Fiskbestånden i Östersjön har sedan början av 1980-talet genomgått en omfattande förändring. Stora predatorer, som torsk (Gadus morhua) och abborre (Perca fluviatilis) har minskat i antal medan det finns tecken på att storspigg (Gasterosteus aculeatus) har ökat. Denna sannolika ökning av storspigg skulle kunna ha att göra med minskningen av både torsk och abborre som predatorer i de kustnära tångbältena. För att undersöka detta utfördes ett mesokosmexperiment där torskens och abborrens förmåga att predera på storspigg undersöktes, både i ljus och mörker. Hypoteserna som arbetet utgick ifrån var att torsk var en bättre predator i mörker än i ljus och att torsk var en bättre predator än abborre i mörker. Resultaten visar på att torsk är den bättre predatorn i både ljus och mörker, samt att den är lika framgångsrik i mörker som i ljus. Detta tyder på att torskens försvinnande skulle kunna vara en bidragande faktor till ökningen av storspigg. Ytterligare visades abborren vara en mer framgångsrik predator i mörker än i ljus, detta trots att den alltid anges som en visuell predator. Detta visar att även minskningen av abborre skulle kunna vara en anledning till att storspiggen ökar.

Diss. (sammanfattning) Arkitektkopia AB, Umeå : Sveriges lantbruksuniv., 2009. / Härtill 4 uppsatser.

Diss. (sammanfattning). Umeå : Sveriges lantbruksuniv. / Härtill 6 uppsatser.

The eurasian perch (Perca fluviatilis Linnaeus, 1758) is considered as very perspective species for breeding at intensive aquaculture, where was successful domesticated. Consumption of eurasian perch is increased at present. The greatest grow of consumption is mainly in countries of alpine region and in Scandinavian countries. The aim of experiment was monitor and character spawning of domesticated eurasian perch in controlled conditions of breed. It was determinated fertility and then fertilization of eggs. The next aim was make incubation of fertilization eggs and determinate hatching. After hatch was determinated total length of larvae and its quality by the help of osmotic shock. Domesticated eurasian perch is spawned without problems in controlled conditions of breed. The resulting data of domesticated perch are worse than date of non-domesticated perch in some spawning characteristic. This problem will resolve with gaining knowledge about spawning of eurasian perch. The greatest problem is hatching of eggs, which is very low during spawning of domesticated perch.

The growth in perch (Perca fluviatilis) is generally slow but varies depending on living conditions. For instance, growth is more rapid in warmer water temperature and when there is reduced intra- and interspecific competition for food. The cormorant (Phalacrocorax carbo) was established in Lake Tåkern in 1994 and could possibly have an effect on the growth of perch due to predation of small perch and competition for food with larger perch. The aim of this study was to examine whether the growth of perch had changed from year 1978, when a previous study on perch was preformed, to a recent fish survey in 2019 in lake Tåkern. The aim of the study was to assess if any changes in growth could be explained by predation and competition from cormorants. The aim of the study was also to examine whether there was a difference in growth between females and males. The age was determined by using the opercular bone and an age analysis was done to compare the growth between year 1978 and 2019. The results showed that the growth of 1-3-year-old perch was higher in year 1978 than in 2019. This was contrary to the expected outcome, that the predation from cormorants should had decreased competition for young perch in 2019. Previous studies on perch have shown a difference between males and females with an age over 2 years old. However, by the results there is no support that differences between males and females have affected the difference in growth at ages 1-3 years old between 1978 and 2019. As there was no difference between the sexes, any difference in growth between 1978 and 2019 could not be explained by an altered sex ratio. Since there were only a few older individuals 2019 comparison of growth for individuals over 4 years old were not possible to do. The conclusion is that there was no support that cormorants reduced the competition for smaller perch. Cormorants could possibly have contributed to low number of older individuals in 2019.

