Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2008. / Härtill 6 uppsatser.

The aim of this thesis was to monitor mortality or more precisely population changes of freshwater pearl mussel (Margaritifera margaritifera L.), which settle in oligothropic stream. Brown trout (Salmo trutta morpha fario L.) is the only one fish host of larval stage of freshwater pearl mussel. The counting of the population was pursued at 2 localities: on the Blanice river and on the stream of Lužní potok in the Czech Republic. For general counting of population a net instrument and an optical instrument were used, that enabling to see them. Population of freshwater pear mussel is in decline in all Europe due to many factors like eutrophication, water pollution, etc. Results of work indicated a decline in population of freshwater pearl mussel at the first area about 15,38 % and at the second area about 15,22 % of the stream Lužní potok. There was not recorded a decline on the Blanice river, on the contrary, the number of population was higher. Among others, the habitation of juveniles was recorded at the first area.

Thesis (M. Sc. (Agriculture)) -- University of Limpopo, 2016 / Fish assemblages in relation to environmental variables within the Broederstroom and Debengeni Rivers were investigated. Both rivers were characterized by coarse substrates (pebble and gravel), temperatures below 20°C and moderate depth. Trout dominated fish assemblages in terms of numbers caught and was only distributed at higher altitude sites >1400 m (a.s.l). Coarse substrates, temperatures below 15°C, flow rate, depth and riparian cover were the variables shown important for the distribution of trout by multivariate analysis. The confinement of the trout to higher altitude and lack of optimal habitat variables at lower altitude sites contributed to the assertion that the area is marginal for trout distribution. It was therefore inferred that the marginality of the area is the possible explanation for trout failure to self-sustain its population, therefore dependent on the continuous restocks by the local hatchery. The continuous restocks of small size trout in the Broederstroom River prompted a subsequent study where trout’s impact on macroinvertebrate communities was evaluated through surveys and field experiments. The ability of small trout to utilize macroinvertebrates made them suitable candidates to evaluating their impact in the area. Aquatic invertebrates were found to be the main food source for the trout in the area. Taxa such as Gomphidae and Potamonautidae were the most frequent food items from the analyzed stomachs of trout. However, observations from both field surveys and experiments showed that trout is a weak regulator of macroinvertebrate diversity in the area, since there were no significant differences (ANOVA, P<0.05) in the diversity of invertebrates from trout invaded and uninvaded sites. Trout being a weak regulator of macroinvertebrate diversity in the area, it prompted surveys to the Ebenezer Dam to determine its competitive interactions with native predatory species. If the introduced species is a more efficient predator than the native predator species, it may affect changes in the structure of the habitat and food resource. Trout in the Ebenezer Dam was found to be selective to habitat variables whilst C. gariepinus was cosmopolitan to all habitat categories. The catfish also had a broader food preference than trout and the diversity of the food items was significantly different (ANOVA, P<0.05) between the two species. Unfortunately, the interspecific food overlap between trout and the catfish could not be determined in Ebenezer Dam, because of the small sample size of trout but food selection between vii them was evident. It was then concluded that the native catfish has a wider niche and it is a more efficient predator than the introduced trout. This observation contributed further to the assertion that the area is marginal for trout to thrive. Due to trout selection of habitat variables, it became prudent to carry out another study where the past climate and land use changes were analyzed to determine their effect on the habitat that could have affected the distribution of trout in the area. Future projections were also made to determine possible future impacts of climate change on the distribution of trout in the area. The effects of climate and land use change resulted in warmer water temperature, altered riparian cover and altered stream flow patterns. The changes could have influenced the confinement of trout to higher altitude catchments. The projected maximum temperatures by 2050 shows an increase from 2014 with a decline in precipitation. If these projections are to be the same for water temperature and flow regimes, coupled with current land uses in the area, they will continue to affect the distribution of trout negatively.

