Rheophilic Fish Research Articles

Assessing spirlin Alburnoides bipunctatus (Bloch, 1782) as an early indicator of climate change and anthropogenic stressors using ecological modeling and machine learning

Combining single-species ecological modeling with advanced machine learning to investigate the long-term population dynamics of the rheophilic fish spirlin offers a powerful approach to understanding environmental changes and climate shifts in aquatic ecosystems. A new ESHIPPOClim model was developed by integrating climate change assessment into the ESHIPPO model. The model identifies spirlin as a potential early indicator of environmental changes, highlighting the interactive effects of climate change and anthropogenic stressors on fish populations and freshwater ecosystems. The ESHIPPOClim model reveals that 28.57 % of the spirlin's data indicates high resilience and ecological responsiveness, with 34.92 % showing medium-high adaptability, suggesting its substantial ability to withstand environmental stressors. With 36.51 % of the data in medium level and no data in the low category, spirlin may serve as a sentinel species, providing early warnings of environmental stressors before they severely impact other species or ecosystems. The results of uniform manifold approximation and projection (UMAP) and a decision tree show that pollution has the highest impact on the population dynamics of spirlin, followed by annual water temperature, overexploitation, and invasive species. Despite the obtained key drivers, higher abundance, dominance, and frequency values were detected in habitats with higher HIPPO stressors and climate change effects. Integrating state-of-the-art machine learning models has enhanced the predictive power of the ESHIPPOClim model, achieving approximately 90 % accuracy in identifying spirlin as an early indicator of climate change and anthropogenic stressors. The ESHIPPOClim model offers a holistic approach with broad practical applications using a simplified three-point scale, adaptable to various fish species, communities, and regions. The ecological modeling supported with advanced machine learning could serve as a foundation for rapid and cost-effective management of aquatic ecosystems, revealing the adaptability potential of fish species, which is crucial in rapidly changing environments.

Reduction of large vessel traffic improves water quality and alters fish habitat-use throughout a large river

Rivers are increasingly used as superhighways for the continental-scale transportation of freight goods, but the ecological impact of large vessel traffic on river ecosystems is difficult to study. Recently, the temporary maintenance closure of lock and dam systems on the Illinois Waterway (USA) brought commercial vessel traffic to a halt along the river's length, offering a rare opportunity to study the response of the ecosystem before, during, and after an extended pause of this persistent anthropogenic disturbance. We observed improvements in main- and side-channel water quality and a redistribution of fish habitat-use during a months-long, near-complete reduction of large vessel traffic. Over 3600 water quality and 1300 fish community samples indicate that large vessel traffic reduction coincided with a 33 % reduction in turbidity as well as increased use of sampling strata near vessel navigation corridors by sound-sensitive and rheophilic fishes. Gizzard shad (Dorosoma cepedianum), the most abundant species in the system, also expanded their use of these ‘impact’ areas. Though inland waterway transport is an economically- and climate-friendly alternative to trucking and rail for the shipment of freight, our data suggest that intense vessel traffic may have profound physical and biological impacts across a large river. Monitoring and mitigation of ecological impacts of the ongoing expansion of inland waterway transport around the world will be critical to balancing large rivers as both useful navigation corridors and functional ecosystems.

Fish conservation in streams of the agrarian Mississippi Alluvial Valley: conceptual model, management actions, and field verification

The effects of agriculture and flood control practices accrued over more than a century have impaired aquatic habitats and their fish communities in the Mississippi Alluvial Valley, the historic floodplain of the Lower Mississippi River prior to leveeing. As a first step to conservation planning and adaptive management, we developed and tested a conceptual model of how changes to this floodplain have affected stream environments and fish assemblages. The model is deliberately simple in structure because it needs to be understood by stakeholders ranging from engineers to farmers who must remain engaged to ensure effective conservation. Testing involved multivariate correlative analyses that included descriptors of land setting, water quality, and fish assemblages representing 376 stream samples taken over two decades and ranging in Strahler stream order from 1 to 8. The conceptual model was adequately corroborated by empirical data, but with unexplained variability that is not uncommon in field surveys where gear biases, temporal biases, and scale biases prevent accurate characterizations. Our conceptual model distinguishes three types of conservation actions relevant to large agricultural floodplains: reforestation of large parcels and riparian zone conservation, in-channel interventions and connectivity preservation, and flow augmentation. Complete restoration of the floodplain may not be an acceptable option to the agriculture community. However, in most cases the application of even the most basic measures can support the return of sensitive aquatic species. We suggest that together these types of conservation actions can bring improved water properties to impacted reaches, higher reach biodiversity, more intolerant species, and more rheophilic fishes.

