Fish Assemblage Integrity Research Articles

How influential is the role of oligotrophication on the integrity of fish assemblages in the littoral zone?

Food web theory predicts that one of the consequences of oligotrophication is the decline in fisheries following the establishment of nutrient-deficient conditions and low biogenic production. However, emerging evidence suggests that more complex trophic interactions, induced by plankton composition, dietary diversification, temporal and spatial heterogeneity, variations in fish age and size structure can lead to ecosystem responses that deviate from theoretical predictions; especially in the shallow littoral zone. In this study, two end-to-end modelling strategies are used to characterize potential food web structural shifts and overall ecosystem productivity in response to oligotrophication. Our modelling strategy draws upon empirical and theoretical evidence from the Bay of Quinte, a semi-enclosed embayment in northeastern Lake Ontario that has been subjected to phosphorus (P) abatement strategies in the 1970s. We first show that the role of food abundance has been a primary factor shaping fish production, but the fish community gradually responded to the reduced availability of pelagic staples of their diet by displaying greater reliance upon alternative sources, including benthic and other autochthonous (or even allochthonous) food items. Our analysis further suggests that degree of diet overlap between competing trophic guilds can significantly modulate realized biomass levels. The composition of the autotrophic community is another major confounding factor that can induce significant variations from the predicted food web productivity patterns in response to oligotrophication. Overall, our analysis suggests that the proposed reduction of the ambient total phosphorus levels may not necessarily trigger a significant decline in fish biomass in the Bay of Quinte.

Reduced dry season fish biomass and depleted carnivorous fish assemblages in unprotected tropical oxbow lakes

The effectiveness of protected areas in maintaining biodiversity is increasingly under debate. Specifically, the responses of animal populations in freshwater ecosystems to disturbances outside protected areas are not well understood. Fish assemblages can serve as an indicator of such responses. We used dry season oxbow lake fish occurrence data implemented within a Measurement of Biodiversity framework to examine the influence of extractive activities on the richness, structure and abundance of fish assemblages. We compared oxbow lakes in protected areas with lakes subject to artisanal small-scale gold mining (ASGM) and other human activities. The main components of fish biodiversity maintained by lake protection were abundance and biomass. The strongest predictors of community structure were fishing intensity and water transparency. As variation in these factors are likely a consequence of ASGM, our results may indicate indirect impacts of ASGM on freshwater ecosystems. Our analysis of fish trophic guilds also suggested that carnivores dominated fish assemblages in protected lakes, whereas in disturbed lakes detritivores were more frequent, suggesting a trophic downgrading of freshwater ecosystems subject to ASGM. Taken together, our results indicate responses of fish assemblages to human activity associated with ASGM. In the western Amazon, protected and isolated areas appear to be successful at maintaining the integrity of fish assemblages. Given the vulnerability of freshwater habitats and their high value for ecosystem services, we recommend local community engagement and resource allocation to prevent the degradation of oxbow lake habitats and the depletion of local aquatic biodiversity in unprotected areas.

The application of a Fish Assemblage Integrity Index (FAII) in a Southern African river system

The Fish Assemblage Integrity Index (FAII) was used to determine the status of the fish assemblage in relation to human-induced factors in 3 segments of the Nyagui River, Zimbabwe. The 1st and upstream segment, with a relative score of 56.5%, was classified as largely modified. The presence of exotic predators, Micropterus salmoides, that constituted >10% of the fish population sample, was linked to this low score in this segment that had low habitat diversity. The 2nd and middle segment had a relative score of 91.6% and was classified as unmodified. Species that are intolerant to habitat modification, which included Opsaridium zambezense, Chiloglanis neumanni and Zaireichthys rotundiceps, were collected. Habitat diversity increased while the proportional abundance of M. salmoides decreased in this segment. The 3rd and downstream segment, with a score of 81.5%, was classified as largely natural. This score was mainly obscured by rare and migratory species that were expected at low altitude but were not collected. Nevertheless, intolerant species were collected from this segment. Habitat diversity was highest while the proportional abundance of largemouth bass, Micropterus salmoides, was lowest. It is recommended that more studies be carried out to test the consistency of the FAII in determining the impact of introduced species on native species, and to test the impact of other human activities on fish communities in Zimbabwean rivers.

