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Migration patterns and habitat use of adult barbel (Barbus barbus) and nase (Chondrostoma nasus) were monitored by radio telemetry over a period of 13 months along a 58-km-long section of the Austrian part of the Danube River. The study site is confined upstream and downstream by two hydropower plants, and contains a larger tributary, the Pielach River. Telemetry transmitters were implanted into fish caught in this tributary after spawning in June (25 individuals per species). The results show that both species use the entire available width and depth spectrum of the Danube along the full migratable river length. Nase had an average home range of 22.4 km, while that of barbel was 34.4 km. The habitat use of the two species differs significantly. While the nase was primarily encountered in the free-flowing section, barbel mainly used deep areas of the impoundment during the year. Nase showed a distinct site fidelity to certain areas in the free-flowing reach which were periodically revisited. During the spawning season, distinct homing behavior was observed in both species. All seven nase that could still be detected during the spawning season returned to the tributary (homing rate 100%). Six homing nase migrated up to the first migration barrier in the tributary but did not pass the existing fish passage facility. In contrast, only nine barbel returned to spawn in the tributary (homing rate 50%), while nine barbel were most likely using a spawning location in the head of impoundment section. Homing fish entered the tributary during darkness.

Proliferative kidney disease (PKD) is an emerging parasitic disease that affects wild and farmed salmonid fishes worldwide. Currently, it is widespread in Europe with records in many countries. This study assessed the status of PKD in the river Wulka, a small Austrian river, which was known to host a vital brown trout population despite having high water temperatures. Contrary to the initial hypothesis that the river was free from PKD, we observed an overall PKD prevalence of 92%. Noninfected fish were restricted to the uppermost river section. Twenty‐two out of 87 PKD‐positive fish of all age classes showed clinical signs, while five individuals exhibited signs of recovering from PKD infection. The severity of clinical signs was significantly dependent on the fish length and age, with smaller or younger individuals being more severely affected. Comparison of data from the earlier fish sampling events with those results from 2017 and 2018, together with the analyses of the pattern of water temperature since 2010, indicates that Wulka's brown trout population might become extinct in the near future.

In this study the effects of abiotic factors (discharge, water temperature, turbidity, light and weather conditions) on the behaviour of lake running brown trout (Salmo trutta) during spawning up- and downstream migration in the Hasliaare, Switzerland, were investigated. Trouts were counted during spawning migration in a residual flow section of the Hasliaare. The fish counting system consisted of a counting chamber (resistivity fish counter including several monitoring cameras) and a fish weir. 269 lake running brown trout movements were recorded between 15.09.2019 and 30.12.2019. Point pattern comparison was used to distinguish 104 trouts individually with 66.3 % females and 33.7 % males. Water temperatures below 4.9 °C interrupted or inhibited upstream spawning migration in the residual flow section of the Hasliaare. During downstream migration, activity increased at low barometric pressure and increased flows supported downstream migration of males and large females (≥60 cm). Furthermore, the entire migration preferably occurred in darkness.

Proliferative kidney disease (PKD) is a disease found in salmonid fish that is widespread in Europe and North America. The dependency of the clinical signs on the water temperature is extensively reported in rainbow trout, but detailed information on brown trout is lacking. In this study, juvenile brown trout were exposed to the spores of Tetracapsuloides bryosalmonae and then kept at different ambient water temperatures (16°C, 19°C and 22°C) for 10 weeks along with recording of morbidity throughout the experiment. At 6, 8 and 10 weeks post‐exposure, fish from each temperature group were sampled and underwent pathoanatomical examination to survey disease progression. At 16°C, brown trout showed a significantly higher survival probability compared to those kept in 19°C and 22°C water. Additionally, the parasitic burden (MSQ) was higher and the clinical signs were more pronounced in the brown trout kept at 19°C and 22°C compared with the ones kept at 16°C. This study highlights the correlation of PKD outbreaks and water temperature increases related to global climate change, which will impact the future distribution of brown trout in natural waters.

