Master Research while studing in (Français)

Since the 1970s, there have been significant fluctuations in landlocked salmon’s populations in Lac Saint-Jean (LSJ). This variability raises many questions in regards to the factors responsible for these changes and the long-term population trend of this species. Despite the economic importance and symbolic meaning of this salmon, known locally as the ouananiche, little is known about the role of primary production changes on the higher trophic levels of the lake. Therefore, it becomes essential to clarify whether the observed variability represents a natural aspect of LSJ, or does this pattern stem from more recent anthropogenic developments. The aim of this Master thesis project is to reconstruct the limnological and environmental conditions of the LSJ over the last 250 years in order to provide a reliable analysis of the current status of its fisheries resources. My research hypothesis is that the installation of the dam in 1926 and the subsequent water level rise (~3 m) have contributed to a significant change in the limnological conditions of LSJ. A paleolimnological approach based on the analysis of fossil diatom assemblages allows for a reliable reconstruction of lake evolution and assessment of the impacts from anthropogenic influence. A pair of sediment cores recovered from two different sites (4 cores in total) will be subsampled for microfossils and radiometric dating by ²¹⁰Pb and ¹³⁷Cs. The second core from each site will be preserved intact to allow for analysis of the physical and chemical properties of the cores. This project provides tangible data for fisheries management and represents an essential first step in a research program that aims to assess the aquatic ecosystem LSJ over the much longer term.