The brown trout (Salmo trutta) in Lake Siljan in the central of Sweden is one of the country´s few remaining populations of trout that migrates between large lakes and rivers. Because of antropogenic impact the number of mature individuals is small and the population is therefore supported by stocking of hatchery fish since several decades. Data have been collected using acoustic telemetry during 2018-2019 with the aim to study the population with the final goal to increase numbers of wild individuals. The results showed that most parts of Lake Siljan is utilized by both wild and hatchery trout. There is therefor no good measure to avoid wild bycatch by directing fishery of hatchery fish to specific geographic areas.  Measures like catch and release and low bag limits of wild fish will probably be more sufficient. The result also shows that the wild fish was most likely to home to the main source, River Österdalälven, and the tributary Hemulån for spawning. Protection of these areas is therefor highly motivated. The lake survival of the newly released 2-year-old hatchery smolt and the 4-years-old hatchery adults was low, 3 and 25 percent, respectively. The survival of wild and semidomestic adults was higher, 86 and 77 percent, respectively. This is another reason for increasing the number of reproducing wild individuals. Repeating of this study is important to get information of any possible variance between years in the utilization of the different areas in the Lake Siljan, the knowledge of spawning habitats and survival. This study has added some new and additional knowledge of a less studied field of the diverse life histories of the brown trout. / Öringen (Salmo trutta) i sjön Siljan i mellersta Sverige är en av landets få kvarvarande bestånd av öring som vandrar mellan ytstora sjöar och rinnande vatten.  Den självreproducerande delen av populationen är liten på grund av antropogen påverkan och har under flera decennier understötts med utsättning av odlade individer. Med akustisk telemetri har data samlats in under 2018-2019 i syftet att bygga kunskap som ska öka möjligheterna för att öka antalet av naturligt reproducerande individer. Resultaten visade att merparten av Siljans olika delområden nyttjades av både vilda och odlade individer utan någon uppdelning av dessa två delpopulationer. Förutsättningar för ett riktat fiske efter odlade individer i vissa geografiska delområden av Siljan föreligger därför inte. Fisket måste därav regleras gemensamt och likartat på över hela sjön. Resultaten visade också att vilda individer i huvudsak använder Österdalälven och biflödet Hemulån för reproduktion vilket motiverar ett ökat skydd för dessa områden. Överlevnaden av nyligen utsatta odlade 2-åriga smolt och 4-åriga adulter var låg, 3 respektive 25 %, vilket ger ytterligare skäl för arbetet med öka den självreproducerande andelen av populationen. Hos de frilevande adulta vilda och odlade individerna sågs en högre överlevnad, 86 respektive 77 %.  Upprepning av denna studie krävs för att detektera eventuell mellanårsvariation i nyttjandet av delområden, reproduktionslokaler samt överlevnad. Detta arbete har tillfört ny och kompletterande kunskap till en ringa studerad del av öringens många och diversa livshistorier.

Den anadroma öringen i Östersjöns avrinningsområde uppnår inte tillfredsställande status och uppskattningsvis upprätthålls ungefär hälften av populationerna med kompensationsodling. En av dem är Dalälvens anadroma öring som numer har sitt reproduktionsområde vid Älvkarleby, ca 10 km uppströms älvmynningen till Östersjön. Där finns även ett vattenkraftverk som innebär ett definitivt vandringshinder för Dalälvens migrerande arter. Vid Älvkarleby bedriver SLU Aqua forskning på öring och lax, samt ansvarar för kompensationsodlingen av Dalälvens anadroma öring. Tack vare det långvariga kompensationsodlingsprogrammet finns långa tidsserier innehållandes populationsdynamiska och strukturella data om populationen i Dalälven. I denna studie beskrivs långtidstrender i detta data, och med hjälp av statistiska metoder identifieras potentiella påverkansfaktorer. Resultaten visar att studieperioden kännetecknas av kraftiga populationsdynamiska fluktuationer, och temperatur identifierades som en stark påverkansfaktor. / Anadromous trout populations in the Baltic Sea area are in a less than optimal state and about half of the populations are maintained by hatchery-reared trout. One of the populations spawns near Älvkarleby of river Dalälven, about 10 km upstream of the estuary in the Baltic Sea. A hydroelectric dam located in the same area blocks the routes of migratory species. SLU Aqua operates the cultivation of trout native to river Dalälven and conducts research at the research center in Älvkarleby. Owing to the long-term cultivation in river Dalälven, long time-series containing population-specific data is available. Based on the collected data, this study describes long-term trends in the trout population native to river Dalälven and tries to identify potential factors effecting these by using statistical methods. The results show that the study period is characterized by large fluctuations in population dynamics, and that temperature is a major influencing factor.