Evaluation of the biotic integrity of fish assemblages in the Yellow River estuary and its adjacent waters

Evaluation of the biotic integrity of fish assemblages in the Yellow River estuary and its adjacent waters

Nearshore fish community assessment on Lake Ontario and the St. Lawrence River: A trap net-based index of biotic integrity

Abstract An index of biotic integrity (IBI) based on an Ontario provincial standard nearshore community index netting (NSCIN) protocol was developed to assess nearshore fish communities and ecosystem health in the Lake Ontario/St. Lawrence River ecoregion. The IBI was based on 11 individual metrics representing aspects of fish assemblage integrity: taxonomic richness, habitat guilds, trophic guilds, and overall abundance and biomass. Thirteen geographic areas were sampled and grouped into three habitat types: sheltered embayments, exposed embayments, and riverine. IBI values were higher for sheltered embayments (mean IBI = 71, excluding Hamilton Harbour) than for exposed embayments (62, excluding Toronto Harbour) and riverine areas (64). The IBI accurately reflected anticipated contemporary differences in ecosystem health among geographic areas as well as historical changes within the Bay of Quinte. Two designated areas of concern (AOCs) where remedial action plans (RAP) are ongoing, Hamilton Harbour, a sheltered embayment, and Toronto Harbour, a more exposed area, had lowest IBI values (45 and 47, respectively). IBI values on Bay of Quinte and Lake St. Francis AOCs, where RAPs are nearing completion, were very similar to IBI values from less affected embayments and nearshore areas within their respective habitat types. Upper and middle Bay of Quinte IBIs increased from 47.3 and 45.9, respectively, to 71.8 and 69.2 over a 45-year time period (1969–2013) consistent with previously documented major ecosystem change.

Fish-based Index of Biotic Integrity for wadeable streams from Atlantic Forest of south São Paulo State, Brazil

Abstract: Understanding the relationship between environmental quality of streams and biological integrity of fish assemblages is critical to successful ecosystem management. Aim We adapted the Index of Biotic Integrity (IBI) using ecological data of the fish assemblages that occur in headwater streams from the Atlantic Forest in southern São Paulo State. Methods We sampled the ichthyofauna and collected environmental data in 27 streams stretches during the dry season of 2010. The fish species were categorized into trophic group, position in the water column and preference for rapid meso-habitats. Candidate metrics were screened for range, responsiveness and redundancy. Results Of the 17 metrics tested, four metrics were included in the IBI. They belonged to attributes species diversity: percentage of individuals as Loricariidae family; habitat use: percentage of individuals as benthic riffles; and trophic function: percentage of individuals as omnivores and percentage of individuals as herbivores/detritivores. Eight streams (30%) were classified as excellent or good and fourteen (50%) as poor or very poor. Conclusions On a regional scale, many aspects of biological integrity were altered but there are streams that can be used as biological reference.

Choice of biota in stream assessment and monitoring programs in tropical streams: A comparison of diatoms, macroinvertebrates and fish