Fish populations vary naturally but are also affected by anthropogenic factors such as changes in land use, climate, acidification, invasive species and eutrophication. An overall picture is important for understanding the changes that are taking place and their effects. In this study, I have linked several environmental factors, such as turbidity and chlorophyll-a, with the presence of pikeperch and perch in Lake Mjörn. I have also investigated how the size of the perch has changed between the years 2000 and 2018 for the entire population, and specifically within the size class 80 - 120 mm. Gill net surveys from 2000, 2007 and 2018 shows that the median length of pikeperch decreased from 2007 to 2018 by 39.6% and increased in average per net effort by 630% between 2000 and 2018, a clear shift in the population from few and older to more, and a larger proportion of, younger individuals. The turbidity has had a clear downward trend with a decrease of 3.9 cm per year since 1985, with a Secchi depth of less than 4 meters in the last 10 years, which is probably an important factor contributing to the increase of the pikeperch population. At the same time, the chlorophyll-a concentration has shown an upward trend of 0.174 μg/l per year. An observed decrease in macrophytes around the lake over the past 20 years may have caused some increased wind-driven mixing and a greater amount of suspended solute particles. An increased amount of nutrients from the sediment could have explained the increasing amount of phytoplankton, but sampling carried out at the inlet to and the outlet of Lake Mjörn shows that the concentrations of nutrients in the lake have decreased. The median length of perch has decreased by 52.3% from the year 2000 to 2018, and the median length of 2 summer old perch shows a decrease of 17.5% during the same period. The difference in median length between the entire perch population and the 2 summer old individuals was 47% in 2000 but only 8.3% in 2018, which indicates that the population in 2018 largely consisted of 2 - 3 year old individuals.

In the center of Stockholm, a lock by the name Victoriaslussen is being renovated, where in conjunction with this, a fishway is being designed. The purpose of the fishway is to facilitate migration of weak-swimming fish between the Lake Mälaren and the Salt Lake. Perch (Perca fluviatilis) is counted among these weak swimming species. The aim of the study is to, based on research results, reports, and interviews, create an analysis of the challenges the perch face today, and in the future, as well as assessing the need of a fishway in this location. Data show that the perch population in Sweden is in a steady state today, although a reduction in catches in the study area has occurred during the last 25 years. Based on the accessible data it was stated that there is sufficient scientific evidence to draw conclusions about the sustainability of the perch’s stock in lake Mälaren today. The study shows that the decrease in stock can be attributed to human impact on the environment in the form of pollution of the water as well as to climate change. Furthermore, the impact of climate change on the lake’s ecological status, for instance, through an increase in temperature, resulting in eutrophication and descending oxygen levels, will amount to consequences for the perch such as changes in metabolism, size structure in the stock (population and body size). The fishway system created is a circuit (In Swedish: omlöp), which is the most natural and gentle system for a wide diversity of weak-swimming fish. The study concluded that the perch would benefit from a fishway in Victoriaslussen. It would improve the perch’s situation in Mälaren. Although the stock is in a steady state for the time being, climate change in the future will bring new challenges which would make the fishway useful solution.

Durch die Flutung stillgelegter Tagebaue entstehen zahlreiche Seen in den ostdeutschen Braunkohlerevieren. Sie sind überwiegend groß, oligo- bis mesotroph, und ihr Litoral ist nur in geringem Umfang durch Makrophyten strukturiert. Viele von ihnen sind versauert oder versauerungsgefährdet. In einer Feldstudie wurden (1) die Auswirkung von Seemorphologie und Habitatstruktur auf die Fischgemeinschaft des Senftenberger Sees, eines 1050 ha großen mesotrophen Tagebausees, und (2) die Säuretoleranz einheimischer Fischarten unter den hydrochemischen Bedingungen der geogen versauerten Tagebauseen untersucht. Die Fischgemeinschaft des Senftenberger Sees wurde von Barschen (Perca fluviatilis) und Plötzen (Rutilus rutilus) dominiert, wobei die verschiedenen Barsch- und Plötzengrößenklassen ihre Habitate durch Nutzung verschiedener Tiefenbereiche des Litorals segregierten. Innerhalb der flachen Litoralbereiche waren juvenile Plötzen und juvenile Güstern deutlich stärker auf die wenigen Makrophytenbestände fixiert als juvenile Barsche. Die Habitatwahl der Barsche zeigt, dass diese in mesotrophen Seen wahrscheinlich eher von den guten Sichtverhältnissen als von der strukturellen Komplexität submerser Makrophytenbestände profitieren. Als Ursache für die unterschiedliche Habitatwahl juveniler Barsche, Plötzen und Güstern wird postuliert, dass diese generell verschiedene Habitatwahlstrategien verfolgen. Während der entscheidende Parameter für die Habitatwahl juveniler Barsche die Optimierung der Energieaufnahme ist, folgen juvenile Plötzen und Güstern vorrangig einer Räubervermeidungsstrategie und sind daher sehr viel stärker auf strukturreiche Bereiche angewiesen. Die kritischen pH-Untergrenzen für die einzelnen Fischarten entsprachen weitgehend den publizierten Ergebnissen aus regenversauerten Weichwasserseen. Vermutlich wurde in den Tagebauseen der Säurestress, den die erhöhte Al-Konzentration von bis zu 0,6 mg/L verursachte, durch die ebenfalls erhöhte Ca-Konzentration kompensiert. / Numerous post-mining lakes are created by flooding the pits remaining from open-cast lignite mining in eastern Germany. They are typically large, oligo- or mesotrophic and only sparsely structured by macrophytes. Many of them are acidified or at risk of acidification. The aim of this study was (1) to determine the effects of lake morphology and habitat structure on the fish community of Lake Senftenberg, a large mesotrophic post-mining lake, and (2) to determine the acid tolerance of indigenous fish species under the hydrochemical conditions of geogenically acidified post-mining lakes. The most abundant fish species in Lake Senftenberg were Eurasian perch (Perca fluviatilis) and roach (Rutilus rutilus). Different size classes of both species segregated along a depth gradient within the littoral zone. Unvegetated shallow littoral areas (depth 1-3 m) were mainly used by juvenile perch, whereas juvenile roach and juvenile white bream (Blicca bjoerkna) preferred macrophyte stands. This indicates that the structural complexity of submersed macrophytes is not the key factor favouring perch over roach under mesotrophic conditions. Instead, low turbidity is probably the most important factor. The habitat choice of juvenile perch, roach and white bream is suggested to reflect different habitat selection strategies. Whereas habitat selection of juvenile perch is predominantly driven by maximisation of food consumption rates, juvenile roach and juvenile white bream aim at minimising predation risk. Consequently, they are much more dependent on structurally complex habitats. The critical lower pH-thresholds of the fish species investigated in this study were similar to the values derived from soft water lakes affected by acid rain. The deleterious effects of elevated Al-concentrations (up to 0.6 mg/L) in the post-mining lakes were probably mitigated by high Ca-concentrations.

