Diss. (sammanfattning) Uppsala : Uppsala universitet, 2009. / Härtill 5 uppsatser.

<p>Three different laboratory studies have been carried out in order to elucidate the interactions between two predators and their prey in the Fucus vesiculosus community. The first study investigated the behavioural response of Gammarus oceanicus, Idotea baltica and Palaemon adspersus in the chemicai presence of their predators Gadus morhua and Perca fluviatilis. A lowering of night activity among the crustaceans was expected. The second study was carried out in 1 m³ mesocosm-tanks were the predators had the opportunity to actively prey on both I. baltica and G. oceanicus among live F. vesiculosus plants. This experiment lasted före one week and the decrease of the crustaceans during this period was noted as result. In the third study was the predators ability to forage in complete darkness investigated. This was carried out in the same mesocosm tanks but without Fucus and for 5 hours. None of the crustacean species decreased their night activity as response to the smell of the predators. This may indicate that chemically mediateda signals are of less importance in the Fucus community due to high turbulence and swift waterexchange in this splashzone habitat.  Cod consumer more of both G. oceanicus and  I. baltica than perch in the two different foraging-studies. In these conditions the cod was the most efficient predator. The decreased stocks of cod was the most efficient predator. The decreased socks of cod in the Baltic Sea may have reduced the top-down control in the foodweb of the fucus community.</p><p> </p><p> </p>

Three different laboratory studies have been carried out in order to elucidate the interactions between two predators and their prey in the Fucus vesiculosus community. The first study investigated the behavioural response of Gammarus oceanicus, Idotea baltica and Palaemon adspersus in the chemicai presence of their predators Gadus morhua and Perca fluviatilis. A lowering of night activity among the crustaceans was expected. The second study was carried out in 1 m3 mesocosm-tanks were the predators had the opportunity to actively prey on both I. baltica and G. oceanicus among live F. vesiculosus plants. This experiment lasted före one week and the decrease of the crustaceans during this period was noted as result. In the third study was the predators ability to forage in complete darkness investigated. This was carried out in the same mesocosm tanks but without Fucus and for 5 hours. None of the crustacean species decreased their night activity as response to the smell of the predators. This may indicate that chemically mediateda signals are of less importance in the Fucus community due to high turbulence and swift waterexchange in this splashzone habitat.  Cod consumer more of both G. oceanicus and  I. baltica than perch in the two different foraging-studies. In these conditions the cod was the most efficient predator. The decreased stocks of cod was the most efficient predator. The decreased socks of cod in the Baltic Sea may have reduced the top-down control in the foodweb of the fucus community.

The lake Spexhultasjön is a moderate humic mesotrophic lake that is not acidified. The fish fauna was investigated by using a standard method for sampling freshwater fish with multi mesh gill nets. The fish fauna was diverse with perch, pike, tench, common whitefish, and roach. Perch and roach dominated. There were few pikes. The tench were few but big. The common whitefish was caught in deep water. The lake has condition class 2 according to the national environment protection board. The perch has a reproduction disorder. The roach has probably forced the perch into the benthoseating stage to early. A proposal intended to the county administrative board is to increase the production of a predator like pike or pike-pirch. The county administrative board ought to investigate why the share of pike is low and the roaches reproduction disorder.

<p>The lake Spexhultasjön is a moderate humic mesotrophic lake that is not acidified. The fish fauna was investigated by using a standard method for sampling freshwater fish with multi mesh gill nets. The fish fauna was diverse with perch, pike, tench, common whitefish, and roach. Perch and roach dominated. There were few pikes. The tench were few but big. The common whitefish was caught in deep water. The lake has condition class 2 according to the national environment protection board. The perch has a reproduction disorder. The roach has probably forced the perch into the benthoseating stage to early. A proposal intended to the county administrative board is to increase the production of a predator like pike or pike-pirch. The county administrative board ought to investigate why the share of pike is low and the roaches reproduction disorder.</p>

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2009. / Härtill 5 uppsatser.

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) Uppsala : Uppsala universitet, 2006. / Härtill 5 uppsatser.

Forskare förutspår att den globala uppvärmningen kommer att påverka Öster-sjön och omgivande landmassor med högre temperatur och mer nederbörd. En konsekvens av högre nederbörd är ökat läckage och avrinning av sötvatten från landmassorna vilket leder till högre näringstillgång i Östersjön. Ytterligare en konsekvens av ökad tillförsel av sötvatten är utspädningseffekten av salthalten i Östersjön. Dessa förändringar kommer att påverka Östersjöns ekosystem och arterna i. Hur väl ett ekologiskt samhälle klarar av en förändrad miljö beror på minst tre faktorer; diversitet, artsammansättning och interaktionsmönster mellan arter. Denna studie undersöker interaktionen mellan mört och abborre samt hur interaktionen påverkas då salthalt, näringstillgång och temperatur förändras. Med provfiskedata från elva lokaler har interaktionen beräknats med tidsserieanalys genom att använda en multivariat autoregressiv modell. Resultaten visar att både abborre och mört har negativ effekt på varandra. Dessutom är båda arterna kraftigt täthetsberoende. Hur interaktionen påverkas av förändringar av påverkansvariablerna har studerats grafiskt. Abborres effekt på mört är den enda interaktionen som med statistisk signifikans konstateras temperaturberoende. Resultaten från studien visar att den negativa effekt abborre har på mört blir mindre då temperaturen ökar. Effekten avtar linjärt då vattentemperaturen är 15 °C. Detta tyder på att abborres reglerande effekt på mört eventuellt kommer att minska under de förväntade klimatförändringarna. / The science community predict that the rising global temperature will affect the region of Scandinavia with more precipitation and as a consequence more runoff and leakage of nutrients to the Baltic Sea. During this century salinity in the Baltic Sea is expected to decrease with up to 1.5 - 2 g / kg due to dilution from the higher runoff volumes and the temperature is expected to increase with 3 - 5 °C. All these changes will affect the Baltic Sea ecosystem and the species within it. How well an ecological community can adapt to these changes is determined by the community stability which is based on at least three factors; diversity, species composition and interaction patterns between species. This study aims to investigate the interaction patterns between perch and roach, two well represented species along the Swedish coastline, and how these interaction patterns are effected by changes in salinity, watertemperature, and nutrient load. The study used a multivariate autoregressive model (MAR(1)), which is a linear model that can be used to investigate interaction patterns. The input in the MAR(1)-model was time series based on catch per unit effort of perch and roach from eleven different places along the Swedish east coast. Both perch and roach have a negative impact on the other species, also a strong density dependence for both species were found. Temperatures effect on the interaction; perch effect on roach, is the only one in this study that is statistically significant. Perch has a strong negative effect on roach when the temperature is around 15 °C. This negative effect decreases linearly with higher temperatures.

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.