The objective of this study was to compare the responses of diatoms, macroinvertebrates and fish to agriculture, urbanization and mining in the Manyame River Basin. Water quality sampling and benthic diatom, macroinvertebrate and fish community data were collected in April (end of the rain season) and September (dry season) 2013 at 44 sampling stations spread out across three land-use categories: commercial agricultural, communal agricultural and urban-mining areas. Commercial agricultural areas were relatively pristine as they were characterized by mature deciduous riparian forest strips which acted as riparian buffers thus protecting water resources from nonpoint source pollution. In communal agricultural areas a combination of poor agricultural practices (stream bank cultivation, overgrazing, soil erosions) and high human population densities had negative effects on water quality of streams draining these areas. Streams in urban-mining areas were highly stressed, being impacted primarily by physical habitat degradation and both point and nonpoint sources of pollution. A suite of environmental variables that varied with land-use pattern was assessed to find the combination of variables that best explained patterns of biota community composition. Community metrics i.e. the Trophic Diatom Index (TDI) based on diatoms, the South African Scoring system version 5 (SASS 5) based on macroinvertebrates and the Fish Assemblage Integrity Index (FAII) were used to determine the ecological status of study streams in relation to human-induced stressors. Data were also subjected to multivariate statistical techniques; canonical correspondence analysis (CCA), mantel test and cluster analysis to determine environmental gradients along which the diatom, macroinvertebrate and fish assemblages were distributed as well as to elucidate hypothesized differences in response to stressors among communities per land-use type. Using CCA, we assessed the individual importance of a set of environmental variables on each biotic community structure. ANOVA, showed a significant difference (p<0.05) in physical and chemical variables among commercial agricultural, communal agricultural and urban-mining sampling stations with no significant differences (p>0.05) between the 2 sampling periods. Based on CCAs carried out using individual variables, the strengths of relationships between diatoms and macroinvertebrates was generally high for nutrient levels, organic and metal pollution and other variables. However, fish assemblages showed a relatively low association with all water quality variables in the study; this might be explained by the high abundance of omnivores and air breathers which are able to tolerate a variety of environmental conditions. These patterns were also confirmed by the mantel test as well as the other CCAs carried out to investigate the simultaneous effects of environmental variables. These findings indicate that diatoms are more powerful indicators in accessing ecological stream/river quality and have potential for application in routine monitoring programs in tropical streams.

Effects of Land Use Intensification on Fish Assemblages in Mediterranean Climate Streams

Southern Portugal is experiencing a rapid change in land use due to the spread of intensive farming systems, namely olive production systems, which can cause strong negative environmental impacts and affect the ecological integrity of aquatic ecosystems. This study aimed to identify the main environmental disturbances related with olive grove intensification on Mediterranean-climate streams in southern Portugal, and to evaluate their effects on fish assemblage structure and integrity. Twenty-six stream sites within the direct influence of traditional, intensive, and hyper-intensive olive groves were sampled. Human-induced disturbances were analyzed along the olive grove intensity gradient. The integrity of fish assemblages was evaluated by comparison with an independent set of least disturbed reference sites, considering metrics and guilds, based on multivariate analyses. Along the gradient of olive grove intensification, the study observed overall increases in human disturbance variables and physicochemical parameters, especially organic/nutrient enrichment, sediment load, and riparian degradation. Animal load measured the impact of livestock production. This variable showed an opposite pattern, since traditional olive groves are often combined with high livestock production and are used as grazing pasture by the cattle, unlike more intensive olive groves. Stream sites influenced by olive groves were dominated by non-native and tolerant fish species, while reference sites presented higher fish richness, density and were mainly occupied by native and intolerant species. Fish assemblage structure in olive grove sites was significantly different from the reference set, although significant differences between olive grove types were not observed. Bray-Curtis similarities between olive grove sites and references showed a decreasing trend in fish assemblage integrity along the olive grove intensification gradient. Olive production, even in traditional groves, led to multiple in-stream disturbances, whose cumulative effects promoted the loss of biota integrity. The impacts of low intensity traditional olive groves on aquatic ecosystems can be much greater when they are coupled with livestock production. This paper recommends best practices to reduce negative impacts of olive production on streams, contributing to guide policy decision-makers in agricultural and water management.

