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Baseline data for reference conditions are needed to determine the impacts of human pressures on the structure and functioning of marine ecosystems. However, baseline data are seldom available, and a comprehensive understanding of what good ecological condition is or how to measure it is often lacking. In the absence of true baselines, well established and effective marine protected areas (MPAs) can be used to approximate reference conditions. Thus, the aim of this study was to use effective no-take MPAs to identify suitable indicators that can be used for condition assessments of rocky reefs in South Africa. To achieve this, we tested the response of two types of metrics (compositional and size-based), using in situ fish and benthic community data, to three levels of human pressures in two ecoregions in South Africa. Results showed that traditionally-used structural metrics, such as total abundance or species richness, were less responsive than size-based metrics, including total biomass, average length and proportion of mature fish. Rocky reef ecosystems exposed to low anthropogenic pressure were characterised by a higher biomass, average length and proportion of mature and large (>30 cm) fish than reefs with moderate and high pressures. Benthic communities appeared more resilient than fish communities to the typical human pressures in the study region. Overall, the greatest effect of pressure was observed in the heavily impacted sub-tropical Natal Shelf Ecoregion, while rocky reefs in the warm-temperate Agulhas Shelf Ecoregion appeared to be in better condition than expected. This study identified assemblage patterns and indicators that appeared responsive and sensitive to different levels of human pressure, which can be used to infer good and poor ecological condition of rocky reef ecosystems. These results indicate which species (e.g., target species) and traits (e.g., size) are most vulnerable to local human pressures and will be suitable for condition assessments.

Large river systems are one of the most important water resources for human societies. However, the ecological integrity of large rivers has been altered greatly by human activities. To monitor and manage these ecosystems, multimetric indices (MMI) are considered as efficient tools. This study aimed to develop and validate a fish‐based multimetric index for the Karun River basin, Iran (Karun fish‐based multi‐metric index [KFMMI]). Eighteen rivers and 54 sites in the basin were sampled in July–August 2019, and physico‐chemical and habitat characteristics were used to identify reference sites based on principal components analysis (PCA). Of the 54 sites, 14, 26, and 14 sites were classified as least, moderate, and most disturbed sites, respectively. Fifty‐four candidate metrics were evaluated for range, responsiveness, and redundancy with other metrics. This resulted in the identification of eight metrics (relative abundance of native and endemic taxa, relative richness of migratory taxa, relative richness of Leuciscidae taxa, relative richness of herbivorous taxa, relative abundance of cyprinid taxa, relative richness of vegetative inhabitant taxa, relative abundance of slow water flow, and relative richness of edge inhabitant taxa) that informed on species richness and composition, migratory status, functional feeding groups, and habitat preferences. The KFMMI showed excellent performance in separating least, moderate, and most disturbed sites in our study area. Regarding water quality, the KFMMI was classified 16, 5, and 29 sites as good, moderate, and bad, respectively. The discrimination efficiency of KFMMI was 81.6%, which makes it an effective management tool for directing restoration actions at most disturbed sites and intensifying protection of least disturbed sites. [ABSTRACT FROM AUTHOR]

Context: Untangling relationships between landscape patterns shaped by human stressors and related response of fish communities is important for identifying biodiversity patterns and conservation targets, yet in large rivers this knowledge is extremely limited. Objectives: Our study focuses on how human stressors within a riparian landscape zone, including both riparian land use and in-channel stressors, explained the fish community structure in a large river. Methods: We studied fish community patterns along the upstream-downstream gradient of the Yangtze River, China. The curve estimation was used to test correlations between fish metrics and the distance from the estuary. We linked human stressors to fish metrics by multivariate generalized linear models. Results: We collected a total of 63 freshwater fish species from 6,147 specimens. Limnophilic species had the highest richness, represented by 30 specie. The predominant riparian land uses in the studied reaches were cropland (65.3% ± 13.1%) and urban land (19.7% ± 13.6%). There were strong negative correlations between riparian land use (e.g., urban land) and in-channel stressors (e.g., shoreline modification, navigation, and fishing pressure) and fish assemblages, especially limnophilic fish abundance, biomass, and richness. Conclusions: These results demonstrate influences of both riparian land use and in-channel stressors on fish communities, and highlight the use of landscape descriptors as a valuable approach to assess linkages between human pressures and fish diversity in large river systems. Management recommendations include: establishing or rehabilitating riparian buffers, improving commercial navigation management, implementing shoreline protection measures, and reinforcing fishing laws and regulations. [ABSTRACT FROM AUTHOR]

