Previous studies have shown that ice cover has many positive effects on brown trout (Salmo trutta), including protection from endothermic predators. I tested whether it is the cover provided by the ice itself or the reduction in light that causes behavioral changes in juvenile brown trout. To distinguish between these two effects, behavioural observations were made with and without ice at the same light intensity (500 lux). An additional ice-free, high light (3000 lux) treatment was included to be able to measure brown trout’s response to light reduction. A mink model was used to simulate predation risk to be able to measure the fish’s anti-predator response under these three conditions. I found a significant treatment effect on body and eye coloruration. For eye colouration, I found that fish under ice had a paler eye colouration than fish that experienced high light, which in turn were paler than fish subjected to low light. For body colouration, fish under ice had paler body colouration than fish from the two ice-free treatments, which did not differ from each other. There was no effect of treatment on ventilation rate, time to initiate foraging, time to initiate activity or swimming activity, although both foraging and activity were lowest and swimming activity highest under ice. The changes in body and eye colouration indicate that trout are less stressed under ice, presumably because they perceive ice as a barrier against terrestrial predators. These results suggest that the ongoing climate change, which is leading to shorter periods of sustained ice cover, may have negative consequences for trout populations in the near future. / Tidigare studier har visat att yttäckande is medför många positiva effekter för öring (Salmo trutta), bland annat genom att utgöra skydd mot endoterma predatorer. Jag undersökte om det är den yttäckande isen i sig som medför beteendeförändringar hos juvenila öringar eller om det är det reducerade ljusinsläppet som isen medför. För att separera dessa två effekter gjordes beteendeobservationer med och utan ytis under samma ljusintensitet (500 lux). En ytterligare isfri behandling gjordes, med starkt ljus (3000 lux), för att kunna mäta öringens respons på ljusreduceringen. En uppstoppad mink användes för att simulera predationsrisken, detta för att kunna mäta fiskarnas antipredationsresponser under dessa tre förhållanden. Jag fann en signifikant behandlingseffekt på kropps- och ögonfärg. Under is hade fiskarna en blekare ögonfärg än när de befann sig under starkt ljus, som i sin tur resulterade i blekare färg än när fiskarna utsattes för svagt ljus. När det gäller kroppsfärg uppvisade fiskarna en blekare kroppsfärg under is än när de utsattes för de två isfria behandlingarna, vilka inte skiljde sig från varandra. Behandlingarna gav ingen effekt på gälslagsfrekvens, tid till att initiera födosök, tid till att initiera aktivitet eller simaktivitet, dock var tid till både födosök och aktivitet lägst och simaktivitet störst under is. Förändringarna i kropps- och ögonfärg indikerar att öring är mindre stressad under is, vilket eventuellt kan bero på att de uppfattar isen som en barriär mot terrestra predatorer. Dessa resultat tyder på att den pågående klimatförändringen, som innebär kortare perioder av ihållande yttäckande is, kan medföra negativa konsekvenser för öringpopulationer inom den närmaste framtiden.

In boreal streams, stream salmonids typically face low water temperatures and variable ice conditions during winter, and thus stream salmonids are expected to use different behavioural strategies to cope with these environmental conditions. The studies presented in this thesis explore how temperature, light intensity, and surface ice affect salmonid behaviour, with focus on drift-feeding and ventilation rates. The first paper reports results from a laboratory study designed to measure prey capture probabilities and reaction distances of drift-feeding Atlantic salmon, brown trout, and European grayling at light intensities simulating daylight and moonlight at seven temperatures ranging from 2 to 11°C. There was a positive relationship between water temperature and prey capture probability for all three species at both light levels, but the temperature-dependence did not scale according to the Metabolic Theory of Ecology. Reaction distance was also positively related to temperature for the three species, which may explain the temperature effects on prey capture probability. The results from this study should be of interest for those working with energetic-based drift-foraging models. In the second paper, the effects of ice cover on the diel behaviour and ventilation rate of brown trout were studied in a laboratory stream. Ice cover is believed to afford protection against endothermic predators, and thus the need for vigilance should be reduced under ice cover. This hypothesis was tested by observing ventilation rates at night, dawn, and during the day in the presence and absence of real, light-permeable surface ice. Further, trout were offered drifting prey during the day to test if ice cover increased daytime foraging activity. Ice cover reduced ventilation rates at dawn and during the day, but not at night. Moreover, trout made more daytime foraging attempts in the presence of ice cover than in its absence. These results suggest that ice cover affects the behaviour of brown trout and presumably has a positive effect on winter survival. Global warming, by reducing the extent or duration of surface ice, may therefore have negative consequences for many lotic fish populations in boreal streams. / BAKSIDESTEXT In boreal streams, salmonids typically face low water temperatures and variable ice conditions from autumn to spring. The studies presented in this thesis explore how temperature, light intensity, and ice cover affect salmonid behaviour, with focus on drift-feeding and ventilation rates. In Paper I, drift-foraging was studied at light intensities simulating daylight and moonlight at seven temperatures ranging from 2 to 11°C. There was a positive relationship between temperature and foraging success at both light levels, but the temperature-dependence did not scale according to the Metabolic Theory of Ecology. Moreover, reaction distance was positively related to temperature. In Paper II, the effects of ice cover on behaviour and ventilation rate of brown trout were studied. Ice cover is believed to afford protection against predators, and thus the need for vigilance should be reduced under ice. This hypothesis was tested by observing ventilation rates at night, dawn, and during the day in the presence and absence of surface ice. Ice cover reduced ventilation rates and increased daytime foraging activity, suggesting that ice cover presumably has a positive effect on winter survival.