Effects of damming on the biological integrity of fish assemblages in the middle Lancang-Mekong River basin

The Lancang-Mekong River basin contains a diverse assemblage of freshwater fish species; however, their populations are threatened by current and planned dam construction along the river. Fish assemblages are sensitive indicators of environmental degradation and can be used to assess aquatic ecosystem health. This research compared the fish fauna at the Xiaowan hydropower dam located on the middle reaches of the Lancang-Mekong River at three time periods: in 2008 (before impoundment), 2010 (water storage) and 2011 (full operation). A modified fish index of biological integrity (modified F-IBI) was developed and it synthesized information on the taxonomic composition, trophic guilds, and tolerance levels of the fish and habitat diversity to quantitatively assess the condition of fish populations before and after damming. This index also was used to assess the longitudinal diversity of the fish fauna along the river channel and could assess the barrier effect associated with the dam. Jaccard's index of similarity was used as a feasible tool to assess fish diversity loss and biotic homogenization. The analysis clearly showed a homogenization of the fish communities after damming, and the reservoir impoundment region showed much more serious homogenization than the downstream region. The Xiaowan dam had an immediate and profound effect on the fish fauna in this region of the Lancang-Mekong River. A total of eight cascading dams are planned for development in this region, and, unless conservation mitigation efforts are considered, the results could be devastating on the native fish populations of middle reaches of the Lancang-Mekong River basin.

Development of a fish-based index of biotic integrity (FIBI) to assess the quality of Bandama River in Côte d’Ivoire

The aim of this study was to develop effective tools based on fish assemblages, allowing the development of an effective assessment approach for the ecological status of running waters. Fish samples were collected using gill-nets with mesh sizes of 8, 10, 12, 14, 15, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 and 80 mm. Forty sites were visited from October 2008 to September 2009 in the Bandama River. A large part of the data set on fish descriptors associated with environmental parameters was compiled from regional databases. For each of the fish assemblage descriptors, stepwise multiple linear regressions with habitat variables were carried out. The residuals of the models obtained were used as candidate metrics independent of natural environmental factors. Student t-tests used to compare each metric in reference and disturbed samples indicated significant difference (P < 0.05) for six metrics. The standard residuals of metrics selected were added to constitute the final index. This multimetric index of fish assemblage integrity could serve as a practical technical reference for conducting cost-effective biological assessments of lotic systems.

Structure and integrity of fish assemblages in streams associated to conservation units in Central Brazil

This study aims to characterize the spatial and seasonal distribution of the fish assemblage and evaluate the integrity of streams in a sustainable use area that includes integral protection conservation units in Distrito Federal, Central Brazil (Cerrado biome). For the study, 12 stretches of 8 streams were sampled in 2008 (dry season) and 2009 (wet season). For that evaluation was estimated the Physical Habitat Index (PHI), vegetation cover (VC), pH, dissolved oxygen, turbidity, and conductivity. We recorded 22 species, about eight undescribed species, by a total of 2,327 individuals. The most representative families in number of species were Characidae (31.8%), Loricariidae (31.8%), and Crenuchidae (13.6%). Knodus moenkhausii was the most abundant species with 1,476 individuals, added to Astyanax sp., Phalloceros harpagos, and Hasemania sp. they represent over 95% of the total abundance. The species Astyanax sp. (occurring in 79.2% of the stretches) and K. moenkhausii (50.0%) were considered constant in both seasons. The longitudinal gradient (River Continuum) exerts a strong influence on the studied assemblage. According to CCA, the variables that structure the fish assemblage are based on aspects related to water volume and habitat complexity. No seasonal variation in richness, diversity, abundance, and mass were detected. A cluster analysis suggests a separation of species composition between the stretches of higher and lower orders, which was not observed for seasonality. The streams were considered well preserved (mean PHI 82.9±7.5%), but in some stretches were observed anthropogenic influence, detected in the water quality and, mainly, on the riparian vegetation integrity. The exotic species Poecilia reticulata was sampled in the two stretches considered most affected by anthropogenic activities by PHI, conductivity, and VC.