The Reintroduction of Brown Trout (Salmo trutta fario) in the Upper Scheldt River Basin (Flanders, Belgium): Success or Failure?

In 2017, the reintroduction of juvenile brown trout in the southwestern part of Flanders (the Zwalm River basin) (Belgium) was initiated. Monitoring during the subsequent years indicated that the released juveniles survived and matured, indicating that sufficient food and good habitat conditions were available. Despite recent fulfilment of free fish migration within the Zwalm River basin and several spawning habitats being present, no natural reproduction of brown trout could be observed. To obtain more insight into the reproduction and maturing of brown trout eggs under natural conditions, an in situ experiment was conducted during 3 consecutive years at 10 different sites within the river basin. The results of our research indicated that egg survival was generally low (<5%). The main causes are most likely a heavy sediment load hampering sufficient oxygen and clean water flow through the redds. In this basin, the sediment load originates mainly from agricultural fields during heavy rain events and consequential run-off. Creating grassy and/or woody buffer strips along watercourses, in combination with changes in agricultural practices, is needed to be able to build up a viable and self-sustaining population of brown trout and also, in a larger context, of other rheophilic fish species.

Seasonal variation of Ichthyofaunal diversity and it’s relation with substratum in the River Changa, West Bengal, India

Aim: A survey was conducted at four sampling sites of the River Changa to study the fish diversity in relation to river substratum. The aim of the study was to prepare a check list of ichthyofaunal diversity and their habitat preference guild in relation to sediment type. Methodology: Ichthyofauna was collected from four selected stations at monthly interval with the help of fishermen using gill net and cast net. For the analysis of the riverine substratum, sediment samples were collected from six square inches area at the sampling sites of the river by grab sampling method. The composition of stones, pebbles, sand and mud were evaluated from the sample. Results: A total of 64 fish species belonging to 6 families and 18 orders were recorded. Among which 33 were cold water fishes, 31 were warm water fishes, 28 were rheophilic and 24 were eurytopic fishes. Site 1 and 2 were dominated by rheophilic and cold water fishes and Site 4 was rich in eurytopic and warm water fishes. Cypriniformes was the most dominant order with 42 fish species. River sediment of Site 1, 2 and 3 were dominated by stones, pebbles and sand, while sediments collected from Site 4 was dominated by sand and mud. Cold water and rheophilic fishes were positively influenced by stones and pebbles. Eurytopic and warm water fishes were positively influenced by sand and mud. Interpretation: Cold water and rheophilic fishes were abundant at upstream of the river and eurytopic and warm water fishes were abundant at downstream of the river. Abundance and distribution of fish species depends on the river substratum. Key words: Ichthyofaunal diversity, Rheophilic, River Changa, River substratum

EDNA metabarcoding reveals differences in fish diversity and community structure in heterogeneous habitat areas shaped by cascade hydropower.

Freshwater ecosystems are under great threat from humans, among which habitat heterogeneity is the most obvious, being one of the important reasons for the decline of fish diversity. This phenomenon is particularly prominent in the Wujiang River, where the continuous rapids of the mainstream have been divided into 12 mutually isolated sections by 11 cascade hydropower reservoirs. Based on the fact that conventional survey methods are more harmful to the ecological environment, the efficient and noninvasive environmental DNA metabarcoding (eDNA) approach was used in this study to conduct an aquatic ecological survey of the 12 river sections of the mainstream of the Wujiang River. A total of 2299 operational taxonomic units (OTUs) were obtained, corresponding to 97 species, including four nationally protected fish species and 12 alien species. The results indicate that the fish community structure of the Wujiang River mainstream, which was originally dominated by rheophilic fish species, has been changed. And there are differences in fish species diversity and species composition among the reservoir areas of the mainstream of the Wujiang River. The fish species in the area have gradually declined under the influence of anthropogenic factors such as terraced hydropower and overfishing. The fish populations consequently have demonstrated a tendency to be species miniaturized, and the indigenous fish are severely threatened. In addition, the fish composition monitored by the eDNA approach was found to be close to the fish composition of historical information on the Wujiang River, indicating that eDNA approach may be used as a complementary tool to conventional methods in this basin.

