| Summary: | Mercury (Hg) is a ubiquitous toxic metal that bioaccumulates in organisms and biomagnifies in food webs. Evaluating Hg bioaccumulation and biomagnification in Arctic marine ecosystems is critical for understanding Hg dynamics and estimating exposure to fish and wildlife consumed by humans. In this thesis, I investigated inter-individual variability in biological factors affecting Hg accumulation in anadromous Arctic char (Salvelinus alpinus), as well as food web structure and Hg biomagnification in the benthic, pelagic, and benthopelagic marine food webs of inner Frobisher Bay, in Nunavut, Canada. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N), as well as concentrations of Hg were measured in 119 anadromous Arctic char and 62 taxa of fish, invertebrates, and zooplankton that had been sampled in inner Frobisher Bay in 2018 and 2019. Mean concentrations of total mercury (THg) and relationships between THg and biological variables known to influence Hg concentrations in fish (e.g., fork length, weight, age, growth rate, trophic position, carbon source, Fulton’s condition factor, gonadosomatic index, and hepatosomatic index) were compared between immature and mature Arctic char. The immature Arctic char exhibited greater inter-individual variability in factors affecting THg accumulation compared to the mature Arctic char, and δ15N (i.e., marine prey reliance) was a strong predictor of THg concentrations for all individuals. Biomagnification of methyl mercury (MeHg) in each food web was quantified with Trophic Magnification Slopes (TMS; calculated as the slope of the linear regression of log10 MeHg concentrations and δ15N values) and Trophic Magnification Factors (TMF; calculated as the antilog of the regression slope). Rates of MeHg biomagnification were highest in the benthopelagic food web (TMS = 0.201; TMF = 1.59), followed by the pelagic food web (TMS = 0.183; TMF = 1.52), and lastly the benthic food web (TMS = 0.079; TMF = 1.20), and δ15N explained 88%, 79%, and 9% of variation in MeHg ...
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