Influences of Human Stressors on Fish-Based Metrics for Assessing River Condition in Central Alberta

Abstract Economic developments in Alberta have resulted in widespread changes in land use that may deteriorate river conditions for fish. Fish assemblages were characterized with index of biological integrity metrics for the heavily-developed watershed of the Battle River, Alberta. Metric relationships with human stressors were quantified using regression and information theory methods. Although the fauna comprised 14 native species, 50% of the catch was white sucker (Catostomus commersoni Lacepede, 1803). Five statistically unrelated metrics were identified as being responsive to stressors: two trophic guilds, one habitat guild, one reproductive guild, and one measure of community structure. Regression showed that the cumulative effect of human developments, indexed as road density in the basin, was negatively linked to the relative abundance of lithophils and positively linked to the relative abundance of omnivores. Agriculture also threatened the integrity of fish assemblages. Stream sections with higher cattle densities in their basins had fewer lithophils and benthic invertivores; whereas stream sections with higher nutrient concentrations contained fewer species, as well as fewer top carnivores, but more true omnivores. Understanding effects of human footprints that are expanding in western Canada will be critical to the successful management of aquatic resources.

Environmental indicators of macroinvertebrate and fish assemblage integrity in urbanizing watersheds

Urbanization compromises the biotic integrity and health of streams, and indicators of integrity loss are needed to improve assessment programs and identify mechanisms of urban effects. We investigated linkages between landscapes and assemblages in 31 wadeable Piedmont streams in the Etowah River basin in northern Georgia (USA). Our objectives were to identify the indicators of macroinvertebrate and fish integrity from a large set of best land cover ( n = 45), geomorphology ( n = 115), and water quality ( n = 12) variables, and to evaluate the potential for variables measured with minimal cost and effort to effectively predict biotic integrity. Macroinvertebrate descriptors were better predicted by land cover whereas fish descriptors were better predicted by geomorphology. Water quality variables demonstrated moderate levels of predictive power for biotic descriptors. Macroinvertebrate descriptors were best predicted by urban cover (−), conductivity (−), fines in riffles (−), and local relief (+). Fish descriptors were best predicted by embeddedness (−), turbidity (−), slope (+), and forest cover (+). We used multiple linear regression modeling to predict descriptors using three independent variable sets that varied in difficulty of data collection. “Full” models included a full range of geomorphic, water quality and landscape variables regardless of the intensity of data collection efforts. “Reduced” models included GIS-derived variables describing catchment morphometry and land use as well as variables easily collected in the field with minimal cost and effort. “Simple” models only included GIS-derived variables. Full models explained 63–81% of the variation among descriptors, indicating strong relationships between landscape properties and biotic assemblages across our sites. Reduced and simple models were weaker, explaining 48–79% and 42–79%, respectively, of the variance among descriptors. Considering the difference in predictive power among these model sets, we recommend a tiered approach to variable selection and model development depending upon management goals. GIS variables are simple and inexpensive to collect, and a GIS-based modeling approach would be appropriate for goals such as site screening (e.g., identification of reference streams). As management goals become more complex (e.g., long-term monitoring programs), additional, easily collected field variables (e.g., embeddedness) should be included. Finally, labor-intensive variables (e.g., nutrients and fines in sediments) could be added to meet complex management goals such as restoration of impaired streams or mechanistic studies of land use effects on stream ecosystems.

Assessment of an index of biological integrity (IBI) to quantify the quality of two tributaries of river Chenab, Sialkot, Pakistan

Nullah Aik and Nullah Palkhu, two tributaries of river Chenab, were investigated for the assessment of fish habitat degradation as indicator of stream health. Fish abundance data were collected from 18 sites from September 2004 to April 2006 to develop multimetric indices for fish assemblage integrity and to detect the intensity of habitat degradation. A total of 12 metrics were calculated on the basis of taxonomic richness, habitat preference, trophic guild, stress tolerance and origin of species to develop stepped and continuous index of biological integrity (IBI) criteria. Cluster analysis (CA) classified sites based on species composition into three groups, viz., reference, moderately impaired and impaired groups. Non-metric multidimensional scaling (NMDS) was applied to identify underlying ecological gradient to highlight the habitat degradation. NMDS segregated two sites as less impaired, five sites as moderately impaired and eleven sites as impaired groups. Axes 1 and 2 explained a total variation of 53.3%. First axis explained the level of habitat impairment, whereas axis 2 indicated species richness along longitudinal gradient of streams. Sites located upstream of Nullah Aik showed higher IBI scores which dropped to its lowest in downstream sites near Sialkot city. Lowest values of IBI of sites in close proximity of city indicated the role of anthropogenic activities in catchment areas. The results indicated that variability in water chemistry can be related as a function of stream sites impairments (i.e., unimpaired, moderately impaired, and severely impaired). Water quality parameters showed strong correlation with IBI scores. Significantly negative correlation of IBI scores with COD, TDS, turbidity, Fe, Cr, Zn and positive correlation with DO and pH was found. The results can be used for restoration and future management of small streams passing through urban areas of Pakistan.

