐ and catchment‐scale environmental variables, as well as the spatial structure of the sampling sites, in shaping fish assemblages in Atlantic Forest streams. Local‐scale variables were those measured at the sampling sites, describing the local habitat conditions (e.g. depth, substrate type, altitude). Catchment‐scale variables were those integrating the upstream landscape of the sampling sites (e.g. catchment land use). Spatial distances were calculated from watercourse distance using principal coordinates of neighbour matrices. Altogether, 28 local and seven catchment variables were initially subjected to two processes of eliminating co‐linearity. Redundancy analysis was applied to the three matrices (spatial, local and catchment) to quantify the variance in the structure of the fish assemblages explained by each matrix. Local variables explained more variability in both taxonomic and functional assemblage structure, than catchment and spatial variables. Local variables also changed along the longitudinal gradient, which consequently influenced fish assemblage structure. This pattern was also influenced by anthropogenic alteration and non‐native species, which were more abundant in downstream sites. These results highlight the need to assess Atlantic Forest streams under different environmental scales, especially through the use of quantitative local‐scale metrics, and to consider the effects of longitudinal patterns in structuring fish assemblages when developing and implementing monitoring programmes, impact studies and conservation plans.     

Effects of a rock‐ramp fishway on summer fish assemblage in a Lake Huron tributary

The use of nature‐like fishways to increase ecosystem connectivity has increased in recent years, but their effectiveness has rarely been evaluated. A rock ramp was constructed in the Shiawassee River in 2009, and post‐construction effects (2011–2012) were evaluated on the summer fish assemblage by comparing fish assemblage composition to a nearby free‐flowing river and a nearby river with a dam. Patterns of fish species richness, mean catch‐per‐unit‐effort and proportional abundance in reaches upstream and downstream of the rock ramp, dam and comparable sites in the free‐flowing river were evaluated. Overall, species richness by site and proportional abundance in the rock‐ramp river were more similar to the free‐flowing river, while species richness by reach was more similar to the dammed river. These findings suggest that the rock ramp has improved connectivity for the summer fish assemblage, but has not fully restored conditions to the level observed in a free‐flowing river.     

Fish assemblages structure and function along environmental gradients in rivers of Gabon (Africa)

Abstract –  We examined patterns in fish species assemblages structure and function along environmental gradients in rivers of Gabon. Species presence–absence data from 52 sites were first analysed by canonical correspondence analysis. Results showed that the position of sites along the upstream–downstream gradient, together with elevation and water conductance were the most important predictors of local fish assemblage composition. Assemblage richness and trophic structure were further investigated using regression tree analysis. Results revealed a general increase in species richness from upstream to downstream areas and a transition from insectivorous to omnivorous, herbivorous and piscivorous species along this longitudinal gradient. There were several similarities between these previous patterns and those observed in other temperate streams suggesting a potential convergence in fish assemblage along environmental gradients in tropical and temperate riverine systems. From a conservation standpoint, these results highlight the need to evaluate all habitat types along rivers longitudinal gradient to integrate the full spectrum of species assemblages within conservation plans.     

Fish community responses to stream flow alterations and habitat modifications by small hydropower projects in the Western Ghats biodiversity hotspot,India

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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.

     

Riverine spawning,long distance larval drift,and floodplain recruitment of a pelagophilic fish: A case study of golden perch (Macquaria ambigua) in the arid Darling River,Australia

1. Pelagic spawning riverine fish (pelagophils) spawn in free‐flowing river habitats with downstream drift of eggs and larvae but the spatial scale is often unknown, and this constitutes a major ecological knowledge gap.
2. In the arid Darling River in south‐eastern Australia, the present objectives were: (i) to determine the potential downstream dispersal distance of young golden perch (Macquaria ambigua); and (ii) to evaluate whether provision of environmental water enhanced dispersal of young fish from Menindee Lakes to the lower Darling River (LDR) while also cueing further spawning in downstream lotic reaches.
3. Golden perch spawned in unregulated lotic tributaries on a flood pulse and larvae drifted or dispersed >1,600 km downstream and entered large ephemeral productive floodplain lake nursery habitats as fully scaled fingerlings.
4. Planned releases of environmental water cued golden perch spawning in the LDR and enabled juvenile fish to disperse downstream from the Menindee Lakes nursery into receiving populations in the LDR, Great Darling Anabranch, and southern Murray River, with some fish potentially completing an active migration of >2,100 km by age 1 year.
5. The Darling River case study highlights the need for a system‐scale approach to the conservation management of pelagophilic fish, along with multi‐year perennial flow strategies to improve ecosystem integrity in large rivers globally.

