Quality of populations of brown trout (Salmo trutta m. fario) influence of occurence of freshwater pearl mussel (Margaritifera margaritifera) in river in the Czech Republic. Freshwater pearl mussel is a critically endangered species of animals. It does not have a very specific requirements only on environment but mainly on a specific host for holding glochidia (larval stage of pearl mussel). Thus fish management and migratory permeability of flow for support of existing populations is very important. Basic and essential precondition to support populations of freshwater pearl mussels is the presence of viable populations of brown trout, which represents the only suitable host glochidia. There are five locations with the biggest occurrence of pearl mussel in the Czech Republic - river basins the Blanice, the Teplá Vltava, the Malše, the Rokytnice and the Jankovský potok. The management of these flows is under local organizations of Czech Fishing Union, the National Park and Protected Landscape Area of the Šumava, the Secondary School of Fisheries in Vodňany and Faculty of Fisheries and Protection of Waters. The present management was found in the questionnaire for representatives of farming organizations. According to the answers in the questionnaire, the change of plans of restocking was recommended in the river basins of the Teplá Vltava and the Jankovský potok. There is the cooperation with the Germany was recommended in the river basin of the Rokytnice. The restoration of fish nursery is suitable in the river basin of the Malše. There is the first-rate population of brown trout in the river basin of Blanice, thus the continue in the present fish management for next support of this population in sequence on the populations of freshwater pearl mussel was recommended

The objective of my work was to consider the effect of the Mlýnský potok revitalization on its fish society. My work is based on the ichtyological researches made before and after the revitalization. The brook is situated at the Šumava mountain between the Lipno reservoir and the border with Austria. The revitalisation had a positive effect on biodiversity, abundance and fish biomass. At the same time are here described individual requirements for successful revitalization water stream and in particular fisches, to the these streams. In my work compare achieved results of postponements fishes of the three tracked brooks Horský, Bukový and Mlýnský

Abstract In this thesis I studied lotic trout predation and its ecological effects, and investigated invertebrate predator-prey interactions under natural and anthropogenically modified flow conditions. Given the growing concern about the reliability of extrapolations from small-scale studies to larger spatio-temporal scales, results of mechanistic small-scale experiments were scaled up by linking them to large-scale field surveys. An intensive survey assessed changes in diel feeding periodicity, prey selection and daily ration of juvenile brown trout (Salmo trutta L.) over the course of the open water period. This survey provides the first field estimates of juvenile brown trout daily rations and indicates crepuscular feeding peaks. Trout selectively preyed on medium- to large-sized prey, shifting towards epibenthic feeding with increasing availability of suitable prey. In a small-scale field experiment, trout displayed clear size-related predation concentrating on invertebrate predators and cased caddisflies, a pattern that scaled up successfully in large-scale surveys. Further, predation effects on large-sized prey were also repeated in a meta-analysis on lotic salmonid predation. While dense blackfly populations in lake-outlet streams are common, mass outbreaks of blackflies in short-term regulated rivers are poorly studied. In our studies the principal invertebrate predator of vernal benthic communities, the caseless caddisfly Rhyacophila, displayed significant preference for blackflies and was almost unable to capture any other prey, thus resulting in passive selection for larval blackflies. Rhyacophila larvae displayed highest capture success in intermediate current velocities, whereas further increases in current velocities decreased capture success. Short-term regulation releases increased both predator and prey drift but, unlike for Rhyacophila, magnitude of drift was unrelated to substrate for blackflies. Indeed, field observations indicated that blackflies rarely face detrimental effects of short-term regulation due to their fast growing rates and early emergence. Moss was the most preferred habitat of Rhyacophila and provided the best buffer against sudden increases in current velocities. These results suggest that several factors maintain spring-time outbreaks of blackfly populations in short-term regulated rivers: exaptation of the dominant blackfly species to prevailing conditions, degradation of the key habitat of the predator, and recurring annual drift losses and diminished capture success of Rhyacophila during short-term regulation releases.

