The effects of climate on the bioaccumulation of mercury in two large-bodied fish species in northern Ontario lakes

Abstract

Increasing temperatures and changing precipitation patterns in subarctic Canada are expected to alter many processes in aquatic ecosystems, including mercury bioaccumulation in fish. I investigated patterns of fish mercury concentrations across the current climatic gradient in Ontario in order to assess how future climate change might impact the provisioning of safe fish. Walleye and white sucker were sampled from 70 lakes throughout northern Ontario spanning over 9.0° of latitude and representing a range of climatic conditions (annual growing degree days 604-1599). Muscle total mercury concentrations ([tHg]) were analyzed with respect to climatic variables as well as other chemical, physical, and biological variables. Second order Akaike Information Criterion (AICc) model ranking indicated that neither temperature nor precipitation were dominant drivers of mercury accumulation in walleye or white sucker. Instead, lake and watershed physical structure and δ13C best predicted white sucker [tHg], while water chemistry and fish condition best predicted walleye [tHg]. Specifically, walleye [tHg] showed a curvilinear pattern when related to [SO4] and [DOC]. The inhibitory effect of high lake [SO4] on mercury accumulation in fish has, to the best of my knowledge, only been theorised. Although fish mercury accumulation is not strongly driven by the current climatic conditions, a changing climate may indirectly affect mercury availability, methylmercury production, and the rate of methylmercury assimilation into fish tissue in ways that are not yet clear to us.