Dams play an important role in our society, but their negative impacts on aquatic ecosystems have led to a need for conservation efforts to mitigate the negative effects. In some instances, dam removal has been suggested to be the most economically and ecologically beneficial restoration method to improve longitudinal connectivity. This, however, has increased the need of more research about the effects dam removal have on aquatic ecosystems, since the outcomes of this restoration method can be unpredictable. In this study, I investigated ecological impacts of dam removals in Swedish inland waters. I collected field data from five different lakes in Värmland and Dalarna, two lakes with dam removal in 2017/2018 and three without. I studied how dam removal affected different trophic levels of the aquatic ecosystem, where I predicted that a top-down effect would increase abundances of piscivorous European perch (Perca fluviatilis) and zooplankton, but decrease phytoplankton, whereas a bottom-up effect would lead to increases in biomass at all trophic levels (with most pronounced effects on nutrient concentration). If both top-down and bottom-up effects would operate in parallel, all the above mentioned effects could occur. I also predicted that if dam removal affected the fish community, there would be a change in species diversity and fish biomass. Moreover, if perch demography was affected, there would be a change in perch length and abundance of different age classes. To investigate this, I collected data on fish, plankton, nutrients (P, N), DOC, pH and conductivity in the five lakes and compared this with already existing historical data using a BACI design. Two-way ANOVAs were used to study the effects of dam removals on these variables. There were not enough historical data on P concentration or zoo-and phytoplankton to be analyzed statistically. I did, however, conduct correlation analyses with zoo- and phytoplankton. Contradictory to my prediction, the results showed no effect of dam removal on fish biomass or diversity, water chemistry or perch demography in the studied lakes. There was, however, a statistically significant effect of time on Tot-N, with lower values after the years of 2017/2018 (regardless of dam removal). There were also some differences between the lakes in species diversity, concentration of Tot-N, potentially piscivorous perch and perch length. The outcomes of dam removal are unpredictable, as are the expected time-lapse of the effects, which means that changes may yet occur in the studied lakes. Knowledge about ecosystem responses to dam removal enables managers to better predict the effects of dam removal, and thereby facilitate decision makings related to this restoration method. / Dammar spelar en viktig roll i vårt samhälle, men deras negativa påverkan på akvatiska ekosystem har ökat behovet av bevarandeinsatser för att minska de negativa effekterna. I somliga fall har dammutrivning föreslagits vara den mest ekonomiskt och ekologiskt gynnsamma bevarandemetoden för att förbättra longitudinell konnektivitet. Detta har dock ökat behovet av mer forskning gällande dammutrivningars effekter på akvatiska ekosystem, eftersom utfallen av denna bevarandemetod kan vara oförutsägbara. I denna studie undersökte jag dammutrivningars ekologiska effekter i svenska inlandsvatten. Jag samlade data i fält från fem olika sjöar i Värmland och Dalarna, två sjöar med dammutrivningar under 2017/2018 och tre utan. Jag undersökte hur dammutrivning påverkade olika trofiska nivåer i det akvatiska ekosystemet, med förväntningarna att en top-down-effekt skulle öka abundansen av fiskätande abborre (Perca fluviatilis) samt djurplankton, men minska växtplankton, medan en bottom-up-effekt skulle leda till ökad biomassa inom samtliga trofiska nivåer (men med mest effekter på näringskoncentration). Om både top-down- och bottom-up-effekter skulle verka parallellt kunde samtliga ovanstående nämnda effekter förekomma. Jag förväntade även att om dammutrivning påverkade fisksamhället skulle det ske en förändring i artdiversitet och fiskbiomassa. Därtill bör en effekt på demografi hos abborre leda till förändringar i abborrlängd- och abundans i olika åldersklasser. För att undersöka detta samlade jag in data över fisk, plankton, näringsämnen (P, N), DOC, pH och konduktivitet i de fem sjöarna och jämförde detta med redan existerande historiska data med en BACI design. Tvåvägs-ANOVAs användes för att studera effekterna av dammutrivningar på dessa variabler. Det fanns inte tillräckligt med historiska data över P-koncentration eller djur- och växtplankton för att analyseras statistiskt. Jag utförde dock korrelationsanalyser med djur- och växtplankton. I kontrast till min förväntan visade resultaten ingen effekt av dammutrivning på fiskbiomassa- eller diversitet, vattenkemi eller demografi hos abborre i de studerade sjöarna. Det var däremot en statistiskt signifikant effekt av tid på Tot-N, med lägre värden efter 2017/2018 (oberoende av dammutrivning). Det var även en del skillnader mellan sjöarna i artdiversitet, koncentration av Tot-N, potentiellt fiskätande abborre samt abborrlängder. Utfallen av damutrivningar är oförutsägbara, och detsamma gäller tidsintervallet för effekterna, vilket innebär att det fortfarande kan ske förändringar i de studerade sjöarna. Kunskap om ekosystemrespons till dammutrivning möjliggör för förvaltare att lättare bedöma effekter av dammutrivningar, och underlättar därav beslutsfattning relaterat till denna bevarandemetod.