A review on the threatened species of snow trout Schizothorax richardsonii Gray, 1832 (Cypriniformes: Cyprinidae): From the climate change and conservation perspectives

Snow trout (Schizothorax richardsonii Gray, 1832) occupies the Himalayan domain from the foothills to 3000 m and inhabits all types of water bodies, like rivers, rivulets, lakes, and reservoirs. It is a rheophilic fish species that can thrive in a wide range of ecological and climatic conditions. Globally snow trout is now a 'threatened' species. Invasion of its natural habitats by exotic trouts, river valley hydropower projects as well as destructive fishing in the Himalayan region have long been attributed to the vulnerability of this species. The intrinsic characteristics of snow trout also make it a weak competitor in the Himalayan rivers. Climate change coupling with above mentioned threats poses a new challenge for Himalayan fish, especially snow trout, as it is confined to the Himalaya. Given these threats, an intense drive for snow trout conservation is urgently required. This contribution is an attempt to find out solution to this fact. In line with the opinions of ecologists and conservationists, we suggest a few measures like setting up free-flowing and undammed rivers as 'fish conservation zones', environmental flow to downstream areas of existing dams, prohibition of stocking of exotic fish species in natural habitats and use of hatcheries for stocking and restocking of snow trout in the rivers for the conservation of the species. Keywords: Climate change, Conservation, Himalaya, Hatcheries, Snow trout, Threats, Vulnerable

Diverse environmental cues drive the size of reproductive aggregation in a rheophilic fish

BackgroundAnimal migrations are periodic and relatively predictable events, and their precise timing is essential to the reproductive success. Despite large scientific effort in monitoring animal reproductive phenology, identification of complex environmental cues that determine the timing of reproductive migrations and temporal changes in the size of reproductive aggregations in relation to environmental variables is relatively rare in the current scientific literature.MethodsWe tagged and tracked 1702 individuals of asp (Leuciscus aspius), a large minnow species, and monitored with a resolution of one hour the size of their reproductive aggregations (counts of sexes present at the breeding grounds standardized by the sum of individuals in the season) over seven breeding seasons using passive integrated transponder tag systems. We examined the size of reproductive aggregations in relation to environmental cues of day number within a reproductive season (intra-year seasonality), water temperature, discharge, hour in a day (intra-day pattern), temperature difference between water and air, precipitation, atmospheric pressure, wind speed and lunar phase. A generalized additive model integrating evidence from seven breeding seasons and providing typical dynamics of reproductive aggregations was constructed.ResultsWe demonstrated that all environmental cues considered contributed to the changes in the size of reproductive aggregations during breeding season, and that some effects varied during breeding season. Our model explained approximately 50% of the variability in the data and the effects were sex-dependent (models of the same structure were fitted to each sex separately, so that we effectively stratified on sex). The size of reproductive aggregations increased unimodally in response to day in season, correlated positively with water temperature and wind speed, was highest before and after the full moon, and highest at night (interacting with day in a season). Males responded negatively and females positively to increase in atmospheric pressure.ConclusionThe data demonstrate complex utilization of available environmental cues to time reproductive aggregations in freshwater fish and their interactions during the reproductive season. The study highlights the need to acquire diverse data sets consisting of many environmental cues to achieve high accuracy of interpretation of reproductive timing.Graphical abstract

The influence of flow velocity on the response of rheophilic fish to visual cues.