Riparian influences on stream fish assemblage structure in urbanizing streams

We assessed the influence of land cover at multiple spatial extents on fish assemblage integrity, and the degree to which riparian forests can mitigate the negative effects of catchment urbanization on stream fish assemblages. Riparian cover (urban, forest, and agriculture) was determined within 30 m buffers at longitudinal distances of 200 m, 1 km, and the entire network upstream of 59 non-nested fish sampling locations. Catchment and riparian land cover within the upstream network were highly correlated, so we were unable to distinguish between those variables. Most fish assemblage variables were related to % forest and % urban land cover, with the strongest relations at the largest spatial extent of land cover (catchment), followed by riparian land cover in the 1-km and 200-m reach, respectively. For fish variables related to urban land cover in the catchment, we asked whether the influence of riparian land cover on fish assemblages was dependent on the amount of urban development in the catchment. Several fish assemblage metrics (endemic richness, endemic:cosmopolitan abundance, insectivorous cyprinid richness and abundance, and fluvial specialist richness) were all best predicted by single variable models with % urban land cover. However, endemic:cosmopolitan richness, cosmopolitan abundance, and lentic tolerant abundance were related to % forest cover in the 1-km stream reach, but only in streams that had <15% catchment urban land cover. In these cases, catchment urbanization overwhelmed the potential mitigating effects of riparian forests on stream fishes. Together, these results suggest that catchment land cover is an important driver of fish assemblages in urbanizing catchments, and riparian forests are important but not sufficient for protecting stream ecosystems from the impacts of high levels of urbanization.

Importance of Riparian Forests in Urban Catchments Contingent on Sediment and Hydrologic Regimes

Forested riparian corridors are thought to minimize impacts of landscape disturbance on stream ecosystems; yet, the effectiveness of streamside forests in mitigating disturbance in urbanizing catchments is unknown. We expected that riparian forests would provide minimal benefits for fish assemblages in streams that are highly impaired by sediment or hydrologic alteration. We tested this hypothesis in 30 small streams along a gradient of urban disturbance (1-65% urban land cover). Species expected to be sensitive to disturbance (i.e., fluvial specialists and "sensitive" species that respond negatively to urbanization) were best predicted by models including percent forest cover in the riparian corridor and a principal components axis describing sediment disturbance. Only sites with coarse bed sediment and low bed mobility (vs. sites with high amounts of fine sediment) had increased richness and abundances of sensitive species with higher percent riparian forests, supporting our hypothesis that response to riparian forests is contingent on the sediment regime. Abundances of Etheostoma scotti, the federally threatened Cherokee darter, were best predicted by models with single variables representing stormflow (r(2) = 0.34) and sediment (r(2) = 0.23) conditions. Lentic-tolerant species richness and abundance responded only to a variable representing prolonged duration of low-flow conditions. For these species, hydrologic alteration overwhelmed any influence of riparian forests on stream biota. These results suggest that, at a minimum, catchment management strategies must simultaneously address hydrologic, sediment, and riparian disturbance in order to protect all aspects of fish assemblage integrity.

