Seasonal Dynamics of Mercury Bioaccumulation in Apex Predator Fish (Esox lucius) from Subarctic Shield Lakes: Implications for Human Consumption

Mercury (Hg) contamination in high-latitude aquatic ecosystems poses significant ecological and public health challenges, particularly due to the biomagnification of monomethylmercury (MeHg) in apex predatory teleosts. This study investigated the seasonal dynamics of total mercury (THg) and MeHg concentrations in northern pike (Esox lucius) across four oligotrophic subarctic shield lakes over a 24-month monitoring period. Muscle tissue samples were collected across spring, summer, autumn, and winter under ice to quantify trace metal burdens, stable isotopes (δ¹³C and δ¹⁵N), and physiological condition factors. Mean THg concentrations exhibited marked intra-annual variability, peaking during late summer and early autumn (mean: 0.68 ± 0.12 µg/g wet weight) and reaching nadirs during late winter and post-spawning spring (mean: 0.44 ± 0.09 µg/g wet weight). This temporal fluctuation was driven primarily by temperature-dependent metabolic acceleration, seasonal shifts in foraging ecology toward higher trophic level pelagic prey, and summer epilimnetic methylation spikes. Over 62% of adult pike captured in late summer exceeded the World Health Organization commercial consumption threshold (0.50 µg/g wet weight), compared to only 28% in spring. Consequently, estimated hazard quotients for subsistence consumers varied twofold across seasons. These findings highlight that static annual consumption advisories may fail to protect vulnerable subarctic human populations during peak exposure windows, emphasizing the necessity of integrating seasonal bioenergetics into regional fisheries management.