The strong association with visual cues exhibited by fish that prefer to inhabit flowing water (rheophilic species) may help reduce the energetic costs of maintaining position due to the provision of spatial points of reference. If this "Station Holding Hypothesis" is true, a positive relationship between the association with visual cues and flow velocity is expected. This hypothesis was tested experimentally by quantifying the response of common minnow (Phoxinus phoxinus) and brown trout (Salmo trutta) to visual cues under three flow velocities. In contradiction to the prediction, there was no evidence that the association with strong visual cues was positively related to flow velocity when fish were presented with vertical black stripes in an open channel flume, although interspecific variation in response was observed. The association with visual cues was relatively weak in trout, compared to minnow that spent 660% more time associated with the zone in which visual cues were present during the treatment, than the control when visual cues were absent. Trout tended to be more exploratory and made short visits to the area where visual cues were present, whereas minnow associated with the cues for longer. The strong association with visual cues independent of flow velocity exhibited by minnow and the weak association across all velocities by trout suggest that this behaviour is unlikely to reflect a strategy to minimise the energetic cost of maintaining position in flowing water. Minnow may have used the visual cues as a proxy indicator of physical structure that provides alternative benefits, such as refuge from predators. Trout may have employed alternative cues (e.g. mechanosensory) to seek more energetically favourable regions of the experimental area, reducing the importance of stationary visual stimuli.

Living on the edge: Reservoirs facilitate enhanced interactions among generalist and rheophilic fish species in tributaries

Most lotic ecosystems have been heavily modified in recent centuries to serve human needs, for example, by building dams to form reservoirs. However, reservoirs have major impacts on freshwater ecosystem functions and severely affect rheophilic fishes. The aim of this review is to gather evidence that aside from direct habitat size reductions due to reservoir construction, competition for food and space and predation from generalist fishes affect rheophilic community compositions in tributaries (river/stream not directly affected by water retention). River fragmentation by reservoirs enables the establishment of generalist species in altered river sections. The settlement of generalist species, which proliferate in reservoirs and replace most of the native fish species formerly present in pristine river, may cause further diversity loss in tributaries. Generalist migrations in tributaries, spanning from tens of metres to kilometres, affect fish communities that have not been directly impacted by reservoir construction. This causes “edge effects” where two distinct fish communities meet. Such interactions temporarily or permanently reduce the effective sizes of available habitats for many native specialized rheophilic fish species. We identified gaps that need to be considered to understand the mechanistic functioning of distinct fauna at habitat edges. We call for detailed temporal telemetry and trophic interaction studies to clarify the mechanisms that drive community changes upstream of reservoirs. Finally, we demonstrate how such knowledge may be used in conservation to protect the remnants of rheophilic fish populations.

Anthropogenic nutrient loading affects both individual species and the trophic structure of river fish communities

Although the concept of trophic interactions has been used for a long time, there are still considerable gaps in our understanding of the effect of various environmental factors on trophic interactions within river fish assemblages. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of 20 species of fish belonging to both eurytopic and rheophilic ecological groups from a large temperate rivers were used to evaluate overall trophic niche use and trophic position of species, and to find out how environmental variability associated with nutrient loading affects individual and community-wide aspects of trophic structure. The study was carried out at 11 sites along the European rivers Vltava and Elbe, representing a continuous gradient of pollution and habitat degradation. Corrected Standard Ellipse Area (SEAc) was significantly larger for the group of eurytopic ecological species than for rheophilic species. Despite narrower isotopic niche space, rheophilic fish species occupied a higher trophic position, suggesting that these species use resources more enriched in 15N. Of the 11 environmental variables tested, nutrients had a significant effect on trophic niche area of species (SEAc), indicating that eutrophication is of critical importance for fish assemblages. Isotopic niche area of species was found to be positively influenced by total phosphorus, and negatively affected by concentrations of nitrate (N-NO3−) and ammonia (N-NH4+). A negative association between oxygen demand and a measure of trophic diversity - mean distance to centroid (CD)- and a measure of density and clustering of species - mean nearest neighbor distance (MNND)- were found, indicating that the oxygen demand is a key factor influencing community trophic structure. An observed pattern where nutrient loading influenced both individual species and trophic structure of the fish assemblage provides strong support for an anthropogenic influence on riverine food webs.