In boreal forest streams, woody debris is an important habitat component. Stream invertebrates and salmonids such as brown trout benefit from in-stream wood. The studies presented in this thesis explore how drifting stream invertebrates respond to addition of fine woody debris, and how young-of-the-year (0+) brown trout behave in habitats with and without fine woody debris. The first paper reports results from a field experiment where fine woody debris was added to streams, and invertebrate drift was measured in order to detect impacts of the fine woody debris on drift density, biomass and taxon diversity. In the end of the season, the fine woody debris-affected drift samples showed higher density, biomass and taxon diversity than the control samples. In the second paper, I describe effects of fine woody debris on 0+ brown trout, studied in laboratory stream channels. Trout were tested in habitats without fine woody debris, with an intermediate fine woody debris density, and with a high fine woody debris density. Swimming activity and foraging time were significantly lower when fine woody debris was present than when it was absent. More time was spent sheltering at the high fine woody debris density than at the intermediate one. The increasing exploitation of fine woody debris for biofuel purposes should be considered in relation to the effects on brown trout and stream invertebrate habitat. / <p>Artikel 1 ingick i avhandlingen som manuskript med titeln "Effects of fine wood addition on invertebrate drift in boreal forest streams". Nu publicerad.</p>

One common consequence of ontogenetic niche shifts is that juveniles and adults of the same species often use different resources and habitats. Theory suggests that variation in productivity and/or habitat size for the respective life stage regulates size distribution of individuals and population biomass. Low resources/habitat availability for juveniles relative to adults results in populations with many small juveniles with high mortality and few but large adults, while the opposite situation results in a population with small and slow growing adults with high densities. I tested this theory using lake-living brown trout (Salmo trutta), where adults inhabit lakes and use connected streams for spawning and nurseries for juveniles. My hypothesis was that the relative habitat availability for juveniles respectively adults determines the size structure of adult brown trout in lakes. This was done by quantifying available stream habitats in relation to lake area via GIS analysis of 101 allopatric brown trout lakes in Sweden and Norway. My results showed that the proportion of large trout, mean length and maximum length decreased with increasing juvenile habitat in relation to adult habitat availability. This suggests that relative variation in availability of juvenile and adult habitats can affect the size structure of lake-living brown trout, most likely due to size dependent niche shifts and competitive and cannibalistic interactions. As the lake brown trout is highly valued both for commercial and recreational purposes, these findings can be highly valuable for sustainable management of the ecosystems services that the brown trout provides.

Opening migratory pathways is crucial for the brown trout´s ability to recolonize spawning- and rearing areas, in order to complete its lifecycle. Damming rivers for hydropower production has created obstacles for migration, and nature-like fishways are one measure used to recreate connectivity. The purpose of this bachelor´s thesis was to find out how the nature-like fishway, constructed in 2016, at Billsta power plant, central Sweden, was used by migratory brown trout for upstream and downstream passage, and to observe if the migration pattern changed over time, between 2018-2020. The collected data comes from an automatic fish-counter that has been located upstream of the nature-like fishway. To analyze the data, recorded trout were categorized into two length classes, spawning-size and smolt-size, according to criteria from the Swedish Agency for Marine and Water Management (HaV). Since individual fish could not be identified, a method for daily “net migration” was been developed to estimate the direction of migration. The results showed that net migration of spawning-size trout was greater upstream than downstream. Net upstream migration of spawning size trout tended to increase over time, but not the net downstream migration. There was no difference between net upstream and net downstream migration smolt-size trout, but the net downstream migration smolt-size trout increased over time. The study showed that there was substantial use of Billsta nature-like fishway for brown trout of both spawning- and smolt-sizes, for both upstream and downstream migration. The migration pattern was partly as expected but, upstream migration of smolt-size trout suggests that there is a considerable population of stationary trout passing the fish-counter. The study highlights the importance of monitoring the results of the restoration and implementing improvement measures where necessary. Billstaån has regained open migration pathways, but more time is needed to evaluate its effect and find out if the ecosystem works so that Storsjöns unique, large sized, migratory brown trout stocks once again have the conditions to complete their lifecycle in Billstaån. / Fria vandringsvägar är avgörande för öringens förmåga att återkolonisera lek- och uppväxthabitat, vid fungerande lek- och smoltvandring kan öringen fullborda sin livscykel. Vattenkraftsproduktion har skapat vandringshinder och naturlika fiskvägar är en åtgärd för att återskapa konnektivitet. Syftet med den här kandidatuppsatsen var att ta reda på hur den nedersta naturlika fiskvägen, skapad 2016 vid Billsta kraftverk i mellersta Sverige, nyttjades av vandrande öringar för uppströms och nedströms passage och observera om vandringsmönstret förändrades över tid, mellan 2018–2020. Rådatan kommer från en automatisk fiskräknare som funnits placerad uppströms den naturlika fiskvägen. För att analysera datan delades öringen in efter två längdstorlekar, lek- och smoltstorlek, enligt kriterier från Havs- och vattenmyndigheten. Eftersom individuell fisk inte gick att identifiera har en metod för daglig ”nettovandring” utarbetats för att uppskatta vandringens riktning. Resultatet visade att fler öringar i lekfiskstorlek nettouppvandrade än nettonedvandrade. Nettouppvandring av lekfiskstorlek tenderade att öka över tid men inte nettonedvandringen. Det var ingen skillnad mellan nettoupp- och nettonedvandrande öring i smoltstorlek, men nettonedvandringen av öring i smoltstorlek ökade över tid. Studien visade att Billsta naturlika fiskväg nyttjades väl av öring i både lekfisk- och smoltstorlek för både uppströms- och nedströmsvandring. Vandringsmönstret var delvis som förväntat, men när det gäller smoltstorlekens vandring var det snarare bäcköringens vandring än smoltens vandringsmönster som analyserades. Studien belyser vikten av att övervaka resultatet av restaureringen och implementera förbättringsåtgärder där så behövs. Billstaåån har återfått fria vandringsvägar men mer tid behövs för att utvädera dess effekt och ta reda på om ekosystemet fungerar så att Storsjöns unika, storvuxna, lekvandrande öringstam återigen fått förutsättningar att fullborda sin livscykel i Billstaån.