<p>This thesis reports the results of biomarker measurements in three environmental monitoring projects. In the first project, which was part of the Swedish national environmental monitoring, biomarkers were measured annually in female perch (<i>Perca fluviatilis</i>) in two background areas in the Baltic Sea during 1988–2000, resulting in a unique 13-year series of measurements. The most important results were a strong decreasing temporal trend in the gonadosomatic index (GSI) and a strong increasing temporal trend in the hepatic ethoxyresorufin O-deethylase (EROD) activity in the Baltic Proper. In the second project, biomarkers and concentrations of classic pollutants were measured in female perch in the Stockholm recipient 1999–2001. This was the first time a large city was investigated as a point source of pollution, and the gradient was longer and included more stations than customary. Severe pollution conditions in central Stockholm were indicated by the poor health status of the perch: retarded growth, decreased frequency of sexually mature females, low GSI, disturbed visceral fat metabolism, increased hepatic EROD activity, decreased muscle acetylcholinesterase activity, increased frequency of hepatic DNA adducts, and a high concentration of biliary 1-pyrenol. Muscle ΣDDT and ΣPCB were measured as pollution indicators and were 10–28 respectively 12–35 times higher than the background levels in perch from the Baltic Proper. In the Stockholm archipelago two superimposed gradients were found. Whereas the response of several biomarkers consistently decreased with increasing distance from central Stockholm, the response of others first decreased from Stockholm to the middle archipelago and then increased to the open Baltic Sea. The latter biomarkers included the frequency of sexually mature females, GSI, hepatic EROD activity, and hepatic DNA adducts. In the third project, potential toxicity from munitions on the seafloor, at a dumpsite in the Stockholm archipelago, was analysed by the nanoinjection of sediment extracts into newly fertilised rainbow trout (<i>Oncorhynchus mykiss</i>) eggs, followed by the measurement of biomarkers in the developing larvae. No biological effects of the dumped munitions were found. The same stations in the Stockholm archipelago as in the second project were investigated as a positive control. The results of the three projects agreed well, which demonstrated the continuous pollution of the Baltic Sea and the severe pollution conditions and adverse biological effects in central Stockholm. Further investigations are urgently needed to identify which pollutants or other factors are causing the observed biological effects, both in the background areas in the Baltic Sea and in the Stockholm recipient.</p>