     

Salinity and geomorphology drive long‐term changes to local and regional fish assemblage attributes in the lower Pecos River,Texas

River systems throughout arid regions worldwide have been heavily impacted by human activities, resulting in long‐term ecological consequences. The lower Pecos River in the Trans‐Pecos region of Texas is no exception, having undergone anthropogenic changes that include decreased flow, elevated salinity, species loss and species invasion. We compared historical and contemporary fish assemblage attributes from the Pecos River at local (site‐specific) and regional (Trans‐Pecos region) scales across a 24‐year time period. Fish assemblage data were collected in October 1987 and 2011, by seining at 15 sites spanning 430 km of the river in Texas. Additionally, we examined contemporary environmental conditions to determine species–environment relationships. We found that fish assemblages were significantly different between time periods, likely due to increased salinisation in the upper half of the study region. Decreased species richness, species replacement and increases in euryhaline species were documented in the upstream sites. Freshwater springs lower the salinity and maintain flows in the downstream reach, allowing for maintenance of the native fish fauna. Careful management of regional aquifers, irrigation practices and petroleum waste water will be necessary for protecting biodiversity and environmental flows in the lower Pecos River.     

Taxonomic and functional diversity in a subtropical stream: A longitudinal pattern analysis

Identifying the spatial patterns of fish diversity in streams is basic for the conservation and management of stream fishes. The “upstream–downstream” patterns in the taxonomic α-diversity of stream fishes have been widely surveyed. However, the longitudinal patterns in the functional diversity and β-diversity of stream fishes have been given less attention. In this study, we surveyed fishes along an upstream–downstream gradient in a headwater stream of the Qiantang River, China, and examined the longitudinal variations in fish diversity. Our aims were to assess whether the longitudinal patterns in fish diversity were consistent between the taxonomic and functional metrics and between the α- and β-aspects of diversity. We found that both species richness and functional richness of fishes showed a hump-shaped relationship with the distance from headwaters, while both taxonomic and functional β-diversities presented the U-shaped distributions along the river continuum. Functional diversity related more to the distance from headwaters than taxonomic diversity. Despite their similar relationship with the distance from headwaters, taxonomic and functional β-diversities were dominated by species turnover and function nestedness components, respectively. Our results suggest that, along the river continuum in a subtropical stream, the α- and β-aspects of fish diversity present different longitudinal variations. Although the taxonomic and functional diversity shows similar relationships with distance from headwaters, their spatial variations are driven by different ecological processes.     

Spatial and temporal variation in fish community structure and diversity in the largest tropical flood‐pulse system of South‐East Asia

The Tonle Sap River and Lake (TSRL) is South‐East Asia's largest tropical flood pulse with a flow‐reversal system that supports one of the world's largest freshwater fisheries. However, among the world's tropical floodplains, the resources of the TSRL have received little ecological research. Here, we described the spatiotemporal TSRL fish diversity and community variation using daily records from 2012 to 2015 on fish abundance from six sites covering the TSRL system. We found that high fish diversity occurred in sites located in the middle of Tonle Sap Lake, and the lowest diversity was observed in the southern section. The spatial abundance distribution patterns displayed a river–lake gradient, with three fish assemblages that were clustered based on their composition similarities and were characterised by 96 indicator species. In the southern section, fish assemblages were characterised by longitudinal migratory fishes; in contrast, in the middle system, fish assemblages were represented by species with combined ecological attributes (i.e. longitudinal and lateral migratory species and floodplain residents). Towards the northern section, fish assemblages were composed of lateral migratory and floodplain resident species. Species richness and abundance peaked at approximately 2–2.5 and 4 months, respectively, after the peak flow in early October, during which Tonle Sap River resumes its normal flow direction (outflow). This suggests that seasonal flood pulses (i.e. rising and falling water levels) play a pivotal role in structuring spatiotemporal variation in the TSRL fish assemblages. Our study has implications for fisheries monitoring and conservation initiatives.     

Nested patterns of spatial diversity revealed for fish assemblages in a west European river

Abstract –  The longitudinal distribution of fish assemblages across a large west European river basin, the Garonne river (south-west France) were investigated using a self-organising map. This nonlinear statistical method was employed to classify sampling sites according to their species composition. We found three main nested patterns in an aggregated hierarchy: a replacement and succession of species along a gradient without defined boundaries, four main zones of fish assemblages and an upstream-downstream shift of fish communities. We suggest that fish assemblages are too complex to be identified with a single species as in the zonation model, and that the diversity patterns found might be part of the same ecological process influencing fish assemblages on different spatial scales. Thus, discrepancies in the analysis of longitudinal patterns of fish communities in streams may have been basically a matter of local conditions and of conceptual perception.     