Population recovery and occurrence of the endemic Rhine sculpin (Cottus rhenanus)

The Rhine sculpin (Cottus rhenanus) is a benthic rheophilic fish species that is endemic to tributaries of the rivers Rhine and Meuse in North-western Europe. Little is known about its occurrence and individuals density in relation to habitat characteristics. A core population of C. rhenanus occurs in the River Geul in the Netherlands. Since the late 19th century, this river was heavily polluted by communal and industrial wastewater, causing a strong population decline. As the core population of C. rhenanus is recovering, the status, distribution, and habitat use could be studied to facilitate recovery in other locations. Cottus rhenanus density of individuals significantly increased over the period 2005–2015 and it became one of the most abundant fish species in assemblages. Negative relationships were observed between C. rhenanus densities and a high abundance of boulders (>200 mm), large structures such as woody debris, and water depth. The population increase and recolonization of C. rhenanus coincided with water quality improvement, which suggests that this fish species can be used to assess small streams ecosystem integrity. The recent range expansion of the Ponto-Caspian round goby (Neogobius melanostomus) poses a high risk of negative effects on C. rhenanus populations via food and shelter competition. Further water quality improvement, habitat conservation, and prevention of the spread of invasive gobies could favour C. rhenanus populations within their natural range.

An assessment of the state of the fish fauna in the lower course of rivers and floodplain water bodies in Lake Ilmen catchment based on the data from surveys with fine-mesh fishing gear in 2020–2021

Having analyzed fry seine catches from the lower reaches of the rivers flowing into Lake Ilmen and from floodplain lakes in the Msta and Lovat river deltas, we have updated information on the composition of the fish population of reservoirs and watercourses of the Lake Ilmen catchment. In total, 19 fish species belonging to six families were present in the catches in 2020–2021. The fish communities of the lower reaches of the rivers Volkhov, Lovat, Shelon, Veronda and floodplain lakes of the Lovat and Msta deltas featured high similarity, with the predominance of limnophilic species, in contrast to the riffle sections of the Msta, where rheophilic fish species dominated in abundance. At most survey sites, the catches were dominated by the main harvestable fish species of Lake Ilmen. The biomass of fish underyearlings in the autumn period of 2020 in floodplain lakes of the Lovat and Msta deltas was four to six times that of in the littoral zone of Lake Ilmen and comparable to the levels at survey sites in the lower reaches of the rivers Msta and Volkhov. Fry seining of river and lake areas within the Novgorod Region revealed fish species not previously reported for the Lake Ilmen catchment or formerly considered rare in the catchment. Lake Ilmen catchment being hydrologically isolated from the main invasion pathways as well as the absence of intentional acclimatization activities are factors promoting the stability of the native composition of the fish fauna and the reason why only one naturally dispersing species, the silver carp, has become naturalized in Lake Ilmen.

Hatchery tanks induce intense reduction in microbiota diversity associated with gills and guts of two endemic species of the São Francisco River.

The São Francisco River (SFR), one of the main Brazilian rivers, has suffered cumulative anthropogenic impacts, leading to ever-decreasing fish stocks and environmental, economic, and social consequences. Rhinelepis aspera and Prochilodus argenteus are medium-sized, bottom-feeding, and rheophilic fishes from the SFR that suffer from these actions. Both species are targeted for spawning and restocking operations due to their relevance in artisanal fisheries, commercial activities, and conservation concerns. Using high-throughput sequencing of the 16S rRNA gene, we characterized the microbiome present in the gills and guts of these species recruited from an impacted SFR region and hatchery tanks (HT). Our results showed that bacterial diversity from the gill and gut at the genera level in both fish species from HT is 87% smaller than in species from the SFR. Furthermore, only 15 and 29% of bacterial genera are shared between gills and guts in R. aspera and P. argenteus from SFR, respectively, showing an intimate relationship between functional differences in organs. In both species from SFR, pathogenic, xenobiont-degrading, and cyanotoxin-producer bacterial genera were found, indicating the critical pollution scenario in which the river finds itself. This study allowed us to conclude that the conditions imposed on fish in the HT act as important modulators of microbial diversity in the analyzed tissues. It also raises questions regarding the effects of these conditions on hatchery spawn fish and their suitability for restocking activities, aggravated by the narrow genetic diversity associated with such freshwater systems.

