Mercury Bioaccumulation in Lacustrine Fish Populations Along a Climatic Gradient in Northern Ontario, Canada

Climate change is predicted to alter many processes in boreal aquatic ecosystems, including mercury (Hg) bioaccumulation in fish. We investigated current patterns in fish Hg across a climatic gradient in northern Ontario, Canada, to assess the possible influence of further climate change. Cohabiting populations of walleye (a piscivore) and white sucker (a benthivore) were sampled from lakes spanning over 9.0 degrees of latitude (45 degrees 24 ' N-54 degrees 20 ' N). Latitudinal trends were evident in climatic conditions, as well as several other ecosystem characteristics over this range. Muscle total Hg concentration ([THg]) was modelled with respect to climatic variables as well as other physical, chemical, and biological variables, and all models were ranked by Akaike information criterion. Neither long-term mean temperature nor precipitation was a strong predictor of current muscle [THg] in either species across this region. Instead, drainage basin characteristics (for example, mean slope) and lake water chemistry (for example, [DOC], [SO4]) were the strongest predictors, followed by fish biological traits (for example, muscle delta C-13). Walleye [THg] was more strongly related to water chemistry, and white sucker [THg] was more strongly related to drainage basin physical characteristics. For both species, muscle [THg] showed unimodal relationships with several predictors (for example, latitude, [SO4], [DOC]), peaking in their mid-ranges. Fish [THg] is not strongly associated with current climatic conditions across northern Ontario but may be influenced by climate change in future through indirect effects on water chemistry and food web structure.