湑水河流域鱼类资源现状

2009年9月和2010年5月在湑水河流域对鱼类资源进行了调查,共捕获鱼类4目、10科、29种;湑水河上游太白段以山区溪流冷水型鱼类为主,种类较少;下游城固段海拔低,鱼类种类相对上游河段丰富.不同河段在不同季节的鱼类组成和质量密度有显著差异.与相邻山区的河流相比,湑水河鱼类资源较为丰富,但目前外部因素已经开始影响鱼类的生存与繁衍,河流污染和其他人为干扰可能对该流域鱼类造成不可逆转的生态影响.     

Beaver dams shift desert fish assemblages toward dominance by non‐native species (Verde River,Arizona, USA)

The reintroduction of beaver (Castor canadensis) into arid and semi‐arid rivers is receiving increasing management and conservation attention in recent years, yet very little is known about native versus non‐native fish occupancy in beaver pond habitats. Streams of the American Southwest support a highly endemic, highly endangered native fish fauna and abundant non‐native fishes, and here we investigated the hypothesis that beaver ponds in this region may lead to fish assemblages dominated by non‐native species that favour slower‐water habitat. We sampled fish assemblages within beaver ponds and within unimpounded lotic stream reaches in the mainstem and in tributaries of the free‐flowing upper Verde River, Arizona, USA. Non‐native fishes consistently outnumbered native species, and this dominance was greater in pond than in lotic assemblages. Few native species were recorded within ponds. Multivariate analysis indicated that fish assemblages in beaver ponds were distinct from those in lotic reaches, in both mainstem and tributary locations. Individual species driving this distinction included abundant non‐native green sunfish (Lepomis cyanellus) and western mosquitofish (Gambusia affinis) in pond sites, and native desert sucker (Catostomus clarkii) in lotic sites. Overall, this study provides the first evidence that, relative to unimpounded lotic habitat, beaver ponds in arid and semi‐arid rivers support abundant non‐native fishes; these ponds could thus serve as important non‐native source areas and negatively impact co‐occurring native fish populations.     

Damming and seasonality as modulators of fish community structure in a small tributary

River damming alters the physical–chemical variables of water and often causes compartmentalisation of aquatic habitats. Seasonality can add complexity to the longitudinal compartmentalisation. The spatial and temporal effects of these two phenomena on the structure of ichthyofauna from a tributary under the influence of damming were evaluated, based on the following hypotheses: (1) transition habitats have the greatest species richness; (2) community similarity decreases with increasing distance between sites; (3) conservation of free‐flowing areas upstream reservoir contributes to the maintenance of migratory species. To evaluate the effects of these two phenomena, twelve monthly fish samples (September/12 to August/13) were performed with gillnets in three sample areas distributed longitudinally in the tributary. Limnological variables were measured in the same sample areas to confirm compartmentalisation. We observed three distinct limnological compartments (lotic, transition and lentic), with increase differentiation during the rainy season. This compartmentalisation influenced fish fauna where localised communities exhibited different compositions among the three sampled habitats. During the rainy season, these differences become pronounced, with transition habitat showing greater species richness than the others. More pronounced differences in species composition and structure in extremes sampling sites were also observed. Migratory fish presented higher proportion of fish composition in lotic habitat. In conclusion, damming and seasonality acted concomitantly as modulators of fish fauna in a tributary influenced by damming. However, compartmentalisation of habitats was the primary driver of ichthyofauna community structure with the rainy season increasing differences in community composition.     

Fish diversity assessment in the headwaters of the Volga River using environmental DNA metabarcoding

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新疆渭干河流域鱼类资源现状

2019年5月、8月和11月,在上、中、下游共设5个采样点,采用单层刺网(网目1、2、3 cm,网长20、30、40 m)和地笼网(开口40 cm×40 cm,长8 m)调查新疆天山南麓中段塔里木河流域九大水系之一的渭干河(N 41°06′～42°42′,E 80°40′～84°10′)的鱼类资源状况.调查共采集鱼类1...     