Aquaculture is the fastest-growing animal food production sector and is expected to become increasingly important to meet future food demands. As a landlocked country, Austria’s self-sufficiency rate for fish is rather low with 6% in total and 48% for freshwater fish. Therefore, and in order to enable sustainable growth of the sector while avoiding negative impacts on the aquatic ecosystem and other uses, we developed aquaZone, a decision support tool for sustainable trout farm zoning. Thereby, 30 spatially explicit criteria related to environmental prerequisites, land use, legal constraints and water quality/quantity were defined, collected and classified according to their suitability for sustainable trout production. Criteria were combined in an integrative GIS-based modelling approach in order to perform the first countrywide and spatially-explicit zonation of suitable areas for aquaculture in Austria. Thereby, 7920 suitable areas with a mean size of 8.2 ha located in 1129 out of 5011 sub-basins (23%) were identified. The decision tree assigned the highest variable importance to water temperature, slope, agricultural unit, geology, nitrate retention capacity, fish region, minimum flow and pollution risk. These results should support decision making of investors and authorities in order to avoid conflicts and stranded investments at an early stage.

Rivers of the large Alpine valleys constitute iconic ecosystems that are highly threatened by multiple anthropogenic stressors. This stressor mix, however, makes it difficult to develop and refine conservation and restoration strategies. It is, therefore, urgent to acquire more detailed knowledge on the consequences and interactions of prevalent stressors on fish populations, in particular, on indicator species such as the European grayling Thymallus thymallus. Here, we conducted a multi-river, multi-stressor investigation to analyze the population status of grayling. Using explorative decision-tree approaches, we disentangled the main and interaction effects of four prevalent stressor groups: flow modification (i.e., hydropeaking), channelization, fragmentation, and water quality alteration. Moreover, using a modified variant of the bootstrapping method, pooled bootstrapping, we determined the optimal number of characteristics that adequately describe fish population status. In our dataset, hydropeaking had the strongest single effect on grayling populations. Grayling biomass at hydrological control sites was around eight times higher than at sites affected by hydropeaking. The primary parameters for predicting population status were downramping rate and peak amplitude, with critical ranges of 0.2–0.4 cm min-1 and 10–25 cm. In hydropeaking rivers, river morphology and connectivity were the preceding subordinated parameters. Repeating the procedure with pooled bootstrapping datasets strengthened the hypothesis that the identified parameters are most relevant in predicting grayling population status. Hence, hydropeaking mitigation based on ecological thresholds is key to protect and restore already threatened grayling populations. In hydropeaking rivers, high river network connectivity and heterogenous habitat features can dampen the adverse effects of pulsed-flow releases by offering shelter and habitats for all life cycle stages of fish. The presented approach of explorative tree analysis followed by post-hoc tests of identified effects, as well as the pooled bootstrapping method, offers a simple framework for researchers and managers to analyze multi-factorial datasets and draw solid management conclusions info:eu-repo/semantics/publishedVersion

Water temperature is one of the most important abiotic parameters in rivers having direct and indirect effects on fish. Especially cold-water species like the brown trout (Salmo trutta) are limited by high temperatures. Beside direct physiological stress, higher water temperatures also reinforce the emergence of diseases. In this study we investigate thermal regimes of rivers based on a large-scale dataset covering Austria (approximately 70,000 km²). The analyses aim to clarify to what extent water temperatures support the emergence of proliferative kidney disease (PKD) and assemble physiological stress for brown trout under current and future climate conditions. Data from 274 gauging stations at 184 rivers were used to calibrate a water temperature model and to investigate critical water temperature thresholds. Therefore, we developed a risk assessment scheme to identify river reaches that already have or will develop critical thermal regimes for brown trout in respect of PKD emergence and thermal physiological stress. The results revealed severe changes in the thermal regimes of the investigated rivers under climate change. Furthermore, the variable characterising riparian vegetation played a vital role to explain cooling of the water in downstream direction. In respect of PKD, the amount of river reaches having unlikely outbreaks of PKD decreased from 72.6 % under current conditions to 37.7 % in the far future RCP8.5 scenario. Within small rivers that currently showed optimal thermal regimes over large extents (10,244 km), the habitat suitability will be reduced by combined effects of PKD and physiological stress to 6,554 km. In general, suitable habitats of S. trutta will shift upstream, thus to higher altitudes, and to smaller, alpine rivers in Austria. The warming leads to physiological stress that induces a diminished growth due to the non-positive transition of caloric values to growth as well as cardiac dysfunction in brown trout. These factors will further restrict the distribution of brown trout. However, the results also underline the enormous importance of the alpine region as a future refuge for brown trout in Central Europe. Thus, this study will help to inform managers to timely develop robust conservation strategies.