No description available.

Antarctica is home to numerous perennially ice-covered (PIC) lakes that host rich benthic microbial ecosystems. These lakes are covered by a thick floating ice cover year-round and often have water columns supersaturated in dissolved gases, resulting in heavily bubbled ice covers, altering the optical properties of the ice and the amount of light that penetrates into the water column. Thus, understanding the optical properties of perennial lake ice can have important scientific implications to the study of life on Earth and the search for extraterrestrial life. Synthetic aperture radar (SAR) remote sensing has been used rigorously for over 50 years to study and monitor the seasonal response and long-term trends of backscatter over seasonally ice-covered (SIC) Arctic lakes. Limited studies have assessed the impacts of dissolved gases and ice/water interface bubbles on SAR backscatter variability over SIC lakes. The seasonal backscatter response of Antarctic PIC lakes remains unexplored; their physical nature asserts that their backscatter response should largely be decoupled from seasonal factors according to SIC lake backscatter theory. Additionally, gas supersaturated PIC lakes are ideal candidates to better understand the role of gas buildup and bubble formation on the backscatter response from floating ice covers. This thesis leverages a dense stack of Sentinel-1 C-band SAR imagery over Lake Untersee, a well-sealed PIC lake in East Antarctica, to explore the relationships between SAR backscatter and ice/water interface bubbles. This analysis integrates field measurements and temporal observations at the ice/water interface. Lastly, a brief comparative analysis extends to other ice covers, including moat-forming PIC lakes, as well as first-year and multi-year Arctic sea and lake ice. It is shown that Lake Untersee has a seasonal backscatter regime that is linked to air temperature. A strong correlation is found between the timing of backscatter intensity increase in winter and ice thickness. This relationship is attributed to variations in ice thickness which affect the length of the freezing period under the ice, the rate of dissolved gas accumulation, and ultimately, the nucleation and abundance of bubbles at the ice/water interface. These findings can be applied to other PIC lakes that have seasonal gas regimes. This research provides valuable insights into the complex interplay between ice cover characteristics, gas dynamics, interface bubbles, and SAR backscatter, enhancing our understanding of polar aquatic ecosystems and their broader implications for global environments.

No description available.

No description available.

Winter conditions are believed to play an important role in the population dynamics of northern temperate stream fish, challenging the ability of fish to physiologically and behaviourally adapt. Climate change is predicted to increase both mean temperature and temperature fluctuations, especially during winter, leading to dynamic environmental conditions in terms of river ice production and flow. Therefore, knowledge about the winter ecology of stream fish is important for predicting and mitigating anthropogenic impacts on fish production in boreal streams. Stream salmonids are relatively active throughout winter, and behavioural responses to different winter conditions may be critical for survival. Yet, relatively little is known about overwintering behaviour of salmonids, particularly in streams with ice. In this doctoral thesis, I report the results from experimental field and laboratory studies on the behavioural ecology of juvenile salmonids under winter conditions. My results from the field show that salmonids grow more and use a broader range of habitats in the presence of surface ice than in its absence. Results from the laboratory experiments show that the presence of surface ice increases food intake rates, reduces stress and affects social interactions. These laboratory results may explain the positive effects of ice cover on growth that was found in the field experiment. Moreover, I show that drift-feeding ability is reduced at low temperatures, and that nocturnal drift foraging under winter conditions has a low efficiency. / Vinterförhållanden kan spela en avgörande roll för förekomsten av fisk i våra vattendrag. Laxfiskar, som till exempel lax, öring och harr, är vinteraktiva och måste därför anpassa sin fysiologi och sitt beteende till en miljö som karakteriseras av låga och föränderliga vattenflöden, liten tillgång på föda, kallt vatten, is och mörker. Trots att dessa anpassningar är avgörande för chansen att överleva vintern, vet man relativt lite om laxfiskars vinterbeteende, speciellt i vattendrag som täcks av is. I denna avhandling presenterar jag resultat från fält- och laboratoriestudier av laxfiskars beteende under vinterförhållanden och resultaten visar att närvaron av yttäckande is ökar tillväxt och födointag, minskar stress samt påverkar var fiskar uppehåller sig och hur fiskarna interagerar med varandra. Jag har också undersökt hur laxfiskars beteende i rinnande vatten påverkas av ljusintensitet och vattentemperatur i samband med födointag. Resultaten visar att den minskade dagaktiviteten som laxfiskar uppvisar på vintern medför en kostnad i form av försämrad förmåga att fånga byten. / Winter conditions are believed to play an important role in the population dynamics of northern temperate stream fish, challenging the ability of fish to physiologically and behaviourally adapt. Climate change is predicted to increase both mean temperature and temperature fluctuations, especially during winter, leading to dynamic environmental conditions in terms of river ice production and flow. Therefore, knowledge about the winter ecology of stream fish is important for predicting and mitigating anthropogenic impacts on fish production in boreal streams. Stream salmonids are active throughout winter, and behavioural responses to different winter conditions may be critical for survival. Yet, relatively little is known about overwintering behaviour of salmonids, particularly in streams with ice. This doctoral thesis focuses on the behavioural ecology of salmonids under winter conditions, and results from field and laboratory experiments show that the presence of surface ice increases food intake rates, reduces stress and affects social interactions, with effects on growth and habitat use. Moreover, drift-feeding ability is reduced at low temperatures, and nocturnal drift foraging under winter conditions has a low efficiency. / <p>Artikel 1 i avhandlingen som manuskript. Nu publicerad.</p>