Abstract Alterations of abiotic factors (e.g., river water temperature and discharge) will definitely affect the fundamental processes of aquatic ecosystems. The purpose of this study was to examine the impact of climate change on the structure of fish assemblages in fast-flowing rivers belonging to the catchment of the major Eastern European river, the Nemunas. Five catchments of semi-natural rivers were selected for the study. Projections of abiotic factors were developed for the near (2016–2035) and far future (2081–2100) periods, according to four RCP scenarios and three climate models using the HBV hydrological modelling tool. Fish metric projections were developed based on a multiple regression using spatial data. No significant changes in projections of abiotic and biotic variables are generally expected in the near future. In the far future period, the abiotic factors are projected to change significantly, i.e., river water temperature is going to increase by 4.0–5.1 °C, and river discharge is projected to decrease by 16.7–40.6%, according to RCP8.5. By the end of century, the relative abundance of stenothermal fish is projected to decline from 24 to 51% in the reference period to 0–20% under RCP8.5. Eurythermal fish should benefit from climate change, and their abundance is likely to increase from 16 to 38% in the reference period to 38–65% under RCP8.5. Future alterations of river water temperature will have significantly more influence on the abundance of the analysed fish assemblages than river discharge. Graphical abstract Unlabelled Image Highlights • Future climate changes are likely to affect fish assemblages in rivers. • Projections were made using hydrological modelling and statistical methods. • River discharge is projected to decrease, while temperature is likely to increase. • Changes of abiotic factors will cause changes in abundance of investigated fishes. • Changes of river temperature will have most significant impact on fish abundance. [ABSTRACT FROM AUTHOR]

Monitoring of biota in heterogeneous ecosystems requires sampling in different habitats and across environmental gradients. The resulting multivariate community data are typically aggregated into one or several indicator values for the entire ecosystem, but the relationship between the robustness of such indicators and sampling effort, including the identification of minimum acceptable sampling designs, is not fully understood. [ABSTRACT FROM AUTHOR]

This work addresses human stressors and their impacts on fish assemblages at pan-European scale by analysing single and multiple stressors and their interactions. Based on an extensive dataset with 3105 fish sampling sites, patterns of stressors, their combination and nature of interactions, i.e. synergistic, antagonistic and additive were investigated. Geographical distribution and patterns of seven human stressor variables, belonging to four stressor groups (hydrological-, morphological-, water quality- and connectivity stressors), were examined, considering both single and multiple stressor combinations. To quantify the stressors' ecological impact, a set of 22 fish metrics for various fish assemblage types (headwaters, medium gradient rivers, lowland rivers and Mediterranean streams) was analysed by comparing their observed and expected response to different stressors, both acting individually and in combination. Overall, investigated fish sampling sites are affected by 15 different stressor combinations, including 4 stressors acting individually and 11 combinations of two or more stressors; up to 4 stressor groups per fish sampling site occur. Stressor-response analysis shows divergent results among different stressor categories, even though a general trend of decreasing ecological integrity with increasing stressor quantity can be observed. Fish metrics based on density of species ‘intolerant to water quality degradation’ and ‘intolerant to oxygen depletion” responded best to single and multiple stressors and their interactions. Interactions of stressors were additive (40%), synergistic (30%) or antagonistic (30%), emphasizing the importance to consider interactions in multi-stressor analyses. While antagonistic effects are only observed in headwaters and medium-gradient rivers, synergistic effects increase from headwaters over medium gradient rivers and Mediterranean streams to large lowland rivers. The knowledge gained in this work provides a basis for advanced investigations in European river basins and helps prioritizing further restoration and management actions. [ABSTRACT FROM AUTHOR]