Trout and char (hereafter, trout) represent some of the more cul-turally, economically and ecologically important taxa of freshwater fishes worldwide (Kershner, Williams, Gresswell, & Lobón-Cerviá, 2019a). Native to all continents in the Northern Hemisphere (as well as western Mediterranean Africa), trout belong to seven genera (Oncorhynchus, Salvelinus, Salmo, Hucho, Parahucho, Brachymystax and Salvethymus), which are distributed across more than 60 countries (Muhlfeld et al., 2019). Despite their broad im-portance as indicators of biodiversity in cold-water ecosystems (Haak & Williams, 2013), as well as cultural icons for food and rec-reation, nearly half of the world's recognised trout species (IUCN, 2018) are imperilled or at risk of global extinction (Muhlfeld et al., 2018, 2019). The root causes of their vulnerability include broad-scale alteration of landscapes and watersheds, dams, overhar-vest, pollution, interactions with hatchery-bred conspecifics and non-native species. However, emerging threats such as climate change and related problems such as the spread of diseases and parasites pose significant challenges and uncertainties to native trout and their habitats (Kovach et al., 2016; Muhlfeld et al., 2018). Ultimately, conservation of native trout depends on understand-ing their diversity, a willingness to address threats at their root causes and implementing progressive conservation solutions that promote persistence of these iconic species in the face of growing human pressures.

Zusammenfassung Der Unterlauf der Traisen wurde von 2012 bis 2016 im Rahmen eines LIFE+ Projektes auf rund 10 km Länge gänzlich neu gestaltet. Dabei wurde der alte kanalisierte Arm mit mehreren Sohlschwellen als Altwasser bzw. Überwasserkanal erhalten und ein völlig neuer, naturnaher Lauf durch den Auwald angelegt. Das begleitende Monitoring der Fischfauna wird jährlich mittels verschiedener Methoden durchgeführt und zeigt bereits im kurzen Zeitraum seit der Fertigstellung eine schnelle Besiedelung durch eine Vielzahl von Arten und sehr hohe Dichten. Während der alte Lauf keine Laich- und kaum Juvenilhabitate aufwies, sind im neuen Lauf sehr hohe Jungfischzahlen verschiedenster Arten zu beobachten. Vor allem die vollständige Öffnung des Kontinuums zur Donau am Ende der Bauarbeiten führte unmittelbar zu einem Anstieg und dem Nachweis der Reproduktion donautypischer Fischarten.

The FishProtector, an Electric Flexible Fish Fence is investigated in ethohydraulic experiments. Fish protection potential is tested using an outdoor, experimental channel. To find optimum parameter settings, cable clearance, approach flow angle, and the size of the electric field vary within predefined limits. Due to the combination of both, the physical barrier (tensioned steel cables) and the behavioral barrier (pulsed electric field in the low voltage range), fish protection no longer depends solely on cable clearance. Generally, all investigated setups with combined physical and behavioral barriers show mean fish protection rates of higher than 97%. Cable clearances of 60 mm (largest cable clearances investigated within this study) show the same fish protection rates as cable clearances of 30 mm, each in combination with an electric field. The setup was a non-scaled section-model of a runoff river power plant. The behavioral experiments were performed with wild and PIT-tagged brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), grayling (Thymallus thymallus), and chub (Squalius cephalus). Measured body lengths were between 100 and 285 mm. The FishProtector with wide cable clearances and moderate electric fields in both size and voltage significantly improves the fish protection rate, showing significant potential for operating hydropower plants.

Review Peak-operating hydropower plants are usually the energy grid’s backbone by providing flexible energy production. At the same time, hydropeaking operations are considered one of the most adverse impacts on rivers, whereby aquatic organisms and their life-history stages can be affected in many ways. Therefore, we propose specific seasonal regulations to protect ecologically sensitive life cycle stages. By reviewing hydropeaking literature, we establish a framework for hydrological mitigation based on life-history stages of salmonid fish and their relationship with key parameters of the hydrograph. During migration and spawning, flows should be kept relatively stable, and a flow cap should be implemented to prevent the dewatering of spawning grounds during intragravel life stages. While eggs may be comparably tolerant to dewatering, post-hatch stages are very vulnerable, which calls for minimizing or eliminating the duration of drawdown situations and providing adequate minimum flows. Especially emerging fry are extremely sensitive to flow fluctuations. As fish then grow in size, they become less vulnerable. Therefore, an ‘emergence window’, where stringent thresholds on ramping rates are enforced, is proposed. Furthermore, time of day, morphology, and temperature changes must be considered as they may interact with hydropeaking. We conclude that the presented mitigation framework can aid the environmental enhancement of hydropeaking rivers while maintaining flexible energy production info:eu-repo/semantics/publishedVersion