Supporting fish populations by restocking with artificially bred young fish is a common practice worldwide, which may sometimes have a negative effect on natural genetic diversity. In this study, the currently ongoing restocking program of brown trout (Salmo trutta Linnaeus, 1758) in the subarctic Pasvik river in Norway was investigated. Previous investigations of this population showed a loss of genetic diversity and both genetic and morphological differentiation between historical breeding stocks and wild trout populations. However, the genetic impact of the breeding program used in this river today has never been investigated. To accomplish this, I compared the parent fish, the offspring, and fish caught in the river using 16 short tandem repeat loci and estimated pairwise relatedness, inbreeding, genetic distances, and differentiation. The results showed, by estimating the effective population size, that the number of parents used in the breeding program was generally insufficient to maintain a genetically sustainable river population. Further, genetic diversity in stocked fish was typically not maximized due to lack of performing all possible crossings between males and females. In combination, this induced genetic drift in the offspring generations and thus genetic differentiation away from the river populations. In summary, the results from this study show that the current stocking practises used in the Pasvik river are not sustainable and that measures need to be taken to prevent continued loss of genetic diversity in this large-growing trout population.

Los estudios acerca de la ecología de los peces tienen como una de sus principales bases la evaluación de las poblaciones, encaminados a definir el conjunto de los individuos de una misma especie que vive en un espacio común. Por lo tanto, el análisis del hábitat es clave para la estructura de las poblaciones. Desde el punto de vista de la teoría jerárquica ecológica, los patrones biológicos que gobiernan a las poblaciones de peces de los ríos son controlados y ajustados por los patrones físicos del hábitat. Así pues, una descripción exacta de los ríos es un primer paso en la descripción de los requerimientos ecológicos de los organismos durante su vida así como en los procesos que influyen en su abundancia y distribución. En este sentido, esta tesis aporta un mayor conocimiento de las poblaciones de trucha común (Salmo trutta) y de sus hábitats en ríos mediterráneos. El estudio se llevó a cabo en cuatro ríos de la Comunidad Valenciana (España) donde hoy en día la especie habita de forma natural; Ebrón y Vallanca (en la provincia de Valencia), Villahermosa y Palancia (en la provincia de Castellón). Los muestreos se realizaron entre los meses de Junio y Agosto entre los años 2003 y 2006. El primer año se establecieron dos estaciones de muestreo en cada río. En los restantes años se amplió a cuatro estaciones de muestreo en cada río. Se destaca el hecho de que en los dos últimos años de estudio (2005 y 2006) hubo una fuerte sequía que hizo que los tramos más altos de los ríos Vallanca y Villahermosa se secaran, perdiéndose tres de las dieciséis estaciones establecidas. En total se muestrearon 50 tramos en los cuatro años de muestreo. Para la caracterización del hábitat se adaptó el protocolo de muestreo "Basinwide Visual Estimation Technique - BVET". Esta técnica consiste en estratificar visualmente el cauce según sus diferentes biotopos (unidades hidromorfológicas o mesohábitats), registrándose en ellos las distintas características hidromorfológicas. / Alcaraz Hernández, JD. (2011). Estado de las poblaciones de trucha en los ríos de la Comunidad Valenciana y caracterización de sus hábitats [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14271