Quantifying how human disturbance affects biotic communities in the context of other natural and spatial factors is a vital precursor to develop environmental management strategies to effectively conserve and restore ecosystem. This is particularly so for freshwater ecosystems in heavily populated and increasingly disturbed regions such as the Wei River basin in north-west China. In this paper, we employed both species’ abundance and functional metrics (displaying species diversity, habitat, trophic level, tolerance and abundance) to quantify the effect of human disturbance using canonical correspondence analysis. The results showed that spatial, natural and human disturbance variables can explain 40.1% and 33.7% of the total variation in fish abundance without rare species and with all species, respectively. 37.1% and 37.9% variation can be explained in fish metrics without rare species and with all species. Human disturbance variables explained most of the total variations in the four fish matrices. Inclusion or exclusion of rare species will influence the total explained variation from three factors in fish metrics, but little in fish abundance. Rare species will highlight this relationship with human disturbance gradient. For fish metrics, removing rare species will reflect some wrong information for human disturbance gradient. We recommend to include rare species for fish metrics to assess the impact of environment. [ABSTRACT FROM AUTHOR]

ABSTRACT Large-scale irrigation projects are being undertaken in the Mediterranean region, and agricultural practices are being intensified, but their impacts on instream biota remain poorly documented. The present study assesses the effects of an irrigation scheme on fish community structure in Mediterranean streams. Fish assemblages were sampled in unregulated intermittent streams over 6 years concurrently with the development of a new irrigation project in southwestern Iberia, and the biotic variation was separately related to increases in human activity and environmental gradients. Overall, fish assemblages were influenced by reservoir proximity (likely functioning as a source of non-native species), the proportion of irrigated lands, average water depth and wetted width (likely related with habitat permanency), and elevation. Results indicated that human actions linked to the irrigation project significantly shaped fish assemblage changes, after accounting for the effect of environmental variables. The proportion of irrigated lands in the catchment was related to some fish metrics (proportion of less tolerant specimens, proportion of invertivores and proportion of non-native specimens, except G. holbrooki). Our results support the thesis that the development and exploitation of irrigation schemes impact fish assemblages and reinforce the need to ensure that the ongoing agricultural intensification is compatible with the ecological integrity of Mediterranean intermittent streams. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We classified homogenous river types across Europe and searched for fish metrics qualified to show responses to specific pressures (hydromorphological pressures or water quality pressures) vs. multiple pressures in these river types. We analysed fish taxa lists from 3105 sites in 16 ecoregions and 14 countries. Sites were pre-classified for 15 selected pressures to separate unimpacted from impacted sites. Hierarchical cluster analysis was used to split unimpacted sites into four homogenous river types based on species composition and geographical location. Classification trees were employed to predict associated river types for impacted sites with four environmental variables. We defined a set of 129 candidate fish metrics to select the best reacting metrics for each river type. The candidate metrics represented tolerances/intolerances of species associated with six metric types: habitat, migration, water quality sensitivity, reproduction, trophic level and biodiversity. The results showed that 17 uncorrelated metrics reacted to pressures in the four river types. Metrics responded specifically to water quality pressures and hydromorphological pressures in three river types and to multiple pressures in all river types. Four metrics associated with water quality sensitivity showed a significant reaction in up to three river types, whereas 13 metrics were specific to individual river types. Our results contribute to the better understanding of fish assemblage response to human pressures at a pan-European scale. The results are especially important for European river management and restoration, as it is necessary to uncover underlying processes and effects of human pressures on aquatic communities. [Copyright &y& Elsevier]

The catchment land-use composition of 249 fish sampling sites in Austrian running waters revealed effects on the biological integrity. Beyond correlative analysis, we investigated (1) which land-use category had the strongest effect on fish, (2) whether metrics of functional fish guilds reacted differently, (3) whether there were cumulative effects of land-use categories, and (4) whether effects varied in strength across river types. We fed 5 land-use categories into regression trees to predict the European Fish Index or fish metric of intolerant species (mainly Salmo trutta fario) . Agriculture and urbanisation were the best predictors and indicated significant effects at levels of >23.3 and >2%, respectively. Model performance was R = 0.15 with the Fish Index and R = 0.46 with intolerant species. The tree structure showed a cumulative effect from agriculture and urbanisation. For the intolerant species metric, a combination of high percentages for agriculture and urbanisation was related to moderate status, whereas <7.3% agriculture were related to good status, although urbanisation was higher than 1.8%. Headwater river types showed stronger responses to land use than river types of lower gradient and turned out to be more sensitive to urbanisation than agriculture. [ABSTRACT FROM AUTHOR]