Using an outdoor experimental channel, this study evaluates downstream passage behavior of potamodromous fish species at an innovative fish protection and guidance system, the Flexible Fish Fence (FFF). Under variation of the spacing between the cables, the exposition angle and the approach velocity, the fish protection and the guidance efficiency are investigated. Experiments were carried out using wild born and PIT-tagged chubs (Squalius chephalus), graylings (Thymallus thymallus), brown trouts (Salmo trutta) and rainbow trouts (Oncorhynchus mykiss) with body lengths between 100 and 200 mm. The results show that fish protection efficiency is predominately dependent on the cable spacing and varies strongly between fish species. While all fish (100%) are prevented from passing through the FFF at 10 mm spacing, it is far less effective at 20 mm spacing (83% of chubs, 59% of trouts and 26% of graylings). The effects of the exposition angle, the approach velocity, and the fish length are identified using multinomial logistic regression models: fish protection efficiency increases significantly with increasing fish length and increasing approach velocity (particularly for the highest angle) for chubs and trouts. Increasing flow velocity induces cable vibrations presumably triggering avoidance behavior. Unfavourable hydraulic conditions at the bypass entrance (approach velocity of 0.65 m s-1, velocity changes or turbulences) negatively affect the bypass efficiency for all fish species, pointing out that the design of bypasses for downstream migration is of major relevance.

The dynamic component in hydrology, sedimentology, and, consequently, river morphology serves as a backbone for the entire river environment (Maddock 1999). In addition to water pollution, the hydro-morphological/sedimentological degradation is one of the main pressures on river systems (Ward and Stanford 1995; Dudgeon et al. 2006). The EU Water Framework Directive (WFD, Directive 2000/60/EC) mentions various aspects of hydro-morphological disturbances that must be addressed by management plans to achieve the aims of a good ecological status or a good ecological potential (Article 3/Article 4). However, to reach these goals, the sediment conditions of a river (e.g., sediment continuum) are not part of the evaluation needs. Here, to achieve “good ecological status,” it is assumed that the biotic criteria reflect the hydro-morphological status, while direct assessments of dynamic sedimentological processes are not taken into account (Hauer 2015).

Fishing is an ancient practice in the acquisition of natural resources dating back to the Middle Stone Age. The principal reasons why humans visit waters to catch fish underwent a substantial transition in many countries throughout the preceding decades. While fishing to gain food still is an important factor in tropical areas of the world, especially in Africa and Asia, it is mostly for sport in inland waters of economically higher developed countries, as in major parts of Europe and North America (Welcomme 2016). There, the majority of fishermen nowadays fish solely to obtain recreation or to experience the aesthetics of nature.

Wasserkraftanlagen verzogern bzw. verhindern Wanderungen von Fischen. Wahrend die Errichtung von Fischaufstiegshilfen (FAH) mittlerweile als Stand der Technik vorgeschrieben ist und fur Osterreich auch ein entsprechender Leitfaden zum Bau von Fischaufstiegshilfen (BMFLUW 2012) erschienen ist, liegen Losungsansatze hinsichtlich der Problematik des Fischabstieges aufgrund von Wissensdefiziten noch nicht in vergleichbarer Form vor. Folgender Beitrag soll einen Uberblick uber bisherige Erkenntnisse hinsichtlich flussab gerichteter Wanderungen heimischer, potamodromer Fischarten sowie uber verschiedene technische Losungsmoglichkeiten, deren Anforderungen und Anwendungsgrenzen fur den Einsatz an Wasserkraftanlagen liefern. Daruber hinaus werden aktuell laufende, nationale Forschungsprojekte zu dieser Thematik vorstellt.

Stocking of fish into streams is a common practice in fisheries management to increase the yield for anglers and support fish populations. European otter (Lutra lutra) predation on fish stocks of both economical and recreational value causes conflicts in many European countries. However, these stocking activities may also attract additional predators to a site. This case study aimed to investigate whether stocking of fish leads to higher otter densities in linear freshwater habitats in Central Europe. Otter faeces and data on fish stocks were collected in the province of Lower Austria along two salmonid streams, which differ considerably in fisheries management strategies. We used non-invasive genetic sampling (NGS) methods (genetic analysis of otter faeces) to ascertain otter individuals. Prey fish populations were assessed comparing length frequencies and fish biomass obtained from electrofishing series and data on stocking measures. Individual identification and socio-spatial organisation of resident otters revealed similar otter densities for both streams with 0.22 and 0.23 resident adult otters per stream kilometre. Length frequency distribution and biomass of fish indicated disappearance of stocked specimen at the time of electrofishing surveys and showed no significant difference of fish stocks between the streams. These results suggest that stocking activities may not affect the number of otter territories along the two streams studied, because availability of stocked fish is limited to angling season. We conclude that stocked streams may provide seasonally important food resources for otters, but raise the question whether stocked fish substantially contribute to the diet to raise carrying capacity for otters in linear freshwater habitats throughout a year. Furthermore we discuss the efficiency of stocking measures in streams where both self-sustaining fish populations and fish-eating predators occur.

