Epsilon Archive for Student Projects

Abstract

This study investigated the potential influence of open cage fish farming on nutrient poor, hydropower regulated lakes in Sweden and how perch diet is affected. The aim of this study was to determine a) whether there is a difference in the amount of stomach content in perch between the two lakes b) whether there is a difference in perch diet regarding fish and invertebrates and c) whether the size at which perch shift their niche differs between the lakes. A total of 136 perch were sampled, 80 from the lake Storuman that was affected by fish farming and 56 from the reference lake Hornavan. A detailed analysis of perch stomach contents was then done in the lab. The stomach contents were measured, and divided into different categories. Statistical analyses were then conducted to examine the research questions. Results showed that perch in Storuman had more than twice the food consumption compared to those in Hornavan, this was likely due to increased food availability resulting from an increase of the production in the lake. Perch from Storuman also consumed a higher proportion of fish, this was potentially due to increased fish availability and a decline in other prey groups, such as invertebrates, which was negatively affected by fish farming. No differences were observed in the timing of the ontogenetic diet shift between the lakes. The findings in this study are consistent with previous research, indicating that fish farming can impact nutrient poor lakes by input of extra nutrients, which in turn can change the food web. More research is needed to understand how fish farming affects nutrient poor lakes over time and to maintain a stable ecosystem.