In temperate climate with pronounced seasonality, ice and snow cover reduces light conditions during winter which in turn reduce search efficiency for visual feeding consumers like fish. Furthermore, a suggested major effect of future climate change is an increased input of allochtonous DOC to aquatic systems which causes an increased brownification and hence reduced overall light conditions. In this study, I sampled YOY three-spined sticklebacks (Gasterosteus aculeatus) of different sizes overwintering in clear and brown water model ecosystems to examine if consumption were dependent on light conditions (natural light variability over winter) and if consumption were reduced in brown water. Three-spined sticklebacks were able to feed at different winter conditions and the prey biomass in stomachs was higher in clear- than in brown water despite higher resource levels in brown water treatments. Moreover when light intensity increased in late winter compared to midwinter conditions prey biomass in stomachs increased in both clear and brown water systems. Dominated prey taxa in the diet were chironomids and copepods. Results from this study suggest that when fish species are able to feed at low temperature and resource availability are sufficient light conditions during winter can be an important factor affecting overwinter survival in YOY fish because visual prey encounters and hence consumption rates are affected by light conditions. Future climate change scenarios with predicted increased brownification may therefore affect over winter survival in fish because of the negative effect of low light intensity (brownification) on prey consumption in fish in turn potentially changing recruitment success and densities of fish.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第19037号 / 農博第2115号 / 新制||農||1031(附属図書館) / 学位論文||H27||N4919(農学部図書室) / 31988 / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 神﨑 護, 教授 北島 薫, 教授 北山 兼弘 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Vissa vattenkraftverk drivs med korttidsreglering som möjliggör snabb anpassning av elproduktion, vilket sker genom hastiga förändringar i vattenflöde. Flera olika typer av organismer påverkas negativt av korttidsreglering, till exempel fiskar. En möjlig konsekvens är strandning, vilket innebär att fiskar hamnar i torrlagt substrat eller annat ogynnsamt habitat. Risken för strandning påverkas av flera faktorer. I denna studie undersöktes hur strandningsrisk hos öringyngel (Salmo trutta) påverkas av tillgång till skydd och ljusförhållande, där prediktionerna var att strandningsrisken skulle vara större vid tillgång till skydd och i mörker. Dessa två faktorer testades i en 2x2 design. Det fanns en tendens till en större andel strandade yngel vid tillgång till skydd (48 ± 8,2 %) jämfört med när det inte fanns skydd (35,7 ± 23,7 %) och en större andel strandade vid ljusa förhållanden (50,2 ± 16 %) än i mörker (33,4 ± 17,3 %). Påverkan av tillgång till skydd på strandningsrisk var inte annorlunda vid de olika ljusförhållandena. Utifrån dessa resultat är rekommendationen för att minska strandningsrisken hos öringyngel att flödesreglering genomförs i mörker och att bottenstrukturen beaktas, vilket måste göras i varje enskilt fall. / Some hydropower stations use hydropeaking to be able to swiftly adjust electricity production, which is done through rapid alterations in water flow. Several types of organisms are negatively affected by hydropeaking, including fishes. One possible consequence of hydropeaking is stranding, which occurs when fish are separated from the water body and end up in dewatered substrate. The risk of stranding is influenced by several factors. The aim of this study was to investigate how stranding risk in brown trout fry (Salmo trutta) is affected by shelter availability and light conditions. The predictions were that stranding risk would be higher in conditions with available shelters and in darkness. The two factors were tested in a 2x2-design. There was a tendency for stranding rate to be higher when shelters were available (48 ± 8.2 %) compared to when there were none (35.7 ± 23.7 %), and stranding rate was higher in light (50.2 ± 16 %) than in darkness (33.4 ± 17.3 %). The effect of shelter availability on stranding risk did not differ between the two light treatments. Based on these results, in order to reduce stranding risk in brown trout fry the recommendation is that flow regulation should be carried out in darkness and that the bottom structure should be considered, which must be done on a case-by-case basis.

Indoor light energy harvesting plays an important role in field of renewable energy. Indoor lighting condition is usually described by level of illumination. However, measured data alone does not by classification of different light sources, result is not representative. Energy harvesting system needs to be evaluated after classification to obtain more accurate value. This is also importance of different light source classification. In this thesis, a complete set of indoor light energy harvesting system is introduced, two models are proposed to evaluate energy, robustness is improved by mixing complex light condition during data collection. Main task of this thesis is to verify importance of indoor light classification. Main contribution of this thesis is to fill a gap in energy evaluation, and built a model with superior performance. In terms of collecting data, this thesis researches influence factor of data collection to ensure reliability of accuracy. This work can more accurately collect spectral under different light conditions. Finally, light energy is evaluated by classification of indoor light. This model is proven to be closer to true energy value under real condition. The result shows that classified data is more accurate than direct calculation of energy,it has a smaller error. In addition, performance of classifier model used in this thesis has been proven to be excellent, classifier model can still carry on high-accuracy classification when measurement data are not included in training data set. This makes it a low-cost alternative to measuring light condition without spectrometer.