Brown trout are among the fishes most valued by humans for food and recreation. This has not prevented their decline, however, and today native brown trout are found at only a fraction of their his ...

Summary In this study a time- and cost effective method for marking early life stages of brown trout (Salmo trutta L.) with alizarin red S (ARS) is presented. The main intention was the development of a protocol to mark embryos. When stocking eyed-eggs, later recognition depends on an adequate tagging method featuring reasonable expenditures, low mortality and high marking success. Best results were obtained using ARS concentrations of 500 mg/l. Consistently clearly visible marks could be detected under a fluorescence-stereomicroscope equipped with a dsRed filter, without processing the otoliths.

The impact of climate-induced discharge change on fish habitats, based on 1951–2008 time series, was investigated within the crystalline catchment of the Grosse Muhl River in Northern Austria. A significant trend change of air temperature, based on Mann–Whitney statistical testing, was recorded for spring 1989 (P = 98.9 %) and summer 1990 (P = 99.9 %). This led to a pronounced increase in summer low flow periods. Hydrodynamic-numerical (one-dimensional/two-dimensional) modelling was applied to simulate the changing habitat characteristics due to decreasing discharge in relation to various morphological patterns (riffle-pool/plane-bed reaches). Using bathymetric data, which were sampled on cross sectional measurements, we clearly determined that plane-bed reaches (featureless bed forms) are sensitive to climate-related, reduced discharge, whereas riffle-pool reaches continued to exhibit suitable physical fish habitats even under extreme low-flow conditions. The impact of the decreased summer discharge on instream habitats was strong for subadult and adult grayling which have been used as target fish species. In situ measurements in microhabitats (velocity/depth) revealed habitat suitabilities. These values were taken as biotic input for habitat evaluation on the micro scale. The findings clearly show that river morphology is a decisive parameter in terms of habitat preservation and restoration in the context of the future impacts of climate change (decreased discharge).

Numerical fish-habitat modelling on various scales is considered to be state of the art in river management. However, most of the concepts applied use steady-state hydraulic parameters such as flow velocity and water depth. Herein we present analysis and discussion of the possibility of including a drift-feeding parameter (SIF) into habitat evaluations based on multiplying suitability indices. “Sources” and “sinks” of benthic drift were identified according to both the zero-crossing and hydraulic-threshold methods in an alpine gravel-bed river. Minor differences could be determined between the two methods in a well-developed riffle–pool section. Macroinvertebrates, used for simulating benthic drift, were collected by multi-habitat sampling and appraised according to their critical threshold (τcr) for motion on the bed surface and sinking velocity (vs). The findings of the calculation of drift rates using one- (1D) and two-dimensional (2D) hydrodynamic numerical models highlight a specification of best feeding position for drift-feeding fish (i.e. brown trout, grayling) considering the SIF parameter. Riffle–pool sequences are characteristic of pristine alpine streams; our findings underline their importance as production (riffles) and consumption areas (pools) in terms of holistic river function. Moreover, the results indicate that (artificial) lateral obstruction (e.g. dams) may lead to a reduced transport rate of benthic organisms due to low bottom shear stress (

In der steirischen Mur gibt es derzeit 29 Wasserkraftwerke, 26 % der Mur sind gestaut und 11 % ausgeleitet (Restwasser). Etwa 25 % des Flusslaufes weisen noch einen guten hydromorphologischen Zustand auf. Hohe Fliesstreckenanteile existieren im Abschnitt Landesgrenze bis Bruck/Murzmundung und in der Grenzmur. Die Huchenpopulation der Mur ist von sehr hoher internationaler Schutzwurdigkeit und weist eigenstandige Reproduktion auf. Mit ca. 1.500 Adulttieren liegt die Huchenpopulation der Mur bereits unter der kritischen Grenze langfristig uberlebensfahiger Minimalpopulationsgrosen. Teilpopulationen mit jeweils uber 100 Adulttieren befinden sich nur in langeren durchgehenden Fliesstrecken, v.a. flussauf von Leoben. Ein Verschwinden des Huchens in Abschnitten mit gutem Zustand entsprechend FIA fuhrt zu einer Verschlechterung zum masigen Zustand. Generell weisen Stauhaltungen starke Defizite im Artenspektrum und Fischokologischen Zustand auf (Zustandsklasse 4 bis 5). Vollwasser-Fliesstrecken weisen zu 89 % den Guten oder sehr Guten Zustand auf, Restwasserstrecken noch zu 77 % den Guten Zustand. Mit zunehmenden Stau- oder Restwasseranteil verschlechtert sich der Fischokologische Zustand.