No description available.

Recently, Hudson Bay experienced unidirectional trends in temperature, sea-ice extent, time of break-up, and length of the open-water season. Predicted impacts on population dynamics of ice-associated species include habitat loss and shift in prey availability. The ringed seal (Phoca hispida) depends on a stable ice platform with sufficient snow depth and a productive open-water season for reproduction and survival. Evidence of ringed seal sensitivity to environmental variations has been reported, but mechanisms involved were poorly understood. In western Hudson Bay, density, life-history traits, and diet of ringed seals were monitored over two decades, providing an opportunity to understand the effects of climatic variations on the population dynamics of this long-lived carnivore. Ringed seal density was estimated through strip-transect analyses after aerial surveys were flown in western Hudson Bay in late spring during the annual moult in the 1990s and 2000s. During these periods, ringed seals were also sampled from Inuit subsistence fall harvests In Arviat, NU, and ages, reproductive status, percentage of pups in the harvest, body condition, and diet were assessed. Strong inter-annual variations in these parameters were observed, and a decadal cycle was suggested and related to variations in the sea-ice regime. The cold and heavy ice conditions that prevailed in western Hudson Bay in 1991-92 likely induced a decrease in pelagic productivity, reducing the availability to ringed seals of sand lances (Ammodytes sp.), their major prey. The nutritional stress endured, combined with a strong predation pressure, led to a decrease in ringed seal reproductive performances, pup survival, and density during the 1990s. The recovery of ringed seal demographic parameters and number in the 2000s was associated with the immigration of pups, juveniles, and young adults into western Hudson Bay. Impact of current climatic trends on ringed seal population dynamics was not apparent, but considering the limited range of environmental variations tolerated by ringed seals, the response of this species to climate warming might be of a catastrophic type. Ringed seals were found to be good indicators of ecosystem changes, and long-term monitoring of the species in Hudson Bay should be a priority.

Recently, Hudson Bay experienced unidirectional trends in temperature, sea-ice extent, time of break-up, and length of the open-water season. Predicted impacts on population dynamics of ice-associated species include habitat loss and shift in prey availability. The ringed seal (Phoca hispida) depends on a stable ice platform with sufficient snow depth and a productive open-water season for reproduction and survival. Evidence of ringed seal sensitivity to environmental variations has been reported, but mechanisms involved were poorly understood. In western Hudson Bay, density, life-history traits, and diet of ringed seals were monitored over two decades, providing an opportunity to understand the effects of climatic variations on the population dynamics of this long-lived carnivore. Ringed seal density was estimated through strip-transect analyses after aerial surveys were flown in western Hudson Bay in late spring during the annual moult in the 1990s and 2000s. During these periods, ringed seals were also sampled from Inuit subsistence fall harvests In Arviat, NU, and ages, reproductive status, percentage of pups in the harvest, body condition, and diet were assessed. Strong inter-annual variations in these parameters were observed, and a decadal cycle was suggested and related to variations in the sea-ice regime. The cold and heavy ice conditions that prevailed in western Hudson Bay in 1991-92 likely induced a decrease in pelagic productivity, reducing the availability to ringed seals of sand lances (Ammodytes sp.), their major prey. The nutritional stress endured, combined with a strong predation pressure, led to a decrease in ringed seal reproductive performances, pup survival, and density during the 1990s. The recovery of ringed seal demographic parameters and number in the 2000s was associated with the immigration of pups, juveniles, and young adults into western Hudson Bay. Impact of current climatic trends on ringed seal population dynamics was not apparent, but considering the limited range of environmental variations tolerated by ringed seals, the response of this species to climate warming might be of a catastrophic type. Ringed seals were found to be good indicators of ecosystem changes, and long-term monitoring of the species in Hudson Bay should be a priority.