Brown trout (Salmo trutta), demonstrated an avoidance response to a range of intensities of artificial ultraviolet radiation in a laboratory setting. UV field measurements were made under a variety of riparian canopies in a mountain river system. UV values at various depth regimes were compared with laboratory response values. Results suggested that ultraviolet light could be a factor in the absence of brown trout in particular habitat types at various times during the daylight hours. Visible light intensity response values were also obtained under the same experimental and field conditions. These data suggested that visible light also could be a contributing factor in the absence of brown trout in different habitat types. Visible light may be of equal importance to ultraviolet light in eliciting an avoidance response in brown trout.

The productivity or availability of juvenile habitats have theoretically been shown to determine size distributions of adult individuals and population abundance. Brown trout (Salmo trutta) is a species where adults may inhabit lakes and use connected streams for spawning and as nursery habitats for juveniles. This project aimed to estimate what factors determine the density and growth of juvenile brown trout in mountain streams. This was done by sampling 21 mountain streams for juvenile brown trout densities and growth, habitat availability and stream size, productivity, and resource availability. Additional data were obtained from other mountain streams from the Swedish Electrofishing Register. My results showed that measures of stream productivity and estimated benthic resource availability did not affect the densities and biomass of older juvenile brown trout. Instead, higher densities of older juvenile brown trout were related to increasing stream size (stream width x water depth). This is likely due to interference competition for space, where territory size influences the growth and densities of brown trout in streams but also that larger streams can provide refuges for larger individuals during periods of drying and thermal stress. This indicates that my estimate of stream size is an important factor determining densities of older juvenile brown trout in low-productive mountain streams. Stream size can be suggested to be a used as proxy for density and production of larger juvenile brown trout and therefore it may also be used to predict adult lake-living brown trout population size structure and abundance.

As all of Sweden's hydropower is to be re-examined within a 20-year period, methods are needed to carry out ecological investigations of dammed waterways. The first aim of this thesis is to evaluate whether methods for salmon and trout habitat mapping take all relevant indicators into account. In addition, the report aims to investigate which factors affect the results of habitat mapping based on hydraulic simulation and to investigate whether this method can be made more efficient through the use of simpler models, drone images and calculations. The work began with a literature study. A model was then built over a dammed stretch where mapping through hydraulic simulation was carried out. A mapping was then carried out on another stretch of stream based on a simpler model, drone images and shadow calculations, in parallel with a field mapping. The results of the literature study showed that the mapping methods capture the physical indicators well and indirectly link to certain chemical and ecological indicators. The method could be improved by including the water's nitrogen content and pH in the assessment.Important factors in habitat estimation with hydraulic simulation are the flow and the accuracy of the terrain model, as well as how the result is produced. The result from mapping with a simpler hydraulic model showed large deviations from the results obtained in the field, with respect above all to depth and width. Drone imagery for substrate assessment works well in shallow and clear water bodies. Shadow calculations based on how they were applied in this work to habitat mapping have not given satisfactory results, why the method needs to be developed. / Då all Sveriges vattenkraft ska omprövas inom en 20-årsperiod behövs metoder för att genomföra ekologiska utredningar av uppdämda vattendrag. Det första syftet med detta examensarbete är att utvärdera om metoder för lax- och öringhabitatkartering tar hänsyn till alla relevanta indikatorer. Därutöver syftar rapporten till att undersöka vilka faktorer som påverkar resultatet vid habitatkartering utifrån hydraulisk simulering och att undersöka om denna metod kan effektiviseras genom användning av enklare modeller, drönarbilder och beräkningar. Arbetet inleddes med en litteraturstudie. Därpå byggdes en modell upp över en indämd sträcka där kartering genom hydraulisk simulering genomfördes. En kartering genomfördes sedan på en annan strömsträcka utifrån en enklare modell, drönarbilder och skuggberäkningar, parallellt med en fältkartering. Litteraturstudiens resultat visade på att karteringsmetoderna väl fångar upp de fysikaliska indikatorerna och indirekt kopplar till vissa kemiska och ekologiska indikatorer. Metoden skulle kunna förbättras genom att ta in vattnets kvävehalt och pH i bedömningen. Viktiga faktorer vid habitatskattning med hydraulisk simulering är flödet och terrängmodellens noggrannhet, samt klassningen för vad som anses som goda habitat. Resultatet från kartering med en enklare hydraulisk modell visar på stora avvikelser mot resultaten inhämtade i fält, med avseende på framför allt djup och bredd. Drönarbilder för substratbedömning fungerar väl vid grunda och klara vattendrag. Skuggberäkningar utifrån hur de i detta arbete applicerats på habitatkartering har inte gett tillfredställande resultat, varför metoden behöver utvecklas.

