Zur Ökologie der Bachforelle unter besonderer Berücksichtigung des ersten Lebensjahres

Die Dissertation, als Kompendium eingereicht, beschäftigt sich mit der Ökologie der Bachforelle (Salmo trutta) unter besonderer Berücksichtigung des ersten Lebensjahres. Die Arbeit ist in zwei Abschnitte unterteilt. Im ersten Teil werden einleitend die Entwicklungsgeschichte der Salmonidae und der internationale Stand des Wissens zur Ökologie der Bachforelle umrissen. Anschließend wird die Ökologie der Bachforelle behandelt wobei der Fokus am ersten Lebensjahr liegt. Themen dabei sind die Ansprüche der Bachforelle hinsichtlich Temperatur, Sauerstoff, Nahrung und v. a. die hydromorphologischen Habitatkomponenten im Laich-, Intersitital-, Jungfisch- und Adulthabitat. Dabei wird Bezug zu den unten folgenden Publikationen hergestellt und die wesentlichsten Ergebnisse bzw. daraus abzuleitende Schlussfolgerungen in einem breiteren Kontext diskutiert. Den zweiten Teil der Dissertation bilden fünf Publikationen, die in wissenschaftlichen Fachjournalen erschienen sind. Kernstück ist ein Artikel der den wesentlichen Einfluss des Abflussgeschehens, insbesondere von Hochwasserereignissen, auf die Rekrutierung von Jungfischen eines alpinen Gewässers, der Oberen Ybbs, aufzeigt. Die zweite Publikation beschäftigt sich mit einer Methode, mit der es möglich ist, Fische bereits vor dem Schlüpfen aus dem Ei, im so genannten Augenpunktstadium zu markieren. Die Markierungsmethode verwendet den Farbstoff Alizarin Rot S. Publikation drei zeigt den Einfluss von Abfluss, Gewässermorphologie und Sedimenttransport auf die Umlagerung bzw. Neubildung von Laichplätzen für Bachforelle und Äsche am Beispiel der Großen Mühl in Oberösterreich auf. Der vierte Artikel präsentiert eine Methode zur Bewertung kleiner Bäche hinsichtlich ihrer Lebensraumeignung für juvenile Bachforellen. Und schließlich beschäftigt sich Publikation fünf mit der Restauration von Bachforellenlaichplätzen in einem voralpinen Kalkgewässer.The present PhD thesis, submitted as a compendium, deals with the ecology of brown trout (salmo trutta) whereat special emphasis is placed on the first year of development in life history. The thesis is divided into two sections. Prefacing the evolution of the family Salmonidae and international state-of-the-art in science concerning brown trout ecology is outlined. This is followed by a chapter on brown trout ecology with emphasis on the first year in life history. Main issues are the species requirements concerning temperature, oxygen, food as well as the hydro-morphological components of habitat, divided into spawning- interstitial-, juvenile- and adult habitats. The different life history aspects are related to the publications below; the main results and derived implications are discussed in a broader ecological context. The second section of the thesis comprises the five publications, published in scientific journals. Key part of the PhD thesis is an article dealing with the crucial influence of flow, respectively flood events on the recruitment of brown trout in an Alpine river, the Ybbs River. The second article deals with a marking method to label embryos of brown trout during the eye-point egg stadium. Publication three highlights the meaning of flow, morphology and sediment transport processes for the formation and reshaping of spawning grounds for brown trout and grayling at the example of the Große Mühl River in Upper Austria. Article four presents a method to assess the habitat quality for juvenile brown trout in small streams. Finally article five deals with the restoration of spawning habitats for brown trout in an regulated chalk stream.verf. und eingereicht von Günther UnferZsfassung in dt. und engl. SpracheWien, Univ. für Bodenkultur, Diss., 2012OeBB(VLID)193112

aquaZone: An Integrative Tool for Sustainable Fish Farm Zoning

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

aquaZone: An Integrative Tool for Sustainable Fish Farm Zoning

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

Die Seeforellenlaichwanderung in der Hasliaare 2019 im Kontext abiotischer Faktoren

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

A Physical and Behavioral Barrier for Enhancing Fish Downstream Migration at Hydropower Dams: The Flexible FishProtector

Fish protection at hydropower plants is important for the sustainability of hosting ecosystems and the acceptance of hydropower. On their way downstream, fish are exposed to hydropower plants and various related negative effects, ranging from a delay in downstream movement to being injured or killed by a turbine. Understanding the behavior of fish in close proximity to protection devices is essential in order to establish efficient fish protection facilities. In this study, physical (horizontal steel cables) and behavioral barriers (electric field) for fish protection were developed (Flexible FishProtector) and their effectiveness was investigated. The behavior of brown trout (Salmo trutta fario), rainbow trout (Oncorhynchus mykiss), grayling (Thymallus thymallus) and chub (Squalius cephalus) at the Flexible FishProtector was analyzed using video evaluation. The experimental setup was a non-scaled section model of a runoff river power plant. The used electric field induced a flight reaction at a corresponding distance to the Flexible FishProtector that significantly increased the protection rate. Furthermore, an increase in guiding efficiency was achieved with the use of a physical as well as a physical and behavioral barrier, supporting safe downstream migration with the narrower cable clearance (30 mm versus 60 mm)