This paper investigates the variability of mesohabitat characteristics in various riffle-pool reaches. The tested river sections (n = 13) feature clear variation in slope (0.0004–0.0132) and low flow discharge (0.05–915 m3s−1) in different river types (straight to meandering). Mesohabitat characteristics (water depth, flow velocity, bottom shear stress) were calibrated according to the MEM-concept (MEM—Mesohabitat Evaluation Model). Statistical analysis clearly revealed significant differences (p

– We monitored yearly recruitment (1997–2008) of brown trout (Salmo trutta) in a fourth-order Austrian Alpine river. The relative proportion of recruits to adult fish varied strongly among years (5.6–66.4%). These proportions were strongly correlated with specific flow patterns. High flows before and during the spawning period were positively correlated with recruitment, whereas high flows during incubation and emergence were negatively correlated with recruitment success. Unsteady flow modelling supported a causal hypothesis for these relationships in demonstrating that discharges > 30 m3·s−1 resulted in substantial sediment motion (erosion and deposition) in suitable spawning areas within the study stretch.

The effects of stream channel morphology, transport processes and effective discharge on the salmonid spawning habitats of Thymallus thymallus and Salmo trutta ff. were investigated within the catchment of the Gr. Muhl River, Austria. Based on field survey, one-dimensional and two-dimensional hydraulic and sediment transport modelling, the abiotic characteristics of the spawning sites have been investigated. Application of the Meyer-Peter, Muller and Shields equations for determining critical discharge and critical shear stress revealed differences in the threshold of sediment motion due to the specific grain size sorting of the surface layer, which was dominated by cobbles and sand. Suitable grain sizes for spawning were found mainly in the subsurface layer of the free-flowing sections. The findings highlighted the necessity for upstream delivery to downstream of suitable spawning material during floods. Moreover, the study demonstrates that discharge-related sediment transport does not mean a simultaneous renewal of spawning material (fine gravel, gravel) transported from upstream reaches. Thus, an effective discharge for spawning habitats was determined using a standardized deposition index (Di), based on two-dimensional sediment transport modelling. The results show that the effective discharge for spawning habitats is a useful tool for spawning habitat restoration, representing the frequency of turnover and renewal of spawning habitats over the long term. Copyright © 2010 John Wiley & Sons, Ltd.

An ecologically orientated flood protection project was implemented at the Austrian lowland Sulm River. Habitat modelling was conducted during a 3-year monitoring program to assess the effects of river bed embankment and the initiation of a new meander by constructing an initial side channel, and allowing self-developing side erosion. Hydrodynamic and physical habitat models were combined with statistical methods. This study focused on the necessity for including stability analysis when modelling spawning grounds. The critical erosion parameter of the cobbles at spawning grounds was analysed using numerical modelling combined with substrate maps of potential spawning grounds of nase (Chondrostoma nasus). Due to the specific characteristics of this reach of the Sulm River, instability of the riffles can hamper successful reproduction in nase. Spawning grounds of Chondrostoma nasus and their stability must be guaranteed at least for the duration of incubation. This morphodynamic necessity should be incorporated in future restoration projects and when artificially restoring spawning habitats.