Over the past decade, research on microplastic pollution has gained significant attention. Research regarding microplastic occurrence in freshwater fish, however is still scarce. While possible pathways have been investigated, passive transfer via ingestion of prey, and possible bioaccumulation in different organs remains relatively unstudied. The scope of the work presented here was to examine microplastic occurrence in brown trout (Salmo trutta) and its main prey European smelt (Osmerus eperlanus) from Lake Vänern, Sweden. Further, my aim was to investigate for microplastics different organs such as stomach, liver, heart and intestine. Brown trout were collected by sport fishermen at sport fishing contests in Lake Vänern. All dissected organs were treated with hydrogen peroxide (H2O2) and particles were analysed and identified using Fourier transform infrared spectroscopy (FTIR). Microplastics were found in 94% of brown trout with 43% coming from the intestine, 41% from the stomach and 16% from the gastrointestinal tract of smelt. There was a significant difference in microplastic abundance between organs. No microplastics were fund in the liver or heart of brown trout. Fibres were the most abundant shape (95%) and black the most occurring colour (44%). The most abundant polymer types were neoprene, chlorosulfonated polyethylene and hydrogenated nitrile rubber and the smallest analysed particle was 100 m while the largest was 4.9 mm. In conclusion, my study confirmed the presence of microplastics in brown trout and its main prey from Lake Vänern, Sweden. Future research should focus on prey fish and different organs to give a better understanding of trophic transfer within the aquatic food web, and its possible bioaccumulation. / Under det senaste decenniet har forskningen om mikroplastföroreningar fått stor uppmärksamhet, men det finns fortfarande få undersökningar om mikroplastens förekomst i sötvattensfisk. Även om möjliga vägar har undersökts, är forskning på passiv överföring via intag av bytesdjur och eventuell bioackumulering i olika organ fortfarande relativt outforskat. Syftet med det arbete som presenteras här var att undersöka förekomsten av mikroplaster i öring (Salmo trutta) och dess huvudsakliga bytesdjur europeisk nors (Osmerus eperlanus) från Vänern, Sverige. Vidare var mitt mål att undersöka om det fanns mikroplaster i olika organ som mage, lever, hjärta och tarm. Öring samlades in av sportfiskare vid olika sportfisketävlingar i Vänern. Alla dissekerade organ behandlades med väteperoxid (H2O2) och partiklar analyserades och identifierades med hjälp av Fourier transform infraröd spektroskopi (FTIR). Mikroplaster hittades i 94 % av öringarna, där 43% kom från tarmen, 41% från magsäcken och 16% från mag- och tarmkanalen hos nors. Det fanns en signifikant skillnad i mikroplastmängden mellan organen. Inga mikroplaster hittades i lever eller hjärta hos öring. Fibrer var den vanligaste formen (95%) och svart den vanligaste färgen (44%). De vanligaste polymertyperna var neopren, klorsulfonerad polyeten och hydrerat nitrilgummi. Den minsta analyserade partikeln var 100 m medan den största var 4,9 mm. Sammanfattningsvis bekräftar min studie förekomsten av mikroplaster i öring och dess huvudsakliga föda från Vänern, Sverige. Framtida forskning bör fokusera på bytesfiskar och olika organ för att ge en bättre förståelse för trofisk överföring inom den akvatiska näringsväven, såsom möjlig bioackumulering.