Seasonal variation of mercury and δ15N in fish from Lake Heddalsvatn, southern Norway

Seasonal variations of mercury (Hg) concentration in muscle tissue of northern pike (Esox lucius L), European whitefish (Coregonus lavaretus L) and European perch (Perca fluviatilis L) have been investigated in Lake Heddalsvatn, southern Norway. Our data confirmed seasonal differences in the Hg concentrations in fish, but the causes for that may vary depending on fish species. Length (pike and perch) and age (perch and whitefish) were the strongest explanatory factors for the Hg fluctuations. Fish caught in December (pike and whitefish) had the highest Hg concentrations, while the concentrations in May were higher than in September for all 3 species, statistically significant for perch (P