There are five endemic populations of migratory Atlantic salmon (Salmo salar, Salmonidae) and brown trout (Salmo trutta, Salmonidae) remaining in Lake Vänern, whereof two are salmon and three are trout. There is one population of each species in Klarälven, also one of each in Gullspångsälven and there is a population of trout still remaining in Tidan River. Since the beginning of the 20th century endemic populations of salmon and trout have either vanished or declined dramatically due to the construction of hydropower in the rivers around the lake, and still today the future of the remaining populations remains uncertain. To manage salmonid fishes effectively more knowledge of their ecology throughout their different life-stages is needed. A large part of the Lake Vänern salmonoids lives are spent in the lake, where a mayor mortality factor is recreational fishing, especially angling. Estimation of fishing effort and catch is important in order to remain a sustainable fishery. In Lake Vänern commercial fishers are bound to report their catch, but anglers are not, -even though they are now thought to be responsible for the largest proportion of the catch. Angler interviews and access point surveys are the best ways to get accurate information in order to assess sport fish effort and catch. There are drawbacks of this method though that includes large costs, logistical problems and biased results due to the higher chance of interviewing the most avid anglers. To hand out mail-surveys is a kind of off-site survey that is less costly compare to interviews, but the drawbacks are bigger in getting correct information due to biased results from non-respondence. A study was conducted to compare an interview-survey with a mail-in survey, in which the interviews were conducted in Lillängshamnen, a port on the northern coast of Lake Vänern, and the mail-in surveys were distributed in different ports around the lake, though not in Lillängshamnen. This study shows a significant difference in catch per boat day between the interviews and mail-in survey. To find out more about how to develop the interview-survey there was also an analysis done on the correlation between weather and the number of interviews that were collected. One could find a negative correlation between numbers of interviews collected and the wind ratio, where very few interviews were collected once the wind speed measured more than 5-8 meters per second. There are improvements to be made both for the conduction of interviews and mail-in surveys, including more staff for conducting interviews at different ports and follow-ups on the non-respondents for the mail-in survey. / Av atlantlax (Salmo salar, Salmonidae) och öring (Salmo trutta, Salmonidae) finns idag fem endemiska populationer kvar i Vänern varav två är av lax och tre av öring. Det finns en klarälvsvariant av båda arterna, likaså finns det en gullspångsvariant av varje och sen finns även en öringpopulation kvar i Tidan. Sen början av 1900-talet har populationer av lax och öring utrotats eller minskat kraftigt till följd av vattenkraftens utbyggnad i vattendragen runt Vänern, och än idag är de resterande populationernas framtid oviss. För att kunna förvalta laxfiskarna på ett bra sätt krävs kunskaper om deras ekologi i dess olika livsstadier. En stor del av laxfiskarna runt Vänerns liv tillbringas i Vänern, där en mortalitetsfaktor består av fritidsfisket, då främst trolling. Uppskattning av ansträngning och fångst är viktigt för att hålla fisket i sjön på en hållbar nivå. Yrkesfisket måste rapportera all sin fångst men detta krävs inte av trollingfisket som idag tros stå för den största proportionen lax- och öringsfångst i Vänern. Genomförandet av intervjuer är en typ av plats- och åtkomstpunktsundersökning och är den bästa metoden att samla in korrekt information för att uppskatta sportfiskets ansträngning och fångst. Det finns dock nackdelar i form av stora kostnader, svår logistik och vinklade resultat då de mest entusiastiska fiskarna löper större chans att bli intervjuade. Att dela ut enkäter är en form av distansundersökning och även brevundersökning som kostar betydligt mindre än att genomföra intervjuer men brister vad gäller svarsfrekvens som i sin tur leder till vinklade resultat. En studie gjordes för att jämföra intervjuer med enkäter, där intervjuer genomfördes i Lillängshamnen på Vänerns norra kust och enkäter delades ut i olika hamnar runt hela Vänern, dock ej i Lillängshamnen. Denna undersökning visade att enkäter har en signifikant större fångst per båt än intervjuer. För att ta reda på mer om hur genomförandet av intervjuer skulle kunna förbättras undersöktes hur vädret påverkade antalet intervjuer som genomfördes. Man fick en negativ korrelation mellan antalet genomförda intervjuer och vindhastighet där ytterst få intervjuer genomfördes i vindhastigheter över 5-8 meter per sekund. Det finns förbättringspotential vad gäller både genomförandet av intervjuer och enkätundersökningar, bland annat mer personal till att kunna intervjua fler folk i olika hamnar och uppföljning på de enkäter som inte svarats på.