Complex influences of low-head dams and artificial wetlands on fishes in a Colorado River tributary system

Abstract  Low-head dams in arid regions restrict fish movement and create novel habitats that have complex effects on fish assemblages. The influence of low-head dams and artificial wetlands on fishes in Muddy Creek, a tributary of the Colorado River system in the USA was examined. Upstream, fish assemblages were dominated by native species including two species of conservation concern, bluehead sucker, Catostomus discobolus Cope, and roundtail chub, Gila robusta Baird and Girard. The artificial wetlands contained almost exclusively non-native fathead minnow, Pimephales promelas Rafinesque, and white sucker, Catostomus commersonii (Lacepède). Downstream, fish assemblages were dominated by non-native species. Upstream spawning migrations by non-native white suckers were blocked by dams associated with the wetlands. However, the wetlands do not provide habitat for native fishes and likely inhibit fish movement. The wetlands appear to be a source habitat for non-native fishes and a sink habitat for native fishes. Two non-native species, sand shiner, Notropis stramineus (Cope), and redside shiner, Richardsonius balteatus (Richardson), were present only downstream of the wetlands, suggesting a beneficial role of the wetlands in preventing upstream colonisation by non-native fishes.     

Priority habitats for the conservation of large river fish in the Ganges river basin

• 1. Three classes of habitat used by groups of fish species classified as conservation and management priorities were developed for the Gerua River (also known as the Girwa River, Karnali River) in the Ganges river basin. This river is large (mean annual discharge ca 1500 m³ s^?1, up to 900 m wide), surrounded by protected lands of India and Nepal, and upstream of major diversions and river alterations.
• 2. Fish and habitat sampling was conducted at 45 sites from 2000 to 2003. Data were analysed for 2172 fish of 14 species. Species and life stages found occupying a statistically distinct subset of the river habitats were grouped to identify classes of river habitat for conservation.
• 3. Most species and life‐stage groups specialized on specific habitat conditions revealed by multivariate analyses of variance and a principal component analysis. The most numerous and diverse group (six species, 15 life stages) was associated with deep depositional habitats with sandy substrate. Two species covering three life stages were primarily oriented to erosional habitat marked by fast current velocity with pebble and cobble substrate. A third group of three species of adults and juveniles were intermediate in habitat use.
• 4. River conservation for fish faunas should maintain both erosional and depositional channel habitats with depths, substrates, and current velocity inclusive of the ranges reported. The erosional and depositional nature of the key habitats requires that rivers be maintained with flows capable of channel‐forming functions.

Copyright © 2006 John Wiley & Sons, Ltd.     

流溪河保护区鱼类群落结构及其时空变动

为了解流溪河光倒刺鲃国家级水产种质资源保护区鱼类群落结构,分析不同河段、不同季节鱼类群落多样性的变化,于2017年12月-2018年10月对保护区上、中、下游的鱼类开展了每个季度一次的调查。调查结果显示,共采集鱼类57种,隶属于5目14科50属,其中鲤形目43种、鲈形目6种、鲇形目5种,合鳃鱼目2种,鳉形目1种;计算57种鱼类的相对重要性指数,结果显示,尼罗罗非鱼、越南■及鲤鱼为2017-2018年度优势种;Shannon-Wiener多样性指数、Margalef丰富度指数和Pielou均匀度指数计算结果显示,下游鱼类群落的多样性及均匀度最高,夏季鱼类群落的多样性、丰富度及均匀度最高;各监测点之间的种类相似性系数显示,保护区上中游、上下游之间鱼类种类组成为中等不相似,中下游种类组成为中等相似,春夏、春冬、夏冬及夏秋季节鱼类种类组成为中等不相似,春秋、秋冬季节为中等相似;ABC分析结果显示,春、夏及冬季鱼类群落处于稳定状态,秋季处于中度干扰状态。     

Assessing the opportunities for upstream migration of non-salmonid fishes in the weir-regulated River Vecht

The degree of obstruction posed by weirs to potential upstream movements of non-salmonid fish (predominantly cyprinids) in the River Vecht, the Netherlands, was assessed. This rain-fed river showed high variability in discharge, providing opportunities for passage at high discharge when weirs were free flowing. Daily recorded discharge and water levels between 1960 and 1984, and an analysis of swimming capacities and migratory behaviour, were used to assess whether hydraulic conditions each day and for each species were suitable for ascent. The assessment demonstrated that migratory opportunities along the six weirs were extremely limited. Only 10 of 32 species were able to ascend all weirs in 5–30% of the years. Opportunities were the greatest for large-sized species during November–March at the downstream-situated weirs, whereas small-sized species had no opportunities year-round. The approach used is widely applicable for barrier assessment in other rivers, because it requires only basic hydraulic measurements that are often available.