In diesem Beitrag werden Ergebnisse aus dem Projekt „Nachhaltige Entwicklung der Kamptal Flusslandschaft” vorgestellt, die sich mit der Dokumentation bzw. Prozessanalyse von flussmorphologischen Veranderungen durch das Hochwasser 2002 auseinandersetzen. Es galt, (1) Umlagerungsflachen/Verwerfungen auszuweisen bzw. Erosionen zu quantifizieren, (2) Verwerfungstypen zu klassifizieren, um in der Folge (3) physikalische Prozesse in diesen Umlagerungsflachen mit Hilfe von hydrodynamisch-numerischen (HN) Modellen zu beschreiben. Fur ein zukunftiges Management dieser Umlagerungsflachen wurden (4) Untersuchungen nach Hochwasserschutz-bzw. okologischen Kriterien an Hand eines Fallbeispiels durchgefuhrt. Die Ergebnisse zeigten, dass vor allem Abflusskontraktionen bzw. flussab folgende Abflussexpansionen wesentlich zur Verwerfungsbildung durch das Hochwasser 2002 beitrugen. Die Umlagerungsflachen brachten lokal sowohl aus Sicht des Hochwasserschutzes, als auch aus Sicht der Fischokologie, eine Verbesserung gegenuber dem Zustand vor dem Hochwasser 2002. Die hier vorgestellten Projektergebnisse wurden im Auftrag der NO Landesakademie in Kooperation mit der Gruppe Wasser beim Amt der NO Landesregierung vom Institut fur Wasserwirtschaft, Hydrologie und Konstruktiven Wasserbau (IWHW) gemeinsam mit dem Institut fur Hydrobiologie und Gewassermanagement (IHG) des Departments fur Wasser-Atmosphare-Umwelt der Universitat fur Bodenkultur erarbeitet.

Examination of a nase Chondrostoma nasus, that was carrying an implanted telemetry transmitter for 7 months, showed that the external trailing antenna of the transmitter had migrated c. 3 cm to the posterior edge of the incision. The absorbable sutures were still present, and there was epithelial tissue within the granulation encapsulating the transmitter. This tissue may have grown down from the surface along the antenna providing a potential entryway for pathogens.

A total of 10 649 larval and juvenile fishes of 24 species were caught in the drift at Marchfeldkanal, a man-made side branch of the Danube River near Vienna, Austria, with tubenose goby Proterorhinus marmoratus being the dominant species. Distinct differences in inter- and intraspecific drift patterns among different sampling stations along the course of the channel were found. The percentage of the rheophilic and rheoparous ecological guild was highest at the inlet of the channel, where it is directly fed with water from the Danube. For individual species, significant differences in drift densities among sites were found for tubenose goby, barbel Barbus barbus, ide Leuciscus idus, roach Rutilus rutilus and for the two most abundant percids, the pike-perch Sander lucioperca and zingel Zingel zingel combined. The occurrence of larval and juvenile fishes in the drift was related to certain developmental stages and differed between species and sites. Most species (common bream Abramis brama, bleak Alburnus alburnus, gudgeon species Gobio spp., chub Leuciscus cephalus, ide and roach) occurred with highest densities at the earliest developmental larval stage, but some species (e.g. common bream and roach) were also found abundantly in drift at later developmental stages. Application of Ivlev‘s index of electivity as a drift index describing the propensity of the different species to drift, yielded the highest indices for the gudgeon species, common bream and bleak and the lowest for perch Perca fluviatilis, Prussian carp Carassius auratus gibelio and rudd Scardinius erythrophthalmus.

Hydropeaking leads to artificial fluctuations in discharge and corresponding water levels with pronounced dewatering areas between base and peak flow along gravel bars and channel banks. In the present study, 16 hydropeaking reaches in Austria were investigated to assess possible differences in the estimated stranding risk for young of the year brown trout according to different gravel bar types and differences in microtopography roughness. Based on hydrodynamic-numerical modelling, a predictive habitat modelling approach was implemented in the study design. Accompanied by grain size sampling along the various channel bars, a conceptual stranding risk model (SRM) was developed. The results showed that a high variability in estimated stranding risk exists for the tested sites considering discharge ratios of 1:3, 1:5 and 1:10. With respect to the discussion of establishing legal thresholds for ramping ratios in discharge, it was documented that, exemplarily, a discharge ratio base flow/peak flow of 1:5 (winter base flow conditions) could cause minor differences in the spatial extent of dewatering areas and the related estimated stranding risk for juvenile brown trout compared to a ratio of 1:2 for summer base flow conditions. Microtopographic roughness was addressed due to sampling and analysis of grain size distributions. Statistical testing of grain size distributions revealed significant differences between the surface material compositions of the investigated gravel bars. Those differences are evident, particularly for the coarser fraction (d90), which is important as cover for young of the year brown trout. These aspects of grain size in habitat use and hydraulics have been addressed in the conceptual SRM. The results showed that point bar morphology, in particular, was less sensitive to the risk of stranding compared to, for example, alternating gravel bars. Considering the multiple pressures for alpine rivers, the improvement of structural features due to bar formation and related self-forming processes is discussed as a possible alternative for future mitigation measures to reduce the negative impacts of hydropeaking. Copyright © 2014 John Wiley & Sons, Ltd.