Use of a flow deflector to protect rheophilic fish spawning grounds during hydropeaking

AbstractRheophilic fishes are one of the ecological groups of fishes declining most quickly in number due to various habitat modifications and discharge regulations. Artificial rapid increases and decreases in discharge (hydropeaking) can cause severe damage to the eggs of rheophilic fishes. We investigated whether the effects of a water increase in hydropeaking on a spawning ground may be mitigated by a deflector installed at the top of the weir that diverts flow to other sections. At the research site, rheophilic asp (Leuciscus aspius) spawn annually in early spring, and their success might be affected by hydropeaking, with base discharge ranging from 3 to 7 m3 × s−1 and peak discharge ranging from 16 to 25 m3 × s−1 occurring 4 to 7 times during the asp spawning season and egg development period. To protect the adhesive eggs from detachment during peak discharge, a flow deflector (a wooden wall at the selected part of the weir) was installed to regulate discharge on the protected spawning ground. This measure allowed normal discharge under base flow conditions. During peak flow, a significant portion of the additional water was directed to the part of the river channel where egg abundance was lower and to the mill channel, where asp spawning was not present. While the total discharge increased 4.1 times compared to the base flow, the water discharge in the protected spawning ground increased only 2.7 times. This resulted in more than half of the asp eggs being retained in the protected channel. Although the use of such a measure is limited to specific local conditions where eggs are located just downstream of the weir, it can be a valid solution in highly fragmented rivers with hydropeaking and can lead to higher recruitment of rheophilic fishes.

Fish Diversity and Abundance Patterns in Small Watercourses of the Central European Plain Ecoregion in Relation to Environmental Factors

Because of their size, small depth, periodic drying out, and often lack of buffer zone, small watercourses are especially sensitive to environmental changes, anthropopressure, and biodegradation which makes them extremely prone to decline in biodiversity. Small watercourses can harbor many species of fish, including alien and invasive species. The objectives of this study were the assessment of environmental conditions, the determination of the number of fish species, their density and diversity in 10 small water courses of the European ecoregion ‘Central Plains’, and to estimate the effect of individual habitat parameters on the ichthyofauna. The total number of fish caught during the study was 9339, representing 33 species. Statistical analyses showed that the density of rheophilous fish was under the effect of flow velocity, discharge, width, depth, oxygen content, and pH; for the limnophilous species, the decisive factors were: discharge, depth, width, and P-PO4. The density of the euryoecious species was affected by depth, pH, electric conductivity (EC), oxygen, as well as N-NO3. All the species were significantly influenced by sandy substratum and the development of aquatic vegetation. Each guild, and even individual species, had their preferred habitat conditions, which is important for water management, renaturisation, and restitution.

Characterizing egg transport of Chondrostoma nasus (L.): a combined laboratory and field experiment

Population recruitment of endangered rheophilic fish species strongly depends on the survival of critical egg and larvae life stages. However, the transportation and fate of eggs after spawning is not well understood. This study analyzed the egg transport and settling patterns of the endangered European nase (Chondrostoma nasus L.), testing the transferability of physical modelling approaches for simple solid sphere surrogates to the eggs of lithophilic fish species. This model approach was validated in both laboratory and field experiments, where wetted millet corns were used as surrogates excluding deformability and stickiness of natural nase eggs. The transport and settling patterns of the surrogate accurately modelled the transportation of C. nasus eggs. Results further indicate that transport processes of eggs are small-scaled in the range of less than 3 m. These findings provide helpful information for restoration planning of C. nasus spawning grounds. They also highlight the importance of the interstitial zone regarding the egg settling process, which conforms to the ecological relevance of this habitat for egg and larval development. While the surrogate was suitable for this model approach, further investigations are necessary to confirm transferability to other species.