A Physical and Behavioral Barrier for Enhancing Fish Downstream Migration at Hydropower Dams: The Flexible FishProtector

Fish protection at hydropower plants is important for the sustainability of hosting ecosystems and the acceptance of hydropower. On their way downstream, fish are exposed to hydropower plants and various related negative effects, ranging from a delay in downstream movement to being injured or killed by a turbine. Understanding the behavior of fish in close proximity to protection devices is essential in order to establish efficient fish protection facilities. In this study, physical (horizontal steel cables) and behavioral barriers (electric field) for fish protection were developed (Flexible FishProtector) and their effectiveness was investigated. The behavior of brown trout (Salmo trutta fario), rainbow trout (Oncorhynchus mykiss), grayling (Thymallus thymallus) and chub (Squalius cephalus) at the Flexible FishProtector was analyzed using video evaluation. The experimental setup was a non-scaled section model of a runoff river power plant. The used electric field induced a flight reaction at a corresponding distance to the Flexible FishProtector that significantly increased the protection rate. Furthermore, an increase in guiding efficiency was achieved with the use of a physical as well as a physical and behavioral barrier, supporting safe downstream migration with the narrower cable clearance (30 mm versus 60 mm)

River continuum disruptions in a highly altered system: The perspective of potamodromous fish

In this study, we explored how barriers such as dams have affected the longitudinal connectivity of riverine habitats from the perspective of potamodromous fish. For this purpose, connectivity changes are investigated in the central part of the Austrian Danube system, where the national reporting for the EU Water Framework Directive provides detailed information on the position and characteristics of barriers as well as the distribution range of native fish species. This assessment is based on an estimation regarding the quantitative upstream and downstream passability of individual barriers, where we further investigate three different passability scenarios to account for uncertainties. We then apply several combinations of passability scenarios and assumptions on dispersal distances to calculate a series of network-based reach and catchment connectivity indices. On average, the estimation of barrier passability indicated a high downstream passability, while upstream passability was substantially lower across scenarios. Furthermore, existing fish passes were estimated to have increased passability on average between 20 % and 24 %. Overall, the results indicated a strong effect of barriers on the longitudinal connectivity of the investigated river network. Catchment scale indices revealed a loss of connectivity, which increased with dispersal distance. Reach connectivity indices displayed a strong disruption of the natural connectivity gradient along the river network and indicated that individual river reaches have, on average, become more isolated in addition to the overall decrease in connectivity. The average loss of connectivity across scenarios was estimated at 72 % (SD = 16 %) when taking into account all connections to other reaches and 66 % (SD = 7 %) when only connections to upstream reaches were considered. We conclude that longitudinal connectivity in the Austrian Danube system is still severely compromised, making it increasingly challenging for potamodromous fish species to complete their life cycle. This issue is further amplified by the severe loss of fish habitats as a consequence of river engineering

Reviving Europe's rivers: Seven challenges in the implementation of the Nature Restoration Law to restore free-flowing rivers

The EU Nature Restoration Law represents an important opportunity for freshwater habitat restoration and, consequently, freshwater biodiversity protection. However, a number of challenges must be anticipated in its implementation, which may compromise its success. Some aspects, particularly those relating to freshwater ecosystems, require more clarification. We use riverine ecosystems to illustrate existing ambiguities in the proposed legislation and the potential consequences of leaving these aspects open to interpretation during the implementation process. We also discuss potential solutions to these problems which could help ensure that the law's objectives are met. We argue that river network structure and connectivity dimensions, which result into river meta-ecosystems, must be explicitly considered. For that purpose, we ask for clear definitions of the critical terms “free-flowing rivers,” “barriers,” and “reference areas.” In addition, we recommend developing methods for integrated assessment of connectivity across river networks. As a key property of river ecosystems, this must be used to prioritize actions to increase the length and number of free-flowing rivers. Adequate restoration planning at larger spatial scales will benefit from a meta-ecosystem perspective and accurate representation of aquatic-terrestrial linkages, which will significantly improve the efficacy of restoration efforts. Furthermore, stakeholder and citizen engagement offer important opportunities at local, national, and European scales, and should be fostered to ensure inclusive decision-making. The conservation challenges outlined here are particularly important for rivers, but they also have implications for other ecosystems. These considerations are useful for policymakers, conservationists, and other stakeholders involved in the Nature Restoration Law and related policy initiatives.This study was supported by the following funding sources: the MERLIN project funded under the European Commission's Horizon 2020 programme, Grant agreement No. 101036337; the DANUBE4ALL project funded by the European Union's Horizon Europe Research and Innovation Programme under grant agreement no. 101093985; the BioAgora project funded by the European Union's Horizon Europe Research and Innovation Programme under grant agreement No. 101059438; the Austrian Federal Ministry for Digital and Economic Affairs and the Christian Doppler Research Association (CD Laboratory MERI); the Austrian Science Fund (FWF) project RIMECO (I 5006); a Hungarian ANN-OTKA 141884 grant; project FLUFLUX (ERC-STG 716196); and the Leibniz Competition project “Freshwater Megafauna Futures” (P74/2018).info:eu-repo/semantics/publishedVersio