The Marchfeld, north-east of the river Danube between the cities of Vienna and Hainburg (Austria) is known for its special geological and climatic conditions, including water shortage. Water is heavily used for agricultural purposes and for domestic use due to the proximity of Vienna, Austria's capital. An artificial channel resembling a natural river of 18.8 km was built to carry up to 15 m3/s of water diverted from the Danube. It is supposed to increase the groundwater level, supply sufficient water for irrigation and supplement flows in two small rivers, the Russbach and the Stempfelbach. In 1992 the channel was finally filled. This project review describes the development of the fluvial ecosystem. The research encompassed limnology (nutrients, algae, macrophytes, invertebrates), fish-ecology (colonisation, migration, habitat preference, fish pass function), hydrology (current patterns, current model), sedimentology (surveys, types of structures, quality and quantity of the sediment) and bioclimatology (bioclimate, physical limnology). Main differences between the newly created watercourse and a natural river are highlighted. From an ecological point of view, the Marchfeld Canal could be regarded more like an artificial branch of the river Danube than an independent river system. © 1998 John Wiley & Sons, Ltd.

In the last few decades, numerous populations of European grayling, Thymallus thymallus, have been suffering from stocking-induced genetic admixture of foreign strains into wild populations. Concordantly, genetic introgression was also reportedfor grayling stocks inhabiting the Upper Drava River, but all published genetic data based on specimens caught at least a decade ago, when stocking load was strong. Here, we applied mitochondrial control region sequencing and nuclear microsatellite genotyping to Upper Drava grayling fry collections and reference samples to update patterns and extent of human-mediated introgression. In contrast to previous data, we highlighted an almost genetic integrity of Drava grayling, evidencing limited genetic signatures of trans-basin stocking for grayling of Northern Alpine Danubian origin. Recent hybridisation was detected only twice among sixty-nine samples, while several cases of later-generation hybrids were disclosed by linking mitochondrial sequence to nuclear genetic data. The observed past, but very limited recent genetic introgression in grayling from Upper Drava seems to reflect shifting stocking trends, changing from massive introduction of trans-basin fish to more conservation-oriented strategies during the last 27 years. In a conservation context, we encourage pursuing the use of local wild grayling for supportive- and captive-breeding, but underline the need for genetic approaches in brood-stock selection programs. Finally, our integrated results from sibship reconstruction validate our strictly fry-based sampling scheme, thus offering a reasonable alternative also for other rheophilic fish species with similar life-history characteristics.

A camera inside an underwater housing was used to record a pair of Danube huchen, Hucho hucho (L.) spawning at the Ybbs River, Austria. A description of spawning behaviour is made including observations of two other Danube huchen pairs recorded at the Rivers Mur and Pielach. Results were compared with the spawning behaviour of Siberian taimen, Hucho taimen (Pall.), Manchurian trout, Brachymystax lenok (Pall.) and Sakhalin taimen, Parahucho perryi (Brevoort). Danube huchen females, likewise the Siberian taimen and Manchurian trout females, rest for a variable number of minutes after the spawning act, before covering the eggs with gentle tail beating. This behaviour joins Danube huchen with Siberian taimen intragenerically and Hucho with Brachymystax intergenerically, distinguishing it from Parahucho and strengthening our current conception of the Salmoninae subfamily.

At the Sulm River, an Austrian lowland river, an ecologically orientated flood protection project was carried out from 1998–2000. Habitat modeling over a subsequent 3-year monitoring program (2001–2003) helped assess the effects of river bed embankment and of initiating a new meander by constructing a side channel and allowing self-developing side erosion. Hydrodynamic and physical habitat models were combined with fish-ecological methods. The results show a strong influence of riverbed dynamics on the habitat quality and quantity for the juvenile age classes (0+, 1+, 2+) of nase (Chondrostoma nasus), a key fish species of the Sulm River. The morphological conditions modified by floods changed significantly and decreased the amount of weighted usable areas. The primary factor was river bed aggradation, especially along the inner bend of the meander. This was a consequence of the reduced sediment transport capacity due to channel widening in the modeling area. The higher flow velocities and shallower depths, combined with the steeper bank angle, reduced the Weighted Useable Areas (WUAs) of habitats for juvenile nase. The modeling results were evaluated by combining results of mesohabitat-fishing surveys and habitat quality assessments. Both, the modeling and the fishing results demonstrated a reduced suitability of the habitats after the morphological modifications, but the situation was still improved compared to the pre-restoration conditions at the Sulm River.