Bien que l’écologie de la truite (Salmo trutta) ait déjà été bien étudiée, les processus expliquant la dynamique spatio-temporelle des populations restent à caractériser. L’objectif de cette thèse était d’identifier les processus démographiques (ex. survie ou déplacements) et l’influence des processus biotiques (interactions entre individus) et abiotiques (conditions environnementales) qui structurent dans le temps et dans l’espace les différentes classes d’âge (alevins, juvéniles et adultes) de ces populations. J’ai étudié l’influence sur la survie apparente de (1) la densité-dépendance et (2) des conditions environnementales vécues directement par les truites (habitat hydraulique et température de l’eau). Pour évaluer la transférabilité des résultats, j’ai évalué (3) l’échelle spatiale (globale ou locale) à laquelle opéraient les processus et (4) si ces processus variaient entre populations (approche hiérarchique). J’ai considéré la dynamique de 45 populations de truites dont 22 sont situées à l’aval d’un ouvrage hydroélectrique. A large échelle, il est apparu que le recrutement de populations séparées par des distances allant jusqu’à 75km peut être synchronisé par de fortes crues lors de l’émergence des alevins ou des déplacements du substrat de ponte. Nous avons synthétisé les résultats de l’application d’un modèle déterministe de dynamique de population, calibrés localement sur neuf stations aux conditions environnementales bien caractérisées. Cette synthèse a montré que des processus locaux influençaient directement la dynamique des populations. Enfin, la construction d’un modèle hiérarchique a montré le rôle structurant de la mortalité densité-dépendante des juvéniles et des adultes, dont l’intensité augmentait en l’absence d’abris (<2% de la surface) ou variait avec la température de l’eau (diminution pour les juvéniles et augmentation pour les adultes). Ce travail fournit des bases scientifiques aux gestionnaires d’ouvrages hydro-électriques pour leur permettre de limiter leur influence sur les populations de poissons et répondre ainsi aux demandes réglementaires / Brown trout (Salmo trutta) ecology was largely studied. However, the process structuring the spatiotemporal patterns of population dynamics remains unclear. The objective of this thesis was to identify the demographic processes (e.g. survival or displacements) and the influence of biotic (between-individuals interactions) and abiotic (environmental conditions) processes structuring the age-stages (fry, juveniles and adults) of these populations in time and space.I studied (1) the role of density-dependence on survival and (2) the influence of environmental conditions experienced by trouts (hydraulics and water temperature). To assess the results’ transferability, I studied (3) the spatial scale (global or local) of influence of the processes and (4) if those processes varied among populations (hierarchical approach).I considered the dynamics of 45 trout populations, 22 being located downstream a hydropower facility. At a large scale, the recruitment of distant populations (up to 75 km apart) may be synchronized by large floods during emergence of fry or by spawning substratum displacements. We summarized the results of a determinist population dynamics models, locally calibrated on nine reaches showing well-described environmental conditions. This summary revealed the influence of various local drivers on population dynamics. Finally, a hierarchical model showed that density-dependent mortality among juveniles and adults was a key biotic process. The strength of the competition was greater in absence of shelter (<2% of the surface) and varied with water temperature (decreasing for juveniles and increasing for adults).The results of this work will provide scientific basis to hydropower facility managers. This will help them to reduce their influence on trout populations and respond to regulatory demands

<p>The passage efficiency of downstream migrating brown trout (Salmo trutta) smolts past two hydropower plants in the River Emån, southeastern Sweden, was evaluated by telemetry. From 26 April to 17 May 2005, 40 wild brown trout smolts were radio-tagged, and their positions were recorded daily until 14 June. Approximately 45% of the individuals passed both power plants, and 15% made it to the sea, some 28 km downstream of the power plants. About 20% of the individuals ceased migrating, residing in a lotic habitat. Mortality due to predation was 33%, and the predation rate was higher in the power plant dams than it was downstream of the power plants. Turbine-induced mortality was greater in the upper power plant (40%) than in the lower one (13%). Fish that chose the alternative routes, through the gates, swam past the upper dam faster than fish that swam through the turbines. The results confirm previous work in the river, namely that measures need to be taken to improve passage efficiency past the power plants, particularly passage of the upper power plant. Such measures are of crucial importance if the nature-like bypass channels at the power plants in Finsjö are going to have any long-term effects on the brown trout population.</p> / <p>Passageeffektiviteten för nedströms vandrande havsöringssmolt (Salmo trutta) förbi två vattenkraftverk i Emån, i sydöstra Sverige, utvärderades med telemetri. Från 26 april till och med 17 maj 2005 märktes 40 vilda havsöringssmolt med radiosändare och de positionsbestämdes dagligen till och med 14 juni. Ungefär 45% av individerna passerade båda kraftverken, och 15% klarade sig till havet, cirka 28 km nedströms kraftverken. Omkring 20% av individerna avbröt vandringen och stannade i ett lotiskt habitat. Mortalitet på grund av predation uppgick till 33%, och predationshastigheten var högre i kraftverksdammarna än nedströms kraftverken. Den turbininducerade mortaliteten var högre i det övre kraftverket (40%) än i det nedre (13%). Det gick fortare att passera den övre kraftverksdammen för fisk som valde de alternativa rutterna, genom dammluckorna, jämfört med att passera genom turbinerna. Dessa resultat bekräftar tidigare studier i ån, nämligen att åtgärder krävs för att förbättra passageeffektiviteten förbi kraftverken, i synnerhet passagen av det övre kraftverket. Sådana åtgärder är av avgörande betydelse om de naturlika fiskvägarna vid kraftverken i Finsjö ska få några långsiktiga effekter på havsöringspopulationen.</p>