1. Water abstraction strongly affects streams in arid and semiarid ecosystems, particularly where there is a Mediterranean climate. Excessive abstraction reduces the availability of water for human uses downstream and impairs the capacity of streams to support native biota. 2. We investigated the flow regime and related variables in six river basins of the Iberian Peninsula and show that they have been strongly altered, with declining flows (autoregressive models) and groundwater levels during the 20th century. These streams had lower flows and more frequent droughts than predicted by the official hydrological model used in this region. Three of these rivers were sometimes dry, whereas there were predicted by the model to be permanently flowing. Meanwhile, there has been no decrease in annual precipitation. 3. We also investigated the fish assemblage of a stream in one of these river basins (Tordera) for 6 years and show that sites more affected by water abstraction display significant differences in four fish metrics (catch per unit effort, number of benthic species, number of intolerant species and proportional abundance of intolerant individuals) commonly used to assess the biotic condition of streams. 4. We discuss the utility of these metrics in assessing impacts of water abstraction and point out the need for detailed characterisation of the natural flow regime (and hence drought events) prior to the application of biotic indices in streams severely affected by water abstraction. In particular, in cases of artificially dry streams, it is more appropriate for regulatory agencies to assign index scores that reflect biotic degradation than to assign ‘missing’ scores, as is presently customary in assessments of Iberian streams. [ABSTRACT FROM AUTHOR]

A spatially based approach was used to analyse the response of fish-based metrics to human impacts in the Iberian Peninsula. A fish-based typology was established that distinguished one salmonid type (fish assemblages dominated by Salmo trutta fario L.), two mixed types ( S. trutta fario associated with different cyprinids) and six cyprinid types (dominated by different species of barbel [ Barbus spp.], nase [ Chondrostoma spp.] or chub [ Leuciscus spp.]). These types broadly correspond to different forms of ecosystem functioning, ranging from the cold, northern and high altitude sections to warmwater, lowland and southern sections. Twenty metrics were identified that responded to disturbance – four to 14 per fish type. The highest correlations were −0.795 for abundance of Squalius sp. and segment (localised) disturbance and 0.754 for abundance of limnophilic specimens and water quality disturbance. Disturbance of segment, habitat and hydrological regime yielded more metric responses in western Iberian fish types, while that of habitat and water quality gave more in north-eastern Iberian fish types. Global (catchment scale) disturbance generally gave more responsive metrics and higher correlations than partial disturbances. All guilds were represented and a number of metrics were responsive across fish types – namely native species, alien abundance, water column (natives), eurytopic and invertivorous (natives). However, several metrics were only reactive in one or a few types, such as benthic and S. trutta fario in north-western mixed fish type. Different trends in metric reaction occurred for total abundance in north-western mixed fish type, and for eurytopic and phytophilic (natives) in the north-eastern fish types. [ABSTRACT FROM AUTHOR]

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.)). [ABSTRACT FROM AUTHOR]

Multi-metric indices of biological integrity (IBIs) are most frequently created by examining single biological metrics along gradients of environmental degradation, and then combining multiple metrics using “best professional judgment” to characterize and calibrate stressor–response relationships. We aim to provide an efficient data analysis and visualization tool to assess the simultaneous effects of anthropogenic stressors on the fish population through the fish metrics and the associated Index of Biotic Integrity (IBI). Kohonen''s self-organizing feature maps (SOM), unsupervised neural networks, are employed to pattern the sampling sites in the state of Ohio based on similar metrics characteristics. Canonical correspondence analysis (CCA) allows us then to draw conclusions about the role of the environmental variables in maintaining the perfect abode for fishes. Different visualizations superimposed with SOM clustering are realized to explore the complex interrelationships in the aquatic system and aid watershed managers to comprehend the effects of the environment on the fish. [Copyright &y& Elsevier]