Development and application of a fish-based Sensitivity-weighted Index of Biotic Integrity (SIBI) for use in the assessment of biotic integrity in the Klip River, Gauteng, South Africa

Biotic indices using fish assemblage characteristics have been applied with great success in river assessments around the world. Internationally the most commonly applied fish index is the Index of Biotic Integrity (IBI), whilst in South Africa the most commonly applied index is the Fish Assemblage Integrity Index (FAII). The Sensitivity-weighted Index of Biotic Integrity (SIBI) was developed as an alternative multimetric fish index, incorporating important principles from both the IBI and FAII. This study indicated that the SIBI was a valuable index which used fish as indicators of biotic integrity in the Klip River. The SIBI was also suited to the analysis of site-specific data and the investigation of specific impacts. It is envisaged that the SIBI concept could be applied to other aquatic systems and could possibly be used as an alternative fish index for South African rivers, especially when investigations necessitate site-specific evaluations. The application of the SIBI and IBI in this study also emphasised the FAII's potential underestimation of biotic integrity. The results obtained from the use of the SIBI indicated that the biotic integrity of the Klip River System is currently moderately to critically modified from its natural condition.

Electrofishing Distance Needed to Estimate Fish Species Richness in Raftable Oregon Rivers

Abstract One critical issue surrounding river biomonitoring is the minimum amount of sampling distance required to adequately represent the fish assemblage of a reach. Determining adequate sampling distance is important because it affects the estimates of fish assemblage integrity and diversity at the local and regional scales. We sought to answer the sampling distance question by sampling 45 raftable Oregon river reaches for an entire day and then assessing the minimum effort needed to collect 95% of the species obtained in 75% of the reaches sampled. We also resampled 10 reaches to estimate the measurement and sampling period errors. Fish were collected by means of an electrofishing raft, and physical and chemical habitats were sampled to aid in data interpretation. The collected numbers of species were typically only 0–3 species fewer than those predicted for true species richness by simulated species accumulation curves and nonparametric models. We concluded that a sampling distance equal to 85 times ...

Evaluation of biological integrity of a small urban stream system by investigating longitudinal variability of the fish assemblage

We investigated the integrity of fish assemblages of a small anthropogenically impacted urban stream system in south-western Germany. Heavy point and non-point pollution physiologically stresses the aquatic fauna while migration barriers and river morphological alterations negatively influence habitat availability. Investigations conducted in 1998 and 1999 revealed that the fish assemblage was altered and several site-specific fish species were missing while non-site-specific species were relatively common. Highest species diversity was recorded in a reach downstream of the main migration barrier, while upstream only a few species were present. In general, a shift to ubiquitous and limnophilic species as well as to less pollution sensitive species was observed. Adult fish dominated the population structure throughout the stream course. Recruitment was confined mainly to the less polluted headwater. In the present study we introduce an assessment system based on the similarity of the potential natural and the actually established fish assemblage as demanded by the Water Framework Directive of the European Union for the evaluation of the ecological status of a fish assemblage in a stream [EC of the European Parliament and of the Council of Europe establishing a framework for community action in the field of water policy. Brussels, 30 June, 2000. 1997/0067 (COD)]. Both, stream morphological quality and pollution data sampled within the two study years confirm the validity of the suggested assessment method.

Native Invasions, Homogenization, and the Mismeasure of Integrity of Fish Assemblages

Abstract Human activities, particularly habitat destruction and species introductions, are resulting in increased homogenization of once unique biogeographic regions. In the southeastern United States, extensive endemism occurs among highland fish species that have specialized ecologies, are adapted to cool, clear, nutrient-poor conditions, and are sediment-intolerant. Highland streams flow into lower elevation systems, which are often inhabited by more widespread, generalist fish species adapted to warmer, more turbid, fine-sediment-rich, and nutrient-rich conditions. Common land use practices, such as deforestation, degrade stream habitats and reduce habitat diversity, which is often correlated with taxonomic and ecological diversity. Habitat homogenization can thus cause assemblage homogenization via loss of native species and addition of nonindigenous species. However, midpoints in the homogenization process may be characterized by constant or even increased species diversity because generalist, sedim...