Freshwater fish biodiversity restoration in floodplain rivers requires connectivity and habitat heterogeneity at multiple spatial scales

With a sixth mass extinction looming and freshwater biodiversity declining at unprecedented rates, evaluating ecological efficacy of river restoration efforts is critical in combatting global biodiversity loss. Here, we present a comprehensive study of the functioning for fishes of 46 river restoration projects in the river Rhine, one of the world's most heavily engineered lowland rivers. Floodplains with permanent, either one- or two-sided lateral connectivity to the main channel, favour total fish abundance, and are essential as nursery areas for riverine fishes. Habitat heterogeneity had a strong positive effect on species richness but was negatively related with fish abundances. However, the effects of environmental variables varied between ecological groups and spatial scales. Surprisingly, richness of critical rheophilic fishes declined with large-scale habitat heterogeneity (~1000 m), while it increased at small scales (~100 m), possibly because of the presence of unfavourable habitats for this ecological group at larger scales. Clearly, there is no one-size-fits-all design for river restoration projects. Whether a river section is free-flowing or impounded dictates the scope and efficacy of restoration projects and, within a river section, multiple complementary restoration projects might be key to mitigate freshwater fish biodiversity loss. An essential element for success is that these projects should retain permanent lateral connection to the main channel.

Multispecies fishways in a Mediterranean river: Contributions as migration corridors and compensatory habitat for fish

River connectivity is essential for the resilience of fish assemblages and populations and is a priority goal to reach good ecological status for river systems. Increasing knowledge on the functionality of restoration tools such as fishways is relevant for future management strategies. The present two-year assessment showed clear ecological contributions of different types of multispecies fishways in the fish assemblage of a strongly modified Mediterranean-type river. Just after their implementation, early and extended use by dominant river-resident fish of both naturelike and technical fishways were observed. All fishways were used in different seasons, especially during the migratory periods by potamodromous cyprinids, suggesting a possible use as migration corridors. Fishways also may provide compensatory habitats for small and juvenile individuals throughout the annual cycles, mostly for rheophilic fish inside nature-like bypasses and for limnophilics inside technical types. Fluvial habitat characteristics and lower flow variability inside the fishways could favour their role as a fish refuge, mainly to juveniles of cyprinids, in heavily regulated rivers where large flow fluctuations occurred. Nature-like fishways could be a better option to function as a compensatory habitat for rheophilic cyprinids in Mediterranean-type Rivers, even more because their use by large nonnative limnophilics seems to be very scarce. However, technical fishways could offer the opportunity to establish control traps of some nonnative fish, which could be of interest to reduce the risk of spreading invasive fish. Therefore, fish ecology and local hydrology should drive the decision between the types to implement. The obtained information on the ecological functionality of multispecies fishways should be considered for applying successful river restorations that are demanded by water and wildlife management schemes (e.g., the European Water Framework Directive).

Initial biological development of a newly established side channel at the Lower Rhine

AbstractWithin the EU LIFE‐Nature project ‘River and floodplain revitalisation Emmericher Ward’, three small temporary waters and a former gravel pit were connected by a side channel running parallel to the river Rhine through former groyne fields. The initial status of macrozoobenthos, fish, avifauna, flora, vegetation, and habitats before and their development after implementation of the project's measures were recorded and compared. The monitoring years 2018 and 2019 were exceptionally dry and accompanied by an extremely low runoff in the Rhine and the side channel. These conditions likely affected the development of habitats and species populations in the new side channel. The new side channel showed intensive morphodynamic development and differentiation of its structures. While the more complex vegetation and habitat types appeared as mostly species‐poor initial stages, short‐lived species‐rich pioneer habitats such as annual mud banks in the water exchange area were already established. Two years after the implementation, the benthic invertebrate fauna was still predominantly species‐poor and dominated by neozoans. Occasionally, representatives of the more sensitive EPT fauna (Ephemeroptera, Plecoptera, Trichoptera) were already detected but were, in general, strongly underrepresented in the main stream. Low colonisation potential, nonpermanent flow, and lack of river wood limit the development of the macrozoobenthos community. The relative abundance of rheophilic fish species increased in the project area and high juvenile fish densities proved the function as a nursery habitat. As pioneer species of riverine landscapes, sand martins and little ringed plovers colonised the new structures already in the first year. The initial state of the side channel represented a typical dynamic pioneer habitat pattern of a sandy lowland river, which was almost absent in the Lower Rhine area. The new habitats were quickly colonised by pioneer flora and fauna, but the potential for more demanding and complex communities was restricted by the poor structural and biological states of the Lower Rhine.