Impacts of large seasonal hydropower-generated water level fluctuations on Arctic char (Salvelinus alpinus) recruitment in a Norwegian alpine reservoir
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Lake Møsvatn at Hardangervidda, South-Eastern Norway was developed for hydropower production in the early 19-hundreds. It is extensively regulated, with a regulation high of 18.5m and thus, comes into the category of highly impacted water resources. The reservoir is dominated by Arctic char (Salvelinus alpinus). The population is heavily harvested. Reports of a suspected decrease in abundance due to larger sizes and fewer individuals resulted in the precent study, which aimed to investigate the population’s health and eventually correlation to low water levels. Gillnetted Arctic char from two different years were investigated in the laboratory. Parameters from whole and dissected fish were sampled. Otoliths were used for age determination and data were sampled from organs in the abdominal cavity. Mean length and age was found to be increasing. Condition factor was rather low (mean<1). Co-findings indicate that post-spawners eat more than in-spawning individuals. Hatching time was explored. The littoral spawning population could be susceptible to the hydropower-generated annual water level drawdowns due to desiccation of roe. Year-class differences were found between years with high and low water levels, but the correlation was weak. Recruitment limitation might have confounding factors, such as water temperature. Wash-out of benthos from the littoral fauna may impact on food-webs and habitat competition. The Arctic char population might be left to feed on large pelagial zooplankton. Allover, the population seems to be bottom-up regulated by recruitment and food limitations.